A Comparative Study of Hydrodeoxygenation of Furfural Over Fe/Pt(111) and Fe/Mo 2C Surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, Weiming; Jiang, Zhifeng; Chen, Jingguang G.

It is desirable to convert biomass-derived furfural to 2-methylfuran through the hydrodeoxygenation (HDO) reaction using an inexpensive catalyst with high stability. In this work, Mo 2C was used as an alternative substrate to replace precious Pt to support monolayer Fe for the HDO reaction of furfural. The HDO activity and stability of Fe/Pt(111) and Fe/Mo 2C/Mo(110) surfaces were compared. Density functional theory calculations and vibrational spectroscopy results indicated that both surfaces bonded to furfural with similar adsorption geometries and should be active toward the furfural HDO reaction. Temperature programmed desorption experiments confirmed a similar HDO activity between the two surfaces,more » with Fe/Mo 2C/Mo(110) being more thermally stable than Fe/Pt(111). As a result, the combined theoretical and experimental results demonstrated that Fe/Mo 2C should be a promising non-precious metal catalyst for the HDO reaction of furfural to produce 2-methylfuran.« less

A Comparative Study of Hydrodeoxygenation of Furfural Over Fe/Pt(111) and Fe/Mo 2C Surfaces

DOE PAGES

Wan, Weiming; Jiang, Zhifeng; Chen, Jingguang G.

2018-01-19

It is desirable to convert biomass-derived furfural to 2-methylfuran through the hydrodeoxygenation (HDO) reaction using an inexpensive catalyst with high stability. In this work, Mo 2C was used as an alternative substrate to replace precious Pt to support monolayer Fe for the HDO reaction of furfural. The HDO activity and stability of Fe/Pt(111) and Fe/Mo 2C/Mo(110) surfaces were compared. Density functional theory calculations and vibrational spectroscopy results indicated that both surfaces bonded to furfural with similar adsorption geometries and should be active toward the furfural HDO reaction. Temperature programmed desorption experiments confirmed a similar HDO activity between the two surfaces,more » with Fe/Mo 2C/Mo(110) being more thermally stable than Fe/Pt(111). As a result, the combined theoretical and experimental results demonstrated that Fe/Mo 2C should be a promising non-precious metal catalyst for the HDO reaction of furfural to produce 2-methylfuran.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maiti, Debtanu; Daza, Yolanda A.; Yung, Matthew M.

Density functional theory (DFT) based investigation of two parameters of prime interest -- oxygen vacancy and surface terminations along (100) and (110) planes -- has been conducted for La (1-x)Sr xFe(1-y)Co yO (3-more » $$\\delta$$) perovskite oxides in view of their application towards thermochemical carbon dioxide conversion reactions. The bulk oxygen vacancy formation energies for these mixed perovskite oxides are found to increase with increasing lanthanum and iron contents in the 'A' site and 'B' site, respectively. Surface terminations along (100) and (110) crystal planes are studied to probe their stability and their capabilities to accommodate surface oxygen vacancies. Amongst the various terminations, the oxygen-rich (110) surface and strontium-rich (100) surface are the most stable, while transition metal-rich terminations along (100) revealed preference towards the production of oxygen vacancies. The carbon dioxide adsorption strength, a key descriptor for CO 2 conversion reactions, is found to increase on oxygen vacant surfaces thus establishing the importance of oxygen vacancies in CO 2 conversion reactions. Amongst all the surface terminations, the lanthanum-oxygen terminated surface exhibited the strongest CO 2 adsorption strength. Finally, the theoretical prediction of the oxygen vacancy trends and the stability of the samples were corroborated by the temperature-programmed reduction and oxidation reactions and in situ XRD crystallography.« less

Does trampoline or hard surface jumping influence lower extremity alignment?

PubMed

Akasaka, Kiyokazu; Tamura, Akihiro; Katsuta, Aoi; Sagawa, Ayako; Otsudo, Takahiro; Okubo, Yu; Sawada, Yutaka; Hall, Toby

2017-12-01

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations.

Does trampoline or hard surface jumping influence lower extremity alignment?

PubMed Central

Akasaka, Kiyokazu; Tamura, Akihiro; Katsuta, Aoi; Sagawa, Ayako; Otsudo, Takahiro; Okubo, Yu; Sawada, Yutaka; Hall, Toby

2017-01-01

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations. PMID:29643592

Reaction formulation for radiation and scattering from plates, corner reflectors and dielectric-coated cylinders

NASA Technical Reports Server (NTRS)

Wang, N. N.

1974-01-01

The reaction concept is employed to formulate an integral equation for radiation and scattering from plates, corner reflectors, and dielectric-coated conducting cylinders. The surface-current density on the conducting surface is expanded with subsectional bases. The dielectric layer is modeled with polarization currents radiating in free space. Maxwell's equation and the boundary conditions are employed to express the polarization-current distribution in terms of the surface-current density on the conducting surface. By enforcing reaction tests with an array of electric test sources, the moment method is employed to reduce the integral equation to a matrix equation. Inversion of the matrix equation yields the current distribution, and the scattered field is then obtained by integrating the current distribution. The theory, computer program and numerical results are presented for radiation and scattering from plates, corner reflectors, and dielectric-coated conducting cylinders.

Reaction pathways of model compounds of biomass-derived oxygenates on Fe/Ni bimetallic surfaces

NASA Astrophysics Data System (ADS)

Yu, Weiting; Chen, Jingguang G.

2015-10-01

Controlling the activity and selectivity of converting biomass-derivatives to fuels and valuable chemicals is critical for the utilization of biomass feedstocks. There are primarily three classes of non-food competing biomass, cellulose, hemicellulose and lignin. In the current work, glycolaldehyde, furfural and acetaldehyde are studied as model compounds of the three classes of biomass-derivatives. Monometallic Ni(111) and monolayer (ML) Fe/Ni(111) bimetallic surfaces are studied for the reaction pathways of the three biomass surrogates. The ML Fe/Ni(111) surface is identified as an efficient surface for the conversion of biomass-derivatives from the combined results of density functional theory (DFT) calculations and temperature programmed desorption (TPD) experiments. A correlation is also established between the optimized adsorption geometry and experimental reaction pathways. These results should provide helpful insights in catalyst design for the upgrading and conversion of biomass.

Seventh BES (Basic Energy Sciences) catalysis and surface chemistry research conference

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1990-03-01

Research programs on catalysis and surface chemistry are presented. A total of fifty-seven topics are included. Areas of research include heterogeneous catalysis; catalysis in hydrogenation, desulfurization, gasification, and redox reactions; studies of surface properties and surface active sites; catalyst supports; chemical activation, deactivation; selectivity, chemical preparation; molecular structure studies; sorption and dissociation. Individual projects are processed separately for the data bases. (CBS)

Biomass-derived oxygenate reforming on Pt(111): A demonstration of surface science using D-glucose and its model surrogate glycolaldehyde

NASA Astrophysics Data System (ADS)

McManus, Jesse R.; Yu, Weiting; Salciccioli, Michael; Vlachos, Dionisios G.; Chen, Jingguang G.; Vohs, John M.

2012-12-01

Molecules derived from cellulosic biomass, such as glucose, represent an important renewable feedstock for the production of hydrogen and hydrocarbon-based fuels and chemicals. Development of efficient catalysts for their reformation into useful products is needed; however, this requires a detailed understanding of their adsorption and reaction on catalytically active transition metal surfaces. In this paper we demonstrate that the standard surface science techniques routinely used to characterize the reaction of small molecules on metals are also amenable for use in studying the adsorption and reaction of complex biomass-derivatives on single crystal metal surfaces. In particular, Temperature Programmed Desorption (TPD) and High Resolution Electron Energy Loss Spectroscopy (HREELS) combined with Density Functional Theory (DFT) calculations were used to elucidate the adsorption configuration of D-glucose and glycolaldehye on Pt(111). Both molecules were found to adsorb in an η1 aldehyde configuration partially validating the use of simple, functionally-equivalent model compounds for surface studies of cellulosic oxygenates.

Perspectives on Program Duplication

ERIC Educational Resources Information Center

Morrison, Gail M.

2010-01-01

Concerns about program duplication in higher education are often reminiscent of Supreme Court Justice Potter Stewart's now famous remark about pornography: "I know it when I see it." The problem with that reaction is that, at least on its surface, this response seems intuitive and emotional, to say nothing of subjective and personal. The…

Quantum calculations of the rate constant for the O(3P)+HCl reaction on new ab initio 3A″ and 3A' surfaces

NASA Astrophysics Data System (ADS)

Xie, Tiao; Bowman, Joel M.; Peterson, K. A.; Ramachandran, B.

2003-11-01

We report the thermal rate constant of the O(3P)+HCl→OH+Cl reaction calculated from 200 to 3200 K, using new fits to extensive ab initio calculations [B. Ramachandran and K. A. Peterson, J. Chem. Phys. 119, 9590 (2003), preceding paper]. The rate constants are obtained for both the 3A″ and 3A' surfaces using exact quantum reactive scattering calculations for selected values of the total angular momentum and the J-shifting approximation for both the 3A″ and 3A' surfaces. The results are compared with the ICVT/μOMT rate constants calculated by the POLYRATE program and all available experimental data. Other related high-energy reaction channels are also studied qualitatively for their contribution to the total thermal rate constant at high temperature.

Comprehensive investigation of HgCdTe metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Raupp, Gregory B.

1993-01-01

The principal objective of this experimental and theoretical research program was to explore the possibility of depositing high quality epitaxial CdTe and HgCdTe at very low pressures through metalorganic chemical vapor deposition (MOCVD). We explored two important aspects of this potential process: (1) the interaction of molecular flow transport and deposition in an MOCVD reactor with a commercial configuration, and (2) the kinetics of metal alkyl source gas adsorption, decomposition and desorption from the growing film surface using ultra high vacuum surface science reaction techniques. To explore the transport-reaction issue, we have developed a reaction engineering analysis of a multiple wafer-in-tube ultrahigh vacuum chemical vapor deposition (UHV/CVD) reactor which allows an estimate of wafer or substrate throughput for a reactor of fixed geometry and a given deposition chemistry with specified film thickness uniformity constraints. The model employs a description of ballistic transport and reaction based on the pseudo-steady approximation to the Boltzmann equation in the limit of pure molecular flow. The model representation takes the form of an integral equation for the flux of each reactant or intermediate species to the wafer surfaces. Expressions for the reactive sticking coefficients (RSC) for each species must be incorporated in the term which represents reemission from a wafer surface. The interactions of MOCVD precursors with Si and CdTe were investigated using temperature programmed desorption (TPD) in ultra high vacuum combined with Auger electron spectroscopy (AES). These studies revealed that diethyltellurium (DETe) and dimethylcadmium (DMCd) adsorb weakly on clean Si(100) and desorb upon heating without decomposing. These precursors adsorb both weakly and strongly on CdTe(111)A, with DMCd exhibiting the stronger interaction with the surface than DETe.

Effects of the low Earth orbital environment on spacecraft materials

NASA Technical Reports Server (NTRS)

Leger, L. J.

1986-01-01

It is evident from space flights during the last three years that the low Earth orbital (LEO) environment interacts with spacecraft surfaces in significant ways. One manifestation of these interactions is recession of, in particular, organic-polymer-based surfaces presumably due to oxidation by atomic oxygen, the major component of the LEO environment. Three experiments have been conducted on Space Shuttle flights 5, 8 and 41-G to measure reaction rates and the effects of various parameters on reaction rates. Surface recession on these flights indicates reaction efficiencies approximately 3 x 10(-24) cu cm/atoms for unfilled organic polymers. Of the metals, silver and osmium are very reactive. Effects on spacecraft or experiment surfaces can be evaluated using the derived reaction efficiencies and a definition of the total exposure to atomic oxygen. This exposure is obtained using an ambient density model, solar activity data and spacecraft parameters of altitude, attitude and operational date. Oxygen flux on a given surface is obtained from the ambient density and spacecraft velocity and can then be integrated to provide the total exposure or fluence. Such information can be generated using simple computational programs and can be converted to various formats. Overall, the extent of damage is strongly dependent on the type of surface and total exposure time.

Contour temperature programmed desorption for monitoring multiple chemical reaction products

NASA Astrophysics Data System (ADS)

Chusuei, C. C.; de la Peña, J. V.; Schreifels, J. A.

1999-09-01

A simple method for obtaining a comprehensive overview of major compounds desorbing from the surface during temperature programmed desorption (TPD) experiments is outlined. Standard commercially available equipment is used to perform the experiment. The method is particularly valuable when high molecular mass compounds are being studied. The acquisition of contour temperature programmed desorption (CTPD) spectra, sampling 50-dalton mass ranges at a time in the thermal desorption experiments, is described and demonstrated for the interaction of benzotriazole adsorbed on a Ni(111) surface. Conventional two-dimensional TPD spectra can be extracted from the CTPD by taking vertical slices of the contour.

User's guide to PHREEQC, a computer program for speciation, reaction-path, advective-transport, and inverse geochemical calculations

USGS Publications Warehouse

Parkhurst, D.L.

1995-01-01

PHREEQC is a computer program written in the C pwgranuning language that is designed to perform a wide variety of aqueous geochemical calculations. PHREEQC is based on an ion-association aqueous model and has capabilities for (1) speciation and saturation-index calculations, (2) reaction-path and advective-transport calculations involving specified irreversible reactions, mixing of solutions, mineral and gas equilibria surface-complex-ation reactions, and ion-exchange reactions, and (3) inverse modeling, which finds sets of mineral and gas mole transfers that account for composition differences between waters, within specified compositional uncertainties. PHREEQC is derived from the Fortran program PHREEQE, but it has been completely rewritten in C with the addition many new capabilities. New features include the capabilities to use redox couples to distribute redox elements among their valence states in speciation calculations; to model ion-exchange and surface-compiexation reactions; to model reactions with a fixed-pressure, multicomponent gas phase (that is, a gas bubble); to calculate the mass of water in the aqueous phase during reaction and transport calculations; to keep track of the moles of minerals present in the solid phases and determine antomaticaHy the thermodynamically stable phase assemblage; to simulate advective transport in combination with PHREEQC's reaction-modeling capability; and to make inverse modeling calculations that allow for uncertainties in the analytical data. The user interface is improved through the use of a simplified approach to redox reactions, which includes explicit mole-balance equations for hydrogen and oxygen; the use of a revised input that is modular and completely free format; and the use of mineral names and standard chemical symbolism rather than index numbers. The use of (2 eliminates nearly all limitations on army sizes, including numbers of elements, aqueous species, solutions, phases, and lengths of character strings. A new equation solver that optimizes a set of equalities subject to both equality and inequality constraints is used to determine the thermodynamically stable set of phases in equilibrium with a solution. A more complete Newton-Raphson formulation, master-species switching, and scaling of the algebraic equations reduce the number of failures of the nunmrical method in PHREEQC relative to PHREEQE. This report presents the equations that are the basis for chemical equilibrium and inverse-modeling calculations in PHREEQC, describes the input for the program, and presents twelve examples that demonstrate most of the program's capabilities.

Oxygen vacancy formation characteristics in the bulk and across different surface terminations of La (1₋x)Sr xFe (1₋y)Co yO (3₋δ) perovskite oxides for CO 2 conversion

DOE PAGES

Maiti, Debtanu; Daza, Yolanda A.; Yung, Matthew M.; ...

2016-03-07

Density functional theory (DFT) based investigation of two parameters of prime interest -- oxygen vacancy and surface terminations along (100) and (110) planes -- has been conducted for La (1-x)Sr xFe(1-y)Co yO (3-more » $$\\delta$$) perovskite oxides in view of their application towards thermochemical carbon dioxide conversion reactions. The bulk oxygen vacancy formation energies for these mixed perovskite oxides are found to increase with increasing lanthanum and iron contents in the 'A' site and 'B' site, respectively. Surface terminations along (100) and (110) crystal planes are studied to probe their stability and their capabilities to accommodate surface oxygen vacancies. Amongst the various terminations, the oxygen-rich (110) surface and strontium-rich (100) surface are the most stable, while transition metal-rich terminations along (100) revealed preference towards the production of oxygen vacancies. The carbon dioxide adsorption strength, a key descriptor for CO 2 conversion reactions, is found to increase on oxygen vacant surfaces thus establishing the importance of oxygen vacancies in CO 2 conversion reactions. Amongst all the surface terminations, the lanthanum-oxygen terminated surface exhibited the strongest CO 2 adsorption strength. Finally, the theoretical prediction of the oxygen vacancy trends and the stability of the samples were corroborated by the temperature-programmed reduction and oxidation reactions and in situ XRD crystallography.« less

Formation of Germa-ketenimine on the Ge(100) Surface by Adsorption of tert-Butyl Isocyanide.

PubMed

Shong, Bonggeun; Yoo, Jong Suk; Sandoval, Tania E; Bent, Stacey F

2017-06-28

Reactions of the (100) surfaces of Ge and Si with organic molecules have been generally understood within the concept of "dimers" formed by the 2 × 1 surface reconstruction. In this work, the adsorption of tert-butyl isocyanide on the Ge(100)-2 × 1 surface at large exposures is investigated under ultrahigh vacuum conditions. A combination of infrared spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption experiments along with dispersion-corrected density functional theory calculations is used to determine the surface products. Upon adsorption of a dense monolayer of tert-butyl isocyanide, a product whose structure resembles a germa-ketenimine (N=C=Ge) with σ donation toward and π back-donation from the Ge(100) surface appears. Formation of this structure involves divalent-type surface Ge atoms that arise from cleavage of the Ge(100)-2 × 1 surface dimers. Our results reveal an unprecedented class of reactions of organic molecules at the Ge(100) surface.

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

Progress is reported on fundamental research in: crystal physics, reactions at metal surfaces, spectroscopy of ionic media, structure of metals, theory of alloying, physical properties, sintering, deformation of crystalline solids, x ray diffraction, metallurgy of superconducting materials, and electron microscope studies. Long-randge applied research studies were conducted for: zirconium metallurgy, materials compatibility, solid reactions, fuel element development, mechanical properties, non-destructive testing, and high-temperature materials. Reactor development support work was carried out for: gas-cooled reactor program, molten-salt reactor, high-flux isotope reactor, space-power program, thorium-utilization program, advanced-test reactor, Army Package Power Reactor, Enrico Fermi fast-breeder reactor, and water desalination program. Other programmore » activities, for which research was conducted, included: thermonuclear project, transuraniunn program, and post-irradiation examination laboratory. Separate abstracts were prepared for 30 sections of the report. (B.O.G.)« less

Responsive hairpin DNA aptamer switch to program the strand displacement reaction for the enhanced electrochemical assay of ATP.

PubMed

Wang, Li; Fang, Li; Liu, Shufeng

2015-09-07

A responsive hairpin DNA aptamer switch was ingeniously designed for enzyme-free, sensitive and selective electrochemical detection of ATP. It takes full advantage of the target-triggered liberation effect of the toehold region and the concomitant proximity effect with the branch-migration region to execute the toehold-mediated strand displacement reaction on the electrode surface.

Theoretical research program to study transition metal trimers and embedded clusters

NASA Technical Reports Server (NTRS)

Walch, Stephen P.

1987-01-01

The results of ab-initio calculations are reported for (1) small transition metal clusters and (2) potential energy surfaces for chemical reactions important in hydrogen combustion and high temperature air chemistry.

Two-dimensional free-energy surface on the exchange reaction of alkyl chloride/chloride using the QM/MM-MC method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohisa, M.; Yamataka, H.; Dupuis, Michel

2007-12-05

Two-dimensional free-energy surfaces are calculated for alkyl chloride/chloride exchange/inversion reactions: Cl- + RCl (R = Me and t-Bu) surrounded by one hundred H2O molecules as a model of solvent. The methodology of free-energy calculation by perturbation theory based on a mixed-Hamiltonian model (QM/MM) combined with Monte Carlo sampling of the solvent configurations was used to obtain the changes in solvation free energy. We devised a special procedure to analyze the two-dimensional free-energy surfaces to gain unique insight into the differences in the reaction mechanisms between the two systems. The inversion reaction path for R = t-Bu on the free-energy surfacemore » is found to proceed in an asynchronous way within a concerted framework via the ion-pair region. This is in contrast to the R = Me system that proceeds as a typical SN2 reaction. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.« less

CCl 4 chemistry on the magnetite selvedge of single-crystal hematite: competitive surface reactions

NASA Astrophysics Data System (ADS)

Adib, K.; Camillone, N., III; Fitts, J. P.; Rim, K. T.; Flynn, G. W.; Joyce, S. A.; Osgood, R. M., Jr.

2002-01-01

Temperature programmed reaction/desorption (TPR/D) studies were undertaken to characterize the surface chemistry which occurs between CCl 4 and the Fe 3O 4 (1 1 1) selvedge of single crystal α-Fe 2O 3 (0 0 0 1). Six separate desorption events are clearly observed and four desorbing species are identified: CCl 4, OCCl 2, C 2Cl 4 and FeCl 2. It is proposed that OCCl 2, CCl 4 and C 2Cl 4 are produced in reactions involving the same precursor, CCl 2. Three reaction paths compete for the CCl 2 precursor: oxygen atom abstraction (for OCCl 2), molecular recombinative desorption (for CCl 4) and associative desorption (for C 2Cl 4). During the TPR/D temperature ramp, the branching ratio is observed to depend upon temperature and the availability of reactive sites. The data are consistent with a rich site-dependent chemistry.

Shape-dependence of the thermal and photochemical reactions of methanol on nanocrystalline anatase TiO2

NASA Astrophysics Data System (ADS)

Bennett, David A.; Cargnello, Matteo; Diroll, Benjamin T.; Murray, Christopher B.; Vohs, John M.

2016-12-01

Structure-activity relationships and the influence of particle size and shape on the partial- and photo-oxidation of methanol on nanocrystalline anatase TiO2 were investigated using temperature-programmed desorption. The study employed two distinct nanoparticle morphologies: truncated bipyramids exposing primarily {101} facets, and flatter platelets exposing primarily {001} surfaces, whose nominal sizes ranged from 10 to 25 nm. The platelets were found to be more active for thermally-driven reactions, such as coupling of methoxide groups to produce dimethyl ether, and deoxygenation to produce methane. A dependence of the reactivity of {001} facets for the coupling of methoxide groups to produce dimethyl ether on facet size was also observed. In contrast to the thermally-driven reactions, the bipyramidal nanoparticles were observed to be more active for a range of photochemical reactions, including oxidation and coupling to produce methyl formate, and photo-decomposition of surface methoxide species. This study also shows how well-defined nanocrystals can be used to help bridge the materials gap between studies of single crystal model catalysts and their high surface area industrial analogs.

Transpiration cooling of hypersonic blunt bodies with finite rate surface reactions

NASA Technical Reports Server (NTRS)

Henline, William D.

1989-01-01

The convective heat flux blockage to blunt body and hypersonic vehicles by transpiration cooling are presented. The general problem of mass addition to laminar boundary layers is reviewed. Results of similarity analysis of the boundary layer problem are provided for surface heat flux with transpiration cooling. Detailed non-similar results are presented from the numerical program, BLIMPK. Comparisons are made with the similarity theory. The effects of surface catalysis are investigated.

Modules based on the geochemical model PHREEQC for use in scripting and programming languages

USGS Publications Warehouse

Charlton, Scott R.; Parkhurst, David L.

2011-01-01

The geochemical model PHREEQC is capable of simulating a wide range of equilibrium reactions between water and minerals, ion exchangers, surface complexes, solid solutions, and gases. It also has a general kinetic formulation that allows modeling of nonequilibrium mineral dissolution and precipitation, microbial reactions, decomposition of organic compounds, and other kinetic reactions. To facilitate use of these reaction capabilities in scripting languages and other models, PHREEQC has been implemented in modules that easily interface with other software. A Microsoft COM (component object model) has been implemented, which allows PHREEQC to be used by any software that can interface with a COM server—for example, Excel®, Visual Basic®, Python, or MATLAB". PHREEQC has been converted to a C++ class, which can be included in programs written in C++. The class also has been compiled in libraries for Linux and Windows that allow PHREEQC to be called from C++, C, and Fortran. A limited set of methods implements the full reaction capabilities of PHREEQC for each module. Input methods use strings or files to define reaction calculations in exactly the same formats used by PHREEQC. Output methods provide a table of user-selected model results, such as concentrations, activities, saturation indices, and densities. The PHREEQC module can add geochemical reaction capabilities to surface-water, groundwater, and watershed transport models. It is possible to store and manipulate solution compositions and reaction information for many cells within the module. In addition, the object-oriented nature of the PHREEQC modules simplifies implementation of parallel processing for reactive-transport models. The PHREEQC COM module may be used in scripting languages to fit parameters; to plot PHREEQC results for field, laboratory, or theoretical investigations; or to develop new models that include simple or complex geochemical calculations.

Modules based on the geochemical model PHREEQC for use in scripting and programming languages

USGS Publications Warehouse

Charlton, S.R.; Parkhurst, D.L.

2011-01-01

The geochemical model PHREEQC is capable of simulating a wide range of equilibrium reactions between water and minerals, ion exchangers, surface complexes, solid solutions, and gases. It also has a general kinetic formulation that allows modeling of nonequilibrium mineral dissolution and precipitation, microbial reactions, decomposition of organic compounds, and other kinetic reactions. To facilitate use of these reaction capabilities in scripting languages and other models, PHREEQC has been implemented in modules that easily interface with other software. A Microsoft COM (component object model) has been implemented, which allows PHREEQC to be used by any software that can interface with a COM server-for example, Excel??, Visual Basic??, Python, or MATLAB??. PHREEQC has been converted to a C++ class, which can be included in programs written in C++. The class also has been compiled in libraries for Linux and Windows that allow PHREEQC to be called from C++, C, and Fortran. A limited set of methods implements the full reaction capabilities of PHREEQC for each module. Input methods use strings or files to define reaction calculations in exactly the same formats used by PHREEQC. Output methods provide a table of user-selected model results, such as concentrations, activities, saturation indices, and densities. The PHREEQC module can add geochemical reaction capabilities to surface-water, groundwater, and watershed transport models. It is possible to store and manipulate solution compositions and reaction information for many cells within the module. In addition, the object-oriented nature of the PHREEQC modules simplifies implementation of parallel processing for reactive-transport models. The PHREEQC COM module may be used in scripting languages to fit parameters; to plot PHREEQC results for field, laboratory, or theoretical investigations; or to develop new models that include simple or complex geochemical calculations. ?? 2011.

The formation of diethyl ether via the reaction of iodoethane with atomic oxygen on the Ag(110) surface

NASA Astrophysics Data System (ADS)

Jones, G. Scott; Barteau, Mark A.; Vohs, John M.

1999-01-01

The reactions of iodoethane (ICH 2CH 3) on clean and oxygen-covered Ag(110) surfaces were investigated using temperature-programmed desorption (TPD) and high-resolution electron energy-loss spectroscopy (HREELS). Iodoethane adsorbs dissociatively at 150 K to produce surface ethyl groups on both clean and oxygen-covered Ag(110) surfaces. The ethyl species couple to form butane on both surfaces, with the desorption peak maximum located between 218 and 238 K, depending on the ethyl coverage. In addition to butane, a number of oxidation products including diethyl ether, ethanol, acetaldehyde, surface acetate, ethylene, carbon dioxide and water were formed on the oxygen-dosed Ag(110) surface. Diethyl ether was the major oxygenate produced at all ethyl:oxygen ratios, and the peak temperature for ether evolution varied from 220 to 266 K depending on the relative coverages of these reactants. The total combustion products, CO 2 and H 2O, were primarily formed at low ethyl coverages in the presence of excess oxygen. The formation of ethylene near 240 K probably involves an oxygen-assisted dehydrogenation pathway since ethylene is not formed from ethyl groups on the clean surface. Acetaldehyde and ethanol evolve coincidentally with a peak centered at 270-280 K, and are attributed to the reactions of surface ethoxide species. The surface acetate which decomposes near 620 K is formed from subsequent reactions of acetaldehyde with oxygen atoms. The addition of ethyl to oxygen to form surface ethoxides was verified by HREELS results. The yields of all products exhibited a strong dependence on the relative coverages of ethyl and oxygen.

Lignin-derived oxygenate reforming on a bimetallic surface: The reaction of benzaldehyde on Zn/Pt(111)

NASA Astrophysics Data System (ADS)

Shi, Daming; Vohs, John M.

2016-08-01

Temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) were used to characterize the adsorption and reaction of benzaldehyde (C6H5CHO) on hydrogen-covered Pt(111) and Zn-modified Pt(111) surfaces. Benzaldehyde was found to interact with Pt(111) via both the phenyl ring and carbonyl of the aldehyde group. This bonding configuration facilitates unselective decomposition of the benzaldehyde to produce CO, H2, and small hydrocarbon fragments at relatively low temperatures. On the other hand, benzaldehyde was found to bond to Zn-decorated Pt(111) surface exclusively via the carbonyl group in an η2(C, O) configuration, with the phenyl ring tilted away from the surface. This configuration weakens Csbnd O bond in the carbonyl facilitating its cleavage and helps prevent hydrogenation of the phenyl ring.

Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo 2 C (001) Surface: A Density Functional Theory Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Mingxia; Cheng, Lei; Choi, Jae-Soon

Density functional theory (DFT) calculations were used to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (T-Mo) and C-terminated (Tc) Mo2C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O* removal were compared among undoped and Ni-doped Mo2C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such as Ni adsorbed on T-Mo and Tc Mo2C(001)more » surfaces enable weaker binding of important reactive intermediates (O*, OH*) compared to the undoped counterparts, which is beneficial for the O* removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O* removal reaction on the T-Mo Mo2C(001) and Tc Mo2C(001) surfaces. This computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo2C and Ni-doped Mo2C catalysts, which had been passivated and stored in an oxygen environment.« less

Improving catalytic selectivity through control of adsorption orientation

NASA Astrophysics Data System (ADS)

Pang, Simon H.

In this thesis, we present an investigation, starting from surface science experiments, leading to design of supported catalysts, of how adsorption orientation can be used to affect reaction selectivity of highly functional molecules. The surface chemistry of furfuryl alcohol and benzyl alcohol and their respective aldehydes was studied on a Pd(111) single-crystal surface under ultra-high vacuum conditions. Temperature-programmed desorption experiments showed that synergistic chemistry existed between the aromatic ring and the oxygen-containing functional group, each allowing the other to participate in reaction pathways that a monofunctional molecule could not. Most important of these was a deoxygenation reaction that occurred more readily when the surface was crowded by the highest exposures. High-resolution electron energy loss spectroscopy revealed that at these high exposures, molecules were oriented upright on the surface, with the aromatic function extending into vacuum. In contrast, at low exposures, molecules were oriented flat on the surface. The upright adsorption geometry was correlated with deoxygenation, whereas the flat-lying geometry was correlated with decarbonylation. The insight gained from surface science experiments was utilized in catalyst design. Self-assembled monolayers of alkanethiolates were used to systematically reduce the average surface ensemble size, and the reaction selectivity was tracked. When a sparsely-packed monolayer was used, such as one formed by 1-adamantanethiol, the reactant furfural was still able to lie flat on the surface and the reaction selectivity was similar to that of the uncoated catalyst. However, when a densely-packed monolayer, formed by 1-octadecanethiol, was used, furfural was not able to adsorb flat on the surface and instead adopted an upright conformation, leading to a drastic increase in aldehyde hydrogenation and hydrodeoxygenation reaction selectivity. Using an even higher sulfur coverage from a monolayer formed by 1,2-benzenedithiol, we determined that hydrodeoxygenation selectively occurred on catalyst particle steps and edges from an upright structure, whereas decarbonylation occurred on particle terraces from a flat-lying structure. Control of furfural adsorption orientation was also achieved through the use of NiCu bimetallic catalysts. The aromatic furan ring was repelled from surface Cu, leading to an upright structure. However, under hydrogenation conditions, Ni tended to be near the surface of thin films and catalysts, leading to less dramatic selectivity enhancement. The presence of a 1-octadecanethiol monolayer kinetically stabilized the surface termination, allowing Cu to remain at the surface.

Reaction pathways of furfural, furfuryl alcohol and 2-methylfuran on Cu(111) and NiCu bimetallic surfaces

DOE PAGES

Xiong, Ke; Wan, Weiming; Chen, Jingguang G.

2016-02-23

Hydrodeoxygenation (HDO) is an important reaction for converting biomass-derived furfural to value-added 2-methylfuran, which is a promising fuel additive. In this work, the HDO of furfural to produce 2-methylfuran occurred on the NiCu bimetallic surfaces prepared on either Ni(111) or Cu(111). The reaction pathways of furfural were investigated on Cu(111) and Ni/Cu(111) surfaces using density functional theory (DFT) calculations, temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS) experiments. These studies provided mechanistic insights into the effects of bimetallic formation on enhancing the HDO activity. Specifically, furfural weakly adsorbed on Cu(111), while it strongly adsorbed on Ni/Cu(111)more » through an η 2(C,O) configuration which led to the HDO of furfural on Ni/Cu(111). Lastly, the ability to dissociate H 2 on Ni/Cu(111) is also an important factor for enhancing the HDO activity over Cu(111).« less

Reaction pathways of furfural, furfuryl alcohol and 2-methylfuran on Cu(111) and NiCu bimetallic surfaces

NASA Astrophysics Data System (ADS)

Xiong, Ke; Wan, Weiming; Chen, Jingguang G.

2016-10-01

Hydrodeoxygenation (HDO) is an important reaction for converting biomass-derived furfural to value-added 2-methylfuran, which is a promising fuel additive. In this work, the HDO of furfural to produce 2-methylfuran occurred on the NiCu bimetallic surfaces prepared on either Ni(111) or Cu(111). The reaction pathways of furfural were investigated on Cu(111) and Ni/Cu(111) surfaces using density functional theory (DFT) calculations, temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) experiments. These studies provided mechanistic insights into the effects of bimetallic formation on enhancing the HDO activity. Specifically, furfural weakly adsorbed on Cu(111), while it strongly adsorbed on Ni/Cu(111) through an η2(C,O) configuration, which led to the HDO of furfural on Ni/Cu(111). The ability to dissociate H2 on Ni/Cu(111) is also an important factor for enhancing the HDO activity over Cu(111).

(100) facets of γ-Al2O3: the active surfaces for alcohol dehydration reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwak, Ja Hun; Mei, Donghai; Peden, Charles HF

2011-05-01

Temperature programmed desorption (TPD) of ethanol, and methanol dehydration reaction were studied on γ-Al2O3 in order to identify the catalytic active sites for alcohol dehydration reactions. Two high temperature (> 473 K) desorption features were observed following ethanol adsorption. Samples calcined at T≤473 K displayed a desorption feature in the 523-533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. The switch from the high to low temperature ethanol desorption correlated well with the dehydroxylation of the (100) facets of γ-Al2O3 that was predicted at 550 K DFT calculations. Theoreticalmore » DFT simulations of the mechanism of dehydration. on clean and hydroxylated γ-Al2O3(100) surfaces, find that a concerted elimination of ethylene from an ethanol molecule chemisorbed at an Al3+ pentacoordinated site is the rate limiting step for catalytic cycle on both surfaces. Furthermore, titration of the pentacoordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely turned off the methanol dehydration reaction activity. These results unambiguously demonstrate that only the (100) facets on γ-Al2O3 are the catalytic active surfaces for alcohol dehydration.« less

Experiments Developed to Study Microgravity Smoldering Combustion

NASA Technical Reports Server (NTRS)

Vergilii, Franklin

2001-01-01

The overall objective of the Microgravity Smoldering Combustion (MSC) research program is to understand and predict smoldering combustion under normal and microgravity (near-zero-gravity) conditions to help prevent and control smolder-originated fires, in both environments. Smoldering is defined as a nonflaming, self-sustaining, propagating, exothermic surface reaction. If a material is sufficiently permeable, smoldering is not confined to its outer surface, but can propagate as a reaction wave through the interior of the material. The MSC program will accomplish its goals by conducting smolder experiments on the ground and in a space-based laboratory, and developing theoretical models of the process. Space-based experiments are necessary because smoldering is a very slow process and, consequently, its study in a microgravity environment requires extended periods of time that can only be achieved in space. Smoldering can occur in a variety of processes ranging from the smolder of porous insulating materials to underground coal combustion. Many materials can sustain smoldering, including wood, cloth, foams, tobacco, other dry organic materials, and charcoal. The ignition, propagation, transition to flaming, and extinction of the smolder reaction are controlled by complex, thermochemical mechanisms that are not well understood. As with many forms of combustion, gravity affects the availability of the oxidizer and the transport of heat, and therefore, the rate of combustion. The smoldering combustion of porous materials has been studied both experimentally and theoretically, usually in the context of fire safety. Smoldering encompasses a number of fundamental processes, including heat and mass transfer in a porous media; endothermic pyrolysis of combustible material; ignition, propagation, and extinction of heterogeneous exothermic reactions at the solid-gas pore interface; and the onset of gas phase reactions (flaming) from existing surface reactions. Smoldering presents a serious fire risk because the combustion can propagate slowly in a material's interior and go undetected for long periods of time. It typically yields a substantially higher conversion of fuel to toxic compounds than does flaming (though more slowly), and may undergo a sudden transition to flaming.

Realistic multisite lattice-gas modeling and KMC simulation of catalytic surface reactions: Kinetics and multiscale spatial behavior for CO-oxidation on metal (1 0 0) surfaces

NASA Astrophysics Data System (ADS)

Liu, Da-Jiang; Evans, James W.

2013-12-01

A realistic molecular-level description of catalytic reactions on single-crystal metal surfaces can be provided by stochastic multisite lattice-gas (msLG) models. This approach has general applicability, although in this report, we will focus on the example of CO-oxidation on the unreconstructed fcc metal (1 0 0) or M(1 0 0) surfaces of common catalyst metals M = Pd, Rh, Pt and Ir (i.e., avoiding regimes where Pt and Ir reconstruct). These models can capture the thermodynamics and kinetics of adsorbed layers for the individual reactants species, such as CO/M(1 0 0) and O/M(1 0 0), as well as the interaction and reaction between different reactant species in mixed adlayers, such as (CO + O)/M(1 0 0). The msLG models allow population of any of hollow, bridge, and top sites. This enables a more flexible and realistic description of adsorption and adlayer ordering, as well as of reaction configurations and configuration-dependent barriers. Adspecies adsorption and interaction energies, as well as barriers for various processes, constitute key model input. The choice of these energies is guided by experimental observations, as well as by extensive Density Functional Theory analysis. Model behavior is assessed via Kinetic Monte Carlo (KMC) simulation. We also address the simulation challenges and theoretical ramifications associated with very rapid diffusion and local equilibration of reactant adspecies such as CO. These msLG models are applied to describe adsorption, ordering, and temperature programmed desorption (TPD) for individual CO/M(1 0 0) and O/M(1 0 0) reactant adlayers. In addition, they are also applied to predict mixed (CO + O)/M(1 0 0) adlayer structure on the nanoscale, the complete bifurcation diagram for reactive steady-states under continuous flow conditions, temperature programmed reaction (TPR) spectra, and titration reactions for the CO-oxidation reaction. Extensive and reasonably successful comparison of model predictions is made with experimental data. Furthermore, we discuss the possible transition from traditional mean-field-type bistability and reaction kinetics for lower-pressure to multistability and enhanced fluctuation effects for moderate- or higher-pressure. Behavior in the latter regime reflects a stronger influence of adspecies interactions and also lower diffusivity in the higher-coverage mixed adlayer. We also analyze mesoscale spatiotemporal behavior including the propagation of reaction-diffusion fronts between bistable reactive and inactive states, and associated nucleation-mediated transitions between these states. This behavior is controlled by complex surface mass transport processes, specifically chemical diffusion in mixed reactant adlayers for which we provide a precise theoretical formulation. The msLG models together with an appropriate treatment of chemical diffusivity enable equation-free heterogeneous coupled lattice-gas (HCLG) simulations of spatiotemporal behavior. In addition, msLG + HCLG modeling can describe coverage variations across polycrystalline catalysts surfaces, pressure variations across catalyst surfaces in microreactors, and could be incorporated into a multiphysics framework to describe mass and heat transfer limitations for high-pressure catalysis.

Realistic multisite lattice-gas modeling and KMC simulation of catalytic surface reactions: Kinetics and multiscale spatial behavior for CO-oxidation on metal (100) surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Dajiang; Evans, James W.

2013-12-01

A realistic molecular-level description of catalytic reactions on single-crystal metal surfaces can be provided by stochastic multisite lattice-gas (msLG) models. This approach has general applicability, although in this report, we will focus on the example of CO-oxidation on the unreconstructed fcc metal (100) or M(100) surfaces of common catalyst metals M = Pd, Rh, Pt and Ir (i.e., avoiding regimes where Pt and Ir reconstruct). These models can capture the thermodynamics and kinetics of adsorbed layers for the individual reactants species, such as CO/M(100) and O/M(100), as well as the interaction and reaction between different reactant species in mixed adlayers,more » such as (CO + O)/M(100). The msLG models allow population of any of hollow, bridge, and top sites. This enables a more flexible and realistic description of adsorption and adlayer ordering, as well as of reaction configurations and configuration-dependent barriers. Adspecies adsorption and interaction energies, as well as barriers for various processes, constitute key model input. The choice of these energies is guided by experimental observations, as well as by extensive Density Functional Theory analysis. Model behavior is assessed via Kinetic Monte Carlo (KMC) simulation. We also address the simulation challenges and theoretical ramifications associated with very rapid diffusion and local equilibration of reactant adspecies such as CO. These msLG models are applied to describe adsorption, ordering, and temperature programmed desorption (TPD) for individual CO/M(100) and O/M(100) reactant adlayers. In addition, they are also applied to predict mixed (CO + O)/M(100) adlayer structure on the nanoscale, the complete bifurcation diagram for reactive steady-states under continuous flow conditions, temperature programmed reaction (TPR) spectra, and titration reactions for the CO-oxidation reaction. Extensive and reasonably successful comparison of model predictions is made with experimental data. Furthermore, we discuss the possible transition from traditional mean-field-type bistability and reaction kinetics for lower-pressure to multistability and enhanced fluctuation effects for moderate- or higher-pressure. Behavior in the latter regime reflects a stronger influence of adspecies interactions and also lower diffusivity in the higher-coverage mixed adlayer. We also analyze mesoscale spatiotemporal behavior including the propagation of reaction diffusion fronts between bistable reactive and inactive states, and associated nucleation-mediated transitions between these states. This behavior is controlled by complex surface mass transport processes, specifically chemical diffusion in mixed reactant adlayers for which we provide a precise theoretical formulation. The msLG models together with an appropriate treatment of chemical diffusivity enable equation-free heterogeneous coupled lattice-gas (HCLG) simulations of spatiotemporal behavior. In addition, msLG + HCLG modeling can describe coverage variations across polycrystalline catalysts surfaces, pressure variations across catalyst surfaces in microreactors, and could be incorporated into a multiphysics framework to describe mass and heat transfer limitations for high-pressure catalysis. (C) 2013 Elsevier Ltd. All rights reserved.« less

Roles of oxyanions in promoting the partial oxidation of styrene on Ag(110): nitrate, carbonate, sulfite, and sulfate.

PubMed

Zhou, Ling; Madix, Robert J

2010-11-02

The promotion roles of nitrate, carbonate, sulfite, and sulfate in oxidation of styrene on Ag(110) have been studied by means of temperature-programmed reaction spectroscopy (TPRS) and X-ray photoelectron spectroscopy (XPS). While isolated nitrate leads only to the secondary oxidation of styrene, a surface co-covered by nitrate, oxygen, and 0.1 ML cesium promotes a low-temperature epoxidation pathway. XPS indicates that adsorbed surface oxygen is the oxidant in this selective reaction pathway, and, though it affects the reactivity of the surface oxygen, nitrate is a spectator. Carbonate acts as an oxygen transfer agent and exhibits similar reactivity and selectivity as an oxidant for styrene as does atomic oxygen on Ag(110). The reactivities of sulfite and sulfate are strongly dependent on their surface structures, the c(6 × 2) sulfite showing the capacity to transfer oxygen to styrene.

Fundamental studies of catalytic processing of synthetic liquids. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watson, P.R.

1994-06-15

Liquids derived from coal contain relatively high amounts of oxygenated organic compounds, mainly in the form of phenols and furans that are deleterious to the stability and quality of these liquids as fuels. Hydrodeoxygenation (HDO) using Mo/W sulfide catalysts is a promising method to accomplish this removal, but our understanding of the reactions occurring on the catalyst surface during HDO is very limited. Rather than attempting to examine the complexities of real liquids and catalysts we have adopted an approach here using model systems amenable to surface-sensitive techniques that enable us to probe in detail the fundamental processes occurring duringmore » HDO at the surfaces of well-defined model catalysts. The results of this work may lead to the development of more efficient, selective and stable catalysts. Above a S/Mo ratio of about 0.5 ML, furan does not adsorb on sulfided Mo surfaces; as the sulfur coverage is lowered increasing amounts of furan can be adsorbed. Temperature-programmed reaction spectroscopy (TPRS) reveals that C-H, C-C and C-O bond scission occurs on these surfaces. Auger spectra show characteristic changes in the nature and amount of surface carbon. Comparisons with experiments carried out with CO, H{sub 2} and alkenes show that reaction pathways include -- direct abstraction of CO at low temperatures; cracking and release of hydrogen below its normal desorption temperature; dehydrogenatin of adsorbed hydrocarbon fragments; recombination of C and O atoms and dissolution of carbon into the bulk at high temperatures. Performing the adsorption or thermal reaction in 10{sup {minus}5} torr of hydrogen does not change the mode of reaction significantly.« less

Modeling the Reaction of Fe Atoms with CCl4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Camaioni, Donald M.; Ginovska, Bojana; Dupuis, Michel

2009-01-05

The reaction of zero-valent iron with carbon tetrachloride (CCl4) in gas phase was studied using density functional theory. Temperature programmed desorption experiments over a range of Fe and CCl4 coverages on a FeO(111) surface, demonstrate a rich surface chemistry with several reaction products (C2Cl4, C2Cl6, OCCl2, CO, FeCl2, FeCl3) observed. The reactivity of Fe and CCl4 was studied under three stoichiometries, one Fe with one CCl4, one Fe with two CCl4 molecules and two Fe with one CCl4, modeling the environment of the experimental work. The electronic structure calculations give insight into the reactions leading to the experimentally observed productsmore » and suggest that novel Fe-C-Cl containing species are important intermediates in these reactions. The intermediate complexes are formed in highly exothermic reactions, in agreement with the experimentally observed reactivity with the surface at low temperature (30 K). This initial survey of the reactivity of Fe with CCl4 identifies some potential reaction pathways that are important in the effort to use Fe nano-particles to differentiate harmful pathways that lead to the formation of contaminants like chloroform (CHCl3) from harmless pathways that lead to products such as formate (HCO2-) or carbon oxides in water and soil. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.« less

PHAST Version 2-A Program for Simulating Groundwater Flow, Solute Transport, and Multicomponent Geochemical Reactions

USGS Publications Warehouse

Parkhurst, David L.; Kipp, Kenneth L.; Charlton, Scott R.

2010-01-01

The computer program PHAST (PHREEQC And HST3D) simulates multicomponent, reactive solute transport in three-dimensional saturated groundwater flow systems. PHAST is a versatile groundwater flow and solute-transport simulator with capabilities to model a wide range of equilibrium and kinetic geochemical reactions. The flow and transport calculations are based on a modified version of HST3D that is restricted to constant fluid density and constant temperature. The geochemical reactions are simulated with the geochemical model PHREEQC, which is embedded in PHAST. Major enhancements in PHAST Version 2 allow spatial data to be defined in a combination of map and grid coordinate systems, independent of a specific model grid (without node-by-node input). At run time, aquifer properties are interpolated from the spatial data to the model grid; regridding requires only redefinition of the grid without modification of the spatial data. PHAST is applicable to the study of natural and contaminated groundwater systems at a variety of scales ranging from laboratory experiments to local and regional field scales. PHAST can be used in studies of migration of nutrients, inorganic and organic contaminants, and radionuclides; in projects such as aquifer storage and recovery or engineered remediation; and in investigations of the natural rock/water interactions in aquifers. PHAST is not appropriate for unsaturated-zone flow, multiphase flow, or density-dependent flow. A variety of boundary conditions are available in PHAST to simulate flow and transport, including specified-head, flux (specified-flux), and leaky (head-dependent) conditions, as well as the special cases of rivers, drains, and wells. Chemical reactions in PHAST include (1) homogeneous equilibria using an ion-association or Pitzer specific interaction thermodynamic model; (2) heterogeneous equilibria between the aqueous solution and minerals, ion exchange sites, surface complexation sites, solid solutions, and gases; and (3) kinetic reactions with rates that are a function of solution composition. The aqueous model (elements, chemical reactions, and equilibrium constants), minerals, exchangers, surfaces, gases, kinetic reactants, and rate expressions may be defined or modified by the user. A number of options are available to save results of simulations to output files. The data may be saved in three formats: a format suitable for viewing with a text editor; a format suitable for exporting to spreadsheets and postprocessing programs; and in Hierarchical Data Format (HDF), which is a compressed binary format. Data in the HDF file can be visualized on Windows computers with the program Model Viewer and extracted with the utility program PHASTHDF; both programs are distributed with PHAST.

Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo 2C (001) Surface: A Density Functional Theory Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Mingxia; Cheng, Lei; Choi, Jae-Soon

Density functional theory (DFT) calculations were used in this paper to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (T Mo) and C-terminated (T C) Mo 2C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O* removal were compared among undoped and Ni-doped Mo 2C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such asmore » Ni adsorbed on T Mo and T C Mo 2C(001) surfaces enable weaker binding of important reactive intermediates (O*, OH*) compared to the undoped counterparts, which is beneficial for the O* removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O* removal reaction on the T Mo Mo 2C(001) and T C Mo 2C(001) surfaces. Finally, this computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo 2C and Ni-doped Mo 2C catalysts, which had been passivated and stored in an oxygen environment.« less

Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo 2C (001) Surface: A Density Functional Theory Study

DOE PAGES

Zhou, Mingxia; Cheng, Lei; Choi, Jae-Soon; ...

2017-12-22

Density functional theory (DFT) calculations were used in this paper to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (T Mo) and C-terminated (T C) Mo 2C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O* removal were compared among undoped and Ni-doped Mo 2C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such asmore » Ni adsorbed on T Mo and T C Mo 2C(001) surfaces enable weaker binding of important reactive intermediates (O*, OH*) compared to the undoped counterparts, which is beneficial for the O* removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O* removal reaction on the T Mo Mo 2C(001) and T C Mo 2C(001) surfaces. Finally, this computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo 2C and Ni-doped Mo 2C catalysts, which had been passivated and stored in an oxygen environment.« less

Characterization of porosity via secondary reactions. Final technical report, 1 September 1991--30 November 1995

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calo, J.M.; Zhang, L.; Hall, P.J.

1997-09-01

A new approach to the study of porosity and porosity development in coal chars during gasification was investigated. This approach involves the establishment of the relationships between the amount and type of surface complexes evolved during post-activation temperature programmed desorption (TPD), and the porosity, as measured by gas adsorption and small angle neutron scattering (SANS) techniques. With this new method, the total surface area and micropore volume can be determined by the interpretation of post-activation TPD spectra. The primary conclusion of this work is that it is possible to predict total surface area and micropore volume from TPD spectra. Frommore » the extended random pore model, additional information about the micropore surface area, the nonmicroporous surface area, and the mean micropore size development as a function of reaction time (or burn-off) can also be predicted. Therefore, combining the TPD technique and the extended random pore model provides a new method for the characterization of char porosity.« less

Activation calculations for trapped protons below 200 MeV: Appendix

NASA Technical Reports Server (NTRS)

Laird, C. E.

1991-01-01

Tables are given displaying of the results of the activation calculations of metal samples and other material aboard the Long Duration Exposure Facility-1 (LDEF-1) and Spacelab-2 with the computer program, PTRAP4. The computer printouts give the reaction, the reactant product, the proton reaction cross sections as a function of the energy of the incident protons, and the activation as a function of distance into the sample from the exposed surface.

International Conference on Chemical Kinetics: Program and Abstracts Held in Gaithersburg, Maryland on 17-19 June 1985.

DTIC Science & Technology

1985-06-01

relative to reactant and with the free energy of reaction. The correlation equations were derived from hyperbolic paraboloid models of the energy...obtained the differen- tial equations which define the best dividing surfaces of this type for both microcanonical and canonical cases. We have...is now generalized to non-uniform reaction systems. For kinetics-diffusion problems the equations of the generalized PAM were (similar in form to

Theoretical research program to study chemical reactions in AOTV bow shock tubes

NASA Technical Reports Server (NTRS)

Taylor, Peter

1992-01-01

Effort continued through this period to refine and expand the SIRIUS/ABACUS program package for CASSCF and RASSCF second derivatives. A new approach to computing the Gaussian integral derivatives that require much of the time in gradient and Hessian calculations was devised. Several different studies were undertaken in the area of application calculations. These include a study of proton transfer in the HF trimer, which provides an analog of rearrangement reactions, and the extension of our previous work on Be and Mg clusters to Ca clusters. In addition, a very accurate investigation of the lowest-lying potential curves of the O2 molecule was completed. These curves are essential for evaluating different models of the terrestrial atmosphere nightglow. The most effort this year was devoted to a large scale investigation of stationary points on the C4H4 surface, and the thermochemistry of acetylene/acetylene reaction.

Photodecomposition of Mo(CO)/sub 6/ adsorbed on Si(100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Creighton, J.R.

1985-01-01

The photochemical decomposition of Mo(CO)/sub 6/ layers physisorbed on Si(100) was investigated to determine the feasibility of molybdenum deposition and also to examine the photochemical reaction mechanism and efficiency. Temperature programmed desorption (TPD) was used to investigate the interaction of Mo(CO)/sub 6/ with the silicon surface before and after irradiation. Auger spectroscopy was used to determine surface elemental composition before Mo(CO)/sub 6/ adsorption and after photodecomposition.

Surface-Activated Coupling Reactions Confined on a Surface.

PubMed

Dong, Lei; Liu, Pei Nian; Lin, Nian

2015-10-20

Chemical reactions may take place in a pure phase of gas or liquid or at the interface of two phases (gas-solid or liquid-solid). Recently, the emerging field of "surface-confined coupling reactions" has attracted intensive attention. In this process, reactants, intermediates, and products of a coupling reaction are adsorbed on a solid-vacuum or a solid-liquid interface. The solid surface restricts all reaction steps on the interface, in other words, the reaction takes place within a lower-dimensional, for example, two-dimensional, space. Surface atoms that are fixed in the surface and adatoms that move on the surface often activate the surface-confined coupling reactions. The synergy of surface morphology and activity allow some reactions that are inefficient or prohibited in the gas or liquid phase to proceed efficiently when the reactions are confined on a surface. Over the past decade, dozens of well-known "textbook" coupling reactions have been shown to proceed as surface-confined coupling reactions. In most cases, the surface-confined coupling reactions were discovered by trial and error, and the reaction pathways are largely unknown. It is thus highly desirable to unravel the mechanisms, mechanisms of surface activation in particular, of the surface-confined coupling reactions. Because the reactions take place on surfaces, advanced surface science techniques can be applied to study the surface-confined coupling reactions. Among them, scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) are the two most extensively used experimental tools. The former resolves submolecular structures of individual reactants, intermediates, and products in real space, while the latter monitors the chemical states during the reactions in real time. Combination of the two methods provides unprecedented spatial and temporal information on the reaction pathways. The experimental findings are complemented by theoretical modeling. In particular, density-functional theory (DFT) transition-state calculations have been used to shed light on reaction mechanisms and to unravel the trends of different surface materials. In this Account, we discuss recent progress made in two widely studied surface-confined coupling reactions, aryl-aryl (Ullmann-type) coupling and alkyne-alkyne (Glaser-type) coupling, and focus on surface activation effects. Combined experimental and theoretical studies on the same reactions taking place on different metal surfaces have clearly demonstrated that different surfaces not only reduce the reaction barrier differently and render different reaction pathways but also control the morphology of the reaction products and, to some degree, select the reaction products. We end the Account with a list of questions to be addressed in the future. Satisfactorily answering these questions may lead to using the surface-confined coupling reactions to synthesize predefined products with high yield.

COI oxidation on a single Pd atom supported on magnesia.

PubMed

Abbet, S; Heiz, U; Häkkinen, H; Landman, U

2001-06-25

The oxidation of CO on single Pd atoms anchored to MgO(100) surface oxygen vacancies is studied with temperature-programmed-reaction mass spectrometry and infrared spectroscopy. In one-heating-cycle experiments, CO(2), formed from O(2) and CO preadsorbed at 90 K, is detected at 260 and 500 K. Ab-initio simulations suggest two reaction routes, with Pd(CO)(2)O(2) and PdCO(3)CO found as precursors for the low and high temperature channels, respectively. Both reactions result in annealing of the vacancy and induce migration and coalescence of the remaining Pd-CO to form larger clusters.

Surface reaction modification: The effect of structured overlayers of sulfur on the kinetics and mechanism of the decomposition of formic acid on Pt(111)

NASA Astrophysics Data System (ADS)

Abbas, N.; Madix, R. J.

The reaction of formic acid (DCOOH) on Pt(111), Pt(111)-(2×2)S and Pt(111)-(√3×√3)R30°S surfaces was examined by temperature programmed reaction spectroscopy. On the clean surface formic acid decomposed to yield primarily carbon dioxide and the hydrogenic species (H 2, HD and D 2) at low coverages. Although the formation of water and carbon monoxide via a dehydration reaction was observed at these coverages, the yield of these products was small when compared to the other products of reaction. The evolution of CO 2 at low temperature was ascribed to the decomposition of the formate intermediate. In the presence of sulfur the amount of molecularly adsorbed formic acid decreased up to a factor of three on the (√3×√3)R30°S surface, and a decline in the reactivity of over an order of magnitude was also observed. The only products formed were the hydrogenic species and carbon dioxide. The absence of carbon monoxide indicated that the dehydration pathway was blocked by sulfur. In addition to the low temperature CO 2 peak a high temperature CO 2-producing path was also evident. It was inferred from both the stoichiometry and the coincident evolution of D 2 and CO 2 in the high temperature states that these products also evolved due to the decomposition of the formate intermediate. On increasing the sulfur coverage to one-third monolayer this intermediate was further stabilized, and a predominance of the decomposition via the high temperature path was observed. Stability of the formate intermediate was attributed to inhibition of the decomposition reaction by sulfur atoms. The activation energy for formate decomposition increased from 15 kcal/gmole on the clean surface to 24.3 kcal/gmol on the (√3×√3)R30°S overlayer.

Programming Cell Adhesion for On-Chip Sequential Boolean Logic Functions.

PubMed

Qu, Xiangmeng; Wang, Shaopeng; Ge, Zhilei; Wang, Jianbang; Yao, Guangbao; Li, Jiang; Zuo, Xiaolei; Shi, Jiye; Song, Shiping; Wang, Lihua; Li, Li; Pei, Hao; Fan, Chunhai

2017-08-02

Programmable remodelling of cell surfaces enables high-precision regulation of cell behavior. In this work, we developed in vitro constructed DNA-based chemical reaction networks (CRNs) to program on-chip cell adhesion. We found that the RGD-functionalized DNA CRNs are entirely noninvasive when interfaced with the fluidic mosaic membrane of living cells. DNA toehold with different lengths could tunably alter the release kinetics of cells, which shows rapid release in minutes with the use of a 6-base toehold. We further demonstrated the realization of Boolean logic functions by using DNA strand displacement reactions, which include multi-input and sequential cell logic gates (AND, OR, XOR, and AND-OR). This study provides a highly generic tool for self-organization of biological systems.

Structural and surface changes of cobalt modified manganese oxide during activation and ethanol steam reforming reaction

NASA Astrophysics Data System (ADS)

Gac, Wojciech; Greluk, Magdalena; Słowik, Grzegorz; Turczyniak-Surdacka, Sylwia

2018-05-01

Surface and structural changes of unmodified manganese and cobalt-manganese oxide during activation and ethanol steam reforming reaction conditions (ESR) were studied by means of X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction/oxidation (TPR/TPO) and transmission electron microscopy. It was shown that synthesis of cobalt manganese oxide by the redox precipitation method led to the formation of strongly dispersed cobalt ionic species within cryptomelane-based manganese oxide structure. Development of large cube-like MnO nanoparticles with spherical cobalt metallic crystallites decorated by manganese oxide on the high oxidation state and potassium species was observed during reduction. Cobalt manganese catalyst showed high initial activity and selectivity to H2 and CO2 in ethanol stem reforming reaction in the range of 390-480 °C. The drop of ethanol conversion and changes of selectivity with the time-on-stream were observed. An increase of reaction temperature led to intensification of deactivation phenomena. TEM studies evidenced coexistence of Co and CoOx nanoparticles formed under ethanol steam reforming conditions, partially covered by filamentous and encapsulating carbonaceous deposits.

Application of a BOSS – Gaussian Interface for QM/MM Simulations of Henry and Methyl Transfer Reactions

PubMed Central

Vilseck, Jonah Z.; Kostal, Jakub; Tirado-Rives, Julian; Jorgensen, William L.

2015-01-01

Hybrid quantum mechanics and molecular mechanics (QM/MM) computer simulations have become an indispensable tool for studying chemical and biological phenomena for systems too large to treat with quantum mechanics alone. For several decades, semi-empirical QM methods have been used in QM/MM simulations. However, with increased computational resources, the introduction of ab initio and density function methods into on-the-fly QM/MM simulations is being increasingly preferred. This adaptation can be accomplished with a program interface that tethers independent QM and MM software packages. This report introduces such an interface for the BOSS and Gaussian programs, featuring modification of BOSS to request QM energies and partial atomic charges from Gaussian. A customizable C-shell linker script facilitates the inter-program communication. The BOSS–Gaussian interface also provides convenient access to Charge Model 5 (CM5) partial atomic charges for multiple purposes including QM/MM studies of reactions. In this report, the BOSS–Gaussian interface is applied to a nitroaldol (Henry) reaction and two methyl transfer reactions in aqueous solution. Improved agreement with experiment is found by determining free-energy surfaces with MP2/CM5 QM/MM simulations than previously reported investigations employing semiempirical methods. PMID:26311531

Computer program to solve two-dimensional shock-wave interference problems with an equilibrium chemically reacting air model

NASA Technical Reports Server (NTRS)

Glass, Christopher E.

1990-01-01

The computer program EASI, an acronym for Equilibrium Air Shock Interference, was developed to calculate the inviscid flowfield, the maximum surface pressure, and the maximum heat flux produced by six shock wave interference patterns on a 2-D, cylindrical configuration. Thermodynamic properties of the inviscid flowfield are determined using either an 11-specie, 7-reaction equilibrium chemically reacting air model or a calorically perfect air model. The inviscid flowfield is solved using the integral form of the conservation equations. Surface heating calculations at the impingement point for the equilibrium chemically reacting air model use variable transport properties and specific heat. However, for the calorically perfect air model, heating rate calculations use a constant Prandtl number. Sample calculations of the six shock wave interference patterns, a listing of the computer program, and flowcharts of the programming logic are included.

Computer program to solve two-dimensional shock-wave interference problems with an equilibrium chemically reacting air model

NASA Astrophysics Data System (ADS)

Glass, Christopher E.

1990-08-01

The computer program EASI, an acronym for Equilibrium Air Shock Interference, was developed to calculate the inviscid flowfield, the maximum surface pressure, and the maximum heat flux produced by six shock wave interference patterns on a 2-D, cylindrical configuration. Thermodynamic properties of the inviscid flowfield are determined using either an 11-specie, 7-reaction equilibrium chemically reacting air model or a calorically perfect air model. The inviscid flowfield is solved using the integral form of the conservation equations. Surface heating calculations at the impingement point for the equilibrium chemically reacting air model use variable transport properties and specific heat. However, for the calorically perfect air model, heating rate calculations use a constant Prandtl number. Sample calculations of the six shock wave interference patterns, a listing of the computer program, and flowcharts of the programming logic are included.

The NATA code; theory and analysis. Volume 2: User's manual

NASA Technical Reports Server (NTRS)

Bade, W. L.; Yos, J. M.

1975-01-01

The NATA code is a computer program for calculating quasi-one-dimensional gas flow in axisymmetric nozzles and rectangular channels, primarily to describe conditions in electric archeated wind tunnels. The program provides solutions based on frozen chemistry, chemical equilibrium, and nonequilibrium flow with finite reaction rates. The shear and heat flux on the nozzle wall are calculated and boundary layer displacement effects on the inviscid flow are taken into account. The program contains compiled-in thermochemical, chemical kinetic and transport cross section data for high-temperature air, CO2-N2-Ar mixtures, helium, and argon. It calculates stagnation conditions on axisymmetric or two-dimensional models and conditions on the flat surface of a blunt wedge. Included in the report are: definitions of the inputs and outputs; precoded data on gas models, reactions, thermodynamic and transport properties of species, and nozzle geometries; explanations of diagnostic outputs and code abort conditions; test problems; and a user's manual for an auxiliary program (NOZFIT) used to set up analytical curvefits to nozzle profiles.

Surface science studies of ethene containing model interstellar ices

NASA Astrophysics Data System (ADS)

Puletti, F.; Whelan, M.; Brown, W. A.

2011-05-01

The formation of saturated hydrocarbons in the interstellar medium (ISM) is difficult to explain only by taking into account gas phase reactions. This is mostly due to the fact that carbonium ions only react with H_2 to make unsaturated hydrocarbons, and hence no viable route to saturated hydrocarbons has been postulated to date. It is therefore likely that saturation processes occur via surface reactions that take place on interstellar dust grains. One of the species of interest in this family of reactions is C_2H_4 (ethene) which is an intermediate in several molecular formation routes (e.g. C_2H_2 → C_2H_6). To help to understand some of the surface processes involving ethene, a study of ethene deposited on a dust grain analogue surface (highly oriented pyrolytic graphite) held under ultra-high vacuum at 20 K has been performed. The adsorption and desorption of ethene has been studied both in water-free and water-dominated model interstellar ices. A combination of temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) have been used to identify the adsorbed and trapped species and to determine the kinetics of the desorption processes. In all cases, ethene is found to physisorb on the carbonaceous surface. As expected water has a very strong influence on the desorption of ethene, as previously observed for other model interstellar ice systems.

The rate of chemical weathering of pyrite on the surface of Venus

NASA Technical Reports Server (NTRS)

Fegley, B., Jr.; Lodders, K.

1993-01-01

This abstract reports results of an experimental study of the chemical weathering of pyrite (FeS2) under Venus-like conditions. This work, which extends the earlier study by Fegley and Treiman, is part of a long range research program to experimentally measure the rates of thermochemical gas-solid reactions important in the atmospheric-lithospheric sulfur cycle on Venus. The objectives of this research are (1) to measure the kinetics of thermochemical gas-solid reactions responsible for both the production (e.g., anhydrite formation) and destruction (e.g., pyrrhotite oxidation) of sulfur-bearing minerals on the surface of Venus and (2) to incorporate these and other constraints into holistic models of the chemical interactions between the atmosphere and surface of Venus. Experiments were done with single crystal cubes of natural pyrite (Navajun, Logrono, Spain) that were cut and polished into slices of known weight and surface area. The slices were isothermally heated at atmospheric pressure in 99.99 percent CO2 (Coleman Instrument Grade) at either 412 C (685 K) or 465 C (738 K) for time periods up to 10 days. These two isotherms correspond to temperatures at about 6 km and 0 km altitude, respectively, on Venus. The reaction rate was determined by measuring the weight loss of the reacted slices after removal from the furnace. The reaction products were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy on the SEM.

The READY program: Building a global potential energy surface and reactive dynamic simulations for the hydrogen combustion.

PubMed

Mogo, César; Brandão, João

2014-06-30

READY (REActive DYnamics) is a program for studying reactive dynamic systems using a global potential energy surface (PES) built from previously existing PESs corresponding to each of the most important elementary reactions present in the system. We present an application to the combustion dynamics of a mixture of hydrogen and oxygen using accurate PESs for all the systems involving up to four oxygen and hydrogen atoms. Results at the temperature of 4000 K and pressure of 2 atm are presented and compared with model based on rate constants. Drawbacks and advantages of this approach are discussed and future directions of research are pointed out. Copyright © 2014 Wiley Periodicals, Inc.

Cirrus cloud mimic surfaces in the laboratory: organic acids, bases and NOx heterogeneous reactions

NASA Astrophysics Data System (ADS)

Sodeau, J.; Oriordan, B.

2003-04-01

CIRRUS CLOUD MIMIC SURFACES IN THE LABORATORY:ORGANIC ACIDS, BASES AND NOX HETEROGENEOUS REACTIONS. B. ORiordan, J. Sodeau Department of Chemistry and Environment Research Institute, University College Cork, Ireland j.sodeau@ucc.ie /Fax: +353-21-4902680 There are a variety of biogenic and anthropogenic sources for the simple carboxylic acids to be found in the troposphere giving rise to levels as high as 45 ppb in certain urban areas. In this regard it is of note that ants of genus Formica produce some 10Tg of formic acid each year; some ten times that produced by industry. The expected sinks are those generally associated with tropospheric chemistry: the major routes studied, to date, being wet and dry deposition. No studies have been carried out hitherto on the role of water-ice surfaces in the atmospheric chemistry of carboxylic acids and the purpose of this paper is to indicate their potential function in the heterogeneous release of atmospheric species such as HONO. The deposition of formic acid on a water-ice surface was studied using FT-RAIR spectroscopy over a range of temperatures between 100 and 165K. In all cases ionization to the formate (and oxonium) ions was observed. The results were confirmed by TPD (Temperature Programmed Desorption) measurements, which indicated that two distinct surface species adsorb to the ice. Potential reactions between the formic acid/formate ion surface and nitrogen dioxide were subsequently investigated by FT-RAIRS. Co-deposition experiments showed that N2O3 and the NO+ ion (associated with water) were formed as products. A mechanism is proposed to explain these results, which involves direct reaction between the organic acid and nitrogen dioxide. Similar experiments involving acetic acid also indicate ionization on a water-ice surface. The results are put into the context of atmospheric chemistry potentially occuring on cirrus cloud surfaces.

Lithium cell reactions

NASA Astrophysics Data System (ADS)

Clark, W.; Dampier, F.; McDonald, R.; Lombardi, A.; Batson, D.

1985-02-01

The objectives of Part 1 of this program were to: (1) investigate reactions occurring in the Li/SOCl2 cell for a range of specified test conditions, and (2) to perform analyses to identify reactants, intermediates and products generated by the chemical and electrochemical reactions occuring in the cell and to assess their impact upon safety and performance. The stoichiometry of the SOCl2 reduction reaction was investigated in 0.6 Ahr prototype cells by extracting the cells five times with pure SOCl2, after discharge then analyzing the combined extracts for SO2 by quantitative IR spectroscopy. The cells had high electrolyte-to-carbon mass ratios comparable to those in commercial cells. The multiple SOCl2 extraction procedure was developed to recover the SO2 discharge product adsorbed on the high surface area carbon electrode.

Implementation of a vibrationally linked chemical reaction model for DSMC

NASA Technical Reports Server (NTRS)

Carlson, A. B.; Bird, Graeme A.

1994-01-01

A new procedure closely linking dissociation and exchange reactions in air to the vibrational levels of the diatomic molecules has been implemented in both one- and two-dimensional versions of Direct Simulation Monte Carlo (DSMC) programs. The previous modeling of chemical reactions with DSMC was based on the continuum reaction rates for the various possible reactions. The new method is more closely related to the actual physics of dissociation and is more appropriate to the particle nature of DSMC. Two cases are presented: the relaxation to equilibrium of undissociated air initially at 10,000 K, and the axisymmetric calculation of shuttle forebody heating during reentry at 92.35 km and 7500 m/s. Although reaction rates are not used in determining the dissociations or exchange reactions, the new method produces rates which agree astonishingly well with the published rates derived from experiment. The results for gas properties and surface properties also agree well with the results produced by earlier DSMC models, equilibrium air calculations, and experiment.

The surface reactivity of acrylonitrile with oxygen atoms on an analogue of interstellar dust grains

NASA Astrophysics Data System (ADS)

Kimber, Helen J.; Toscano, Jutta; Price, Stephen D.

2018-06-01

Experiments designed to reveal the low-temperature reactivity on the surfaces of interstellar dust grains are used to probe the heterogeneous reaction between oxygen atoms and acrylonitrile (C2H3CN, H2C=CH-CN). The reaction is studied at a series of fixed surface temperatures between 14 and 100 K. After dosing the reactants on to the surface, temperature-programmed desorption, coupled with time-of-flight mass spectrometry, reveals the formation of a product with the molecular formula C3H3NO. This product results from the addition of a single oxygen atom to the acrylonitrile reactant. The oxygen atom attack appears to occur exclusively at the C=C double bond, rather than involving the cyano(-CN) group. The absence of reactivity at the cyano site hints that full saturation of organic molecules on dust grains may not always occur in the interstellar medium. Modelling the experimental data provides a reaction probability of 0.007 ± 0.003 for a Langmuir-Hinshelwood style (diffusive) reaction mechanism. Desorption energies for acrylonitrile, oxygen atoms, and molecular oxygen, from the multilayer mixed ice their deposition forms, are also extracted from the kinetic model and are 22.7 ± 1.0 kJ mol-1 (2730 ± 120 K), 14.2 ± 1.0 kJ mol-1 (1710 ± 120 K), and 8.5 ± 0.8 kJ mol-1 (1020 ± 100 K), respectively. The kinetic parameters we extract from our experiments indicate that the reaction between atomic oxygen and acrylonitrile could occur on interstellar dust grains on an astrophysical time-scale.

Life Sciences Implications of Lunar Surface Operations

NASA Technical Reports Server (NTRS)

Chappell, Steven P.; Norcross, Jason R.; Abercromby, Andrew F.; Gernhardt, Michael L.

2010-01-01

The purpose of this report is to document preliminary, predicted, life sciences implications of expected operational concepts for lunar surface extravehicular activity (EVA). Algorithms developed through simulation and testing in lunar analog environments were used to predict crew metabolic rates and ground reaction forces experienced during lunar EVA. Subsequently, the total metabolic energy consumption, the daily bone load stimulus, total oxygen needed, and other variables were calculated and provided to Human Research Program and Exploration Systems Mission Directorate stakeholders. To provide context to the modeling, the report includes an overview of some scenarios that have been considered. Concise descriptions of the analog testing and development of the algorithms are also provided. This document may be updated to remain current with evolving lunar or other planetary surface operations, assumptions and concepts, and to provide additional data and analyses collected during the ongoing analog research program.

CHAP III- CHARRING ABLATOR PROGRAM FOR ADVANCED INVESTIGATION OF THERMAL PROTECTION SYSTEMS FOR ENTRY

NASA Technical Reports Server (NTRS)

Stroud, C. W.

1994-01-01

The transient response of a thermal protection material to heat applied to the surface can be calculated using the CHAP III computer program. CHAP III can be used to analyze pyrolysis gas chemical kinetics in detail and examine pyrolysis reactions-indepth. The analysis includes the deposition of solid products produced by chemical reactions in the gas phase. CHAP III uses a modelling technique which can approximate a wide range of ablation problems. The energy equation used in CHAP III incorporates pyrolysis (both solid and gas reactions), convection, conduction, storage, work, kinetic energy, and viscous dissipation. The chemically reacting components of the solid are allowed to vary as a function of position and time. CHAP III employs a finite difference method to approximate the energy equations. Input values include specific heat, thermal conductivity, thermocouple locations, enthalpy, heating rates, and a description of the chemical reactions expected. The output tabulates the temperature at locations throughout the ablator, gas flow within the solid, density of the solid, weight of pyrolysis gases, and rate of carbon deposition. A sample case is included, which analyzes an ablator material containing several pyrolysis reactions subjected to an environment typical of entry at lunar return velocity. CHAP III is written in FORTRAN IV for batch execution and has been implemented on a CDC CYBER 170 series computer operating under NOS with a central memory requirement of approximately 102K (octal) of 60 bit words. This program was developed in 1985.

Orion Service Module Reaction Control System Plume Impingement Analysis Using PLIMP/RAMP2

NASA Technical Reports Server (NTRS)

Wang, Xiao-Yen J.; Gati, Frank; Yuko, James R.; Motil, Brian J.; Lumpkin, Forrest E.

2009-01-01

The Orion Crew Exploration Vehicle Service Module Reaction Control System engine plume impingement was computed using the plume impingement program (PLIMP). PLIMP uses the plume solution from RAMP2, which is the refined version of the reacting and multiphase program (RAMP) code. The heating rate and pressure (force and moment) on surfaces or components of the Service Module were computed. The RAMP2 solution of the flow field inside the engine and the plume was compared with those computed using GASP, a computational fluid dynamics code, showing reasonable agreement. The computed heating rate and pressure using PLIMP were compared with the Reaction Control System plume model (RPM) solution and the plume impingement dynamics (PIDYN) solution. RPM uses the GASP-based plume solution, whereas PIDYN uses the SCARF plume solution. Three sets of the heating rate and pressure solutions agree well. Further thermal analysis on the avionic ring of the Service Module showed that thermal protection is necessary because of significant heating from the plume.

A real-time digital computer program for the simulation of automatic spacecraft reentries

NASA Technical Reports Server (NTRS)

Kaylor, J. T.; Powell, L. F.; Powell, R. W.

1977-01-01

The automatic reentry flight dynamics simulator, a nonlinear, six-degree-of-freedom simulation, digital computer program, has been developed. The program includes a rotating, oblate earth model for accurate navigation calculations and contains adjustable gains on the aerodynamic stability and control parameters. This program uses a real-time simulation system and is designed to examine entries of vehicles which have constant mass properties whose attitudes are controlled by both aerodynamic surfaces and reaction control thrusters, and which have automatic guidance and control systems. The program has been used to study the space shuttle orbiter entry. This report includes descriptions of the equations of motion used, the control and guidance schemes that were implemented, the program flow and operation, and the hardware involved.

Effect of different promoter precursors in a model Ru-Cs/graphite system on the catalytic selectivity for Fischer-Tropsch reaction

NASA Astrophysics Data System (ADS)

Eslava, José L.; Iglesias-Juez, Ana; Fernández-García, Marcos; Guerrero-Ruiz, Antonio; Rodríguez-Ramos, Inmaculada

2018-07-01

The effect of using two different promoter precursors on the Fischer-Tropsch synthesis was studied over cesium promoted ruthenium catalysts supported on a high surface area graphite support. In this work we reveal significant modifications in the selectivity values for Fischer-Tropsch reaction depending on the Cs promoter precursor (CsCl vs CsNO3). Specifically the bimetallic catalyst (4Ru-4Cs), prepared from nitrates both for metal and promoter precursors, showed a high selectivity to CO2 during reaction. By modifying the cesium precursor, it was possible to inhibit the water gas shift reaction, decreasing significantly the selectivity to CO2. In order to understand the chemical origin of these modifications a careful characterization of the materials was performed including: X-ray absorption near edge spectroscopy, transmission electron microscopy measurements, temperature programmed reduction studies, determination of the CO uptakes on the catalysts and the evolution of the CO adsorption heats as a function of surface coverages. It was found that upon reduction and under reaction atmosphere the promoter in the ex-nitrate catalyst appears as Cs2O which is considered responsible of the CO2 production, while in the catalysts prepared with Cs chloride the promoter remains as CsCl suffering a slight partial reduction.

Development of a Detailed Surface Chemistry Framework in DSMC

NASA Technical Reports Server (NTRS)

Swaminathan-Gopalan, K.; Borner, A.; Stephani, K. A.

2017-01-01

Many of the current direct simulation Monte Carlo (DSMC) codes still employ only simple surface catalysis models. These include only basic mechanisms such as dissociation, recombination, and exchange reactions, without any provision for adsorption and finite rate kinetics. Incorporating finite rate chemistry at the surface is increasingly becoming a necessity for various applications such as high speed re-entry flows over thermal protection systems (TPS), micro-electro-mechanical systems (MEMS), surface catalysis, etc. In the recent years, relatively few works have examined finite-rate surface reaction modeling using the DSMC method.In this work, a generalized finite-rate surface chemistry framework incorporating a comprehensive list of reaction mechanisms is developed and implemented into the DSMC solver SPARTA. The various mechanisms include adsorption, desorption, Langmuir-Hinshelwood (LH), Eley-Rideal (ER), Collision Induced (CI), condensation, sublimation, etc. The approach is to stochastically model the various competing reactions occurring on a set of active sites. Both gas-surface (e.g., ER, CI) and pure-surface (e.g., LH, desorption) reaction mechanisms are incorporated. The reaction mechanisms could also be catalytic or surface altering based on the participation of the bulk-phase species (e.g., bulk carbon atoms). Marschall and MacLean developed a general formulation in which multiple phases and surface sites are used and we adopt a similar convention in the current work. Microscopic parameters of reaction probabilities (for gas-surface reactions) and frequencies (for pure-surface reactions) that are require for DSMC are computed from the surface properties and macroscopic parameters such as rate constants, sticking coefficients, etc. The energy and angular distributions of the products are decided based on the reaction type and input parameters. Thus, the user has the capability to model various surface reactions via user-specified reaction rate constants, surface properties and parameters.

Final Technical Report. Reactivity of Iron-Bearing Minerals and CO 2 Sequestration and Surface Chemistry of Pyrite. An Interdisciplinary Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strongin, Daniel

2014-12-31

Over the course of the scientific program, two areas of research were pursued: reactions of iron oxides with supercritical CO 2 and sulfide and surface reactivity of pyrite. The latter area of interest was to understand the chemistry that results when supercritical CO 2 (scCO 2 ) with H 2 S and/or SO 2 in deep saline formations (DFS) contacts iron bearing minerals. Understanding the complexities the sulfur co-injectants introduce is a critical step in developing CO 2 sequestration as a climate-mitigating strategy. The research strategy was to understand macroscopic observations of this chemistry with anmore » atomic/molecular level view using surface analytical techniques. Research showed that the exposure of iron (oxyhdr)oxides (which included ferrihydrite, goethite, and hematite) to scCO 2 in the presence of sulfide led to reactions that formed siderite (FeCO 3). The results have important implications for the sequestration of CO 2 via carbonation reactions in the Earth’s subsurface. An earlier area of focus in the project was to understand pyrite oxidation in microscopic detail. This understanding was used to understand macroscopic observations of pyrite reactivity. Results obtained from this research led to a better understanding how pyrite reacts in a range of chemical environments. Geochemical and modern surface science techniques were used to understand the chemistry of pyrite in important environmental conditions. The program relied on a strong integration the results of these techniques to provide a fundamental understanding to the macroscopic chemistry exhibited by pyrite in the environment. Major achievements during these studies included developing an understanding of the surface sites on pyrite that controlled its reactivity under oxidizing conditions. In particular sulfur anion vacancies and/or ferric sites were sites of reactivity. Studies also showed that the adsorption of phospholipid on the surface to selectively suppress the reactivity of these sites could of potential importance for suppressing acid mine drainage in the environment (a problem common to coal-mining sites). Biotic studies showed that microbial activity that promotes the oxidation of pyrite to produce AMD could also be suppressed by the adsorption of phospholipid.« less

Reaction of methyl formate with VC(1 0 0) and TiC(1 0 0) surfaces

NASA Astrophysics Data System (ADS)

Frantz, Peter; Kim, Hyun I.; Didziulis, Stephen V.; Li, Shuang; Chen, Zhiying; Perry, Scott S.

2005-12-01

The chemistry of the (1 0 0) surface of the tribologically important materials vanadium carbide (VC) and titanium carbide (TiC) with methyl formate (CH 3OCHO) has been studied with X-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS), and temperature programmed desorption (TPD). The molecule reacts with each surface at temperatures below 150 K, although the extent of reaction is greater on the TiC surface. XPS and HREELS results indicate that the first step in this chemistry is the cleavage of the CH 3O-CHO bond, generating surface methoxy groups (CH 3O-) and either carbon monoxide on VC or a formyl (CHO) group on TiC. The methoxy group reacts further on both surfaces via pathways expected based on previous methanol adsorption studies, primarily decomposing through a formyl intermediate on VC to generate formaldehyde and evolving methanol on TiC. The formyl group formed directly from methyl formate on TiC enables the production and evolution of formaldehyde, and also appears to break down further to the elements. These results indicate a propensity for these carbides to react with esters, leading potentially to the beneficial formation of friction lowering surface films or the deleterious degradation of ester-based lubricants.

Elucidation of Active Sites for the Reaction of Ethanol on TiO 2 /Au(111)

DOE PAGES

Boyle, David T.; Wilke, Jeremy A.; Palomino, Robert M.; ...

2017-03-17

Obtaining a molecular-level understanding of the reaction of alcohols with heterogeneous model catalysts is critical for improving industrial catalytic processes, such as the production of H 2 from alcohols. Gold has been shown to be an excellent oxidation catalyst once oxygen is added to it. The use of reducible oxides provides a source of oxygen on Au(111) for the reaction of ethanol, which is easily regenerated in the presence of an oxygen background. In this work, ethanol operates as a probe molecule to investigate the role of Au(111), TiO 2 nanoparticles, and TiO 2/Au interfacial surface sites on the catalyticmore » properties of TiO 2/Au(111). Ultrahigh vacuum temperature-programmed desorption (TPD) studies with ethanol/Au(111) elucidate previously unreported adsorption sites for ethanol. Ethanol molecularly adsorbs to Au terrace sites, step edges, and undercoordinated kink sites with adsorption energies of -51.7, -55.8, and -65.1 kJ/mol, respectively. In a TPD coverage study of ethanol on TiO 2/Au(111) indicates ethanol undergoes dissociative adsorption to form H*(a) and CH 3CH 2O*(a) on the inverse model catalyst surface. The desorption temperature of low coverages of ethanol from TiO2/Au(111) (Tdes ≈ 235 K) is at an intermediate temperature between the desorption temperatures from bulk Au(111) and TiO 2(110), indicating both Au and TiO 2 play a role in the adsorption of ethanol. Both low-temperature adsorption and high-temperature reactions are studied and indicate that ethanol-derived products such as acetaldehyde and ethylene desorb from TiO 2/Au(111) at ~500 K. Here, we report the identification of catalytically active sites on TiO 2/Au(111) as interfacial sites between the oxide and Au(111) surface through the use of temperature-programmed desorption and infrared reflection absorption spectroscopy.« less

Elucidation of Active Sites for the Reaction of Ethanol on TiO 2 /Au(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyle, David T.; Wilke, Jeremy A.; Palomino, Robert M.

Obtaining a molecular-level understanding of the reaction of alcohols with heterogeneous model catalysts is critical for improving industrial catalytic processes, such as the production of H 2 from alcohols. Gold has been shown to be an excellent oxidation catalyst once oxygen is added to it. The use of reducible oxides provides a source of oxygen on Au(111) for the reaction of ethanol, which is easily regenerated in the presence of an oxygen background. In this work, ethanol operates as a probe molecule to investigate the role of Au(111), TiO 2 nanoparticles, and TiO 2/Au interfacial surface sites on the catalyticmore » properties of TiO 2/Au(111). Ultrahigh vacuum temperature-programmed desorption (TPD) studies with ethanol/Au(111) elucidate previously unreported adsorption sites for ethanol. Ethanol molecularly adsorbs to Au terrace sites, step edges, and undercoordinated kink sites with adsorption energies of -51.7, -55.8, and -65.1 kJ/mol, respectively. In a TPD coverage study of ethanol on TiO 2/Au(111) indicates ethanol undergoes dissociative adsorption to form H*(a) and CH 3CH 2O*(a) on the inverse model catalyst surface. The desorption temperature of low coverages of ethanol from TiO2/Au(111) (Tdes ≈ 235 K) is at an intermediate temperature between the desorption temperatures from bulk Au(111) and TiO 2(110), indicating both Au and TiO 2 play a role in the adsorption of ethanol. Both low-temperature adsorption and high-temperature reactions are studied and indicate that ethanol-derived products such as acetaldehyde and ethylene desorb from TiO 2/Au(111) at ~500 K. Here, we report the identification of catalytically active sites on TiO 2/Au(111) as interfacial sites between the oxide and Au(111) surface through the use of temperature-programmed desorption and infrared reflection absorption spectroscopy.« less

Structural and surface properties of CuO-ZnO-Cr{sub 2}O{sub 3} catalysts and their relationship with selectivity to higher alcohol synthesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campos-Martin, J.M.; Fierro, J.L.G.; Guerrero-Ruiz, A.

1995-10-01

A series of copper-zinc-chromium catalysts of different compositions and calcination temperatures has been prepared, characterized by several techniques (BET specific surface area, XRD, gravimetric TPR, TPD-CO, and XPS), and tested under high alcohol synthesis (HAS) conditions. CO hydrogenation was carried out at reaction temperatures of 523-598 K and 50 bar total pressure. The influence of catalyst composition, calcination temperature, and surface characteristics on the HAS selectivity was studied. The optimum HAS yields were found in the low Cr content region, but chromium was needed. Although chromium oxide does not seem to be involved in the catalytic site, its presence inmore » the catalyst composition is essential, owing to the larger specific surfaces and catalyst stability obtained at the highest reaction temperatures. For low Cr content composition, the temperature-programmed reduction (TPR) profiles were shifted to higher temperatures and simultaneously larger CO{sub 2} amounts were found in the temperature-programmed desorption profiles of adsorbed CO (TPD-CO). Photoelectron spectra (XPS) revealed that the oxidation state of copper is Cu{sup 2+} in the calcined catalysts and Cu{sup O} in the reduced ones; Cu{sup +} was only stabilized in a CuCr{sub 2}O{sub 4} spinel in the Cr-rich catalysts. These features derived from catalyst characterization are discussed in the framework of the catalytic behaviour for HAS synthesis. 53 refs., 7 figs., 4 tabs.« less

Studies of the kinetics and mechanisms of perfluoroether reactions on iron and oxidized iron surfaces

NASA Technical Reports Server (NTRS)

Napier, Mary E.; Stair, Peter C.

1992-01-01

Polymeric perfluoroalkylethers are being considered for use as lubricants in high temperature applications, but have been observed to catalytically decompose in the presence of metals. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) were used to explore the decomposition of three model fluorinated ethers on clean polycrystalline iron surfaces and iron surfaces chemically modified with oxygen. Low temperature adsorption of the model fluorinated ethers on the clean, oxygen modified and oxidized iron surfaces was molecular. Thermally activated defluorination of the three model compounds was observed on the clean iron surface at remarkably low temperatures, 155 K and below, with formation of iron fluoride. Preferential C-F bond scission occurred at the terminal fluoromethoxy, CF3O, of perfluoro-1-methoxy-2-ethoxy ethane and perfluoro-1-methoxy-2-ethoxy propane and at CF3/CF2O of perfluoro-1,3-diethoxy propane. The reactivity of the clean iron toward perfluoroalkylether decomposition when compared to other metals is due to the strength of the iron fluoride bond and the strong electron donating ability of the metallic iron. Chemisorption of an oxygen overlayer lowered the reactivity of the iron surface to the adsorption and decomposition of the three model fluorinated ethers by blocking active sites on the metal surface. Incomplete coverage of the iron surface with chemisorbed oxygen results in a reaction which resembles the defluorination reaction observed on the clean iron surface. Perfluoro-1-methoxy-2-ethoxy ethane reacts on the oxidized iron surface at 138 K, through a Lewis acid assisted cleavage of the carbon oxygen bond, with preferential attack at the terminal fluoromethoxy, CF3O. The oxidized iron surface did not passivate, but became more reactive with time. Perfluoro-1-methoxy-2-ethoxy propane and perfluoro-1,3-diethoxy propane desorbed prior to the observation of decomposition on the oxidized iron surface.

Kinetic Model Development for the Combustion of Particulate Matter from Conventional and Soy Methyl Ester Diesel Fuels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strzelec, Andrea

2009-12-01

The primary objective of this research has been to investigate how the oxidation characteristics of diesel particulate matter (PM) are affected by blending soy-based biodiesel fuel with conventional ultra low sulfur diesel (ULSD) fuel. PM produced in a light duty engine from different biodiesel-conventional fuel blends was subjected to a range of physical and chemical measurements in order to better understand the mechanisms by which fuel-related changes to oxidation reactivity are brought about. These observations were then incorporated into a kinetic model to predict PM oxidation. Nanostructure of the fixed carbon was investigated by HR-TEM and showed that particulates frommore » biodiesel had a more open structure than particulates generated from conventional diesel fuel, which was confirmed by BET surface area measurements. Surface area evolution with extent of oxidation reaction was measured for PM from ULSD and biodiesel. Biodiesel particulate has a significantly larger surface area for the first 40% of conversion, at which point the samples become quite similar. Oxidation characteristics of nascent PM and the fixed carbon portion were measured by temperature programmed oxidation (TPO) and it was noted that increased biodiesel blending lowered the light-off temperature as well as the temperature where the peak rate of oxidation occurred. A shift in the oxidation profiles of all fuels was seen when the mobile carbon fraction was removed, leaving only the fixed carbon, however the trend in temperature advantage of the biofuel blending remained. The mobile carbon fraction was measured by temperature programmed desorption found to generally increase with increasing biodiesel blend level. The relative change in the light-off temperatures for the nascent and fixed carbon samples was found to be related to the fraction of mobile carbon. Effective Arrhenius parameters for fixed carbon oxidation were directly measured with isothermal, differential oxidation experiments. Normalizing the reaction rate to the total carbon surface area available for reaction allowed for the definition of a single reaction rate with constant activation energy (112.5 {+-} 5.8 kJ/mol) for the oxidation of PM, independent of its fuel source. A kinetic model incorporating the surface area dependence of fixed carbon oxidation rate and the impact of the mobile carbon fraction was constructed and validated against experimental data.« less

On-surface synthesis on a bulk insulator surface

NASA Astrophysics Data System (ADS)

Richter, Antje; Floris, Andrea; Bechstein, Ralf; Kantorovich, Lev; Kühnle, Angelika

2018-04-01

On-surface synthesis has rapidly emerged as a most promising approach to prepare functional molecular structures directly on a support surface. Compared to solution synthesis, performing chemical reactions on a surface offers several exciting new options: due to the absence of a solvent, reactions can be envisioned that are otherwise not feasible due to the insolubility of the reaction product. Perhaps even more important, the confinement to a two-dimensional surface might enable reaction pathways that are not accessible otherwise. Consequently, on-surface synthesis has attracted great attention in the last decade, with an impressive number of classical reactions transferred to a surface as well as new reactions demonstrated that have no classical analogue. So far, the majority of the work has been carried out on conducting surfaces. However, when aiming for electronic decoupling of the resulting structures, e.g. for the use in future molecular electronic devices, non-conducting surfaces are highly desired. Here, we review the current status of on-surface reactions demonstrated on the (10.4) surface of the bulk insulator calcite. Besides thermally induced C-C coupling of halogen-substituted aryls, photochemically induced [2  +  2] cycloaddition has been proven possible on this surface. Moreover, experimental evidence exists for coupling of terminal alkynes as well as diacetylene polymerization. While imaging of the resulting structures with dynamic atomic force microscopy provides a direct means of reaction verification, the detailed reaction pathway often remains unclear. Especially in cases where the presence of metal atoms is known to catalyze the corresponding solution chemistry reaction (e.g. in the case of the Ullmann reaction), disclosing the precise reaction pathway is of importance to understand and generalize on-surface reactivity on a bulk insulator surface. To this end, density-functional theory calculations have proven to provide atomic-scale insights that have greatly contributed to unravelling the details of on-surface synthesis on a bulk insulator surface.

Dehydration and Dehydrogenation of Ethylene Glycol on Rutile TiO2(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhenjun; Kay, Bruce D.; Dohnalek, Zdenek

2013-08-07

The interactions of ethylene glycol (EG) with partially reduced rutile TiO2(110) surface have been studied using temperature programmed desorption (TPD). The saturation coverage on the surface Ti rows is determined to be 0.43 monolayer (ML), slightly less than one EG per two Ti sites. Most of the adsorbed ethanol (~80%) undergoes further reactions to other products. Two major channels are observed, dehydration yielding ethylene and water and dehydrogenation yielding acetaldehyde and hydrogen. Hydrogen formation is rather surprising as it has not been observed previously on TiO2(110) from simple organic molecules. The coverage dependent yields of ethylene and acetaldehyde correlate wellmore » with that of water and hydrogen, respectively. Dehydration dominates at lower EG coverages (< 0.2 ML) and plateaus as the coverage is increased to saturation. Dehydrogenation is observed primarily at higher EG coverages (>0.2 ML). Our results suggest that the observed dehydration and dehydrogenation reactions proceed via different surface intermediates.« less

Surface Characterization of Mesoporous CoOx/SBA-15 Catalyst upon 1,2-Dichloropropane Oxidation.

PubMed

Finocchio, Elisabetta; Gonzalez-Prior, Jonatan; Gutierrez-Ortiz, Jose Ignacio; Lopez-Fonseca, Ruben; Busca, Guido; de Rivas, Beatriz

2018-05-29

The active combustion catalyst that is based on 30 wt % cobalt oxide on mesoporous SBA-15 has been tested in 1,2-dichloropropane oxidation and is characterized by means of FT-IR (Fourier transform infrared spectroscopy) and ammonia-TPD (temperature-programmed desorption). In this work, we report the spectroscopic evidence for the role of surface acidity in chloroalkane conversion. Both Lewis acidity and weakly acidic silanol groups from SBA support are involved in the adsorption and initial conversion steps. Moreover, total oxidation reaction results in the formation of new Bronsted acidic sites, which are likely associated with the generation of HCl at high temperature and its adsorption at the catalyst surface. Highly dispersed Co oxide on the mesoporous support and Co-chloride or oxychloride particles, together with the presence of several families of acidic sites originated from the conditioning effect of reaction products may explain the good activity of this catalyst in the oxidation of Chlorinated Volatile Organic Compounds.

Assessment of surface acidity in mesoporous materials containing aluminum and titanium

NASA Astrophysics Data System (ADS)

Araújo, Rinaldo S.; Maia, Débora A. S.; Azevedo, Diana C. S.; Cavalcante, Célio L., Jr.; Rodríguez-Castellón, E.; Jimenez-Lopez, A.

2009-04-01

The surface acidity of mesoporous molecular sieves of aluminum and titanium was evaluated using four different techniques: n-butylamine volumetry, cyclohexylamine thermodesorption, temperature-programmed desorption of ammonia and adsorption of pyridine. The nature, strength and concentration of the acid sites were determined and correlated to the results of a probe reaction of anthracene oxidation to 9,10-anthraquinone (in liquid phase). In general, the surface acidity was highly influenced by the nature, location and coordination of the metal species (Al and Ti) in the mesoporous samples. Moderate to strong Brönsted acid sites were identified for the Al-MCM-41 sample in a large temperature range. For mesoporous materials containing Ti, the acidity was represented by a combination of weak to moderate Brönsted and Lewis acid sites. The Ti-HMS sample exhibits a higher acidity of moderate strength together with a well-balanced concentration of Brönsted and Lewis acid sites, which enhanced both conversion and selectivity in the oxidation reaction of anthracene.

Carbon monoxide reaction with UO2(111) single crystal surfaces: A theoretical and experimental study

NASA Astrophysics Data System (ADS)

Senanayake, S. D.; Soon, A.; Kohlmeyer, A.; Söhnel, T.; Idriss, H.

2005-07-01

The reaction of CO has been investigated on the surfaces of UO2(111) single crystal. Over the stoichiometric surface CO does not adsorb at 300 K and no further reaction is noticed. Over UO2-x (prepared by Ar+ bombardment), CO molecules adsorb and in presence of traces of H2 they couple to form acetylene molecules that desorb in two temperature domains during temperature programmed desorption (TPD). In the presence of excess H2 the coupling product is found to be ethylene. X-ray photoelectron spectroscopy (XPS) of the core level shows the presence of an U 4f line at 377 eV on the UO2-x surface, attributed to U metal. This line disappears upon CO adsorption (5 L and above) at 300 K indicating oxidation of U metal atoms by O from dissociatively adsorbed CO. XPS C 1s shows that the only C containing species formed is carbide. Computation of a α-U metal 2d-periodic slab was also conducted using plane-wave pseudopotential in the density functional theoretical framework. Two modes of CO adsorption were considered: molecular and dissociative. The dissociative adsorption was found more energetically favoured by 0.46 eV. From TPD, XPS and computation results it is strongly suggested that CO is dissociatively adsorbed on UO2-x and that a stable U-C species is formed at 300 K.

Chemistry of CCl 4 on Fe 3O 4(1 1 1)-(2 × 2) surfaces in the presence of adsorbed D 2O studied by temperature programmed desorption

NASA Astrophysics Data System (ADS)

Adib, K.; Totir, G. G.; Fitts, J. P.; Rim, K. T.; Mueller, T.; Flynn, G. W.; Joyce, S. A.; Osgood, R. M.

2003-07-01

Temperature programmed desorption (TPD) was used to study surface reactions of Fe 3O 4(1 1 1)-(2 × 2) sequentially exposed, at ˜100 K, to vapor-phase D 2O and CCl 4. Previous TPD and XPS results have indicated that in the absence of D 2O, CCl 4 dissociatively adsorbs on Fe 3O 4(1 1 1) producing chemisorbed Cl and CCl 2. Subsequent heating of the surface results in abstraction of lattice iron and oxygen atoms and causes them to desorb as FeCl 2 and OCCl 2, respectively. This study shows that when this Fe 3O 4 surface is exposed only to D 2O, TPD measures a rich surface chemistry with multiple desorption events extending as high as ˜800 K, indicating dissociative adsorption of D 2O on the Fe 3O 4(1 1 1) surface. After sequential exposure to D 2O and then CCl 4, the production of FeCl 2 and OCCl 2 from adsorbed CCl 4 is suppressed, indicating that D 2O fragments block the surface reactive sites.

First-principles-based kinetic Monte Carlo simulation of nitric oxide decomposition over Pt and Rh surfaces under lean-burn conditions

NASA Astrophysics Data System (ADS)

Mei, Donghai; Ge, Qingfeng; Neurock, Matthew; Kieken, Laurent; Lerou, Jan

First-principles-based kinetic Monte Carlo simulation was used to track the elementary surface transformations involved in the catalytic decomposition of NO over Pt(100) and Rh(100) surfaces under lean-burn operating conditions. Density functional theory (DFT) calculations were carried out to establish the structure and energetics for all reactants, intermediates and products over Pt(100) and Rh(100). Lateral interactions which arise from neighbouring adsorbates were calculated by examining changes in the binding energies as a function of coverage and different coadsorbed configurations. These data were fitted to a bond order conservation (BOC) model which is subsequently used to establish the effects of coverage within the simulation. The intrinsic activation barriers for all the elementary reaction steps in the proposed mechanism of NO reduction over Pt(100) were calculated by using DFT. These values are corrected for coverage effects by using the parametrized BOC model internally within the simulation. This enables a site-explicit kinetic Monte Carlo simulation that can follow the kinetics of NO decomposition over Pt(100) and Rh(100) in the presence of excess oxygen. The simulations are used here to model various experimental protocols including temperature programmed desorption as well as batch catalytic kinetics. The simulation results for the temperature programmed desorption and decomposition of NO over Pt(100) and Rh(100) under vacuum condition were found to be in very good agreement with experimental results. NO decomposition is strongly tied to the temporal number of sites that remain vacant. Experimental results show that Pt is active in the catalytic reaction of NO into N2 and NO2 under lean-burn conditions. The simulated reaction orders for NO and O2 were found to be +0.9 and -0.4 at 723 K, respectively. The simulation also indicates that there is no activity over Rh(100) since the surface becomes poisoned by oxygen.

Evaluation of Finite-Rate Gas/Surface Interaction Models for a Carbon Based Ablator

NASA Technical Reports Server (NTRS)

Chen, Yih-Kanq; Goekcen, Tahir

2015-01-01

Two sets of finite-rate gas-surface interaction model between air and the carbon surface are studied. The first set is an engineering model with one-way chemical reactions, and the second set is a more detailed model with two-way chemical reactions. These two proposed models intend to cover the carbon surface ablation conditions including the low temperature rate-controlled oxidation, the mid-temperature diffusion-controlled oxidation, and the high temperature sublimation. The prediction of carbon surface recession is achieved by coupling a material thermal response code and a Navier-Stokes flow code. The material thermal response code used in this study is the Two-dimensional Implicit Thermal-response and Ablation Program, which predicts charring material thermal response and shape change on hypersonic space vehicles. The flow code solves the reacting full Navier-Stokes equations using Data Parallel Line Relaxation method. Recession analyses of stagnation tests conducted in NASA Ames Research Center arc-jet facilities with heat fluxes ranging from 45 to 1100 wcm2 are performed and compared with data for model validation. The ablating material used in these arc-jet tests is Phenolic Impregnated Carbon Ablator. Additionally, computational predictions of surface recession and shape change are in good agreement with measurement for arc-jet conditions of Small Probe Reentry Investigation for Thermal Protection System Engineering.

Reactions of methyl groups on a non-reducible metal oxide: The reaction of iodomethane on stoichiometric α-Cr 2O 3(0001)

DOE PAGES

Dong, Yujung; Brooks, John D.; Chen, Tsung-Liang; ...

2015-06-10

The reaction of iodomethane on the nearly stoichiometric α-Cr 2O 3(0001) surface produces gas phase ethylene, methane, and surface iodine adatoms. The reaction is first initiated by the dissociation of iodomethane into surface methyl fragments, -CH 3, and iodine adatoms. Methyl fragments bound at surface Cr cation sites undergo a rate-limiting dehydrogenation reaction to methylene, =CH 2. The methylene intermediates formed from methyl dehydrogenation can then undergo coupling reactions to produce ethylene via two principle reaction pathways: (1) direct coupling of methylene and (2) methylene insertion into the methyl surface bond to form surface ethyl groups which undergo β-H eliminationmore » to produce ethylene. The liberated hydrogen also combines with methyl groups to form methane. Iodine adatoms from the dissociation of iodomethane deactivate the surface by simple site blocking of the surface Cr 3+ cations.« less

CCl 4 chemistry on the reduced selvedge of a α-Fe 2O 3(0 0 0 1) surface: a scanning tunneling microscopy study

NASA Astrophysics Data System (ADS)

Rim, Kwang Taeg; Fitts, Jeffrey P.; Müller, Thomas; Adib, Kaveh; Camillone, Nicholas; Osgood, Richard M.; Joyce, S. A.; Flynn, George W.

2003-09-01

Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) were used to study the degradation of CCl 4 on the reduced selvedge of a natural single crystal α-Fe 2O 3(0 0 0 1) surface in ultrahigh vacuum. Before exposure to CCl 4, STM images indicate that approximately 85% of the reduced surface exhibits a Fe 3O 4(1 1 1) 2 × 2 termination, while the remaining 15% is terminated by 1 × 1 and superstructure phases. Images obtained after room temperature dosing with CCl 4 and subsequent flashing to 600 K reveal that chlorine atoms are adsorbed only on surface regions with the Fe 3O 4(1 1 1) 2 × 2 termination, not on 1 × 1 and superstructure regions. Chlorine atoms from dissociative adsorption of CCl 4 are observed to occupy two distinct positions located atop lattice protrusions and in threefold oxygen vacancy sites. However, in companion chemical labeling experiments, chlorine atoms provided by room temperature, dissociative Cl 2 adsorption on this surface are found to occupy sites atop lattice protrusions exclusively. The clear dissimilarity in STM feature shape and brightness at the two distinct chlorine adsorption sites arising from CCl 4 dissociation as well as the results of the Cl 2 chemical labeling experiments are best explained via reactions on a Fe 3O 4(1 1 1) 2 × 2 selvedge terminated by a 1/4 monolayer of tetrahedrally coordinated iron atoms. On this surface, adsorption atop an iron atom occurs for both the CCl 4 and Cl 2 dissociative reactions. A second adsorption site, assigned as binding to second layer iron atoms left exposed following surface oxygen atom abstraction resulting in the formation of phosgene (COCl 2), only appears in the case of reaction with CCl 4. The reaction mechanism and active site requirements for CCl 4 degradation on iron oxide surfaces are discussed in light of this evidence and in the context of our previously reported results from Auger electron spectroscopy (AES), LEED, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy studies.

PDMS-co-PVMS Copolymer Synthesis for Microfluidic Devices

NASA Astrophysics Data System (ADS)

Baiamonte, Arissa; Nguyen, Devin; Lwoya, Baraka; Kelly, Giovanni; Albert, Julie N. L.

Poly (dimethylsiloxane) (PDMS) is the predominant material used for the fabrication of microfluidic devices because it is an easily synthesized, biocompatible, and flexible material that forms a good seal with other surfaces. However, PDMS is chemically inert and therefore difficult to functionalize for targeted applications, it can swell in the presence of organic solvents, and it can contaminate microfluidic solutions with unreacted oligomers. Therefore, my research goal is to synthesize random copolymers of PDMS and poly (vinylmethylsiloxane) (PVMS) that retain the benefits of PDMS and can be functionalized easily via thiol-ene click reactions. In the first stage of this work, dichlorodimethylsilane and vinylmethyldichlorosilane were each reacted with water to produce n-membered dimethylsiloxane rings and n-membered vinylmethylsiloxane rings, respectively. In the next step, polymers are synthesized by reacting these rings with potassium hydroxide and heat to form PDMS, PVMS, and PDMS-co-PVMS copolymers. Several reaction conditions have been tested to determine the kinetics and to relate molecular weight of the polymer or copolymer to reaction time. The polymer is then cross-liked through hydroxyl end groups with vinylmethoxysiloxane homopolymer (PVMES) cross-linker, tin catalyst, and heat. Once the polymer is cross-linked, the surface can be modified via thiol-ene click reaction to provide a diversity of surface functionality for microfluidic device applications. In the present work, we functionalize with a fluorinated thiol to impart solvent resistance. Newcomb Tulane College Georges Lurcy Grant, National Academies Gulf Research Program Early Career Research Fellowship, Tulane CIF.

Ammonia formation from NO reaction with surface hydroxyls on rutile TiO2 (110) - 1×1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Boseong; Kay, Bruce D.; Dohnalek, Zdenek

2015-01-15

The reaction of NO with hydroxylated rutile TiO2(110)-1×1 surface (h-TiO2) was investigated as a function of NO coverage using temperature-programmed desorption. Our results show that NO reaction with h-TiO2 leads to formation of NH3 which is observed to desorb at ~ 400 K. Interestingly, the amount of NH3 produced depends nonlinearly on the coverage of NO. The yield increases up to a saturation value of ~1.3×1013 NH3/cm2 at a NO dose of 5×1013 NO/cm2, but subsequently decreases at higher NO doses. Preadsorbed H2O is found to have a negligible effect on the NH3 desorption yield. Additionally, no NH3 is formedmore » in the absence of surface hydroxyls (HOb’s) upon coadsorption of NO and H2O on a stoichiometric TiO2(110) (s-TiO2(110)). Based on these observations, we conclude that nitrogen from NO has a strong preference to react with HOb’s on the bridge-bonded oxygen rows (but not with H2O) to form NH3. The absolute NH3 yield is limited by competing reactions of HOb species with titanium-bound oxygen adatoms to form H2O. Our results provide new mechanistic insight about the interactions of NO with hydroxyl groups on TiO2(110) .« less

Enhanced performance of CO oxidation over Pt/CuCrOx catalyst in the presence of CO2 and H2O

NASA Astrophysics Data System (ADS)

Deng, Yun; Wang, Ting; Zhu, Li; Jia, Ai-Pin; Lu, Ji-Qing; Luo, Meng-Fei

2018-06-01

A Pt catalyst supported on CuO-CrOx composite oxide (Pt/CuCrOx) was prepared and tested for CO oxidation in the presence of CO2 and H2O. It was found that the catalyst was stable in the realistic reaction conditions and the catalytic activity was improved in the presence of CO2 and H2O compared to that in dry condition. Kinetic investigation and temperature - programmed desorption of CO results revealed that the addition of CO2 in the feed resulted in the competitive adsorption of CO/CO2 and the formation of surface carbonate species, which consequently deactivated the catalyst. In contrast, although the presence of H2O also inhibited the adsorption of CO, the possible formation of surface hydroxyl groups may trigger a new and more facile reaction route for CO oxidation, which could explain the promoting effect of H2O. Therefore, the current findings makes the catalyst promising in CO oxidation under realistic reaction conditions.

Transformations of C2-C4 alcohols on the surface of a copper catalyst

NASA Astrophysics Data System (ADS)

Magaeva, A. A.; Lyamina, G. V.; Sudakova, N. N.; Shilyaeva, L. P.; Vodyankina, O. V.

2007-10-01

The interaction of monoatomic alcohols C2-C4 with the surface of a copper catalyst preliminarily oxidized under various conditions was studied by the temperature-programmed reaction method to determine the detailed mechanism of partial oxidation. The conditions of oxygen preadsorption on the surface of copper for the preparation of the desired products were determined. The selective formation of carbonyl compounds was shown to occur at the boundary between reduced and oxidized copper surface regions. The role played by Cu2O was the deep oxidation of alcohols to CO2. Alcohols with branched hydrocarbon structures experienced parallel partial oxidation and dehydrogenation, which was related to the high stability of intermediate keto-type compounds.

Orion Service Module Reaction Control System Plume Impingement Analysis Using PLIMP/RAMP2

NASA Technical Reports Server (NTRS)

Wang, Xiao-Yen; Lumpkin, Forrest E., III; Gati, Frank; Yuko, James R.; Motil, Brian J.

2009-01-01

The Orion Crew Exploration Vehicle Service Module Reaction Control System engine plume impingement was computed using the plume impingement program (PLIMP). PLIMP uses the plume solution from RAMP2, which is the refined version of the reacting and multiphase program (RAMP) code. The heating rate and pressure (force and moment) on surfaces or components of the Service Module were computed. The RAMP2 solution of the flow field inside the engine and the plume was compared with those computed using GASP, a computational fluid dynamics code, showing reasonable agreement. The computed heating rate and pressure using PLIMP were compared with the Reaction Control System plume model (RPM) solution and the plume impingement dynamics (PIDYN) solution. RPM uses the GASP-based plume solution, whereas PIDYN uses the SCARF plume solution. Three sets of the heating rate and pressure solutions agree well. Further thermal analysis on the avionic ring of the Service Module was performed using MSC Patran/Pthermal. The obtained temperature results showed that thermal protection is necessary because of significant heating from the plume.

Time-resolved chromatographic analysis and mechanisms in adsorption and catalysis.

PubMed

Roubani-Kalantzopoulou, Fani

2009-03-06

The main object of this review is the study of fundamentals of adsorption and heterogeneous catalysis, a benefit for the understanding of adsorptive and catalytic properties. This work aims to define and record, with the utmost accuracy, the phenomena and the possible reactions. A new methodology for the study of the adsorption is presented, which is a version of the well-known inverse gas chromatography. This reversed-flow inverse gas chromatography (RF-IGC) is technically very simple, and it is combined with a mathematical analysis that gives the possibility for the estimation of various physicochemical parameters related to adsorbent or catalyst characterization, under conditions compatible with the operation of real adsorbents and catalysts. On this base, this methodology has been successfully applied to the study of the impact of air pollutants, volatile organic and/or inorganic, on many solids such as marbles, ceramics, oxide-pigments of works of art, building materials, authentic statues of the Greek Archaeological Museums. Moreover, this methodology proved to be a powerful tool for studying the topography of active sites of heterogeneous surfaces in the nano-scale domain. Thus, some very important local quantities for the surface chemistry have been determined experimentally for many solids including thin films. These physicochemical local quantities (among which adsorption energy and entropy, surface diffusion coefficient, probability density function) have been determined from the experimental pairs of height of extra chromatographic peaks and time by a nonlinear least-squares method, through personal computer programs written in GW BASIC and lately in FORTRAN. Through the time-resolved analysis the surface characterization of the examined materials took place. In addition, the kinetic constants responsible for adsorption/desorption and surface chemical reactions have also been calculated. Thus, important answers have been provided to the following essential questions: (1) Can RF-IGC define the gnostic regions of adsorption/desorption, surface diffusion, surface reaction? Yes, irrefutably and undeniably. (2) Can RF-IGC deal with issues of catalysis, the existence of more than one reaction? Certainly yes. Indeed, it is impressive to observe the reactions "on line". (3) Can RF-IGC identify peaks of products and reactants simultaneously? Certainly yes. (4) Can RF-IGC be applied to thin films in a nano-scale domain? The answer is "definitely yes". (5) Can it kinetically follow the above? Yes, again.

Effects of specific surface area of metallic nickel particles on carbon deposition kinetics

NASA Astrophysics Data System (ADS)

Chen, Zhi-yuan; Bian, Liu-zhen; Yu, Zi-you; Wang, Li-jun; Li, Fu-shen; Chou, Kuo-Chih

2018-02-01

Carbon deposition on nickel powders in methane involves three stages in different reaction temperature ranges. Temperature programing oxidation test and Raman spectrum results indicated the formation of complex and ordered carbon structures at high deposition temperatures. The values of I(D)/ I(G) of the deposited carbon reached 1.86, 1.30, and 1.22 in the first, second, and third stages, respectively. The structure of carbon in the second stage was similar to that in the third stage. Carbon deposited in the first stage rarely contained homogeneous pyrolytic deposit layers. A kinetic model was developed to analyze the carbon deposition behavior in the first stage. The rate-determining step of the first stage is supposed to be interfacial reaction. Based on the investigation of carbon deposition kinetics on nickel powders from different resources, carbon deposition rate is suggested to have a linear relation with the square of specific surface area of nickel particles.

The effect of solid phase reactions on the ballistic properties of propellants

NASA Technical Reports Server (NTRS)

Schmidt, W. G.

1970-01-01

The combustion of NH4ClO4 composite propellants has been studied between 15 and 3000 psi. The emphasis in the program has been on determining the mechanisms by which the fuel components influence the burning rate of the composites. In order to have flexibility in the choice and concentration of the fuel component all combustion experiments were performed with pressed power strands. The fuels studied included those which affected the combustion mechanism of the composite primarily through their effect on: (1) the oxidizer decomposition mechanism and (2) the composite surface temperature. The combustion of pure and doped NH4ClO4 was studied using both pressed powder strands and pressed end burning motor grains. The experimental approach has been essentially a chemical one with emphasis on perturbing those reactions which occur on or immediately adjacent to the surface (zone of influence) of the composite.

Controlled Chemical Patterns with ThermoChemical NanoLithography (TCNL)

NASA Astrophysics Data System (ADS)

Carroll, Keith; Giordano, Anthony; Wang, Debin; Kodali, Vamsi; King, W. P.; Marder, S. R.; Riedo, E.; Curtis, J. E.

2012-02-01

Many research areas, both fundamental and applied, rely upon the ability to organize non-trivial assemblies of molecules on surfaces. In this work, we introduce a significant extension of ThermoChemical NanoLithography (TCNL), a high throughput chemical patterning technique that uses temperature-driven chemical reactions localized near the tip of a thermal cantilever. By combining a chemical kinetics based model with experiments, we have developed a protocol for varying the concentration of surface bound molecules. The result is an unprecedented ability to fabricate extremely complex patterns comprised of varying chemical concentrations, as demonstrated by sinusoidal patterns of amine groups with varying pitches (˜5-15 μm) and the replication of Leonardo da Vinci's Mona Lisa with dimensions of ˜30 x 40 μm^2. Programmed control of the chemical reaction rate should have widespread applications for a technique which has already been shown to nanopattern various substrates including graphene nanowires, piezoelectric crystals, and optoelectronic materials.

Controlling hydrogenation activity and selectivity of bimetallic surfaces and catalysts

NASA Astrophysics Data System (ADS)

Murillo, Luis E.

Studies of bimetallic systems are of great interest in catalysis due to the novel properties that they often show in comparison with the parent metals. The goals of this dissertation are: (1) to expand the studies of self-hydrogenation and hydrogenation reactions on bimetallic surfaces under ultra high vacuum conditions (UHV) using different hydrocarbon as probe molecules; (2) to attempt to correlate the surface science findings with supported catalyst studies under more realistic conditions; and (3) to investigate the competitive hydrogenation of C=C versus C=O bonds on Pt(111) modified by different 3d transition metals. Hydrogenation studies using temperature programmed desorption (TPD) on Ni/Pt(111) bimetallic surfaces have demonstrated an enhancement in the low temperature hydrogenation activity relative to that of clean Pt(111). This novel hydrogenation pathway can be achieved under UHV conditions by controlling the structures of the bimetallic surfaces. A low temperature hydrogenation activity of 1-hexene and 1-butene has been observed on a Pt-Ni-Pt(111) subsurface structure, where Ni atoms are mainly present on the second layer of the Pt(111) single crystal. These results are in agreement with previous studies of self-hydrogenation and hydrogenation of cyclohexene. However, a much higher dehydrogenation activity is observed in the reaction of cyclohexene to produce benzene, demonstrating that the hydrocarbon structure has an effect on the reaction pathways. On the other hand, self-hydrogenation of 1-butene is not observed on the Pt-Ni-Pt(111) surface, indicating that the chain length (or molecular weight) has a significant effect on the selfhydrogenation activity. The gas phase reaction of cyclohexene on Ni/Pt supported on alumina catalysts has also shown a higher self-hydrogenation activity in comparison with the same reaction performed on supported monometallic catalysts. The effects of metal loading and impregnation sequence of the metal precursors are also discussed. Chemisorption, TPD, FTIR using a batch reactor for the self-hydrogenation of cyclohexene and CO adsorbed on the bimetallic surfaces were carried out to correlate surface science findings with experiments on supported bimetallic catalysts. To expand the studies on the effect of bimetallic structures on hydrogenation reactions, molecules with multiple functional groups such as alpha,beta-unsaturated aldehydes were also investigated. Studies of selective hydrogenation of a,ss-unsaturated aldehydes toward the desired unsaturated alcohols are of interest for the production of fine chemicals and pharmaceuticals. In these compounds, competitive hydrogenation of the C=C and C=O bonds occurs. TPD and HREELS experiments of acrolein (CH2=CH-CH=O) on Pt-based bimetallic surfaces are performed to investigate their effects on the hydrogenation activity of the C-O bond. The production of the desired unsaturated alcohol, allyl alcohol, has been observed for the first time on Pt-Ni-Pt(111) under UHV conditions. However, the propionaldehyde yield is five times higher than the allyl alcohol yield. Thus, a preferential isomerization reaction of allyl alcohol to propionaldehyde is very likely to occur on the Pt-Ni-Pt(111) surface as observed on the desorption studies of allyl alcohol on this surface. The hydrogenation of acrolein is also carried out under UHV conditions on other 3d-transition metal/Pt(111) surfaces such as Co/Pt(111), Fe/Pt(111), and Cu/Pt(111). So far, the highest activity and allyl alcohol yield are found on the Pt-Ni-Pt(111) surface with pre-adsorbed hydrogen.

Selective scanning tunnelling microscope electron-induced reactions of single biphenyl molecules on a Si(100) surface.

PubMed

Riedel, Damien; Bocquet, Marie-Laure; Lesnard, Hervé; Lastapis, Mathieu; Lorente, Nicolas; Sonnet, Philippe; Dujardin, Gérald

2009-06-03

Selective electron-induced reactions of individual biphenyl molecules adsorbed in their weakly chemisorbed configuration on a Si(100) surface are investigated by using the tip of a low-temperature (5 K) scanning tunnelling microscope (STM) as an atomic size source of electrons. Selected types of molecular reactions are produced, depending on the polarity of the surface voltage during STM excitation. At negative surface voltages, the biphenyl molecule diffuses across the surface in its weakly chemisorbed configuration. At positive surface voltages, different types of molecular reactions are activated, which involve the change of adsorption configuration from the weakly chemisorbed to the strongly chemisorbed bistable and quadristable configurations. Calculated reaction pathways of the molecular reactions on the silicon surface, using the nudge elastic band method, provide evidence that the observed selectivity as a function of the surface voltage polarity cannot be ascribed to different activation energies. These results, together with the measured threshold surface voltages and the calculated molecular electronic structures via density functional theory, suggest that the electron-induced molecular reactions are driven by selective electron detachment (oxidation) or attachment (reduction) processes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gorman, Brian P

Project Description: The general objective of the proposed research is to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, pCO 2, and modest ranges in T and P. This will be accomplished by studying both reaction rates and solubility from changes in solution chemistry, and making nanoscale observations of calcite precipitate surface morphology and composition at the micro-to-nano-scale to provide an understanding of controlling reaction mechanisms and pathways. The specific objectives necessary to reach the general objective are: a) determination of how pCO 2, Ca 2+, ionic strength andmore » “foreign” ions influence reaction rates; and b) investigate the influence of these parameters on apparent kinetic solubility from dissolution and precipitation reactions. This information will clearly be central to the construction of reliable reaction-transport models to predict reservoir and formation response to increased CO 2 in saline waters. This program was initially collaborative with John Morse at Texas A&M, however his passing shortly after the beginning of this program resulted in abbreviated research time and effort. Summary of Results: Early studies using electron microscopy and spectroscopy indicated that carbonate precipitation from natural seawater (NSW) conditions onto aragonite substrates was mediated by a surface amorphous calcium carbonate layer. It was hypothesized that this ACC layer (observed after < 5days reaction time) was responsible for the abnormal reaction kinetics and also served as a metastable seed layer for growth of epitaxial aragonite. Further studies of the ACC formation mechanism indicated a strong dependence on the Mg concentration in solution. Subsequent studies at shorter times (10 hrs) on calcite substrates and in a wide range of supersaturation conditions did not indicate any ACC layer. Instead, an epitaxial layer by layer growth mechanism was confirmed by grazing incidence X-ray diffraction, µ-Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and electron diffraction. Extended time studies out to 45 days confirmed the epitaxial relationship of the overgrowth layer with the substrate. Under NSW conditions, overgrowths were found to have ~0.4 to 0.8 nm / hr growth rates and accommodating 4 at% Mg, resulting in a highly strained overgrowth layer. Following the initial layer by layer growth mechanism, the growth changes to Stranski-Krastanov type after a critical thickness of approximately 100 nm.« less

Exploring the nonequilibrium reactivity of molecules with platinum(111)

NASA Astrophysics Data System (ADS)

Dewitt, Kristin Marie

Various aspects of the nonequilibrium reactivity of several, catalytically important, small molecules with Pt(111)were explored. The effect of alkali metal promotion on the thermal chemistry and photochemistry of CH4,N 2, and CO2 was studied. Dissociative sticking coefficients for methane and ethane were measured as a function of gas temperature ( Tg) and surface temperature (Ts) using effusive molecular beam and angle-integrated gas dosing methods. Coupled with physisorbed complex microcanonical unimolecular rate theory these measurements provide a predictive understanding for the kinetics of these C-H bond activation reactions, i.e. allowing us to predict the sticking coefficient of CH 4 and C2H6 for any combination of T s and Tg. Work function thermal programmed desorption was used to examine the correlation between surface structure and surface work function for CH3Br and CO2. Preliminary two-photon photoemission and broad-band infrared-visible sum frequency generation experiments introduce these nonlinear spectroscopy techniques to the arsenal of surface characterization techniques available in our group. All of the disparate components of this work are tied together by one overall theme, developing an improved molecular-level understanding of the reaction dynamics of catalysis.

Some fundamental properties and reactions of ice surfaces at low temperatures.

PubMed

Park, Seong-Chan; Moon, Eui-Seong; Kang, Heon

2010-10-14

Ice surfaces offer a unique chemical environment in which reactions occur quite differently from those in liquid water or gas phases. In this article, we examine the basic properties of ice surfaces below the surface premelting temperature and discuss some of the recent investigations carried out on reactions at the ice surfaces. The static and dynamic properties of an ice surface as a reaction medium, such as its structure, molecule diffusion and proton transfer dynamics, and the surface preference of hydronium and hydroxide ions, are discussed in relation to the reactivity of the surface.

The Installation Restoration Program Toxicology Guide. Volume 2

DTIC Science & Technology

1989-07-01

producing substance. Carcinoma A malignant epithelial tumor. CAS REG NO Numeric designation assigned by the A.~’erican Chemical Socecty’s Chemica ...violent, exothermic, and capable of causing violent rupture of sealed containers. ABBREVIATIONS AB-I1 Polymerization A chemica reaction, usually carried...a deleterious effect on the taste and/or odor of human food derred from aquatic environments cannot be discharged into inland surface waters

Application of a BOSS-Gaussian interface for QM/MM simulations of Henry and methyl transfer reactions.

PubMed

Vilseck, Jonah Z; Kostal, Jakub; Tirado-Rives, Julian; Jorgensen, William L

2015-10-15

Hybrid quantum mechanics and molecular mechanics (QM/MM) computer simulations have become an indispensable tool for studying chemical and biological phenomena for systems too large to treat with QM alone. For several decades, semiempirical QM methods have been used in QM/MM simulations. However, with increased computational resources, the introduction of ab initio and density function methods into on-the-fly QM/MM simulations is being increasingly preferred. This adaptation can be accomplished with a program interface that tethers independent QM and MM software packages. This report introduces such an interface for the BOSS and Gaussian programs, featuring modification of BOSS to request QM energies and partial atomic charges from Gaussian. A customizable C-shell linker script facilitates the interprogram communication. The BOSS-Gaussian interface also provides convenient access to Charge Model 5 (CM5) partial atomic charges for multiple purposes including QM/MM studies of reactions. In this report, the BOSS-Gaussian interface is applied to a nitroaldol (Henry) reaction and two methyl transfer reactions in aqueous solution. Improved agreement with experiment is found by determining free-energy surfaces with MP2/CM5 QM/MM simulations than previously reported investigations using semiempirical methods. © 2015 Wiley Periodicals, Inc.

2013 Chemical reactions at surfaces. Surfaces in Energy and the Environment. Gordon Research Conference and Gordon Research Seminar (April 28 - May 3, 2013 - Les Diablerets, Switzerland)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stair, Peter C.

presentations on chemistry at solid and liquid surfaces of relevance to catalysis, synthesis, photochemistry, environmental science, and tribology. Topics include: Fundamental Surface Chemistry; Catalysis; Solid Liquid and Aerosol Interfaces; Surface Photochemistry; Synthesis of Surfaces; Environmental Interfaces; Hot Topics in Surface Chemical Reactions; Tribology; Gas-Surface Scattering and Reactions; Novel Materials and Environments.

Field ion microscopic studies of the CO oxidation on platinum: Field ion imaging and titration reactions

NASA Astrophysics Data System (ADS)

Gorodetskii, V.; Drachsel, W.; Block, J. H.

1994-05-01

Elementary steps of the CO oxidation—which are important for understanding the oscillatory behavior of this catalytic reaction—are investigated simultaneously on different Pt-single crystal surfaces by field ion microscopy. Due to preferential ionization probabilities of oxygen as imaging gas on those surface sites, which are adsorbed with oxygen, these sites can be imaged in a lateral resolution on the atomic scale. In the titration reaction a COad-precovered field emitter surface reacts with gaseous oxygen adsorbed from the gas phase or, vice versa, the Oad-precovered surface with carbon monoxide adsorbed from the gas phase. The competition of the manifold of single crystal planes exposed to the titration reaction at the field emitter tip is studied. The surface specificity can be documented in the specific reaction delay times of the different planes and in the propagation rates of the reaction-diffusion wave fronts measured on these individual planes during the titration reaction with a time resolution of 40 ms. At 300 K the COad-precovered surfaces display the {011} regions, precisely the {331} planes as the most active, followed by {012}, {122}, {001}, and finally by {111}. Reaction wave fronts move with a velocity of 8 Å/s at {012}, with ≊0.8 Å/s at {111}, and have a very fast ``switch-on'' reaction at the (001) plane with 500 Å/s. At higher temperature, T=350 K, an acceleration of reaction rates is combined with shorter delay times. The titration reaction of a precovered Oad surface with COgas at T=373 K shows the formation of CO islands starting in the {011} regions with a quickly moving reaction front into the other surface areas without showing particular delay times for different surface symmetries. The two reverse titration reactions have a largely different character. The titration of COad with oxygen adsorbed from the gas phase consists of three different steps, (i) the induction times, (ii) the highly surface specific reaction, and (iii) different rates of wave front propagation. The reaction of COgas with a precovered Oad layer on the other hand starts with nucleating islands around the {011} planes from where the whole emitter surface is populated with COad without pronounced surface specifity.

Insight into Chemistry on Cloud/Aerosol Water Surfaces.

PubMed

Zhong, Jie; Kumar, Manoj; Francisco, Joseph S; Zeng, Xiao Cheng

2018-05-15

Cloud/aerosol water surfaces exert significant influence over atmospheric chemical processes. Atmospheric processes at the water surface are observed to follow mechanisms that are quite different from those in the gas phase. This Account summarizes our recent findings of new reaction pathways on the water surface. We have studied these surface reactions using Born-Oppenheimer molecular dynamics simulations. These studies provide useful information on the reaction time scale, the underlying mechanism of surface reactions, and the dynamic behavior of the product formed on the aqueous surface. According to these studies, the aerosol water surfaces confine the atmospheric species into a specific orientation depending on the hydrophilicity of atmospheric species or the hydrogen-bonding interactions between atmospheric species and interfacial water. As a result, atmospheric species are activated toward a particular reaction on the aerosol water surface. For example, the simplest Criegee intermediate (CH 2 OO) exhibits high reactivity toward the interfacial water and hydrogen sulfide, with the reaction times being a few picoseconds, 2-3 orders of magnitude faster than that in the gas phase. The presence of interfacial water molecules induces proton-transfer-based stepwise pathways for these reactions, which are not possible in the gas phase. The strong hydrophobicity of methyl substituents in larger Criegee intermediates (>C1), such as CH 3 CHOO and (CH 3 ) 2 COO, blocks the formation of the necessary prereaction complexes for the Criegee-water reaction to occur at the water droplet surface, which lowers their proton-transfer ability and hampers the reaction. The aerosol water surface provides a solvent medium for acids (e.g., HNO 3 and HCOOH) to participate in reactions via mechanisms that are different from those in the gas and bulk aqueous phases. For example, the anti-CH 3 CHOO-HNO 3 reaction in the gas phase follows a direct reaction between anti-CH 3 CHOO and HNO 3 , whereas on a water surface, the HNO 3 -mediated stepwise hydration of anti-CH 3 CHOO is dominantly observed. The high surface/volume ratio of interfacial water molecules at the aerosol water surface can significantly lower the energy barriers for the proton transfer reactions in the atmosphere. Such catalysis by the aerosol water surface is shown to cause the barrier-less formation of ammonium bisulfate from hydrated NH 3 and SO 3 molecules rather than from the reaction of H 2 SO 4 with NH 3 . Finally, an aerosol water droplet is a polar solvent, which would favorably interact with high polarity substrates. This can accelerate interconversion of different conformers (e.g., anti and syn) of atmospheric species, such as glyoxal, depending on their polarity. The results discussed here enable an improved understanding of atmospheric processes on the aerosol water surface.

GEOSURF: a computer program for modeling adsorption on mineral surfaces from aqueous solution

NASA Astrophysics Data System (ADS)

Sahai, Nita; Sverjensky, Dimitri A.

1998-11-01

A new program, GEOSURF, has been developed for calculating aqueous and surface speciation consistent with the triple-layer model of surface complexation. GEOSURF is an extension of the original programs MINEQL, MICROQL and HYDRAQL. We present, here, the basic algorithm of GEOSURF along with a description of the new features implemented. GEOSURF is linked to internally consistent data bases for surface species (SURFK.DAT) and for aqueous species (AQSOL.DAT). SURFK.DAT contains properties of minerals such as site densities, and equilibrium constants for adsorption of aqueous protons and electrolyte ions on a variety of oxides and hydroxides. The Helgeson, Kirkham and Flowers version of the extended Debye-Huckel Equation for 1:1 electrolytes is implemented for calculating aqueous activity coefficients. This permits the calculation of speciation at ionic strengths greater than 0.5 M. The activity of water is computed explicitly from the osmotic coefficient of the solution, and the total amount of electrolyte cation (or anion) is adjusted to satisfy the electroneutrality condition. Finally, the use of standard symbols for chemical species rather than species identification numbers is included to facilitate use of the program. One of the main limitations of GEOSURF is that aqueous and surface speciation can only be calculated at fixed pH and at fixed concentration of total adsorbate. Thus, the program cannot perform reaction-path calculations: it cannot determine whether or not a solution is over- or under-saturated with respect to one or more solid phases. To check the proper running of GEOSURF, we have compared results generated by GEOSURF with those from two other programs, HYDRAQL and EQ3. The Davies equation and the "bdot" equation, respectively, are used in the latter two programs for calculating aqueous activity coefficients. An example of the model fit to experimental data for rutile in 0.001 M-2.0 M NaNO 3 is included.

High Temperature Degradation Mechanisms in Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Cunningham, Ronan A.

1996-01-01

Polymer matrix composites are increasingly used in demanding structural applications in which they may be exposed to harsh environments. The durability of such materials is a major concern, potentially limiting both the integrity of the structures and their useful lifetimes. The goal of the current investigation is to develop a mechanism-based model of the chemical degradation which occurs, such that given the external chemical environment and temperatures throughout the laminate, laminate geometry, and ply and/or constituent material properties, we can calculate the concentration of diffusing substances and extent of chemical degradation as functions of time and position throughout the laminate. This objective is met through the development and use of analytical models, coupled to an analysis-driven experimental program which offers both quantitative and qualitative information on the degradation mechanism. Preliminary analyses using a coupled diffusion/reaction model are used to gain insight into the physics of the degradation mechanisms and to identify crucial material parameters. An experimental program is defined based on the results of the preliminary analysis which allows the determination of the necessary material coefficients. Thermogravimetric analyses are carried out in nitrogen, air, and oxygen to provide quantitative information on thermal and oxidative reactions. Powdered samples are used to eliminate diffusion effects. Tests in both inert and oxidative environments allow the separation of thermal and oxidative contributions to specimen mass loss. The concentration dependency of the oxidative reactions is determined from the tests in pure oxygen. Short term isothermal tests at different temperatures are carried out on neat resin and unidirectional macroscopic specimens to identify diffusion effects. Mass loss, specimen shrinkage, the formation of degraded surface layers and surface cracking are recorded as functions of exposure time. Geometry effects in the neat resin, and anisotropic diffusion effects in the composites, are identified through the use of specimens with different aspect ratios. The data is used with the model to determine reaction coefficients and effective diffusion coefficients. The empirical and analytical correlations confirm the preliminary model results which suggest that mass loss at lower temperatures is dominated by oxidative reactions and that these reaction are limited by diffusion of oxygen from the surface. The mechanism-based model is able to successfully capture the basic physics of the degradation phenomena under a wide range of test conditions. The analysis-based test design is successful in separating out oxidative, thermal, and diffusion effects to allow the determination of material coefficients. This success confirms the basic picture of the process; however, a more complete understanding of some aspects of the physics are required before truly predictive capability can be achieved.

Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2 \\xAF 01 )

NASA Astrophysics Data System (ADS)

Kollmannsberger, Sebastian L.; Walenta, Constantin A.; Winnerl, Andrea; Knoller, Fabian; Pereira, Rui N.; Tschurl, Martin; Stutzmann, Martin; Heiz, Ueli

2017-09-01

In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α -H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga2O3(2 ¯ 01 ) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2¯01).

PubMed

Kollmannsberger, Sebastian L; Walenta, Constantin A; Winnerl, Andrea; Knoller, Fabian; Pereira, Rui N; Tschurl, Martin; Stutzmann, Martin; Heiz, Ueli

2017-09-28

In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α-H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga 2 O 3 (2¯01) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

Nuclear Physical Uncertainties in Modeling X-Ray Bursts

NASA Astrophysics Data System (ADS)

Regis, Eric; Amthor, A. Matthew

2017-09-01

Type I x-ray bursts occur when a neutron star accretes material from the surface of another star in a compact binary star system. For certain accretion rates and material compositions, much of the nuclear material is burned in short, explosive bursts. Using a one-dimensional stellar model, Kepler, and a comprehensive nuclear reaction rate library, ReacLib, we have simulated chains of type I x-ray bursts. Unfortunately, there are large remaining uncertainties in the nuclear reaction rates involved, since many of the isotopes reacting are unstable and have not yet been studied experimentally. Some individual reactions, when varied within their estimated uncertainty, alter the light curves dramatically. This limits our ability to understand the structure of the neutron star. Previous studies have looked at the effects of individual reaction rate uncertainties. We have applied a Monte Carlo method ``-simultaneously varying a set of reaction rates'' -in order to probe the expected uncertainty in x-ray burst behaviour due to the total uncertainty in all nuclear reaction rates. Furthermore, we aim to discover any nonlinear effects due to the coupling between different reaction rates. Early results show clear non-linear effects. This research was made possible by NSF-DUE Grant 1317446, BUScholars Program.

A density functional theory study on the carbon chain growth of ethanol formation on Cu-Co (111) and (211) surfaces

NASA Astrophysics Data System (ADS)

Ren, Bohua; Dong, Xiuqin; Yu, Yingzhe; Wen, Guobin; Zhang, Minhua

2017-08-01

Calculations based on the first-principle density functional theory were carried out to study the most controversial reactions in ethanol formation from syngas on Cu-Co surfaces: CO dissociation mechanism and the key reactions of carbon chain growth of ethanol formation (HCO insertion reactions) on four model surfaces (Cu-Co (111) and (211) with Cu-rich or Co-rich surfaces) to investigate the synergy of the Cu and Co components since the complete reaction network of ethanol formation from syngas is a huge computational burden to calculate on four Cu-Co surface models. We investigated adsorption of important species involved in these reactions, activation barrier and reaction energy of H-assisted dissociation mechanism, directly dissociation of CO, and HCO insertion reactions (CHx + HCO → CHxCHO (x = 1-3)) on four Cu-Co surface models. It was found that reactions on Cu-rich (111) and (211) surfaces all have lower activation barrier in H-assisted dissociation and HCO insertion reactions, especially CH + HCO → CHCHO reaction. The PDOS of 4d orbitals of surface Cu and Co atoms of all surfaces were studied. Analysis of d-band center of Cu and Co atoms and the activation barrier data suggested the correlation between electronic property and catalytic performance. Cu-Co bimetallic with Cu-rich surface allows Co to have higher catalytic activity through the interaction of Cu and Co atom. Then it will improve the adsorption of CO and catalytic activity of Co. Thus it is more favorable to the carbon chain growth in ethanol formation. Our study revealed the factors influencing the carbon chain growth in ethanol production and explained the internal mechanism from electronic property aspect.

Insight into association reactions on metal surfaces: Density-functional theory studies of hydrogenation reactions on Rh(111)

NASA Astrophysics Data System (ADS)

Liu, Zhi-Pan; Hu, P.; Lee, Ming-Hsien

2003-09-01

Hydrogenation reaction, as one of the simplest association reactions on surfaces, is of great importance both scientifically and technologically. They are essential steps in many industrial processes in heterogeneous catalysis, such as ammonia synthesis (N2+3H2→2NH3). Many issues in hydrogenation reactions remain largely elusive. In this work, the NHx (x=0,1,2) hydrogenation reactions (N+H→NH, NH+H→NH2 and NH2+H→NH3) on Rh(111) are used as a model system to study the hydrogenation reactions on metal surfaces in general using density-functional theory. In addition, C and O hydrogenation (C+H→CH and O+H→OH) and several oxygenation reactions, i.e., C+O, N+O, O+O reactions, are also calculated in order to provide a further understanding of the barrier of association reactions. The reaction pathways and the barriers of all these reactions are determined and reported. For the C, N, NH, and O hydrogenation reactions, it is found that there is a linear relationship between the barrier and the valency of R (R=C, N, NH, and O). Detailed analyses are carried out to rationalize the barriers of the reactions, which shows that: (i) The interaction energy between two reactants in the transition state plays an important role in determining the trend in the barriers; (ii) there are two major components in the interaction energy: The bonding competition and the direct Pauli repulsion; and (iii) the Pauli repulsion effect is responsible for the linear valency-barrier trend in the C, N, NH, and O hydrogenation reactions. For the NH2+H reaction, which is different from other hydrogenation reactions studied, the energy cost of the NH2 activation from the IS to the TS is the main part of the barrier. The potential energy surface of the NH2 on metal surfaces is thus crucial to the barrier of NH2+H reaction. Three important factors that can affect the barrier of association reactions are generalized: (i) The bonding competition effect; (ii) the local charge densities of the reactants along the reaction direction; and (iii) the potential energy surface of the reactants on the surface. The lowest energy pathway for a surface association reaction should correspond to the one with the best compromise of these three factors.

Problems in rarefied flows and chemical kinetics

NASA Astrophysics Data System (ADS)

Zhang, Peng

In Part I, a theory on weakly rarefied, low Mach number flows with surface reactions based on small sticking coefficients was first formulated for a binary gas mixture with an irreversible surface reaction, and then extended to a multicomponent mixture with multi-step surface reactions for situation in which all chemically active species are small in concentration compared to a major inert species. Particular interest was placed on the interaction between the Knudsen layer and the surface reactions. Results show that the Knudsen layer modifies not only the incident flux of the molecules striking the surface, but also the temperature-sensitive sticking coefficients and consequently the surface reaction rates. The surface reactions in turn modify the flow structure in the Knudsen layer through the non-zero net flux at the surface. Rate expressions for the surface reactions based on sticking coefficients were derived, and slip boundary conditions for temperature and species concentration suitable for application were established. The widely-used Motz-Wise correction formula for the surface reaction rate was revised and the underlying assumptions leading to its derivation were shown to be incorrect. As an application of the theory, an activation energy asymptotic analysis with one-step overall reaction was performed for the stabilization and extinction of a premixed flame over a rotating disk at sufficiently low pressures, for its relevance in low-pressure CVD (chemical vapor deposition) operations in which the flow is weakly rarefied. Extinction criteria based on the critical Damkohler number were obtained through the S-curve concept, parametrically demonstrating the influence of the CVD operating conditions, such as the spin rate and temperature of the disk, on flame extinction. It is further shown that, while decreasing pressure and hence the reactivity of the mixture tends to extinguish the flame, the trend can be substantially weakened by taking into account of the influence of the Knudsen layer, which reduces the heat loss to the disk as well as the flow stretch rate at the flame. In Part II, a theoretical analysis was performed for the head-on collision of two identical droplets in a gaseous environment, with the attendant bouncing and coalescence outcomes, for situations in which the extent of droplet deformation upon collision is comparable to the original droplet radius, corresponding to O(1--10) of the droplet Weber number. The model embodies the essential physics that describes the substantial amount of droplet deformation, the viscous loss through droplet internal motion induced by the deformation, the dynamics and rarefied nature of the gas film between the interfaces of the colliding droplets, and the potential destruction and thereby merging of these interfaces due to the van der Waals attraction force. The theoretical model was applied to investigate collisions involving hydrocarbon and water droplets at sub- and super-atmospheric pressures. In Part III, a fitting formula was first proposed to approximate the fall-off curves of the pressure- and temperature-dependent unimolecular reaction rate constants. Compared with the widely used Troe's formula, the present expression has the potential to substantially reduce the computation time in its evaluation because of the mathematical simplicity. Four testing reactions from the VariFlex program package were used to examine the accuracy of the present formula, showing improved performance as compared with previous expressions. Furthermore, the present formula shows improved computational efficiency compared to Troe's formula by savings of more than 60% computation time on its evaluation. Studies on chemical kinetics have also included a separate analysis on the decomposition kinetics of CH3NHNH2 (Monomethylhydrazine) with the ab initio transition state theory based master equation analyses. The simple NN and CN bond fissions to produce the radicals CH 3NH + NH2 or CH3 + NHNH2 are expected to dominate the decomposition kinetics. The transition states for these two bond fissions are studied with variable reaction coordinate transition state theory employing directly determined CASPT2/aug-cc-pVDZ interaction energies. Orientation independent corrections for limitations in the basis set and for the effects of conserved mode geometry relaxation are included. Predictions for the pressure dependence and product branching in the dissociation of CH 3NHNH2 are obtained by solving the master equation. (Abstract shortened by UMI.)

Abstracts and research accomplishments of university coal research projects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1991-06-01

The Principal Investigators of the grants supported by the University Coal Research Program were requested to submit abstracts and highlight accomplishments of their projects in time for distribution at a grantees conference. This book is a compilation of the material received in response to the request. Abstracts discuss the following area: coal science, coal surface science, reaction chemistry, advanced process concepts, engineering fundamentals and thermodynamics, environmental science.

JSC Materials Laboratory Reproduction and Failure Analysis of Cracked Orbiter Reaction Control System Niobium Thruster Injectors

NASA Technical Reports Server (NTRS)

Castner, Willard L.; Jacobs, Jeremy B.

2006-01-01

In April 2004 a Space Shuttle Orbiter Reaction Control System (RCS) thruster was found to be cracked while undergoing a nozzle (niobium/C103 alloy) retrofit. As a failure resulting from an in-flight RCS thruster burn-through (initiated from a crack) could be catastrophic, an official Space Shuttle Program flight constraint was issued until flight safety could be adequately demonstrated. This paper describes the laboratory test program which was undertaken to reproduce the cracking in order to fully understand and bound the driving environments. The associated rationale developed to justify continued safe flight of the Orbiter RCS system is also described. The laboratory testing successfully reproduced the niobium cracking, and established specific bounding conditions necessary to cause cracking in the C103 thruster injectors. Each of the following conditions is necessary in combination together: 1) a mechanically disturbed / cold-worked free surface, 2) an externally applied sustained tensile stress near yield strength, 3) presence of fluorine-containing fluids on exposed tensile / cold-worked free surfaces, and 4) sustained exposure to temperatures greater than 400 F. As a result of this work, it was concluded that fluorine-containing materials (e.g. HF acid, Krytox , Brayco etc.) should be carefully controlled or altogether eliminated during processing of niobium and its alloys.

Identifying the Thermal Decomposition Mechanism of Guaiacol on Pt(111): An Integrated X-ray Photoelectron Spectroscopy and Density Functional Theory Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hensley, Alyssa J.; Wockel, Claudia; Gleichweit, Christoph

Using a concerted effort from both experiment and theory, we determine the thermal decomposition mechanism for guaiacol on Pt(111), a reaction of interest in the area of bio-oil upgrading. This work serves as a demonstration of the power of combining in situ temperature-programmed X-ray photoelectron spectroscopy cos (TPXPS) and density functional theory (DFT) to elucidate complex reaction mechanisms occurring on heterogeneous surfaces. At low temperature (230 K), guaiacol was found to chemisorb with the aromatic ring parallel to the Pt(111) surface with five distinct carbon species and three oxygen species. As the temperature was increased, TPXPS showed several significant changesmore » to the surface species. The increase in the species associated with the decomposition of the functional groups of guaiacol is followed by their subsequent disappearance and an increase in the nonaromatic carbon signal. On the basis of an energetic analysis of the various mechanisms using DFT, along with the comparison of the experimentally and theoretically derived core-level binding energies, we determined that guaiacol's decomposition mechanism occurs via the dehydrogenation of both the methyl and hydroxyl functional groups, followed by demethylation of the CH2 or CH group to form 1,2-benzoquinone. Further heating to above 375 K likely breaks the aromatic ring and results in the rapid formation and desorption of CO, accounting for the disappearance of the 0 is signal above 450 K These results show that a knowledgeable application of TPXPS and DFT can result in the quantitative identification of surface species during complex reactions, providing insight useful for the design of future heterogeneous surfaces.« less

Pyrrole Hydrogenation over Rh(111) and Pt(111) Single-Crystal Surfaces and Hydrogenation Promotion Mediated by 1-Methylpyrrole: A Kinetic and Sum-Frequency Generation Vibrational Spectroscopy Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kliewer, Christopher J.; Bieri, Marco; Somorjai, Gabor A.

Sum-frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to study the adsorption and hydrogenation of pyrrole over both Pt(111) and Rh(111) single-crystal surfaces at Torr pressures (3 Torr pyrrole, 30 Torr H{sub 2}) to form pyrrolidine and the minor product butylamine. Over Pt(111) at 298 K it was found that pyrrole adsorbs in an upright geometry cleaving the N-H bond to bind through the nitrogen evidenced by SFG data. Over Rh(111) at 298 K pyrrole adsorbs in a tilted geometry relative to the surface through the p-aromatic system. A pyrroline surface reaction intermediate,more » which was not detected in the gas phase, was seen by SFG during the hydrogenation over both surfaces. Significant enhancement of the reaction rate was achieved over both metal surfaces by adsorbing 1-methylpyrrole before reaction. SFG vibrational spectroscopic results indicate that reaction promotion is achieved by weakening the bonding between the N-containing products and the metal surface because of lateral interactions on the surface between 1-methylpyrrole and the reaction species, reducing the desorption energy of the products. It was found that the ring-opening product butylamine was a reaction poison over both surfaces, but this effect can be minimized by treating the catalyst surfaces with 1-methylpyrrole before reaction. The reaction rate was not enhanced with elevated temperatures, and SFG suggests desorption of pyrrole at elevated temperatures.« less

Studying Reaction Intermediates Formed at Graphenic Surfaces

NASA Astrophysics Data System (ADS)

Sarkar, Depanjan; Sen Gupta, Soujit; Narayanan, Rahul; Pradeep, Thalappil

2014-03-01

We report in-situ production and detection of intermediates at graphenic surfaces, especially during alcohol oxidation. Alcohol oxidation to acid occurs on graphene oxide-coated paper surface, driven by an electrical potential, in a paper spray mass spectrometry experiment. As paper spray ionization is a fast process and the time scale matches with the reaction time scale, we were able to detect the intermediate, acetal. This is the first observation of acetal formed in surface oxidation. The process is not limited to alcohols and the reaction has been extended to aldehydes, amines, phosphenes, sugars, etc., where reaction products were detected instantaneously. By combining surface reactions with ambient ionization and mass spectrometry, we show that new insights into chemical reactions become feasible. We suggest that several other chemical transformations may be studied this way. This work opens up a new pathway for different industrially and energetically important reactions using different metal catalysts and modified substrate.

Computational Study of Field Initiated Surface Reactions for Synthesis of Diamond and Silicon

NASA Technical Reports Server (NTRS)

Musgrave, Charles Bruce

1999-01-01

This project involves using quantum chemistry to simulate surface chemical reactions in the presence of an electric field for nanofabrication of diamond and silicon. A field delivered by a scanning tunneling microscope (STM) to a nanometer scale region of a surface affects chemical reaction potential energy surfaces (PES) to direct atomic scale surface modification to fabricate sub-nanometer structures. Our original hypothesis is that the applied voltage polarizes the charge distribution of the valence electrons and that these distorted molecular orbitals can be manipulated with the STM so as to change the relative stabilities of the electronic configurations over the reaction coordinates and thus the topology of the PES and reaction kinetics. Our objective is to investigate the effect of applied bias on surface reactions and the extent to which STM delivered fields can be used to direct surface chemical reactions on an atomic scale on diamond and silicon. To analyze the fundamentals of field induced chemistry and to investigate the application of this technique for the fabrication of nanostructures, we have employed methods capable of accurately describing molecular electronic structure. The methods we employ are density functional theory (DFT) quantum chemical (QC) methods. To determine the effect of applied bias on surface reactions we have calculated the QC PESs in various applied external fields for various reaction steps for depositing or etching diamond and silicon. We have chosen reactions which are thought to play a role in etching and the chemical vapor deposition growth of Si and diamond. The PESs of the elementary reaction steps involved are then calculated under the applied fields, which we vary in magnitude and configuration. We pay special attention to the change in the reaction barriers, and transition state locations, and search for low energy reaction channels which were inaccessible without the applied bias.

User's Guide to Galoper: A Program for Simulating the Shapes of Crystal Size Distributions from Growth Mechanisms - and Associated Programs

USGS Publications Warehouse

Eberl, Dennis D.; Drits, V.A.; Srodon, J.

2000-01-01

GALOPER is a computer program that simulates the shapes of crystal size distributions (CSDs) from crystal growth mechanisms. This manual describes how to use the program. The theory for the program's operation has been described previously (Eberl, Drits, and Srodon, 1998). CSDs that can be simulated using GALOPER include those that result from growth mechanisms operating in the open system, such as constant-rate nucleation and growth, nucleation with a decaying nucleation rate and growth, surface-controlled growth, supply-controlled growth, and constant-rate and random growth; and those that result from mechanisms operating in the closed system such as Ostwald ripening, random ripening, and crystal coalescence. In addition, CSDs for two types weathering reactions can be simulated. The operation of associated programs also is described, including two statistical programs used for comparing calculated with measured CSDs, a program used for calculating lognormal CSDs, and a program for arranging measured crystal sizes into size groupings (bins).

Investigation of the wett-ability of various pure metals and alloys and beryllium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilliland, Ralph Gerald

1963-06-13

Thesis submitted to University of Tennessee, Knoxville. Activities in a program to determine the wetting behavior of pure metals such as Au, Ag, Ge, Al, and Cu on solid Be are reported. Results of similar investigations of binary alloys such as Be--Ti, Be-Zr, and Be--Pd are also included. The contact angles of the molten metals on Be as a function of temperature, exposure time, and atmosphere were measured. The solid-liquid interfacial reactions occurring as a function of test temperature and atmosphere were investigated, and the liquid- vapor and internal surface tensions for those systems in which interfacial reactions did notmore » appear to occur were calculated.« less

Propylene oxidation mechanisms and intermediates using in situ soft X-ray fluorescence methods on the Pt(111) surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gabelnick, A.M.; Capitano, A.T.; Kane, S.M.

2000-01-12

The oxidation of propylene preabsorbed on the Pt(111) surface has been characterized in oxygen pressures up to 0.02 Torr using fluorescence yield near-edge spectroscopy (FYNES) and temperature-programmed fluorescence yield near-edge spectroscopy (TP-FYNES) above the carbon K edge. During oxidation of adsorbed propylene, a stable intermediate was observed and characterized using these soft X-ray methods. A general in situ method for determining the stoichiometry of carbon-containing reaction intermediate species has been developed and demonstrated for the first time. Total carbon concentration measured during temperature-programmed reaction studies clearly indicates a reaction intermediate is formed in the 300 K temperature range with amore » surface concentration of 0.55 x 10{sup 15} carbon atoms/cm{sup 2}. By comparing the intensity of the C-H {sigma}* resonance at the magic angle with the intensity in the carbon continuum, the stoichiometry of this intermediate can be determined unambiguously. Based on calibration with molecular propylene (C{sub 3}H{sub 6}) and propylidyne (C{sub 3}H{sub 5}), the intermediate has a C{sub 3}H{sub 5} stoichiometry for oxygen pressures up to 0.02 Torr. A set of normal and glancing angle FYNES spectra above the carbon K edge was used to characterize the bonding and structure of this intermediate. Spectra of known coverages of adsorbed propylene and propylidyne served as standards. The spectra of di-{sigma} propylene, propylidyne, and the intermediate were curve fit as a group with consistent energies and widths of all primary features. Based on this procedure, the intermediate is 1,1,2-tri-{sigma} 1-methylvinyl. The stoichiometry and temperature stability range of the 1-methylvinyl intermediate formed in oxygen pressures up to 0.02 Torr is identical with the stoichiometry and stability of the same intermediate formed during oxidation of preadsorbed propylene by excess coadsorbed atomic oxygen.« less

PHAST--a program for simulating ground-water flow, solute transport, and multicomponent geochemical reactions

USGS Publications Warehouse

Parkhurst, David L.; Kipp, Kenneth L.; Engesgaard, Peter; Charlton, Scott R.

2004-01-01

The computer program PHAST simulates multi-component, reactive solute transport in three-dimensional saturated ground-water flow systems. PHAST is a versatile ground-water flow and solute-transport simulator with capabilities to model a wide range of equilibrium and kinetic geochemical reactions. The flow and transport calculations are based on a modified version of HST3D that is restricted to constant fluid density and constant temperature. The geochemical reactions are simulated with the geochemical model PHREEQC, which is embedded in PHAST. PHAST is applicable to the study of natural and contaminated ground-water systems at a variety of scales ranging from laboratory experiments to local and regional field scales. PHAST can be used in studies of migration of nutrients, inorganic and organic contaminants, and radionuclides; in projects such as aquifer storage and recovery or engineered remediation; and in investigations of the natural rock-water interactions in aquifers. PHAST is not appropriate for unsaturated-zone flow, multiphase flow, density-dependent flow, or waters with high ionic strengths. A variety of boundary conditions are available in PHAST to simulate flow and transport, including specified-head, flux, and leaky conditions, as well as the special cases of rivers and wells. Chemical reactions in PHAST include (1) homogeneous equilibria using an ion-association thermodynamic model; (2) heterogeneous equilibria between the aqueous solution and minerals, gases, surface complexation sites, ion exchange sites, and solid solutions; and (3) kinetic reactions with rates that are a function of solution composition. The aqueous model (elements, chemical reactions, and equilibrium constants), minerals, gases, exchangers, surfaces, and rate expressions may be defined or modified by the user. A number of options are available to save results of simulations to output files. The data may be saved in three formats: a format suitable for viewing with a text editor; a format suitable for exporting to spreadsheets and post-processing programs; or in Hierarchical Data Format (HDF), which is a compressed binary format. Data in the HDF file can be visualized on Windows computers with the program Model Viewer and extracted with the utility program PHASTHDF; both programs are distributed with PHAST. Operator splitting of the flow, transport, and geochemical equations is used to separate the three processes into three sequential calculations. No iterations between transport and reaction calculations are implemented. A three-dimensional Cartesian coordinate system and finite-difference techniques are used for the spatial and temporal discretization of the flow and transport equations. The non-linear chemical equilibrium equations are solved by a Newton-Raphson method, and the kinetic reaction equations are solved by a Runge-Kutta or an implicit method for integrating ordinary differential equations. The PHAST simulator may require large amounts of memory and long Central Processing Unit (CPU) times. To reduce the long CPU times, a parallel version of PHAST has been developed that runs on a multiprocessor computer or on a collection of computers that are networked. The parallel version requires Message Passing Interface, which is currently (2004) freely available. The parallel version is effective in reducing simulation times. This report documents the use of the PHAST simulator, including running the simulator, preparing the input files, selecting the output files, and visualizing the results. It also presents four examples that verify the numerical method and demonstrate the capabilities of the simulator. PHAST requires three input files. Only the flow and transport file is described in detail in this report. The other two files, the chemistry data file and the database file, are identical to PHREEQC files and the detailed description of these files is found in the PHREEQC documentation.

Comparisons of predicted steady-state levels in rooms with extended- and local-reaction bounding surfaces

NASA Astrophysics Data System (ADS)

Hodgson, Murray; Wareing, Andrew

2008-01-01

A combined beam-tracing and transfer-matrix model for predicting steady-state sound-pressure levels in rooms with multilayer bounding surfaces was used to compare the effect of extended- and local-reaction surfaces, and the accuracy of the local-reaction approximation. Three rooms—an office, a corridor and a workshop—with one or more multilayer test surfaces were considered. The test surfaces were a single-glass panel, a double-drywall panel, a carpeted floor, a suspended-acoustical ceiling, a double-steel panel, and glass fibre on a hard backing. Each test surface was modeled as of extended or of local reaction. Sound-pressure levels were predicted and compared to determine the significance of the surface-reaction assumption. The main conclusions were that the difference between modeling a room surface as of extended or of local reaction is not significant when the surface is a single plate or a single layer of material (solid or porous) with a hard backing. The difference is significant when the surface consists of multilayers of solid or porous material and includes a layer of fluid with a large thickness relative to the other layers. The results are partially explained by considering the surface-reflection coefficients at the first-reflection angles.

One-pot reaction for the preparation of biofunctionalized self-assembled monolayers on gold surfaces

NASA Astrophysics Data System (ADS)

Raigoza, Annette F.; Fies, Whitney; Lim, Amber; Onyirioha, Kristeen; Webb, Lauren J.

2017-02-01

The Huisgen cycloaddition reaction (;click; chemistry) has been used extensively to functionalize surfaces with macromolecules in a straightforward manner. We have previously developed a procedure using the copper(I)-catalyzed click reaction to tether synthetic α-helical peptides carrying two alkyne groups to a well-ordered azide-terminated alkanethiol self-assembled monolayer (SAM) on a Au(111) surface. While convenient, click-based strategies potentially pose significant problems from reagents, solvents, and reaction temperatures that may irreversibly damage some molecules or substrates. Tuning click chemistry conditions would allow individual optimization of reaction conditions for a wide variety of biomolecules and substrate materials. Here, we explore the utility of simultaneous SAM formation and peptide-attachment chemistry in a one-pot reaction. We demonstrate that a formerly multistep reaction can be successfully carried out concurrently by mixing azide-terminated alkanethiols, CuCl, and a propargylglycine-containing peptide over a bare gold surface in ethanol and reacting at 70 °C. X-ray photoelectron spectroscopy (XPS), surface infrared spectroscopy, surface circular dichroic (CD) spectroscopy, and scanning tunneling microscopy (STM) were used to determine that this one-pot reaction strategy resulted in a high density of surface-bound α-helices without aggregation. This work demonstrates the simplicity and versatility of a SAM-plus-click chemistry strategy for functionalizing Au surfaces with structured biomolecules.

Promising SiC support for Pd catalyst in selective hydrogenation of acetylene to ethylene

NASA Astrophysics Data System (ADS)

Guo, Zhanglong; Liu, Yuefeng; Liu, Yan; Chu, Wei

2018-06-01

In this study, SiC supported Pd nanoparticles were found to be an efficient catalyst in acetylene selective hydrogenation reaction. The ethylene selectivity can be about 20% higher than that on Pd/TiO2 catalyst at the same acetylene conversion at 90%. Moreover, Pd/SiC catalyst showed a stable catalytic life at 65 °C with 80% ethylene selectivity. With the detailed characterization using temperature-programmed reduction (H2-TPR), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 adsorption/desorption analysis, CO-chemisorption and thermo-gravimetric analysis (TGA), it was found that SiC owns a lower surface area (22.9 m2/g) and a broad distribution of meso-/macro-porosity (from 5 to 65 nm), which enhanced the mass transfer during the chemical process at high reaction rate and decreased the residence time of ethylene on catalyst surface. Importantly, SiC support has the high thermal conductivity, which favored the rapid temperature homogenization through the catalyst bed and inhabited the over-hydrogenation of acetylene. The surface electronic density of Pd on Pd/SiC catalyst was higher than that on Pd/TiO2, which could promote desorption of ethylene from surface of the catalyst. TGA results confirmed a much less coke deposition on Pd/SiC catalyst.

A Cu/Pt Near-Surface Alloy for Water-Gas Shift Catalysis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knudsen, Jan; Nilekar, Anand U.; Vang, Ronnie T.

2007-05-01

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The primary route to hydrogen production from fossil fuels involves the water-gas shift (WGS) reaction, and an improvement in the efficiency of WGS catalysts could therefore lead to a major leap forward in the realization of hydrogen economy. On the basis of a combination of high-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations, we suggestmore » the existence of a new thermodynamically stable Cu/Pt near-surface alloy (NSA). Temperature-programmed desorption and DFT reveal that this Cu/Pt NSA binds CO significantly more weakly than does Pt alone, thereby implying a considerable reduction in the potential for CO poisoning of the Cu/Pt NSA surface as compared to that of pure Pt. In addition, DFT calculations show that this Cu/Pt NSA is able to activate H2O easily, which is the rate-determining step for the WGS on several metal surfaces, and, at the same time, to bind the products of that reaction and formate intermediates rather weakly, thus avoiding possible poisoning of the catalyst surface. The Cu/Pt NSA is thus a promising candidate for an improved WGS catalyst.« less

Surface Interrogation Scanning Electrochemical Microscopy for a Photoelectrochemical Reaction: Water Oxidation on a Hematite Surface.

PubMed

Kim, Jae Young; Ahn, Hyun S; Bard, Allen J

2018-03-06

To understand the pathway of a photoelectrochemical (PEC) reaction, quantitative knowledge of reaction intermediates is important. We describe here surface interrogation scanning electrochemical microscopy for this purpose (PEC SI-SECM), where a light pulse to a photoactive semiconductor film at a given potential generates intermediates that are then analyzed by a tip generated titrant at known times after the light pulse. The improvements were demonstrated for photoelectrochemical water oxidation (oxygen evolution) reaction on a hematite surface. The density of photoactive sites, proposed to be Fe 4+ species, on a hematite surface was successfully quantified, and the photoelectrochemical water oxidation reaction dynamics were elucidated by time-dependent redox titration experiments. The new configuration of PEC SI-SECM should find expanded usage to understand and investigate more complicated PEC reactions with other materials.

Controlling Reaction Selectivity through the Surface Termination of Perovskite Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polo-Garzon, Felipe; Yang, Shi-Ze; Fung, Victor

2017-07-19

Although perovskites have been widely used in catalysis, tuning their surface terminations to control reaction selectivities has not been well established. In this work, we employ multiple surface sensitive techniques to characterize the surface termination (one aspect of surface reconstruction) of SrTiO 3 (STO) after thermal pretreatment (Sr-enrichment) and chemical etching (Ti-enrichment). We show, using the conversion of 2-propanol as a probe reaction, that the surface termination of STO can be controlled to greatly tune catalytic acid/base properties and consequently the reaction selectivities in a wide range, which are inaccessible using single metal oxides, either SrO or TiO 2. Densitymore » functional theory (DFT) calculations well explain the selectivity tuning and reaction mechanism on different surface terminations of STO. Similar catalytic tunability is also observed on BaZrO 3, highlighting the generality of the finding from this work.« less

Direct vs. indirect pathway for nitrobenzene reduction reaction on a Ni catalyst surface: a density functional study.

PubMed

Mahata, Arup; Rai, Rohit K; Choudhuri, Indrani; Singh, Sanjay K; Pathak, Biswarup

2014-12-21

Density functional theory (DFT) calculations are performed to understand and address the previous experimental results that showed the reduction of nitrobenzene to aniline prefers direct over indirect reaction pathways irrespective of the catalyst surface. Nitrobenzene to aniline conversion occurs via the hydroxyl amine intermediate (direct pathway) or via the azoxybenzene intermediate (indirect pathway). Through our computational study we calculated the spin polarized and dispersion corrected reaction energies and activation barriers corresponding to various reaction pathways for the reduction of nitrobenzene to aniline over a Ni catalyst surface. The adsorption behaviour of the substrate, nitrobenzene, on the catalyst surface was also considered and the energetically most preferable structural orientation was elucidated. Our study indicates that the parallel adsorption behaviour of the molecules over a catalyst surface is preferable over vertical adsorption behaviour. Based on the reaction energies and activation barrier of the various elementary steps involved in direct or indirect reaction pathways, we find that the direct reduction pathway of nitrobenzene over the Ni(111) catalyst surface is more favourable than the indirect reaction pathway.

Reaction Dynamics Following Ionization of Ammonia Dimer Adsorbed on Ice Surface.

PubMed

Tachikawa, Hiroto

2016-09-22

The ice surface provides an effective two-dimensional reaction field in interstellar space. However, how the ice surface affects the reaction mechanism is still unknown. In the present study, the reaction of an ammonia dimer cation adsorbed both on water ice and cluster surface was theoretically investigated using direct ab initio molecular dynamics (AIMD) combined with our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) method, and the results were compared with reactions in the gas phase and on water clusters. A rapid proton transfer (PT) from NH3(+) to NH3 takes place after the ionization and the formation of intermediate complex NH2(NH4(+)) is found. The reaction rate of PT was significantly affected by the media connecting to the ammonia dimer. The time of PT was calculated to be 50 fs (in the gas phase), 38 fs (on ice), and 28-33 fs (on water clusters). The dissociation of NH2(NH4(+)) occurred on an ice surface. The reason behind the reaction acceleration on an ice surface is discussed.

Pulsed ion beam investigation of the kinetics of surface reactions

NASA Technical Reports Server (NTRS)

Horton, C. C.; Eck, T. G.; Hoffman, R. W.

1989-01-01

Pulsed ion beam measurements of the kinetics of surface reactions are discussed for the case where the width of the ion pulse is comparable to the measured reaction time, but short compared to the time between successive pulses. Theoretical expressions are derived for the time dependence of the ion-induced signals for linear surface reactions. Results are presented for CO emission from surface carbon and CF emission from Teflon induced by oxygen ion bombardment. The strengths and limitations of this technique are described.

Program and Abstracts for Clay Minerals Society 28th Annual Meeting

NASA Technical Reports Server (NTRS)

1991-01-01

This volume contains abstracts that were accepted for presentation at the annual meeting. Some of the main topics covered include: (1) fundamental properties of minerals and methods of mineral analysis; (2) surface chemistry; (3) extraterrestrial clay minerals; (4) geothermometers and geochronometers; (5) smectite, vermiculite, illite, and related reactions; (6) soils and clays in environmental research; (7) kaolinite, halloysite, iron oxides, and mineral transformations; and (8) clays in lakes, basins, and reservoirs.

General chemical kinetics computer program for static and flow reactions, with application to combustion and shock-tube kinetics

NASA Technical Reports Server (NTRS)

Bittker, D. A.; Scullin, V. J.

1972-01-01

A general chemical kinetics program is described for complex, homogeneous ideal-gas reactions in any chemical system. Its main features are flexibility and convenience in treating many different reaction conditions. The program solves numerically the differential equations describing complex reaction in either a static system or one-dimensional inviscid flow. Applications include ignition and combustion, shock wave reactions, and general reactions in a flowing or static system. An implicit numerical solution method is used which works efficiently for the extreme conditions of a very slow or a very fast reaction. The theory is described, and the computer program and users' manual are included.

Reaction Profiles and Molecular Dynamics Simulations of Cyanide Radical Reactions Relevant to Titan's Atmosphere

NASA Astrophysics Data System (ADS)

Trinidad Pérez-Rivera, Danilo; Romani, Paul N.; Lopez-Encarnacion, Juan Manuel

2016-10-01

Titan's atmosphere is arguably the atmosphere of greatest interest that we have an abundance of data for from both ground based and spacecraft observations. As we have learned more about Titan's atmospheric composition, the presence of pre-biotic molecules in its atmosphere has generated more and more fascination about the photochemical process and pathways it its atmosphere. Our computational laboratory has been extensively working throughout the past year characterizing nitrile synthesis reactions, making significant progress on the energetics and dynamics of the reactions of .CN with the hydrocarbons acetylene (C2H2), propylene (CH3CCH), and benzene (C6H6), developing a clear picture of the mechanistic aspects through which these three reactions proceed. Specifically, first principles calculations of the reaction profiles and molecular dynamics studies for gas-phase reactions of .CN and C2H2, .CN and CH3CCH, and .CN and C6H6 have been carried out. A very accurate determination of potential energy surfaces of these reactions will allow us to compute the reaction rates which are indispensable for photochemical modeling of Titan's atmosphere.The work at University of Puerto Rico at Cayey was supported by Puerto Rico NASA EPSCoR IDEAS-ER program (2015-2016) and DTPR was sponsored by the Puerto Rico NASA Space Grant Consortium Fellowship. *E-mail: juan.lopez15@upr.edu

BEARKIMPE-2: A VBA Excel program for characterizing granular iron in treatability studies

NASA Astrophysics Data System (ADS)

Firdous, R.; Devlin, J. F.

2014-02-01

The selection of a suitable kinetic model to investigate the reaction rate of a contaminant with granular iron (GI) is essential to optimize the permeable reactive barrier (PRB) performance in terms of its reactivity. The newly developed Kinetic Iron Model (KIM) determines the surface rate constant (k) and sorption parameters (Cmax &J) which were not possible to uniquely identify previously. The code was written in Visual Basic (VBA), within Microsoft Excel, was adapted from earlier command line FORTRAN codes, BEARPE and KIMPE. The program is organized with several user interface screens (UserForms) that guide the user step by step through the analysis. BEARKIMPE-2 uses a non-linear optimization algorithm to calculate transport and chemical kinetic parameters. Both reactive and non-reactive sites are considered. A demonstration of the functionality of BEARKIMPE-2, with three nitroaromatic compounds showed that the differences in reaction rates for these compounds could be attributed to differences in their sorption behavior rather than their propensities to accept electrons in the reduction process.

Catalytic Synthesis of Oxygenates: Mechanisms, Catalysts and Controlling Characteristics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klier, Kamil; Herman, Richard G

2005-11-30

This research focused on catalytic synthesis of unsymmetrical ethers as a part of a larger program involving oxygenated products in general, including alcohols, ethers, esters, carboxylic acids and their derivatives that link together environmentally compliant fuels, monomers, and high-value chemicals. The catalysts studied here were solid acids possessing strong Brnsted acid functionalities. The design of these catalysts involved anchoring the acid groups onto inorganic oxides, e.g. surface-grafted acid groups on zirconia, and a new class of mesoporous solid acids, i.e. propylsulfonic acid-derivatized SBA-15. The former catalysts consisted of a high surface concentration of sulfate groups on stable zirconia catalysts. Themore » latter catalyst consists of high surface area, large pore propylsulfonic acid-derivatized silicas, specifically SBA-15. In both cases, the catalyst design and synthesis yielded high concentrations of acid sites in close proximity to one another. These materials have been well-characterization in terms of physical and chemical properties, as well as in regard to surface and bulk characteristics. Both types of catalysts were shown to exhibit high catalytic performance with respect to both activity and selectivity for the bifunctional coupling of alcohols to form ethers, which proceeds via an efficient SN2 reaction mechanism on the proximal acid sites. This commonality of the dual-site SN2 reaction mechanism over acid catalysts provides for maximum reaction rates and control of selectivity by reaction conditions, i.e. pressure, temperature, and reactant concentrations. This research provides the scientific groundwork for synthesis of ethers for energy applications. The synthesized environmentally acceptable ethers, in part derived from natural gas via alcohol intermediates, exhibit high cetane properties, e.g. methylisobutylether with cetane No. of 53 and dimethylether with cetane No. of 55-60, or high octane properties, e.g. diisopropylether with blending octane No. of 105, and can replace aromatics in liquid fuels.« less

Development of the reentry flight dynamics simulator for evaluation of space shuttle orbiter entry systems

NASA Technical Reports Server (NTRS)

Rowell, L. F.; Powell, R. W.; Stone, H. W., Jr.

1980-01-01

A nonlinear, six degree of freedom, digital computer simulation of a vehicle which has constant mass properties and whose attitudes are controlled by both aerodynamic surfaces and reaction control system thrusters was developed. A rotating, oblate Earth model was used to describe the gravitational forces which affect long duration Earth entry trajectories. The program is executed in a nonreal time mode or connected to a simulation cockpit to conduct piloted and autopilot studies. The program guidance and control software used by the space shuttle orbiter for its descent from approximately 121.9 km to touchdown on the runway.

Programming chemistry in DNA-addressable bioreactors

PubMed Central

Fellermann, Harold; Cardelli, Luca

2014-01-01

We present a formal calculus, termed the chemtainer calculus, able to capture the complexity of compartmentalized reaction systems such as populations of possibly nested vesicular compartments. Compartments contain molecular cargo as well as surface markers in the form of DNA single strands. These markers serve as compartment addresses and allow for their targeted transport and fusion, thereby enabling reactions of previously separated chemicals. The overall system organization allows for the set-up of programmable chemistry in microfluidic or other automated environments. We introduce a simple sequential programming language whose instructions are motivated by state-of-the-art microfluidic technology. Our approach integrates electronic control, chemical computing and material production in a unified formal framework that is able to mimic the integrated computational and constructive capabilities of the subcellular matrix. We provide a non-deterministic semantics of our programming language that enables us to analytically derive the computational and constructive power of our machinery. This semantics is used to derive the sets of all constructable chemicals and supermolecular structures that emerge from different underlying instruction sets. Because our proofs are constructive, they can be used to automatically infer control programs for the construction of target structures from a limited set of resource molecules. Finally, we present an example of our framework from the area of oligosaccharide synthesis. PMID:25121647

Methanol partial oxidation on Ag(111) from first principles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aljama, Hassan; Yoo, Jong Suk; Nørskov, Jens K.

In this work, we examine the thermochemistry and kinetics of the partial oxidation of methanol to formaldehyde on silver surfaces. Periodic density functional theory calculations employing the BEEF-vdW functional are used to identify the most stable phases of the silver surface under relevant reaction conditions and the reaction energetics are obtained on these surfaces. The calculated binding energies and transition state energies are used as input in a mean-field microkinetic model providing the reaction kinetics on silver surfaces under different reaction conditions. Our results show that, under conditions pertaining to methanol partial oxidation, oxygen is present at low concentrations andmore » it plays a critical role in the catalytic reaction. Surface oxygen promotes the reaction by activating the OH bond in methanol, thus forming a methoxy intermediate, which can react further to form formaldehyde. Finally, the dissociation of molecular oxygen is identified as the most critical step.« less

Methanol partial oxidation on Ag(111) from first principles

DOE PAGES

Aljama, Hassan; Yoo, Jong Suk; Nørskov, Jens K.; ...

2016-10-26

In this work, we examine the thermochemistry and kinetics of the partial oxidation of methanol to formaldehyde on silver surfaces. Periodic density functional theory calculations employing the BEEF-vdW functional are used to identify the most stable phases of the silver surface under relevant reaction conditions and the reaction energetics are obtained on these surfaces. The calculated binding energies and transition state energies are used as input in a mean-field microkinetic model providing the reaction kinetics on silver surfaces under different reaction conditions. Our results show that, under conditions pertaining to methanol partial oxidation, oxygen is present at low concentrations andmore » it plays a critical role in the catalytic reaction. Surface oxygen promotes the reaction by activating the OH bond in methanol, thus forming a methoxy intermediate, which can react further to form formaldehyde. Finally, the dissociation of molecular oxygen is identified as the most critical step.« less

Unraveling the Reaction Chemistry of Icy Ocean World Surfaces

NASA Astrophysics Data System (ADS)

Hudson, R.; Loeffler, M. J.; Gerakines, P.

2017-12-01

The diverse endogenic chemistry of ocean worlds can be divided among interior, surface, and above-surface process, with contributions from exogenic agents such as solar, cosmic, and magnetospheric radiation. Bombardment from micrometeorites to comets also can influence chemistry by both delivering new materials and altering pre-existing ones, and providing energy to drive reactions. Geological processes further complicate the chemistry by transporting materials from one environment to another. In this presentation the focus will be on some of the thermally driven and radiation-induced changes expected from icy materials, primarily covalent and ionic compounds. Low-temperature conversions of a few relatively simple molecules into ions possessing distinct infrared (IR) features will be covered, with an emphasis on such features as might be identified through either orbiting spacecraft or landers. The low-temperature degradation of a few bioorganic molecules, such as DNA nucleobases and some common amino acids, will be used as examples of the more complex, and potentially misleading, chemistry expected for icy moons of the outer solar system. This work was supported by NASA's Emerging Worlds and Outer Planets Research programs, as well as the NASA Astrobiology Institute's Goddard Center for Astrobiology.

Modified Ni-Cu catalysts for ethanol steam reforming

NASA Astrophysics Data System (ADS)

Dan, M.; Mihet, M.; Almasan, V.; Borodi, G.; Katona, G.; Muresan, L.; Lazar, M. D.

2013-11-01

Three Ni-Cu catalysts, having different Cu content, supported on γ-alumina were synthesized by wet co-impregnation method, characterized and tested in the ethanol steam reforming (ESR) reaction. The catalysts were characterized for determination of: total surface area and porosity (N2 adsorption - desorption using BET and Dollimer Heal methods), Ni surface area (hydrogen chemisorption), crystallinity and Ni crystallites size (X-Ray Diffraction), type of catalytic active centers (Hydrogen Temperature Programmed Reduction). Total surface area and Ni crystallites size are not significantly influenced by the addition of Cu, while Ni surface area is drastically diminished by increasing of Cu concentration. Steam reforming experiments were performed at atmospheric pressure, temperature range 150-350°C, and ethanol - water molar ration of 1 at 30, using Ar as carrier gas. Ethanol conversion and hydrogen production increase by the addition of Cu. At 350°C there is a direct connection between hydrogen production and Cu concentration. Catalysts deactivation in 24h time on stream was studied by Transmission Electron Microscopy (TEM) and temperature-programmed reduction (TPR) on used catalysts. Coke deposition was observed at all studied temperatures; at 150°C amorphous carbon was evidenced, while at 350°C crystalline, filamentous carbon is formed.

Vapor-phase catalytic oxidesulfurization (ODS) of organosulfur compounds over supported metal oxide catalysts

NASA Astrophysics Data System (ADS)

Choi, Sukwon

Sulfur in transportation fuels remains a leading source of SOx emissions from vehicle engines and is a major source of air pollution. The very low levels of sulfur globally mandated for transportation fuels in the near future cannot be achieved by current practices of hydrodesulfurization (HDS) for sulfur removal, which operate under severe conditions (high T, P) and use valuable H2. Novel vapor-phase catalytic oxidesulfurization (ODS) processes of selectively oxidizing various organosulfur compounds (carbonyl sulfide, carbon disulfide, methanethiol, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), thiophene, 2,5-dimenthylthiophene) typically found in various industrial streams (e.g., petroleum refining, pulp and paper) into valuable chemical intermediates (H 2CO, CO, H2, maleic anhydride and concentrated SO2) has been extensively studied. This research has primarily focused on establishing the fundamental kinetics and mechanisms of these selective oxidation reactions over well-defined supported metal oxide catalysts. The selective oxidation reactions of COS + O2 → CO + SO2; 2CS2 + 5O2 → 2CO + 4SO2; CH3SH + 2O 2 → H2CO + SO2 + H2O; C4 H4S + 3O2 → C4H2O 3 + H2O + SO2; were studied. Raman spectroscopy revealed that the supported metal oxide phases were 100% dispersed on the oxide substrate. All the catalysts were highly active and selective for the oxidesulfurization of carbonyl sulfide, carbon disulfide, methanethiol, and thiophene between 290--330°C, 230--270°C, 350--400°C, and 250--400°C, respectively and did not deactivate. The TOFs (turnover frequency, normalized activity per active catalytic site) for all ODS reactions over supported vanadia catalysts, only containing molecularly dispersed surface vanadia species, varied within one order of magnitude and revealed the V-O-Support bridging bond was involved in the critical rate-determining kinetic steps. The surface reaction mechanism for each reaction was revealed by in situ IR (infrared) and temperature programmed surface reaction-mass spectroscopy (TPSR-MS). The systematic investigation of vapor-phase oxidesulfurization (ODS) reactions of organosulfur compounds over catalytic supported metal oxides revealed the facile S-O exchange mechanisms allow for the efficient removal of sulfur while producing value-added chemicals and represents the discovery of a new series of catalytic reactions.

Reactions and Surface Transformations of a Bone-Bioactive Material in a Simulated Microgravity Environment

NASA Technical Reports Server (NTRS)

Radin, S.; Ducheyne, P.; Ayyaswamy, P. S.

1999-01-01

A comprehensive program to investigate the expeditious in vitro formation of three-dimensional bone-like tissue is currently underway at the University of Pennsylvania. The study reported here forms a part of that program. Three-dimensional bone-like tissue structures may be grown under the simulated microgravity conditions of NASA designed Rotating Wall Bioreactor Vessels (RWV's). Such tissue growth will have wide clinical applications. In addition, an understanding of the fundamental changes that occur to bone cells under simulated microgravity would yield important information that will help in preventing or minimizing astronaut bone loss, a major health issue with travel or stay in space over long periods of time. The growth of three-dimensional bone-like tissue structures in RWV's is facilitated by the use of microcarriers which provide structural support. If the microcarrier material additionally promotes bone cell growth, then it is particularly advantageous to employ such microcarriers. We have found that reactive, bone-bioactive glass (BBG) is an attractive candidate for use as microcarrier material. Specifically, it has been found that BBG containing Ca- and P- oxides upregulates osteoprogenitor cells to osteoblasts. This effect on cells is preceded by BBG reactions in solution which result in the formation of a Ca-P surface layer. This surface further transforms to a bone-like mineral (i.e., carbonated crystalline hydroxyapatite (c-HA)). At normal gravity, time-dependent, immersion-induced BBG reactions and transformations are greatly affected both by variations in the composition of the milieu in which the glass is immersed and on the immersion conditions. However, the nature of BBG reactions and phase transformations under the simulated microgravity conditions of RWV's are unknown, and must be understood in order to successfully use BBG as microcarrier material in RWV'S. In this paper, we report some of our recent findings in this regard using experimental and numerical methods. BBG composition 45S5, the most reactive among known bone-bioactive glasses, was chosen for the study. BBG 45S5 behavior in physiological solutions was tested in simulated microgravity and compared with that at normal gravity. On the basis of our numerical study, we have chosen the BBG granule size to be in the range 40-70 microns, and a RWV rotational speed of 10 rpm. Our numerical study has shown that these parameters enable the microcarrier to remain suspended in the medium without experiencing collisions with the wall of the vessel. Immersion-induced changes in the solution composition and the material surface were analyzed after immersion.

Molecular-dynamics analysis of mobile helium cluster reactions near surfaces of plasma-exposed tungsten

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Lin; Maroudas, Dimitrios, E-mail: maroudas@ecs.umass.edu; Hammond, Karl D.

We report the results of a systematic atomic-scale analysis of the reactions of small mobile helium clusters (He{sub n}, 4 ≤ n ≤ 7) near low-Miller-index tungsten (W) surfaces, aiming at a fundamental understanding of the near-surface dynamics of helium-carrying species in plasma-exposed tungsten. These small mobile helium clusters are attracted to the surface and migrate to the surface by Fickian diffusion and drift due to the thermodynamic driving force for surface segregation. As the clusters migrate toward the surface, trap mutation (TM) and cluster dissociation reactions are activated at rates higher than in the bulk. TM produces W adatoms and immobile complexes ofmore » helium clusters surrounding W vacancies located within the lattice planes at a short distance from the surface. These reactions are identified and characterized in detail based on the analysis of a large number of molecular-dynamics trajectories for each such mobile cluster near W(100), W(110), and W(111) surfaces. TM is found to be the dominant cluster reaction for all cluster and surface combinations, except for the He{sub 4} and He{sub 5} clusters near W(100) where cluster partial dissociation following TM dominates. We find that there exists a critical cluster size, n = 4 near W(100) and W(111) and n = 5 near W(110), beyond which the formation of multiple W adatoms and vacancies in the TM reactions is observed. The identified cluster reactions are responsible for important structural, morphological, and compositional features in the plasma-exposed tungsten, including surface adatom populations, near-surface immobile helium-vacancy complexes, and retained helium content, which are expected to influence the amount of hydrogen re-cycling and tritium retention in fusion tokamaks.« less

Reaction Heterogeneity in LiNi 0.8 Co 0.15 Al 0.05 O 2 Induced by Surface Layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grenier, Antonin; Liu, Hao; Wiaderek, Kamila M.

2017-08-15

Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air, through reaction with atmospheric CO2. This surfacemore » impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact vs an eroded Li2CO3 surface-coating. This reaction heterogeneity, with a bimodal distribution of reaction states, has previously been interpreted as a “two-phase” reaction mechanism for NCA, as an activation step that only occurs during the first cycle. Similar surface layers may impact the reaction mechanism observed in other electrode materials using bulk probes such as operando powder XRD.« less

Irradiation effect on deuterium behaviour in low-dose HFIR neutron-irradiated tungsten

DOE PAGES

Shimada, Masashi; Cao, G.; Otsuka, T.; ...

2014-12-01

Tungsten samples were irradiated by neutrons in the High Flux Isotope Reactor, Oak Ridge National Laboratory at reactor coolant temperatures of 50-70°C to low displacement damage of 0.025 and 0.3 dpa under the framework of the US-Japan TITAN program (2007-2013). After cooling down, the HFIR neutron-irradiated tungsten samples were exposed to deuterium plasmas in the Tritium Plasma Experiment, Idaho National Laboratory at 100, 200 and 500 °C twice at the ion fluence of 5×10²⁵ m⁻² to reach a total ion fluence of 1×10²⁶ m⁻² in order to investigate the near surface deuterium retention and saturation via nuclear reaction analysis. Finalmore » thermal desorption spectroscopy was performed to elucidate irradiation effect on total deuterium retention. Nuclear reaction analysis results showed that the maximum near surface (<5 µm depth) deuterium concentration increased from 0.5 at % D/W in 0.025 dpa samples to 0.8 at. % D/W in 0.3 dpa samples. The large discrepancy between the total retention via thermal desorption spectroscopy and the near surface retention via nuclear reaction analysis indicated the deuterium was migrated and trapped in bulk (at least 50 µm depth for 0.025 dpa and 35 µm depth for 0.025 dpa) at 500 °C case even in the relatively low ion fluence of 10²⁶ m⁻².« less

Interaction of Formaldehyde with the Rutile TiO 2 (110) Surface: A Combined Experimental and Theoretical Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Xiaojuan; Zhang, Zhenrong; Yang, Chengwu

2016-06-16

The adsorption and reaction of formaldehyde (CH 2O) on the oxidized rutile TiO 2(110) surface were studied by temperature programmed desorption (TPD), scanning tunneling microscopy (STM), infrared reflection-absorption spectroscopy (IRRAS) and density functional theory (DFT) calculations. The experimental and theoretical data reveal the presence of various species depending on the temperature and coverage. After formaldehyde adsorption on TiO 2(110) at 65 K, the multilayer CH 2O was detected, which desorbs completely upon heating to 120 K. The isolated CH 2O monomer was identified after submonolayer adsorption at low temperatures (45-65 K), in which CH 2O is bound to the surfacemore » Ti5c sites via σ-donation and adopts a tilted geometry. With heating to higher temperatures the CH 2O monomers remain stable up to 70 K and then undergo coupling reactions to form paraformaldehyde (polyoxymethylene, POM) at the Ti 5c rows. The POM chain is oriented primarily along the [001] direction in a slightly disordered configuration. POM becomes the predominant species at 120 K and is decomposed releasing CH 2O at about 250 K. In addition, dioxymethylene (DOM) was detected as minority species formed via reaction of Ti 5c-bound CH 2O with both neighboring O 2c along the [1-10] direction and oxygen adatoms (Oad) at Ti 5c sites along [001] on the oxidized TiO 2(110) surface.« less

Rate and reaction probability of the surface reaction between ozone and dihydromyrcenol measured in a bench scale reactor and a room-sized chamber

NASA Astrophysics Data System (ADS)

Shu, Shi; Morrison, Glenn C.

2012-02-01

Low volatility terpenoids emitted from consumer products can react with ozone on surfaces and may significantly alter concentrations of ozone, terpenoids and reaction products in indoor air. We measured the reaction probability and a second-order surface-specific reaction rate for the ozonation of dihydromyrcenol, a representative indoor terpenoid, adsorbed onto polyvinylchloride (PVC), glass, and latex paint coated spheres. The reaction probability ranged from (0.06-8.97) × 10 -5 and was very sensitive to humidity, substrate and mass adsorbed. The average surface reaction probability is about 10 times greater than that for the gas-phase reaction. The second-order surface-specific rate coefficient ranged from (0.32-7.05) × 10 -15 cm 4 s -1 molecule -1and was much less sensitive to humidity, substrate, or mass adsorbed. We also measured the ozone deposition velocity due to adsorbed dihydromyrcenol on painted drywall in a room-sized chamber, Based on that, we calculated the rate coefficient ((0.42-1.6) × 10 -15 cm 4 molecule -1 s -1), which was consistent with that derived from bench-scale experiments for the latex paint under similar conditions. We predict that more than 95% of dihydromyrcenol oxidation takes place on indoor surfaces, rather than in building air.

Computed potential energy surfaces for chemical reactions

NASA Technical Reports Server (NTRS)

Walch, Stephen P.; Levin, Eugene

1993-01-01

A new global potential energy surface (PES) is being generated for O(P-3) + H2 yields OH + H. This surface is being fit using the rotated Morse oscillator method, which was used to fit the previous POL-CI surface. The new surface is expected to be more accurate and also includes a much more complete sampling of bent geometries. A new study has been undertaken of the reaction N + O2 yields NO + O. The new studies have focused on the region of the surface near a possible minimum corresponding to the peroxy form of NOO. A large portion of the PES for this second reaction has been mapped out. Since state to state cross sections for the reaction are important in the chemistry of high temperature air, these studies will probably be extended to permit generation of a new global potential for reaction.

A multimodal optical and electrochemical device for monitoring surface reactions: redox active surfaces in porous silicon Rugate filters.

PubMed

Ciampi, Simone; Guan, Bin; Darwish, Nadim A; Zhu, Ying; Reece, Peter J; Gooding, J Justin

2012-12-21

Herein, mesoporous silicon (PSi) is configured as a single sensing device that has dual readouts; as a photonic crystal sensor in a Rugate filter configuration, and as a high surface area porous electrode. The as-prepared PSi is chemically modified to provide it with stability in aqueous media and to allow for the subsequent coupling of chemical species, such as via Cu(I)-catalyzed cycloaddition reactions between 1-alkynes and azides ("click" reactions). The utility of the bimodal capabilities of the PSi sensor for monitoring surface coupling procedures is demonstrated by the covalent coupling of a ferrocene derivative, as well as by demonstrating ligand-exchange reactions (LER) at the PSi surface. Both types of reactions were monitored through optical reflectivity measurements, as well as electrochemically via the oxidation/reduction of the surface tethered redox species.

Development of a reaction cell for in-situ/operando studies of surface of a catalyst under a reaction condition and during catalysis.

PubMed

Nguyen, Luan; Tao, Franklin Feng

2016-06-01

Tracking surface chemistry of a catalyst during catalysis is significant for fundamental understanding of catalytic performance of the catalyst since it allows for establishing an intrinsic correlation between surface chemistry of a catalyst at its working status and its corresponding catalytic performance. Ambient pressure X-ray photoelectron spectroscopy can be used for in-situ studies of surfaces of different materials or devices in a gas. To simulate the gaseous environment of a catalyst in a fixed-bed a flowing gaseous environment of reactants around the catalyst is necessary. Here, we report the development of a new flowing reaction cell for simulating in-situ study of a catalyst surface under a reaction condition in gas of one reactant or during catalysis in a mixture of reactants of a catalytic reaction. The homemade reaction cell is installed in a high vacuum (HV) or ultrahigh vacuum (UHV) environment of a chamber. The flowing gas in the reaction cell is separated from the HV or UHV environment through well sealings at three interfaces between the reaction cell and X-ray window, sample door and aperture of front cone of an energy analyzer. Catalyst in the cell is heated through infrared laser beam introduced through a fiber optics interfaced with the reaction cell through a homemade feedthrough. The highly localized heating on the sample holder and Au-passivated internal surface of the reaction cell effectively minimizes any unwanted reactions potentially catalyzed by the reaction cell. The incorporated laser heating allows a fast heating and a high thermal stability of the sample at a high temperature. With this cell, a catalyst at 800 °C in a flowing gas can be tracked readily.

Effect of surface curvature on diffusion-limited reactions on a curved surface

NASA Astrophysics Data System (ADS)

Eun, Changsun

2017-11-01

To investigate how the curvature of a reactive surface can affect reaction kinetics, we use a simple model in which a diffusion-limited bimolecular reaction occurs on a curved surface that is hollowed inward, flat, or extended outward while keeping the reactive area on the surface constant. By numerically solving the diffusion equation for this model using the finite element method, we find that the rate constant is a non-linear function of the surface curvature and that there is an optimal curvature providing the maximum value of the rate constant, which indicates that a spherical reactant whose entire surface is reactive (a uniformly reactive sphere) is not the most reactive species for a given reactive surface area. We discuss how this result arises from the interplay between two opposing effects: the exposedness of the reactive area to its partner reactants, which causes the rate constant to increase as the curvature increases, and the competition occurring on the reactive surface, which decreases the rate constant. This study helps us to understand the role of curvature in surface reactions and allows us to rationally design reactants that provide a high reaction rate.

Surface Defect Passivation and Reaction of c-Si in H2S.

PubMed

Liu, Hsiang-Yu; Das, Ujjwal K; Birkmire, Robert W

2017-12-26

A unique passivation process of Si surface dangling bonds through reaction with hydrogen sulfide (H 2 S) is demonstrated in this paper. A high-level passivation quality with an effective minority carrier lifetime (τ eff ) of >2000 μs corresponding to a surface recombination velocity of <3 cm/s is achieved at a temperature range of 550-650 °C. X-ray photoelectron spectroscopy (XPS) confirmed the bonding states of Si and S and provides insights into the reaction pathway of Si with H 2 S and other impurity elements both during and after the reaction. Quantitative analysis of XPS spectra showed that the τ eff increases with an increase in the surface S content up to ∼3.5% and stabilizes thereafter, indicative of surface passivation by monolayer coverage of S on the Si surface. However, S passivation of the Si surface is highly unstable because of thermodynamically favorable reaction with atmospheric H 2 O and O 2 . This instability can be eliminated by capping the S-passivated Si surface with a protective thin film such as low-temperature-deposited amorphous silicon nitride.

Comparative study on the effect of H2 pre-adsorption on CO oxidation in O2-poor atmosphere over Au/TiO2 and TiO2: Temperature programmed surface reaction by a multiplexed mass spectrometer testing

NASA Astrophysics Data System (ADS)

Si, Ruiru; Liu, Junfeng; Zhang, Yujuan; Chen, Xun; Dai, Wenxin; Fu, Xianzhi

2016-11-01

The behaviors of H2 pre-adsorption on CO oxidation in an O2-poor stream containing a trace H2O over Au/TiO2 and TiO2 have been investigated by a temperature programmed surface reaction testing, respectively. It was found that the H2 pre-adsorption could keep CO oxidation without H2O consumption over Au/TiO2, but suppress CO oxidation over TiO2. The chemisorption testing showed that the H2 adsorption at Au/TiO2 could benefit to the formation of Ti-bonded hydroxyl species (Ti4+-OH), while the H2 adsorption at TiO2 would consume the Ti-bonded hydroxyl species and form the bridge hydroxyl species (Ti4+-OH-Ti4+). These results show that only the Ti-bonded hydroxyl species (not all kinds of hydroxyl species) could act as the active species of oxidizing CO. Furthermore, it is suggested that the dissociative hydrogen adsorbed at Au sites could activate the lattice oxygen of TiO2 to form the active Ti-bonded hydroxyl species (hydrogen spillover from Au to TiO2), which exhibit a strong reducibility than the H directly adsorbed at TiO2.

Mechanochemical Association Reaction of Interfacial Molecules Driven by Shear.

PubMed

Khajeh, Arash; He, Xin; Yeon, Jejoon; Kim, Seong H; Martini, Ashlie

2018-05-29

Shear-driven chemical reaction mechanisms are poorly understood because the relevant reactions are often hidden between two solid surfaces moving in relative motion. Here, this phenomenon is explored by characterizing shear-induced polymerization reactions that occur during vapor phase lubrication of α-pinene between sliding hydroxylated and dehydroxylated silica surfaces, complemented by reactive molecular dynamics simulations. The results suggest that oxidative chemisorption of the α-pinene molecules at reactive surface sites, which transfers oxygen atoms from the surface to the adsorbate molecule, is the critical activation step. Such activation takes place more readily on the dehydroxylated surface. During this activation, the most strained part of the α-pinene molecules undergoes a partial distortion from its equilibrium geometry, which appears to be related to the critical activation volume for mechanical activation. Once α-pinene molecules are activated, association reactions occur between the newly attached oxygen and one of the carbon atoms in another molecule, forming ether bonds. These findings have general implications for mechanochemistry because they reveal that shear-driven reactions may occur through reaction pathways very different from their thermally induced counterparts and specifically the critical role of molecular distortion in such reactions.

Reversible and irreversible reactions of three oxygen precursors on InAs(0 0 1)-(4 × 2)/ c(8 × 2)

NASA Astrophysics Data System (ADS)

Clemens, Jonathon B.; Droopad, Ravi; Kummel, Andrew C.

2010-10-01

The substrate reactions of three common oxygen sources for gate oxide deposition on the group III rich InAs(0 0 1)-(4 × 2)/ c(8 × 2) surface are compared: water, hydrogen peroxide (HOOH), and isopropyl alcohol (IPA). Scanning tunneling microscopy reveals that surface atom displacement occurs in all cases, but via different mechanisms for each oxygen precursor. The reactions are examined as a function of post-deposition annealing temperature. Water reaction shows displacement of surface As atoms, but it does not fully oxidize the As; the reaction is reversed by high temperature (450 °C) annealing. Exposure to IPA and subsequent low-temperature annealing (100 °C) show the preferential reaction on the row features of InAs(0 0 1)-(4 × 2)/ c(8 × 2), but higher temperature anneals result in permanent surface atom displacement/etching. Etching of the substrate is observed with HOOH exposure for all annealing temperatures. While nearly all oxidation reactions on group IV semiconductors are irreversible, the group III rich surface of InAs(0 0 1) shows that oxidation displacement reactions can be reversible at low temperature, thereby providing a mechanism of self-healing during oxidation reactions.

Modification of heterogeneous chemistry by complex substrate morphology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henson, B.F.; Buelow, S.J.; Robinson, J.M.

1998-12-31

This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Chemistry in many environmental systems is determined at some stage by heterogeneous reaction with a surface. Typically the surface exists as a dispersion or matrix of particulate matter or pores, and a determination of the heterogeneous chemistry of the system must address the extent to which the complexity of the environmental surface affects the reaction rates. Reactions that are of current interest are the series of chlorine nitrate reactions important in polar ozone depletion. The authors have applied surfacemore » spectroscopic techniques developed at LANL to address the chemistry of chlorine nitrate reactions on porous nitric and sulfuric acid ice surfaces as a model study of the measurement of complex, heterogeneous reaction rates. The result of the study is an experimental determination of the surface coverage of one adsorbed reagent and a mechanism of reactivity based on the dependence of this coverage on temperature and vapor pressure. The resulting mechanism allows the first comprehensive modeling of chlorine nitrate reaction probability data from several laboratories.« less

Key factor affecting the structural and textural properties of ZSM-5/MCM-41 composite

NASA Astrophysics Data System (ADS)

Boukoussa, Bouhadjar; Aouad, Nafissa; Hamacha, Rachida; Bengueddach, Abdelkader

2015-03-01

ZSM-5/MCM-41 micro/mesoporous composite materials were synthesized by the hydrothermal technique with alkali-treated ZSM-5 zeolite as source of silica and aluminum and characterized by various physico-chemical techniques such as X-ray diffraction (XRD), nitrogen sorption at 77 K, transmission electronic microscopy (TEM), FTIR spectroscopy and NH3 temperature programmed desorption (TPD) techniques. The effect of concentration of CTAB in the synthesis of these solids has been investigated, the mesopore volume, surface area and surface acidity decrease with increasing the concentration of CTAB. Increasing the CTAB concentration causes the recrystallization of zeolite ZSM-5 and it disadvantage the formation of mesoporous materials MCM-41. The catalytic activity of ZSM-5/MCM-41 materials has been evaluated in the Friedel-Crafts acylation of anisole with benzoyl chloride as alkylating agent. The results revealed the reaction to be influenced by surface area, pore volume and surface acidity.

Construction of super - hydrophobic copper alloy surface by one - step mixed solution immersion method

NASA Astrophysics Data System (ADS)

Gu, Qiang; Chen, Ying; Chen, Dong; Zhang, Zeting

2018-01-01

This paper presents a method for preparing a super hydrophobic surface with a fast, simple, low-cost, one-step reaction by immersing copper alloy in an ethanol solution containing silver nitrate and myristic acid. The effects of reaction time, reaction temperature, reactant concentration and reaction time on the wettability of the material were studied. The surface wettability, appearance, chemical composition, durability and chemical stability of the prepared samples was measured by water contact angle (CA), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that when the reaction time is only 10min, the surface WCA of the prepared material can reach 154.9. This study provides an effective method for the rapid preparation of stable super hydrophobic surfaces.

Surface chemistry of rare-earth oxide surfaces at ambient conditions: reactions with water and hydrocarbons

NASA Astrophysics Data System (ADS)

Külah, Elçin; Marot, Laurent; Steiner, Roland; Romanyuk, Andriy; Jung, Thomas A.; Wäckerlin, Aneliia; Meyer, Ernst

2017-03-01

Rare-earth (RE) oxide surfaces are of significant importance for catalysis and were recently reported to possess intrinsic hydrophobicity. The surface chemistry of these oxides in the low temperature regime, however, remains to a large extent unexplored. The reactions occurring at RE surfaces at room temperature (RT) in real air environment, in particular, in presence of polycyclic aromatic hydrocarbons (PAHs), were not addressed until now. Discovering these reactions would shed light onto intermediate steps occurring in automotive exhaust catalysts before reaching the final high operational temperature and full conversion of organics. Here we first address physical properties of the RE oxide, nitride and fluoride surfaces modified by exposure to ambient air and then we report a room temperature reaction between PAH and RE oxide surfaces, exemplified by tetracene (C18H12) on a Gd2O3. Our study evidences a novel effect - oxidation of higher hydrocarbons at significantly lower temperatures (~300 K) than previously reported (>500 K). The evolution of the surface chemical composition of RE compounds in ambient air is investigated and correlated with the surface wetting. Our surprising results reveal the complex behavior of RE surfaces and motivate follow-up studies of reactions between PAH and catalytic surfaces at the single molecule level.

Methanethiol chemistry on TiO 2-supported Ni clusters

NASA Astrophysics Data System (ADS)

Ozturk, O.; Park, J. B.; Black, T. J.; Rodriguez, J. A.; Hrbek, J.; Chen, D. A.

2008-10-01

The thermal decomposition of methanethiol on Ni clusters grown on TiO 2(1 1 0) was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). On all of the Ni surfaces investigated, methane and hydrogen were observed as gaseous products in the TPD experiments, and the only sulfur-containing species that desorbed from the surface was methanethiol itself at low temperatures. The two pathways for methanethiol reaction were hydrodesulfurization to produce methane and nonselective decomposition, which leaves atomic carbon and sulfur on the surface. From high resolution XPS studies, methyl thiolate was identified as the surface intermediate for reaction on TiO 2 and on all of the Ni surfaces investigated, similar to what is observed on single-crystal Ni surfaces. However, the binding sites for methyl thiolate on the 1 ML (monolayer) Ni clusters were different from those on the Ni clusters at coverages of 2.5 ML and higher, based on the S(2p) binding energies for methyl thiolate. No distinct changes in activity or selectivity were observed for the smaller Ni clusters grown at low coverage compared to the more film-like Ni surfaces other than what could be accounted for by changes in total surface area. Interactions between the Ni clusters and the TiO 2 support had two main effects on chemical activity. First, carbon was oxidized by oxygen from the TiO 2 lattice to produce CO at temperatures above 800 K. Second, annealing induced encapsulation of the Ni clusters by reduced TiO x and chemisorbed oxygen. At 800 K, the Ni clusters were totally encapsulated, resulting in a complete loss of methanethiol activity; partial encapsulation at 700 K caused a smaller decrease in activity accompanied by increased oxidation of carbon by lattice oxygen.

Bayesian inversion analysis of nonlinear dynamics in surface heterogeneous reactions.

PubMed

Omori, Toshiaki; Kuwatani, Tatsu; Okamoto, Atsushi; Hukushima, Koji

2016-09-01

It is essential to extract nonlinear dynamics from time-series data as an inverse problem in natural sciences. We propose a Bayesian statistical framework for extracting nonlinear dynamics of surface heterogeneous reactions from sparse and noisy observable data. Surface heterogeneous reactions are chemical reactions with conjugation of multiple phases, and they have the intrinsic nonlinearity of their dynamics caused by the effect of surface-area between different phases. We adapt a belief propagation method and an expectation-maximization (EM) algorithm to partial observation problem, in order to simultaneously estimate the time course of hidden variables and the kinetic parameters underlying dynamics. The proposed belief propagation method is performed by using sequential Monte Carlo algorithm in order to estimate nonlinear dynamical system. Using our proposed method, we show that the rate constants of dissolution and precipitation reactions, which are typical examples of surface heterogeneous reactions, as well as the temporal changes of solid reactants and products, were successfully estimated only from the observable temporal changes in the concentration of the dissolved intermediate product.

Proxy-based accelerated discovery of Fischer–Tropsch catalysts† †Electronic supplementary information (ESI) available: Details of synthesis, analysis and testing, validation experiments for high-throughput XRD and gas treatment, details of statistical analysis and calculations, tabulation of synthesis parameters and XRD results, alternatives to Fig. 3 highlighting different data points, FTS testing results displayed graphically. See DOI: 10.1039/c4sc02116a Click here for additional data file.

PubMed Central

Boldrin, Paul; Gallagher, James R.; Combes, Gary B.; Enache, Dan I.; James, David; Ellis, Peter R.; Kelly, Gordon; Claridge, John B.

2015-01-01

Development of heterogeneous catalysts for complex reactions such as Fischer–Tropsch synthesis of fuels is hampered by difficult reaction conditions, slow characterisation techniques such as chemisorption and temperature-programmed reduction and the need for long term stability. High-throughput (HT) methods may help, but their use has until now focused on bespoke micro-reactors for direct measurements of activity and selectivity. These are specific to individual reactions and do not provide more fundamental information on the materials. Here we report using simpler HT characterisation techniques (XRD and TGA) along with ageing under Fischer–Tropsch reaction conditions to provide information analogous to metal surface area, degree of reduction and thousands of hours of stability testing time for hundreds of samples per month. The use of this method allowed the identification of a series of highly stable, high surface area catalysts promoted by Mg and Ru. In an advance over traditional multichannel HT reactors, the chemical and structural information we obtain on the materials allows us to identify the structural effects of the promoters and their effects on the modes of deactivation observed. PMID:29560180

Vibrations At Surfaces During Heterogeneous Catalytic Reactions

NASA Astrophysics Data System (ADS)

Aragno, A.; Basini, Luca; Marchionna, M.; Raffaelli, A.

1989-12-01

FTIR spectroscopies can be used in a wide range of temperature and pressure conditions to investigate on the chemistry and the physics of heterogeneous catalytic reactions. In this paper we have shortly discussed the spectroscopic results obtained during the study of two different reactions; the skeletal isomerization of 1-butene to obtain 2-methylpropene and the surface aggregation and fragmentation of rhodium carbonyl complexes during thermal treatments in N2, H2, CO, CH4 atmospheres. In the first case high temperature proton tran-sfer reactions are proposed to be responsible for the skeletal isomerization reaction. In the second case our experiments have shown a partial reversibility of the nucleation processes at the surfaces and revealed a low temperature reactivity of methane on rhodium car-bonyl surface complexes.

Laminar Soot Processes (LSP)

NASA Technical Reports Server (NTRS)

Dai, Z.; El-Leathy, A. M.; Kim, C. H.; Krishnan, S. S.; Lin, K.-C.; Xu, F.; Faeth, G. M.

2002-01-01

This is the final report of a research program considering the structure and the soot surface reaction properties of laminar nonpremixed (diffusion) flames. The study was limited to ground-based measurements of buoyant laminar jet diffusion flames at pressures of 0.1-1.0 atm. The motivation for the research is that soot formation in flames is a major unresolved problem of combustion science that influences the pollutant emissions, durability and performance of power and propulsion systems, as well as the potential for developing computational combustion. The investigation was divided into two phases considering the structure of laminar soot-containing diffusion flames and the soot surface reaction properties (soot surface growth and oxidation) of these flames, in turn. The first phase of the research addressed flame and soot structure properties of buoyant laminar jet diffusion flames at various pressures. The measurements showed that H, OH and O radical concentrations were generally in superequilibrium concentrations at atmospheric pressure but tended toward subequilibrium concentrations as pressures decreased. The measurements indicated that the original fuel decomposed into more robust compounds at elevated temperatures, such as acetylene (unless the original fuel was acetylene) and H, which are the major reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. The second phase of the research addressed soot surface reaction properties, e.g., soot surface growth and surface oxidation. It was found that soot surface growth rates in both laminar premixed and diffusion flames were in good agreement, that these rates were relatively independent of fuel type, and that these rates could be correlated by the Hydrogen-Abstraction/Carbon-Addition (HACA) mechanisms of Colket and Hall (1994), Frenklach et al. (1990,1994), and Kazakov et al. (1995). It was also found that soot surface oxidation rates were relatively independent of fuel type, were not correlated with O2, CO2, H2O and O collision rates but were correlated with the collision rates of OH with a collision efficiency of 0.14, in agreement with the early measurements in premixed flames of Neoh et al. (1980), after allowing for oxidation by O2 via the classical rate expression of Nagle and Strickland-Constable (1962).

Effect of Molecule–Surface Reaction Mechanism on the Electronic Characteristics and Photovoltaic Performance of Molecularly Modified Si

PubMed Central

2013-01-01

We report on the passivation properties of molecularly modified, oxide-free Si(111) surfaces. The reaction of 1-alcohol with the H-passivated Si(111) surface can follow two possible paths, nucleophilic substitution (SN) and radical chain reaction (RCR), depending on adsorption conditions. Moderate heating leads to the SN reaction, whereas with UV irradiation RCR dominates, with SN as a secondary path. We show that the site-sensitive SN reaction leads to better electrical passivation, as indicated by smaller surface band bending and a longer lifetime of minority carriers. However, the surface-insensitive RCR reaction leads to more dense monolayers and, therefore, to much better chemical stability, with lasting protection of the Si surface against oxidation. Thus, our study reveals an inherent dissonance between electrical and chemical passivation. Alkoxy monolayers, formed under UV irradiation, benefit, though, from both chemical and electronic passivation because under these conditions both SN and RCR occur. This is reflected in longer minority carrier lifetimes, lower reverse currents in the dark, and improved photovoltaic performance, over what is obtained if only one of the mechanisms operates. These results show how chemical kinetics and reaction paths impact electronic properties at the device level. It further suggests an approach for effective passivation of other semiconductors. PMID:24205409

Single Silver Adatoms on Nanostructured Manganese Oxide Surfaces: Boosting Oxygen Activation for Benzene Abatement.

PubMed

Chen, Yaxin; Huang, Zhiwei; Zhou, Meijuan; Ma, Zhen; Chen, Jianmin; Tang, Xingfu

2017-02-21

The involvement of a great amount of active oxygen species is a crucial requirement for catalytic oxidation of benzene, because complete mineralization of one benzene molecule needs 15 oxygen atoms. Here, we disperse single silver adatoms on nanostructured hollandite manganese oxide (HMO) surfaces by using a thermal diffusion method. The single-atom silver catalyst (Ag 1 /HMO) shows high catalytic activity in benzene oxidation, and 100% conversion is achieved at 220 °C at a high space velocity of 23 000 h -1 . The Mars-van Krevelen mechanism is valid in our case as the reaction orders for both benzene and O 2 approach one, according to reaction kinetics data. Data from H 2 temperature-programmed reduction and O core-level X-ray photoelectron spectra (XPS) reveal that Ag 1 /HMO possesses a great amount of active surface lattice oxygen available for benzene oxidation. Valence-band XPS and density functional theoretical calculations demonstrate that the single Ag adatoms have the upshifted 4d orbitals, thus facilitating the activation of gaseous oxygen. Therefore, the excellent activation abilities of Ag 1 /HMO toward both surface lattice oxygen and gaseous oxygen account for its high catalytic activity in benzene oxidation. This work may assist with the rational design of efficient metal-oxide catalysts for the abatement of volatile organic compounds such as benzene.

Catalytic reaction processes revealed by scanning probe microscopy. [corrected].

PubMed

Jiang, Peng; Bao, Xinhe; Salmeron, Miquel

2015-05-19

Heterogeneous catalysis is of great importance for modern society. About 80% of the chemicals are produced by catalytic reactions. Green energy production and utilization as well as environmental protection also need efficient catalysts. Understanding the reaction mechanisms is crucial to improve the existing catalysts and develop new ones with better activity, selectivity, and stability. Three components are involved in one catalytic reaction: reactant, product, and catalyst. The catalytic reaction process consists of a series of elementary steps: adsorption, diffusion, reaction, and desorption. During reaction, the catalyst surface can change at the atomic level, with roughening, sintering, and segregation processes occurring dynamically in response to the reaction conditions. Therefore, it is imperative to obtain atomic-scale information for understanding catalytic reactions. Scanning probe microscopy (SPM) is a very appropriate tool for catalytic research at the atomic scale because of its unique atomic-resolution capability. A distinguishing feature of SPM, compared to other surface characterization techniques, such as X-ray photoelectron spectroscopy, is that there is no intrinsic limitation for SPM to work under realistic reaction conditions (usually high temperature and high pressure). Therefore, since it was introduced in 1981, scanning tunneling microscopy (STM) has been widely used to investigate the adsorption, diffusion, reaction, and desorption processes on solid catalyst surfaces at the atomic level. STM can also monitor dynamic changes of catalyst surfaces during reactions. These invaluable microscopic insights have not only deepened the understanding of catalytic processes, but also provided important guidance for the development of new catalysts. This Account will focus on elementary reaction processes revealed by SPM. First, we will demonstrate the power of SPM to investigate the adsorption and diffusion process of reactants on catalyst surfaces at the atomic level. Then the dynamic processes, including surface reconstruction, roughening, sintering, and phase separation, studied by SPM will be discussed. Furthermore, SPM provides valuable insights toward identifying the active sites and understanding the reaction mechanisms. We also illustrate here how both ultrahigh vacuum STM and high pressure STM provide valuable information, expanding the understanding provided by traditional surface science. We conclude with highlighting remarkable recent progress in noncontact atomic force microscopy (NC-AFM) and inelastic electron tunneling spectroscopy (IETS), and their impact on single-chemical-bond level characterization for catalytic reaction processes in the future.

Computer program for nonlinear static stress analysis of shuttle thermal protection system: User's manual

NASA Technical Reports Server (NTRS)

Giles, G. L.; Wallas, M.

1981-01-01

User documentation is presented for a computer program which considers the nonlinear properties of the strain isolator pad (SIP) in the static stress analysis of the shuttle thermal protection system. This program is generalized to handle an arbitrary SIP footprint including cutouts for instrumentation and filler bar. Multiple SIP surfaces are defined to model tiles in unique locations such as leading edges, intersections, and penetrations. The nonlinearity of the SIP is characterized by experimental stress displacement data for both normal and shear behavior. Stresses in the SIP are calculated using a Newton iteration procedure to determine the six rigid body displacements of the tile which develop reaction forces in the SIP to equilibrate the externally applied loads. This user documentation gives an overview of the analysis capabilities, a detailed description of required input data and an example to illustrate use of the program.

Chemical reactivity testing for the National Spent Nuclear Fuel Program. Revision 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koester, L.W.

This quality assurance project plan (QAPjP) summarizes requirements used by Lockheed Martin Energy Systems, Incorporated (LMES) Development Division at Y-12 for conducting chemical reactivity testing of Department of Energy (DOE) owned spent nuclear fuel, sponsored by the National Spent Nuclear Fuel Program (NSNFP). The requirements are based on the NSNFP Statement of work PRO-007 (Statement of Work for Laboratory Determination of Uranium Hydride Oxidation Reaction Kinetics.) This QAPjP will utilize the quality assurance program at Y-12, Y60-101PD, Quality Program Description, and existing implementing procedures for the most part in meeting the NSNFP Statement of Work PRO-007 requirements, exceptions will bemore » noted. The project consists of conducting three separate series of related experiments, ''Passivation of Uranium Hydride Powder With Oxygen and Water'', '''Passivation of Uranium Hydride Powder with Surface Characterization'', and ''Electrochemical Measure of Uranium Hydride Corrosion Rate''.« less

Catalytic combustion of hydrogen-air mixtures in stagnation flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ikeda, H.; Libby, P.A.; Williams, F.A.

1993-04-01

The interaction between heterogeneous and homogeneous reactions arising when a mixture of hydrogen and air impinges on a platinum plate at elevated temperature is studied. A reasonably complete description of the kinetic mechanism for homogeneous reactions is employed along with a simplified model for heterogeneous reactions. Four regimes are identified depending on the temperature of the plate, on the rate of strain imposed on the flow adjacent to the plate and on the composition and temperature of the reactant stream: (1) surface reaction alone; (2) surface reaction inhibiting homogeneous reaction; (3) homogeneous reaction inhibiting surface reaction; and (4) homogeneous reactionmore » alone. These regimes are related to those found earlier for other chemical systems and form the basis of future experimental investigation of the chemical system considered in the present study.« less

Synthesis of Supported Pd 0 Nanoparticles from a Single-Site Pd 2+ Surface Complex by Alkene Reduction

DOE PAGES

Mouat, Aidan R.; Whitford, Cassandra L.; Chen, Bor-Rong; ...

2018-02-02

Here, a surface metal–organic complex, (-AlO x)Pd(acac) (acac = acetylacetonate), is prepared by chemically grafting the precursor Pd(acac) 2 onto γ-Al 2O 3 in toluene at 25 °C. The resulting surface complex is characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and dynamic nuclear polarization surface-enhanced solid-state nuclear magnetic resonance spectroscopy (DNP SENS). This surface complex is a precursor in the direct synthesis of size-controlled Pd nanoparticles under mild reductive conditions and in the absence of additional stabilizers or pretreatments. Indeed, upon exposure to gaseous ethylene or liquid 1-octene at 25more » °C, the Pd 2+ species is reduced to form Pd 0 nanoparticles with a mean diameter of 4.3 ± 0.6 nm, as determined by scanning transmission electron microscopy (STEM). These nanoparticles are catalytically relevant using the aerobic 1-phenylethanol oxidation as a probe reaction, with rates comparable to a conventional Pd/Al 2O 3 catalyst but without an induction period. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reaction mass spectrometry (TPR-MS) reveal that the surface complex reduction with ethylene coproduces H 2, acetylene, and 1,3-butadiene. This process reasonably proceeds via an olefin activation/coordination/insertion pathway, followed by β-hydride elimination to generate free Pd 0. Lastly, the well-defined nature of the single-site supported Pd 2+ precursor provides direct mechanistic insights into this unusual and likely general reductive process.« less

Synthesis of Supported Pd 0 Nanoparticles from a Single-Site Pd 2+ Surface Complex by Alkene Reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mouat, Aidan R.; Whitford, Cassandra L.; Chen, Bor-Rong

Here, a surface metal–organic complex, (-AlO x)Pd(acac) (acac = acetylacetonate), is prepared by chemically grafting the precursor Pd(acac) 2 onto γ-Al 2O 3 in toluene at 25 °C. The resulting surface complex is characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and dynamic nuclear polarization surface-enhanced solid-state nuclear magnetic resonance spectroscopy (DNP SENS). This surface complex is a precursor in the direct synthesis of size-controlled Pd nanoparticles under mild reductive conditions and in the absence of additional stabilizers or pretreatments. Indeed, upon exposure to gaseous ethylene or liquid 1-octene at 25more » °C, the Pd 2+ species is reduced to form Pd 0 nanoparticles with a mean diameter of 4.3 ± 0.6 nm, as determined by scanning transmission electron microscopy (STEM). These nanoparticles are catalytically relevant using the aerobic 1-phenylethanol oxidation as a probe reaction, with rates comparable to a conventional Pd/Al 2O 3 catalyst but without an induction period. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reaction mass spectrometry (TPR-MS) reveal that the surface complex reduction with ethylene coproduces H 2, acetylene, and 1,3-butadiene. This process reasonably proceeds via an olefin activation/coordination/insertion pathway, followed by β-hydride elimination to generate free Pd 0. Lastly, the well-defined nature of the single-site supported Pd 2+ precursor provides direct mechanistic insights into this unusual and likely general reductive process.« less

Matrix photochemistry of small molecules: Influencing reaction dynamics on electronically excited hypersurfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laursen, S.L.

Investigations of chemical reactions on electronically excited reaction surfaces are presented. The role of excited-surface multiplicity is of particular interest, as are chemical reactivity and energy transfer in systems in which photochemistry is initiated through a metal atom sensitizer.'' Two approaches are employed: A heavy-atom matrix affords access to forbidden triplet reaction surfaces, eliminating the need for a potentially reactive sensitizer. Later, the role of the metal atom in the photosensitization process is examined directly.

Hydrothermal performance of catalyst supports

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elam, Jeffrey W.; Marshall, Christopher L.; Libera, Joseph A.

A high surface area catalyst with a mesoporous support structure and a thin conformal coating over the surface of the support structure. The high surface area catalyst support is adapted for carrying out a reaction in a reaction environment where the thin conformal coating protects the support structure within the reaction environment. In various embodiments, the support structure is a mesoporous silica catalytic support and the thin conformal coating comprises a layer of metal oxide resistant to the reaction environment which may be a hydrothermal environment.

Cyclic Square Wave Voltammetry of Surface-Confined Quasireversible Electron Transfer Reactions.

PubMed

Mann, Megan A; Bottomley, Lawrence A

2015-09-01

The theory for cyclic square wave voltammetry of surface-confined quasireversible electrode reactions is presented and experimentally verified. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. From the trends obtained, diagnostic criteria for this mechanism were deduced. These criteria were experimentally confirmed using two well-established surface-confined analytes. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure electrode reaction kinetics.

The chemisorption and reactions of formic acid on Cu films on ZnO (000 overline1)-O

NASA Astrophysics Data System (ADS)

Ludviksson, A.; Zhang, R.; Campbell, Charles T.; Griffiths, K.

1994-06-01

The adsorption and reactions of formic acid (HCOOD : HCOOH = 3:1) on the oxygen-terminated ZnO(0001¯)-O surface and on thin Cu films deposited on the ZnO(0001¯)-O surface have been studied with temperature programmed desorption (TPD) and XPS. Small amounts of formic acid dissociate at defect sites on clean ZnO(0001¯)-O to yield surface formate (HCOO). The acid D(H) from this dissociation does not reappear in TPD, and is lost to the ZnO bulk, as confirmed by nuclear reaction analysis. The surface HCOO decomposes to yield nearly simultaneous CO 2 (37%), CO (63%) and H 2 TPD peaks at 560 K. Substantial amounts of D (˜ 20%) are incorporated in this hydrogen TPD peak resulting from formate decomposition at ZnO defects, indicating that bulk D is readily accessible. Submonolayer and multilayer Cu films that are deposited at 130 K and partially cover the ZnO surface as 2D and 3D islands adsorb formic acid and decompose it into formate and hydrogen much like the Cu(110) surface. The surface formate from the Cu film decomposes at 470-500 K to give primarily CO 2 and H 2, also much like Cu(110), although atom-thin Cu islands also give ˜ 40% CO. Annealed Cu films give formate decomposition peaks at 25-50 K lower in temperature, attributed to thickening and ordering of the Cu islands to form Cu(111)-like sites. The acid D(H) atom from the formic acid is partially lost by hydrogen spillover from the Cu islands into the ZnO substrate, especially for thin Cu films. This effect partially desorbs and is enhanced upon preannealing the Cu layers, due to increased H diffusion rates across the annealed Cu islands, and/or the decrease in island size. Bulk D(H) is slowly removed as D 2, HD and H 2 above 400 K in diffusion-limited desorption, catalyzed by Cu.

[Enzymatic conversion of tetradecanol in heterogenous phase by yeast-alcohol dehydrogenase].

PubMed

Rothe, U; Schöpp, W; Aurich, H

1976-01-01

Alcohol dehydrogenase from yeast converts long-chain primary alcohols not only in the dissolved state, but also at the surface of undissolved particles. Tetradecanol beads with a defined surface can be produced and employed as model substrate. The reaction rate was determined by the proton release accomplished in the reaction. The initial reaction rate depends on the enzyme concentration. The relation is nonlinear (vi = k-[e]0,4); the numerical value of the exponent (n = 0.4) argues in favour of a reaction occurring at the interface. The Lineweaver-Burk plots become linear if the substrate concentrations are based on the molar surface concentrations of the particles. The pH optimum for the reaction at the surface is displaced by 0.25 pH units towards the alkaline region (compared with ethanol as substrate). The activation energy of the reaction with tetradecanol beads as substrate is 30% lower than that for the ethanol oxydation.

The role of surface nonuniformity in controlling the initiation of a galvanic replacement reaction.

PubMed

Cobley, Claire M; Zhang, Qiang; Song, Wilbur; Xia, Younan

2011-06-06

The use of silver nanocrystals--asymmetrically truncated octahedrons and nanobars--characterized by a nonuniform surface as substrates for a galvanic replacement reaction was investigated. As the surfaces of these nanocrystals contain facets with a variety of different areas, shapes, and atomic arrangements, we were able to examine the roles of these parameters in different stages of the galvanic replacement reaction with HAuCl(4) (e.g., pitting, hollowing, pit closing, and pore formation), and thus obtain a deeper understanding of the reaction mechanism than is possible with silver nanocubes. We found that the most important of these parameters was the atomic arrangement, that is, whether the surface was capped by a {100} or {111} facet, and that the area and shape of the facet had essentially no effect on the initiation of the reaction. Interestingly, through the reaction with asymmetrically truncated octahedrons, we were also able to demonstrate that even when pitting occurred over a large area, this region would be sealed through a combination of atomic diffusion and deposition during the intermediate stages of the reaction. Consequently, even if pitting occurred across a large percentage of the nanocrystal surface, it was still possible to maintain the morphology of the template throughout the reaction. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Real-time observation of coadsorption layers on Ru(001) using a temperature-programmed ESDIAD/TOF system

NASA Astrophysics Data System (ADS)

Sasaki, T.; Itai, Y.; Iwasawa, Y.

1997-11-01

For the purpose of utilizing ESDIAD as a real-time probe for surface processes, we have developed an instrument which can measure ESDIAD images and time of flight (TOF) spectra of desorbing ions in temperature-programmed surface processes. TOF measurements are carried out to identify the mass and to determine the kinetic energy distribution of the desorbed ions. This temperature-programmed (TP-) ESDIAD/TOF system was used to observe coadsorption layers of methylamine and CO on Ru(001) which have been previously studied by our group using LEED, TPD and HREELS, also drawing upon a comparison of findings with the coadsorption system of CO and ammonia. ESDIAD images acquired for temperature-programmed surface processes in real time were found to provide new insight into the dynamic behaviour of the coadsorption layers. As to the pure adsorption of ammonia and methylamine, the second and the first (chemisorbed) layers can be easily discriminated in their different ESD detection efficiency due to the difference in neutralization rate. The intensity change of H + ions with temperature shows the process of the decomposition of methylamine to be dependent on CO coverage. The intensity of O + originating from CO changes due to the change of CO adsorption site in the reaction process. The angular distribution of H + ions which correspond to CH2NH…Ru species appears at 250-300 K in the presence of high CO pre-coverage.

AFOSR (Air Force Office of Scientific Research) Chemical & Atmospheric Sciences Program Review (28th).

DTIC Science & Technology

1983-06-01

the study of " hydrothermal " reaction of gels as the minimum energy route to ceramic consolidation. Ultra Low Thermal Expansion Ceramics - Dr. H. A...requirements can be accommodated. A series of OCCA’s, in particular, formamide and oxalic acid, and their use in making 100% S102, alkali-silicates, alkali...IIIB glass surface was proposed. The mechanisms of hydrothermal attach of two phase lithia-silicate glass-ceramics were identified and related to the

Influence of surface heterogeneity in electroosmotic flows—Implications in chromatography, fluid mixing, and chemical reactions in microdevices

NASA Astrophysics Data System (ADS)

Adrover, Alessandra; Giona, Massimiliano; Pagnanelli, Francesca; Toro, Luigi

2007-04-01

We analyze the influence of surface heterogeneity, inducing a random ζ-potential at the walls in electroosmotic incompressible flows. Specifically, we focus on how surface heterogeneity modifies the physico-chemical processes (transport, chemical reaction, mixing) occurring in microchannel and microreactors. While the macroscopic short-time features associated with solute transport (e.g. chromatographic patterns) do not depend significantly on ζ-potential heterogeneity, spatial randomness in the surface ζ-potential modifies the spectral properties of the advection-diffusion operator, determining different long-term properties of transport/reaction phenomena compared to the homogeneous case. Examples of physical relevance (chromatography, infinitely fast reactions) are addressed.

The mineralogic evolution of the Martian surface through time: Implications from chemical reaction path modeling studies

NASA Technical Reports Server (NTRS)

Plumlee, G. S.; Ridley, W. I.; Debraal, J. D.; Reed, M. H.

1993-01-01

Chemical reaction path calculations were used to model the minerals that might have formed at or near the Martian surface as a result of volcano or meteorite impact driven hydrothermal systems; weathering at the Martian surface during an early warm, wet climate; and near-zero or sub-zero C brine-regolith reactions in the current cold climate. Although the chemical reaction path calculations carried out do not define the exact mineralogical evolution of the Martian surface over time, they do place valuable geochemical constraints on the types of minerals that formed from an aqueous phase under various surficial and geochemically complex conditions.

Multiple model approach to evaluation of accelerated carbonation for steelmaking slag in a slurry reactor.

PubMed

Pan, Shu-Yuan; Liu, Hsing-Lu; Chang, E-E; Kim, Hyunook; Chen, Yi-Hung; Chiang, Pen-Chi

2016-07-01

Basic oxygen furnace slag (BOFS) exhibits highly alkaline properties due to its high calcium content, which is beneficial to carbonation reaction. In this study, accelerated carbonation of BOFS was evaluated under different reaction times, temperatures, and liquid-to-solid (L/S) ratios in a slurry reactor. CO2 mass balance within the slurry reactor was carried out to validate the technical feasibility of fixing gaseous CO2 into solid precipitates. After that, a multiple model approach, i.e., theoretical kinetics and empirical surface model, for carbonation reaction was presented to determine the maximal carbonation conversion of BOFS in a slurry reactor. On one hand, the reaction kinetics of BOFS carbonation was evaluated by the shrinking core model (SCM). Calcite (CaCO3) was identified as a reaction product through the scanning electronic microscopy and X-ray diffraction analyses, which provided the rationale of applying the SCM in this study. The rate-limiting step of carbonation was found to be ash-diffusion controlled, and the effective diffusivity for carbonation of BOFS in a slurry reactor were determined accordingly. On the other hand, the carbonation conversion of BOFS was predicted by the response surface methodology (RSM) via a nonlinear mathematical programming. According to the experimental data, the highest carbonation conversion of BOFS achieved was 57% under an L/S ratio of 20 mL g(-1), a CO2 flow rate of 0.1 L min(-1), and a pressure of 101.3 kPa at 50 °C for 120 min. Furthermore, the applications and limitations of SCM and RSM were examined and exemplified by the carbonation of steelmaking slags. Copyright © 2016 Elsevier Ltd. All rights reserved.

Selective Catalytic Reduction of NO by NH 3 with WO 3-TiO 2 Catalysts: Influence of Catalyst Synthesis Method

DOE PAGES

He, Yuanyuan; Ford, Michael E.; Zhu, Minghui; ...

2016-02-02

A series of supported WO 3/TiO 2 catalysts was prepared by a new synthesis procedure involving co-precipitation of an aqueous TiO(OH) 2 and (NH 4) 10W 12O 41*5H 2O slurry under controlled pH conditions. The morphological properties, molecular structures, surface acidity and surface chemistry of the supported WO 3/TiO 2 catalysts were determined with BET, in situ Raman, in situ IR and temperature-programmed surface reaction (TPSR) spectroscopy, respectively. Isotopic 18O- 16O exchange demonstrated that tungsten oxide was exclusively present as surface WO x species on the TiO 2 support with mono-oxo W=O coordination. In contrast to previous studies employing impregnationmore » synthesis that found only surface one mono-oxo O=WO 4 site on TiO 2, the co-precipitation procedure resulted in the formation of two distinct surface WO x species: mono-oxo O=WO 4 (~1010-1017 cm -1) on low defect density patches of TiO 2 and a second mono-oxo O=WO 4 (~983-986 cm -1) on high defect density patches of TiO 2. The concentration of the second WO x surface species increases as a function of solution pH. Both surface WOx sites, however, exhibited the same NO/NH 3 SCR reactivity. The co-precipitated WO 3-TiO 2 catalysts synthesized in alkaline solutions exhibited enhanced performance for the NO/NH 3 SCR reaction that is ascribed to the greater number of surface defects on the resulting TiO2 support. For the co-precipitated catalyst prepared at pH10, surface NH 4 + species on Br nsted acid sites were found to be more reactive than surface NH 3* species on Lewis acid sites for SCR of NO with NH 3.« less

Programming chemistry in DNA-addressable bioreactors.

PubMed

Fellermann, Harold; Cardelli, Luca

2014-10-06

We present a formal calculus, termed the chemtainer calculus, able to capture the complexity of compartmentalized reaction systems such as populations of possibly nested vesicular compartments. Compartments contain molecular cargo as well as surface markers in the form of DNA single strands. These markers serve as compartment addresses and allow for their targeted transport and fusion, thereby enabling reactions of previously separated chemicals. The overall system organization allows for the set-up of programmable chemistry in microfluidic or other automated environments. We introduce a simple sequential programming language whose instructions are motivated by state-of-the-art microfluidic technology. Our approach integrates electronic control, chemical computing and material production in a unified formal framework that is able to mimic the integrated computational and constructive capabilities of the subcellular matrix. We provide a non-deterministic semantics of our programming language that enables us to analytically derive the computational and constructive power of our machinery. This semantics is used to derive the sets of all constructable chemicals and supermolecular structures that emerge from different underlying instruction sets. Because our proofs are constructive, they can be used to automatically infer control programs for the construction of target structures from a limited set of resource molecules. Finally, we present an example of our framework from the area of oligosaccharide synthesis. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Adaptable liquid crystal elastomers with transesterification-based bond exchange reactions.

PubMed

Hanzon, Drew W; Traugutt, Nicholas A; McBride, Matthew K; Bowman, Christopher N; Yakacki, Christopher M; Yu, Kai

2018-02-14

Adaptable liquid crystal elastomers (LCEs) have recently emerged to provide a new and robust method to program monodomain LCE samples. When a constant stress is applied with active bond exchange reactions (BERs), polymer chains and mesogens gradually align in the strain direction. Mesogen alignment is maintained after removing the BER stimulus (e.g. by lowering the temperature) and the programmed LCE samples exhibit free-standing two-way shape switching behavior. Here, a new adaptable main-chain LCE system was developed with thermally induced transesterification BERs. The network combines the conventional properties of LCEs, such as an isotropic phase transition and soft elasticity, with the dynamic features of adaptable network polymers, which are malleable to stress relaxation due to the BERs. Polarized Fourier transform infrared measurements confirmed the alignment of polymer chains and mesogens after strain-induced programming. The influence of the creep stress, temperature, and time on the strain amplitude of two-way shape switching was examined. The LCE network demonstrates an innovative feature of reprogrammability, where the reversible shape-switching memory of programmed LCEs is readily deleted by free-standing heating as random BERs disrupt the mesogen alignment, so LCEs are reprogrammed after returning to the polydomain state. Due to the dynamic nature of the LCE network, it also exhibits a surface welding effect and can be fully dissolved in the organic solvent, which might be utilized for green and sustainable recycling of LCEs.

Supersonic molecular beam experiments on surface chemical reactions.

PubMed

Okada, Michio

2014-10-01

The interaction of a molecule and a surface is important in various fields, and in particular in complex systems like biomaterials and their related chemistry. However, the detailed understanding of the elementary steps in the surface chemistry, for example, stereodynamics, is still insufficient even for simple model systems. In this Personal Account, I review our recent studies of chemical reactions on single-crystalline Cu and Si surfaces induced by hyperthermal oxygen molecular beams and by oriented molecular beams, respectively. Studies of oxide formation on Cu induced by hyperthermal molecular beams demonstrate a significant role of the translational energy of the incident molecules. The use of hyperthermal molecular beams enables us to open up new chemical reaction paths specific for the hyperthermal energy region, and to develop new methods for the fabrication of thin films. On the other hand, oriented molecular beams also demonstrate the possibility of understanding surface chemical reactions in detail by varying the orientation of the incident molecules. The steric effects found on Si surfaces hint at new ways of material fabrication on Si surfaces. Controlling the initial conditions of incoming molecules is a powerful tool for finely monitoring the elementary step of the surface chemical reactions and creating new materials on surfaces. Copyright © 2014 The Chemical Society of Japan and Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Covalent-Bond Formation via On-Surface Chemistry.

PubMed

Held, Philipp Alexander; Fuchs, Harald; Studer, Armido

2017-05-02

In this Review article pioneering work and recent achievements in the emerging research area of on-surface chemistry is discussed. On-surface chemistry, sometimes also called two-dimensional chemistry, shows great potential for bottom-up preparation of defined nanostructures. In contrast to traditional organic synthesis, where reactions are generally conducted in well-defined reaction flasks in solution, on-surface chemistry is performed in the cavity of a scanning probe microscope on a metal crystal under ultrahigh vacuum conditions. The metal first acts as a platform for self-assembly of the organic building blocks and in many cases it also acts as a catalyst for the given chemical transformation. Products and hence success of the reaction are directly analyzed by scanning probe microscopy. This Review provides a general overview of this chemistry highlighting advantages and disadvantages as compared to traditional reaction setups. The second part of the Review then focuses on reactions that have been successfully conducted as on-surface processes. On-surface Ullmann and Glaser couplings are addressed. In addition, cyclodehydrogenation reactions and cycloadditions are discussed and reactions involving the carbonyl functionality are highlighted. Finally, the first examples of sequential on-surface chemistry are considered in which two different functionalities are chemoselectively addressed. The Review gives an overview for experts working in the area but also offers a starting point to non-experts to enter into this exciting new interdisciplinary research field. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Role of Electronic Excitations on Chemical Reaction Dynamics at Metal, Semiconductor and Nanoparticle Surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tully, John C.

Chemical reactions are often facilitated and steered when carried out on solid surfaces, essential for applications such as heterogeneous catalysis, solar energy conversion, corrosion, materials processing, and many others. A critical factor that can determine the rates and pathways of chemical reactions at surfaces is the efficiency and specificity of energy transfer; how fast does energy move around and where does it go? For reactions on insulator surfaces energy transfer generally moves in and out of vibrations of the adsorbed molecule and the underlying substrate. By contrast, on metal surfaces, metallic nanoparticles and semiconductors, another pathway for energy flow opensmore » up, excitation and de-excitation of electrons. This so-called “nonadiabatic” mechanism often dominates the transfer of energy and can directly impact the course of a chemical reaction. Conventional computational methods such as molecular dynamics simulation do not account for this nonadiabatic behavior. The current DOE-BES funded project has focused on developing the underlying theoretical foundation and the computational methodology for the prediction of nonadiabatic chemical reaction dynamics at surfaces. The research has successfully opened up new methodology and new applications for molecular simulation. In particular, over the last three years, the “Electronic Friction” theory, pioneered by the PI, has now been developed into a stable and accurate computational method that is sufficiently practical to allow first principles “on-the-fly” simulation of chemical reaction dynamics at metal surfaces.« less

Spectroscopic studies of organometallic compounds on single crystal metal surfaces: Surface acetylides of silver (110)

NASA Astrophysics Data System (ADS)

Madix, Robert J.

The nature of compounds formed by the reaction of organic molecules with metal surfaces can be studied with a battery of analytical methods based on both physicals and chemical understanding. In this paper the application of UPS, XPS, LEED and EELS as well as temperature programmed reaction spectroscopy (TPRS) and chemical titration methods to the characterization of surface complexes is discussed. Particular emphasis is given to the reaction of acetylene with a single crystal surface of silver, Ag(110). Previous work has shown that this surface, when clean, is unreactive to hydrocarbons, alcohols and carboxylic acids under ultra high vacuum conditions. Preadsorption of oxygen, however, renders the surface reactive, and a wide variety of organometallic surface compounds can be formed. As expected then, no stable adsorption state and no reaction was observed with clean Ag(110) following room temperature exposure to acetylene. Following exposure at 150 K, however, a weekly bound chemisorption state was observed to desorb at 195 K, indicating a binding energy to the surface of approximately 12 kcal/gmole. Reaction with preadsorbed oxygen gave water formulation upon dosing and produced surface intermediates which yeilded two acetylene desorption states at 195 and 175 K. Heating above 300 K to completely desorb the higher temperature state produced new, well-defined LEED Features due to residual surface carbon which disappeared when the surface was heated above 550 K. Clearly, there were distinc changes in the nature of the absorbed layer at 195, 300 and 550 K. These changes were reflected in XPS. For the weakly chemisorbed acetylene a large C(ls) peak at 285.6 eV with a small, broad, indistinc shoulder at higher binding energy (288.2) was observed. The spectrum of the species following acetylene desorption at 275 K, however, showed the formulation of a large C(ls) peak at 283.6 eV in addition to peaks characteristics of the weakly chemisorbed state. This result indicated that the carbon atoms in the surface acetylide became inequivalent. Heating to 300 K produced a single peak at 282.8 eV which reverted to 283.4 when heated above 550 K; the carbon atoms became chemically equivalent. This latter state could be removed completely by O 2 to form CO 2(3). The XPS results showed quantitative conversion of all surface carbon from each state observed. Conclusive evidence regarding the identity of these states was obtained with titration experiments with deuterated acetic acid. CH 3COOD was adsorbed on top of the acetylenic residues at 150 K and heated to note the isotopes of acetylene that desorbed. The 275 K acetylene desorption peak, which showed inequivalent carbon atoms, was titrated by CH 3COOD to form C 2HD, indicating C 2H as the stable surface species. The species formed above 300 K, which showed equivalent carbon atoms in XPS, titrated to form C 2D 2, indicating a C 2 surface species. In each case the formulation of surface acetate was quantitative. The structure of these species was probed further with high resolution electron energy loss spectroscopy. The weakly chemisorbed molecular state exhibited vibrational losses at 300, 700 and 3270 cm -1, characteristics of an acetylene-surface stretching motion, a C-C-H bend and the C-H stretch respectively. No C-C stretch was observed, indicating that the molecule lay parallel to the plane of the surface. For adsorbed C 2H, bands were observed at 300, 690 and 3250cm -1. The high C-H stretching frequency indicated that the C-C bound order was near three. The absence of a C-C stretch in the spectrum was somewhat surprising, but was explained by a σ-π bonded complex in which the -C=CH species was flattened toward the surface by an interaction of an Ag atom with the π system of the acetylide.

Computed potential energy surfaces for chemical reactions

NASA Technical Reports Server (NTRS)

Walch, Stephen P.

1990-01-01

The objective was to obtain accurate potential energy surfaces (PES's) for a number of reactions which are important in the H/N/O combustion process. The interest in this is centered around the design of the SCRAM jet engine for the National Aerospace Plane (NASP), which was envisioned as an air-breathing hydrogen-burning vehicle capable of reaching velocities as large as Mach 25. Preliminary studies indicated that the supersonic flow in the combustor region of the scram jet engine required accurate reaction rate data for reactions in the H/N/O system, some of which was not readily available from experiment. The most important class of combustion reactions from the standpoint of the NASP project are radical recombinaton reactions, since these reactions result in most of the heat release in the combustion process. Theoretical characterizations of the potential energy surfaces for these reactions are presented and discussed.

Surface treatment process of Al-Mg alloy powder by BTSPS

NASA Astrophysics Data System (ADS)

Zhao, Ran; Gao, Xinbao; Lu, Yanling; Du, Fengzhen; Zhang, Li; Liu, Dazhi; Chen, Xuefang

2018-04-01

The surface of Al-Mg alloy powder was treated by BTSPS(bis(triethoxysilylpropyl)tetrasulfide) in order to avoid easy oxidation in air. The pH value, reaction temperature, reaction time, and reaction concentration were used as test conditions. The results show that the BTSPS can form a protected film on the surface of Al-Mg alloy powder. Select the best test solution by orthogonal test. The study found that the reaction time and reaction temperature have the biggest influence on the two indexes of the orthogonal test (melting enthalpy of heat and enthalpy of oxidation). The optimal conditions were as follows: pH value is 8, reaction concentration is 2%, reaction temperature is 25 °C, reaction time is 2 h. The oxidation weight gain of the alloy reached 74.45% and the decomposition temperature of silane film is 181.8 °C.

PREFACE Surface Modifications of Diamond and Related Materials (Session D, E-MRS Spring Meeting)

NASA Astrophysics Data System (ADS)

Nebel, Christoph E.

2010-11-01

This special issue contains selected papers which were presented at the E-MRS Symposium BIOMATERIALS, SENSORS & SURFACES, D: 'Surface modifications of diamond and related materials' which was held on 7-9 June 2010 in Strasbourg (France). With about 54 oral and poster presentations given from teams all over the world it was a very interesting, dense and lively meeting. The symposium focused on chemical modifications applied to graft surfaces of diamond, nano-diamond particles, diamond-like carbon, graphene, graphite and carbon nano-tubes with linker molecular layers for realization of bio-sensors, bio-markers, separation techniques, and switchable chemical links. Presented techniques span spontaneous bonding to photo-chemical attachment, electrochemical modifications, to Suzuki-coupling of aryl molecules. Special attention was drawn to mechanisms driving bonding kinetics such as electron transfer reactions, hydrogen cleavage reactions by nucleophilic molecules and growths schemas which vary from correlated two-dimensional chain reactions to three-dimensional cross polymerization. Hydrogen terminations, surface defects, surface roughness and atomic arrangements of surface carbon atoms were of interest to elucidate bonding mechanisms. In addition, bonding stability, either of linker molecules or of complex functionalized surfaces with DNA, proteins and enzymes was discussed by several speakers as well as details of the electronic interfaces between solid transducers and bio-layers. Here the characterization of surface and interface defect densities, of Fermi level pinning and of electron transfer rates was a major topic. Miniaturization of sensor area and application of new detection schemas was discussed. Diamond nano-particles which are increasingly used as biomarkers in drug delivery experiments also attracted attention. The organizers express our gratitude to the international members of the scientific committee who actively contributed to ensure an attractive program in proposing invited speakers. Finally, our symposium would not have been successful without the strong involvement and implication of the EMRS headquarter especially P Siffert, T Lippert, S Schoeffter and C Kocher. They will all find here our sincere thanks. Christoph E Nebel (Chair) Fraunhofer-Institute for Applied Solid State Physics (IAF), Germany Takako Nakamura National Institute of Advanced Industrial Science and Technology (AIST), Japan Philippe Bergonzo CEA-LIST, France John Foord University of Oxford, United Kingdom Kian-Ping Loh National University of Singapore, Singapore

Surface chemistry reactions of alpha-terpineol [(R)-2-(4-methyl-3-cyclohexenyl)isopropanol] with ozone and air on a glass and a vinyl tile.

PubMed

Ham, J E; Wells, J R

2008-10-01

The surface-phase reaction products of alpha-terpineol [(R)-2-(4-methyl-3-cyclohexenyl)isopropanol] with ozone (O(3)), air or nitrogen (N(2)) on both a glass and vinyl flooring tile were investigated using the recently published FLEC Automation and Control System (FACS). The FACS was used to deliver O(3) (100 ppb), air or N(2) to the surface at a specified flow rate (300 ml/min) and relative humidity (50%) after application of a 1.6%alpha-terpineol solution in methanol. Oxidation products were detected using the derivatization agents: O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine and N,O-bis(trimethysilyl)trifluoroacetamide. The positively identified reaction products were glyoxal, methylglyoxal and 4-oxopentanal. The proposed oxidation products based on previously published VOC/O(3) reaction mechanisms were: 4-methylcyclohex-3-en-1-one, 6-hydroxyhept-en-2-one, 3-(1-hydroxy-1-methylethyl)-6-methylcyclohex-2-en-1-one) and one surface-enhanced reaction product: 5-(1-hydroxy-1-methylethyl)-2-methylcyclohex-2-en-1-one. Though similar products were observed in gas-phase alpha-terpineol/O(3) reactions, the ratio of the reaction products were different suggesting stabilization of larger molecular weight species by the surface. Emission profiles of these oxidation products over 72 h are also reported. Volatile organic compounds (VOCs) can interact with indoor initiators [such as hydroxyl radicals (OH*), ozone and nitrate radicals (NO(3)*)] to form a number of oxygenated by-products in the gas-phase. However, when VOCs are applied to or are present on the surface, heterogeneous chemistry with indoor initiators can also occur. The surface can influence the reaction mechanism to produce new surface reaction products. The work, described here, shows the interaction of alpha-terpineol (major component of pine oil) with ozone and air on both glass and vinyl flooring. These results demonstrated emissions of oxygenated organic compounds as a result of reaction and that further investigations of this chemistry are required to accurately estimate indoor occupant exposures.

Converged three-dimensional quantum mechanical reaction probabilities for the F + H2 reaction on a potential energy surface with realistic entrance and exit channels and comparisons to results for three other surfaces

NASA Technical Reports Server (NTRS)

Lynch, Gillian C.; Halvick, Philippe; Zhao, Meishan; Truhlar, Donald G.; Yu, Chin-Hui; Kouri, Donald J.; Schwenke, David W.

1991-01-01

Accurate three-dimensional quantum mechanical reaction probabilities are presented for the reaction F + H2 yields HF + H on the new global potential energy surface 5SEC for total angular momentum J = 0 over a range of translational energies from 0.15 to 4.6 kcal/mol. It is found that the v-prime = 3 HF vibrational product state has a threshold as low as for v-prime = 2.

Scanning Tunneling Microscopy Study of Carbon Tetrachloride Adsorption and Degradation on a Natural a-Fe2O3(0001) Surface in Ultrahigh Vacuum

NASA Astrophysics Data System (ADS)

Taeg Rim, Kwang; Fitts, Jeffrey; Adib, Kaveh; Camillone, Nicholas, III; Schlosser, Peter; Osgood, Richard, Jr.; Flynn, George; Joyce, Stephen

2001-03-01

Scanning tunneling microscopy and low energy electron diffraction have been used to study a natural a-Fe2O3(0001) surface and the adsorption and degradation of carbon tetrachloride on the reduced Fe3O4(111) terminated surface. A natural a-Fe2O3 (0001) surface was prepared by repeated cycles of Ar+ ion sputtering and annealing in vacuum or in O2 at 850 K. STM images and a LEED pattern indicate that an Fe3O4(111) terminated surface and a bi-phase can be formed depending on annealing conditions. The Fe3O4(111) terminated surface was dosed with CCl4 at room temperature, and flashed up to 590 K and 850 K. STM images show adsorbates on the surface at room temperature and the degradation products of CCl4 are isolated on the surface as the flashing temperature increases up to 850 K. Results from a companion temperature programmed desorption investigation are used in conjunction with the STM images to propose site specific reactions of CCl4 on the Fe3O4(111) terminated surface.

Controlling Reaction Selectivity through the Surface Termination of Perovskite Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polo-Garzon, Felipe; Yang, Shi-Ze; Fung, Victor

2017-07-19

Although well known in the material science field, surface reconstruction of perovskites has not been implemented in heterogeneous catalysis. In this work, we employ multiple surface sensitive techniques to characterize the surface reconstruction of SrTiO3 (STO) after thermal pretreatment (Sr-enrichment) and chemical etching (Ti-enrichment). We show, using the conversion of 2-propanol as a probe reaction, that the surface reconstruction of STO can be controlled to greatly tune catalytic acid/base properties and consequently the reaction selectivities in a wide range, which are inaccessible using single metal oxides, either SrO or TiO2. Density functional theory (DFT) calculations well explain the selectivity tuningmore » and reaction mechanism on differently reconstructed surfaces of STO. Similar catalytic tunability is also observed on BaZrO3, highlighting the generality of the finding from this work.« less

Covalent Surface Modification of Silicon Oxides with Alcohols in Polar Aprotic Solvents.

PubMed

Lee, Austin W H; Gates, Byron D

2017-09-05

Alcohol-based monolayers were successfully formed on the surfaces of silicon oxides through reactions performed in polar aprotic solvents. Monolayers prepared from alcohol-based reagents have been previously introduced as an alternative approach to covalently modify the surfaces of silicon oxides. These reagents are readily available, widely distributed, and are minimally susceptible to side reactions with ambient moisture. A limitation of using alcohol-based compounds is that previous reactions required relatively high temperatures in neat solutions, which can degrade some alcohol compounds or could lead to other unwanted side reactions during the formation of the monolayers. To overcome these challenges, we investigate the condensation reaction of alcohols on silicon oxides carried out in polar aprotic solvents. In particular, propylene carbonate has been identified as a polar aprotic solvent that is relatively nontoxic, readily accessible, and can facilitate the formation of alcohol-based monolayers. We have successfully demonstrated this approach for tuning the surface chemistry of silicon oxide surfaces with a variety of alcohol containing compounds. The strategy introduced in this research can be utilized to create silicon oxide surfaces with hydrophobic, oleophobic, or charged functionalities.

Real-space characterization of reactivity towards water at the B i 2 T e 3 (111) surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Kai-Wen; Ding, Ding; Yang, Chao-Long

2016-06-01

Surface reactivity is important in modifying the physical and chemical properties of surface-sensitive materials, such as the topological insulators. Even though many studies addressing the reactivity of topological insulators towards external gases have been reported, it is still under heavy debate whether and how the topological insulators react with H2O. Here, we employ scanning tunneling microscopy to directly probe the surface reaction of Bi2Te3 towards H2O. Surprisingly, it is found that only the top quintuple layer is reactive to H2O, resulting in a hydrated Bi bilayer as well as some Bi islands, which passivate the surface and prevent subsequent reaction.more » A reaction mechanism is proposed with H2Te and hydrated Bi as the products. Unexpectedly, our study indicates that the reaction with water is intrinsic and not dependent on any surface defects. Since water inevitably exists, these findings provide key information when considering the reactions of Bi2Te3 with residual gases or atmosphere.« less

Ozone-surface interactions: Investigations of mechanisms, kinetics, mass transport, and implications for indoor air quality

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morrison, Glenn Charles

1999-12-01

In this dissertation, results are presented of laboratory investigations and mathematical modeling efforts designed to better understand the interactions of ozone with surfaces. In the laboratory, carpet and duct materials were exposed to ozone and measured ozone uptake kinetics and the ozone induced emissions of volatile organic compounds. To understand the results of the experiments, mathematical methods were developed to describe dynamic indoor aldehyde concentrations, mass transport of reactive species to smooth surfaces, the equivalent reaction probability of whole carpet due to the surface reactivity of fibers and carpet backing, and ozone aging of surfaces. Carpets, separated carpet fibers, andmore » separated carpet backing all tended to release aldehydes when exposed to ozone. Secondary emissions were mostly n-nonanal and several other smaller aldehydes. The pattern of emissions suggested that vegetable oils may be precursors for these oxidized emissions. Several possible precursors and experiments in which linseed and tung oils were tested for their secondary emission potential were discussed. Dynamic emission rates of 2-nonenal from a residential carpet may indicate that intermediate species in the oxidation of conjugated olefins can significantly delay aldehyde emissions and act as reservoir for these compounds. The ozone induced emission rate of 2-nonenal, a very odorous compound, can result in odorous indoor concentrations for several years. Surface ozone reactivity is a key parameter in determining the flux of ozone to a surface, is parameterized by the reaction probability, which is simply the probability that an ozone molecule will be irreversibly consumed when it strikes a surface. In laboratory studies of two residential and two commercial carpets, the ozone reaction probability for carpet fibers, carpet backing and the equivalent reaction probability for whole carpet were determined. Typically reaction probability values for these materials were 10 -7, 10 -5, and 10 -5 respectively. To understand how internal surface area influences the equivalent reaction probability of whole carpet, a model of ozone diffusion into and reaction with internal carpet components was developed. This was then used to predict apparent reaction probabilities for carpet. He combines this with a modified model of turbulent mass transfer developed by Liu, et al. to predict deposition rates and indoor ozone concentrations. The model predicts that carpet should have an equivalent reaction probability of about 10 -5, matching laboratory measurements of the reaction probability. For both carpet and duct materials, surfaces become progressively quenched (aging), losing the ability to react or otherwise take up ozone. He evaluated the functional form of aging and find that the reaction probability follows a power function with respect to the cumulative uptake of ozone. To understand ozone aging of surfaces, he developed several mathematical descriptions of aging based on two different mechanisms. The observed functional form of aging is mimicked by a model which describes ozone diffusion with internal reaction in a solid. He shows that the fleecy nature of carpet materials in combination with the model of ozone diffusion below a fiber surface and internal reaction may explain the functional form and the magnitude of power function parameters observed due to ozone interactions with carpet. The ozone induced aldehyde emissions, measured from duct materials, were combined with an indoor air quality model to show that concentrations of aldehydes indoors may approach odorous levels. He shows that ducts are unlikely to be a significant sink for ozone due to the low reaction probability in combination with the short residence time of air in ducts.« less

Reactive solid surface morphology variation via ionic diffusion.

PubMed

Sun, Zhenchao; Zhou, Qiang; Fan, Liang-Shih

2012-08-14

In gas-solid reactions, one of the most important factors that determine the overall reaction rate is the solid morphology, which can be characterized by a combination of smooth, convex and concave structures. Generally, the solid surface structure varies in the course of reactions, which is classically noted as being attributed to one or more of the following three mechanisms: mechanical interaction, molar volume change, and sintering. Here we show that if a gas-solid reaction involves the outward ionic diffusion of a solid-phase reactant then this outward ionic diffusion could eventually smooth the surface with an initial concave and/or convex structure. Specifically, the concave surface is filled via a larger outward diffusing surface pointing to the concave valley, whereas the height of the convex surface decreases via a lower outward diffusion flux in the vertical direction. A quantitative 2-D continuum diffusion model is established to analyze these two morphological variation processes, which shows consistent results with the experiments. This surface morphology variation by solid-phase ionic diffusion serves to provide a fourth mechanism that supplements the traditionally acknowledged solid morphology variation or, in general, porosity variation mechanisms in gas-solid reactions.

Design Strategies for CeO2-MoO3 Catalysts for DeNOx and Hg(0) Oxidation in the Presence of HCl: The Significance of the Surface Acid-Base Properties.

PubMed

Chang, Huazhen; Wu, Qingru; Zhang, Tao; Li, Mingguan; Sun, Xiaoxu; Li, Junhua; Duan, Lei; Hao, Jiming

2015-10-20

A series of CeMoOx catalysts with different surface Ce/Mo ratios was synthesized by a coprecipitation method via changing precipitation pH value. The surface basicity on selective catalytic reduction (SCR) catalysts (CeMoOx and VMo/Ti) was characterized and correlated to the durability and activity of catalyst for simultaneous elimination of NOx and Hg(0). The pH value in the preparation process affected the surface concentrations of Ce and Mo, the Brunauer-Emmett-Teller (BET) specific surface area, and the acid-base properties over the CeMoOx catalysts. The O 1s X-ray photoelectron spectroscopy (XPS) spectra and CO2-temperature programmed desorption (TPD) suggested that the surface basicity increased as the pH value increased. The existence of strong basic sites contributed to the deactivation effect of HCl over the VMo/Ti and CeMoOx catalysts prepared at pH = 12. For the CeMoOx catalysts prepared at pH = 9 and 6, the appearance of surface molybdena species replaced the surface -OH, and the existence of appropriate medium-strength basic sites contributed to their resistance to HCl poisoning in the SCR reaction. Moreover, these sites facilitated the adsorption and activation of HCl and enhanced Hg(0) oxidation. On the other hand, the inhibitory effect of NH3 on Hg(0) oxidation was correlated with the competitive adsorption of NH3 and Hg(0) on acidic surface sites. Therefore, acidic surface sites may play an important role in Hg(0) adsorption. The characterization and balance of basicity and acidity of an SCR catalyst is believed to be helpful in preventing deactivation by acid gas in the SCR reaction and simultaneous Hg(0) oxidation.

Stochastic surface walking reaction sampling for resolving heterogeneous catalytic reaction network: A revisit to the mechanism of water-gas shift reaction on Cu

NASA Astrophysics Data System (ADS)

Zhang, Xiao-Jie; Shang, Cheng; Liu, Zhi-Pan

2017-10-01

Heterogeneous catalytic reactions on surface and interfaces are renowned for ample intermediate adsorbates and complex reaction networks. The common practice to reveal the reaction mechanism is via theoretical computation, which locates all likely transition states based on the pre-guessed reaction mechanism. Here we develop a new theoretical method, namely, stochastic surface walking (SSW)-Cat method, to resolve the lowest energy reaction pathway of heterogeneous catalytic reactions, which combines our recently developed SSW global structure optimization and SSW reaction sampling. The SSW-Cat is automated and massively parallel, taking a rough reaction pattern as input to guide reaction search. We present the detailed algorithm, discuss the key features, and demonstrate the efficiency in a model catalytic reaction, water-gas shift reaction on Cu(111) (CO + H2O → CO2 + H2). The SSW-Cat simulation shows that water dissociation is the rate-determining step and formic acid (HCOOH) is the kinetically favorable product, instead of the observed final products, CO2 and H2. It implies that CO2 and H2 are secondary products from further decomposition of HCOOH at high temperatures. Being a general purpose tool for reaction prediction, the SSW-Cat may be utilized for rational catalyst design via large-scale computations.

Low Energy Nuclear Reaction Products at Surfaces

NASA Astrophysics Data System (ADS)

Nagel, David J.

2008-03-01

This paper examines the evidence for LENR occurring on or very near to the surface of materials. Several types of experimental indications for LENR surface reactions have been reported and will be reviewed. LENR result in two types of products, energy and the appearance of new elements. The level of instantaneous power production can be written as the product of four factors: (1) the total area of the surface on which the reactions can occur, (2) the fraction of the area that is active at any time, (3) the reaction rate, that is, the number of reactions per unit active area per second, and (4) the energy produced per reaction. Each of these factors, and their limits, are reviewed. A graphical means of relating these four factors over their wide variations has been devised. The instantaneous generation of atoms of new elements can also be written as the product of the first three factors and the new elemental mass produced per reaction. Again, a graphical means of presenting the factors and their results over many orders of magnitude has been developed.

Mechanistic understanding of surface plasmon assisted catalysis on a single particle: cyclic redox of 4-aminothiophenol

DOE PAGES

Xu, Ping; Kang, Leilei; Mack, Nathan H.; ...

2013-10-21

We investigate surface plasmon assisted catalysis (SPAC) reactions of 4-aminothiophenol (4ATP) to and back from 4,4'-dimercaptoazobenzene (DMAB) by single particle surface enhanced Raman spectroscopy, using a self-designed gas flow cell to control the reductive/oxidative environment over the reactions. Conversion of 4ATP into DMAB is induced by energy transfer (plasmonic heating) from surface plasmon resonance to 4ATP, where O 2 (as an electron acceptor) is essential and H 2O (as a base) can accelerate the reaction. In contrast, hot electron (from surface plasmon decay) induction drives the reverse reaction of DMAB to 4ATP, where H 2O (or H 2) acts asmore » the hydrogen source. More interestingly, the cyclic redox between 4ATP and DMAB by SPAC approach has been demonstrated. Finally, this SPAC methodology presents a unique platform for studying chemical reactions that are not possible under standard synthetic conditions.« less

Theory of the reaction dynamics of small molecules on metal surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, Bret

The objective of this project has been to develop realistic theoretical models for gas-surface interactions, with a focus on processes important in heterogeneous catalysis. The dissociative chemisorption of a molecule on a metal is a key step in many catalyzed reactions, and is often the rate-limiting step. We have explored the dissociative chemisorption of H 2, H 2O and CH 4 on a variety of metal surfaces. Most recently, our extensive studies of methane dissociation on Ni and Pt surfaces have fully elucidated its dependence on translational energy, vibrational state and surface temperature, providing the first accurate comparisons with experimentalmore » data. We have explored Eley-Rideal and hot atom reactions of H atoms with H- and C-covered metal surfaces. H atom interactions with graphite have also been explored, including both sticking and Eley-Rideal recombination processes. Again, our methods made it possible to explain several experiments studying these reactions. The sticking of atoms on metal surfaces has also been studied. To help elucidate the experiments that study these processes, we examine how the reaction dynamics depend upon the nature of the molecule-metal interaction, as well as experimental variables such as substrate temperature, beam energy, angle of impact, and the internal states of the molecules. Electronic structure methods based on Density Functional Theory are used to compute each molecule-metal potential energy surface. Both time-dependent quantum scattering techniques and quasi-classical methods are used to examine the reaction or scattering dynamics. Much of our effort has been directed towards developing improved quantum methods that can accurately describe reactions, as well as include the effects of substrate temperature (lattice vibration).« less

Reaction of gas phase OH with unsaturated self-assembled monolayers and relevance to atmospheric organic oxidations.

PubMed

Moussa, Samar G; Finlayson-Pitts, Barbara J

2010-08-28

The kinetics and mechanisms of the reaction of gas phase OH radicals with organics on surfaces are of fundamental chemical interest, as well as relevant to understanding the degradation of organics on tropospheric surfaces or when they are components of airborne particles. We report here studies of the oxidation of a terminal alkene self-assembled monolayer (7-octenyltrichlorosilane, C8= SAM) on a germanium attenuated total reflectance crystal by OH radicals at a concentration of 2.1 x 10(5) cm(-3) at 1 atm total pressure and 298 K in air. Loss of the reactant SAM and the formation of surface products were followed in real time using infrared spectroscopy. From the rate of loss of the C=C bond, a reaction probability within experimental error of unity was derived. The products formed on the surface include organic nitrates and carbonyl compounds, with yields of 10 +/- 4% and < or = 7 +/- 4%, respectively, and there is evidence for the formation of organic products with C-O bonds such as alcohols, ethers and/or alkyl peroxides and possibly peroxynitrates. The yield of organic nitrates relative to carbonyl compounds is higher than expected based on analogous gas phase mechanisms, suggesting that the branching ratio for the RO(2) + NO reaction is shifted to favor the formation of organic nitrates when the reaction occurs on a surface. Water uptake onto the surface was only slightly enhanced upon oxidation, suggesting that oxidation per se cannot be taken as a predictor of increased hydrophilicity of atmospheric organics. These experiments indicate that the mechanisms for the surface reactions are different from gas phase reactions, but the OH oxidation of surface species will still be a significant contributor to determining their lifetimes in air.

Tuning Catalytic Performance through a Single or Sequential Post-Synthesis Reaction(s) in a Gas Phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shan, Junjun; Zhang, Shiran; Choksi, Tej

2016-12-05

Catalytic performance of a bimetallic catalyst is determined by geometric structure and electronic state of the surface or even the near-surface region of the catalyst. Here we report that single and sequential postsynthesis reactions of an as-synthesized bimetallic nanoparticle catalyst in one or more gas phases can tailor surface chemistry and structure of the catalyst in a gas phase, by which catalytic performance of this bimetallic catalyst can be tuned. Pt–Cu regular nanocube (Pt–Cu RNC) and concave nanocube (Pt–Cu CNC) are chosen as models of bimetallic catalysts. Surface chemistry and catalyst structure under different reaction conditions and during catalysis weremore » explored in gas phase of one or two reactants with ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The newly formed surface structures of Pt–Cu RNC and Pt–Cu CNC catalysts strongly depend on the reactive gas(es) used in the postsynthesis reaction(s). A reaction of Pt–Cu RNC-as synthesized with H2 at 200 °C generates a near-surface alloy consisting of a Pt skin layer, a Cu-rich subsurface, and a Pt-rich deep layer. This near-surface alloy of Pt–Cu RNC-as synthesized-H2 exhibits a much higher catalytic activity in CO oxidation in terms of a low activation barrier of 39 ± 4 kJ/mol in contrast to 128 ± 7 kJ/mol of Pt–Cu RNC-as synthesized. Here the significant decrease of activation barrier demonstrates a method to tune catalytic performances of as-synthesized bimetallic catalysts. A further reaction of Pt–Cu RNC-as synthesized-H2 with CO forms a Pt–Cu alloy surface, which exhibits quite different catalytic performance in CO oxidation. It suggests the capability of generating a different surface by using another gas. The capability of tuning surface chemistry and structure of bimetallic catalysts was also demonstrated in restructuring of Pt–Cu CNC-as synthesized.« less

Product energy distributions and energy partitioning in O atom reactions on surfaces

NASA Technical Reports Server (NTRS)

Halpern, Bret; Kori, Moris

1987-01-01

Surface reactions involving O atoms are likely to be highly exoergic, with different consequences if energy is channeled mostly to product molecules or surface modes. Thus the surface may become a source of excited species which can react elsewhere, or a sink for localized heat deposition which may disrupt the surface. The vibrational energy distribution of the product molecule contains strong clues about the flow of released energy. Two instructive examples of energy partitioning at surfaces are the Pt catalyzed oxidations: (1) C(ads) + O(ads) yields CO* (T is greater than 1000 K); and (2) CO(ads) + O(gas) yields CO2* (T is approx. 300 K). The infrared emission spectra of the excited product molecules were recorded and the vibrational population distributions were determined. In reaction 1, energy appeared to be statistically partitioned between the product CO and several Pt atoms. In reaction 2, partitioning was non-statistical; the CO2 asymmetric stretch distribution was inverted. In gas reactions these results would indicate a long lived and short lived activated complex. The requirement that Pt be heated in O atoms to promote reaction of atomic O and CO at room temperature is specifically addressed. Finally, the fraction of released energy that is deposited in the catalyst is estimated.

Supramolecular structures on silica surfaces and their adsorptive properties.

PubMed

Belyakov, Vladimir N; Belyakova, Lyudmila A; Varvarin, Anatoly M; Khora, Olexandra V; Vasilyuk, Sergei L; Kazdobin, Konstantin A; Maltseva, Tetyana V; Kotvitskyy, Alexey G; Danil de Namor, Angela F

2005-05-01

The study of adsorptive and chemical immobilization of beta-cyclodextrin on a surface of hydroxylated silicas with various porous structure is described. Using IR spectroscopy, thermal gravimetrical analysis with a programmed heating, and chemical analysis of the silica surface, it is shown that the process of adsorption-desorption of beta-cyclodextrin depends on the porous structure of the silica. The reaction of esterification was used for chemical grafting of beta-cyclodextrin on the surface of hydroxylated silicas. Hydrolytic stability of silicas chemically modified by beta-cyclodextrin apparently is explained by simultaneous formation of chemical and hydrogen bonds between surface silanol groups and hydroxyl groups of beta-cyclodextrin. The uptake of the cations Cu(II), Cd(II), and Pb(II) and the anions Cr(VI) and As(V) by silicas modified with beta-cyclodextrin is investigated as a function of equilibrium ion concentrations. The increase of ion uptake and selectivity of ion extraction in comparison with starting silicas is established. It is due to the formation of surface inclusion complexes of the "host-guest" type in which one molecule of beta-cyclodextrin interacts simultaneously with several ions.

Collisional quenching of atoms and molecules on spacecraft thermal protection surfaces

NASA Technical Reports Server (NTRS)

Marinelli, W. J.; Green, B. D.

1988-01-01

Preliminary results of a research program to determine energy partitioning in spacecraft thermal protection materials due to atom recombination at the gas-surface interface are presented. The primary focus of the research is to understand the catalytic processes which determine heat loading on Shuttle, Aeroassisted OTV, and NASP thermal protection surfaces in nonequilibrium flight regimes. Highly sensitive laser diagnostics based on laser-induced fluorescence and resonantly-enhanced multiphoton ionization spectroscopy are used to detect atoms and metastable molecules. At low temperatures, a discharge flow reactor is employed to measure deactivation/recombination coefficients for O-atoms, N-atoms, and O2. Detection methods are presented for measuring O-atoms, O2 and N2, and results for deactivation of O2 and O-atoms on reaction-cured glass and Ni surfaces. Both atom recombination and metastable product formation are examined. Radio-frequency discharges are used to produce highly dissociated beams of atomic species at energies characteristic of the surface temperature. Auger electron spectroscopy is employed as a diagnostic of surface composition in order to accurately define and control measurement conditions.

THE INFLUENCE OF MINERAL REACTIONS ON THE ENVIRONMENTAL FATE OF METALS IN SOILS AND SEDIMENTS

EPA Science Inventory

Significant progress has been made in elucidating sorption reactions that control the partitioning of metals from solution to mineral surfaces in contaminated soil/sediment systems. Surface complexation models have been developed to quantify the forward reaction, however, these ...

Nickel-Aluminum Layered Double Hydroxide Coating on the Surface of Conductive Substrates by Liquid Phase Deposition.

PubMed

Maki, Hideshi; Takigawa, Masashi; Mizuhata, Minoru

2015-08-12

The direct synthesis of the adhered Ni-Al LDH thin film onto the surface of electrically conductive substrates by the liquid phase deposition (LPD) reaction is carried out for the development of the positive electrode. The complexation and solution equilibria of the dissolved species in the LPD reaction have been clarified by a theoretical approach, and the LPD reaction conditions for the Ni-Al LDH depositions are shown to be optimized by controlling the fluoride ion concentration and the pH of the LPD reaction solutions. The yields of metal oxides and hydroxides by the LPD method are very sensitive to the supersaturation state of the hydroxide in the reaction solution. The surfaces of conductive substrates are completely covered by the minute mesh-like Ni-Al LDH thin film; furthermore, there is no gap between the surfaces of conductive substrates and the deposited Ni-Al LDH thin film. The active material layer thickness was able to be controlled within the range from 100 nm to 1 μm by the LPD reaction time. The high-crystallinity and the arbitrary-thickness thin films on the conductive substrate surface will be beneficial for the interface control of charge transfer reaction fields and the internal resistance reduction of various secondary batteries.

Numerical simulation of two-dimensional flow over a heated carbon surface with coupled heterogeneous and homogeneous reactions

NASA Astrophysics Data System (ADS)

Johnson, Ryan Federick; Chelliah, Harsha Kumar

2017-01-01

For a range of flow and chemical timescales, numerical simulations of two-dimensional laminar flow over a reacting carbon surface were performed to understand further the complex coupling between heterogeneous and homogeneous reactions. An open-source computational package (OpenFOAM®) was used with previously developed lumped heterogeneous reaction models for carbon surfaces and a detailed homogeneous reaction model for CO oxidation. The influence of finite-rate chemical kinetics was explored by varying the surface temperatures from 1800 to 2600 K, while flow residence time effects were explored by varying the free-stream velocity up to 50 m/s. The reacting boundary layer structure dependence on the residence time was analysed by extracting the ratio of chemical source and species diffusion terms. The important contributions of radical species reactions on overall carbon removal rate, which is often neglected in multi-dimensional simulations, are highlighted. The results provide a framework for future development and validation of lumped heterogeneous reaction models based on multi-dimensional reacting flow configurations.

Multifunctional silicon surfaces: reaction of dichlorocarbene generated from Seyferth reagent with hydrogen-terminated silicon (111) surfaces.

PubMed

Liu, Wenjun; Sharp, Ian D; Tilley, T Don

2014-01-14

Insertion of dichlorocarbene (:CCl2), generated by decomposition of the Seyferth reagent PhHgCCl2Br, into the Si-H bond of a tertiary silane to form a Si-CCl2H group is an efficient homogeneous, molecular transformation. A heterogeneous version of this reaction, between PhHgCCl2Br and a silicon (111) surface terminated by tertiary Si-H bonds, was studied using a combination of surface-sensitive infrared and X-ray photoelectron spectroscopies. The insertion of dichlorocarbene into surface Si-H bonds parallels the corresponding reaction of silanes in solution, to produce surface-bound dichloromethyl groups (Si-CCl2H) covering ∼25% of the silicon surface sites. A significant fraction of the remaining Si-H bonds on the surface was converted to Si-Cl/Br groups during the same reaction, with PhHgCCl2Br serving as a halogen atom source. The presence of two distinct environments for the chlorine atoms (Si-CCl2H and Si-Cl) and one type of bromine atom (Si-Br) was confirmed by Cl 2p, Br 3d, and C 1s X-ray photoelectron spectroscopy. The formation of reactive, halogen-terminated atop silicon sites was also verified by reaction with sodium azide or the Grignard reagent (CH3MgBr), to produce Si-N3 or Si-Me functionalities, respectively. Thus, reaction of a hydrogen-terminated silicon (111) surface with PhHgCCl2Br provides a facile route to multifunctional surfaces possessing both stable silicon-carbon and labile silicon-halogen sites, in a single pot synthesis. The reactive silicon-halogen groups can be utilized for subsequent transformations and, potentially, the construction of more complex organic-silicon hybrid systems.

Upscaling of reaction rates in reactive transport using pore-scale reactive transport model

NASA Astrophysics Data System (ADS)

Yoon, H.; Dewers, T. A.; Arnold, B. W.; Major, J. R.; Eichhubl, P.; Srinivasan, S.

2013-12-01

Dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes among hydrodynamics, transport, and reactions at the (sub) pore-scale. In this research pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reaction at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This work is motivated by the observed CO2 seeps from a natural analog to geologic CO2 sequestration at Crystal Geyser, Utah. A key observation is the lateral migration of CO2 seep sites at a scale of ~ 100 meters over time. A pore-scale model provides fundamental mechanistic explanations of how calcite precipitation alters flow paths by pore plugging under different geochemical compositions and pore configurations. In addition, response function of reaction rates will be constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Damkohler and Peclet numbers. Newly developed response functions will be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO2 seeps. Comparison of field observations and simulations results will provide mechanistic explanations of the lateral migration and enhance our understanding of subsurface processes associated with the CO2 injection. This work is supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Formation of interstellar methanol ice prior to the heavy CO freeze-out stage

NASA Astrophysics Data System (ADS)

Qasim, D.; Chuang, K.-J.; Fedoseev, G.; Ioppolo, S.; Boogert, A. C. A.; Linnartz, H.

2018-04-01

Context. The formation of methanol (CH3OH) on icy grain mantles during the star formation cycle is mainly associated with the CO freeze-out stage. Yet there are reasons to believe that CH3OH also can form at an earlier period of interstellar ice evolution in CO-poor and H2O-rich ices. Aims: This work focuses on CH3OH formation in a H2O-rich interstellar ice environment following the OH-mediated H-abstraction in the reaction, CH4 + OH. Experimental conditions are systematically varied to constrain the CH3OH formation yield at astronomically relevant temperatures. Methods: CH4, O2, and hydrogen atoms are co-deposited in an ultrahigh vacuum chamber at 10-20 K. OH radicals are generated by the H + O2 surface reaction. Temperature programmed desorption - quadrupole mass spectrometry (TPD-QMS) is used to characterize CH3OH formation, and is complemented with reflection absorption infrared spectroscopy (RAIRS) for CH3OH characterization and quantitation. Results: CH3OH formation is shown to be possible by the sequential surface reaction chain, CH4 + OH → CH3 + H2O and CH3 + OH → CH3OH at 10-20 K. This reaction is enhanced by tunneling, as noted in a recent theoretical investigation Lamberts et al. (2017, A&A, 599, A132). The CH3OH formation yield via the CH4 + OH route versus the CO + H route is approximately 20 times smaller for the laboratory settings studied. The astronomical relevance of the new formation channel investigated here is discussed.

STM observation of the chemical reaction of atomic hydrogen on the N-adsorbed Cu(001) surface

NASA Astrophysics Data System (ADS)

Hattori, Takuma; Yamada, Masamichi; Komori, Fumio

2017-01-01

Chemical reaction of atomic hydrogen with the N-adsorbed Cu(001) surfaces was investigated at room temperature by scanning tunnel microscopy. At the low exposure of atomic hydrogen, it reacted with the N atoms and turned to be the NH species on the surface. The reaction rate is proportional to the amount of the unreacted N atoms. By increasing the exposure of atomic hydrogen from this condition, the amount of nitrogen species on the surface decreased. This is attributed to the formation of ammonia and its desorption from the surface. The NH species on the surface turn to NH3 through the surface NH2 species by atomic hydrogen. Coexistence of the clean Cu surface enhances the rate of ammonia formation owing to atomic hydrogen migrating on the clean surface.

Lithium-Air Cell Development

NASA Technical Reports Server (NTRS)

Reid, Concha M.; Dobley, Arthur; Seymour, Frasier W.

2014-01-01

Lithium-air (Li-air) primary batteries have a theoretical specific capacity of 11,400 Wh/kg, the highest of any common metal-air system. NASA is developing Li-air technology for a Mobile Oxygen Concentrator for Spacecraft Emergencies, an application which requires an extremely lightweight primary battery that can discharge over 24 hours continuously. Several vendors were funded through the NASA SBIR program to develop Li-air technology to fulfill the requirements of this application. New catalysts and carbon cathode structures were developed to enhance the oxygen reduction reaction and increase surface area to improve cell performance. Techniques to stabilize the lithium metal anode surface were explored. Experimental results for prototype laboratory cells are given. Projections are made for the performance of hypothetical cells constructed from the materials that were developed.

Potential energy surfaces and reaction dynamics of polyatomic molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Yan-Tyng

A simple empirical valence bond (EVB) model approach is suggested for constructing global potential energy surfaces for reactions of polyatomic molecular systems. This approach produces smooth and continuous potential surfaces which can be directly utilized in a dynamical study. Two types of reactions are of special interest, the unimolecular dissociation and the unimolecular isomerization. For the first type, the molecular dissociation dynamics of formaldehyde on the ground electronic surface is investigated through classical trajectory calculations on EVB surfaces. The product state distributions and vector correlations obtained from this study suggest very similar behaviors seen in the experiments. The intramolecular hydrogenmore » atom transfer in the formic acid dimer is an example of the isomerization reaction. High level ab initio quantum chemistry calculations are performed to obtain optimized equilibrium and transition state dimer geometries and also the harmonic frequencies.« less

Surface Protonics Promotes Catalysis

PubMed Central

Manabe, R.; Okada, S.; Inagaki, R.; Oshima, K.; Ogo, S.; Sekine, Y.

2016-01-01

Catalytic steam reforming of methane for hydrogen production proceeds even at 473 K over 1 wt% Pd/CeO2 catalyst in an electric field, thanks to the surface protonics. Kinetic analyses demonstrated the synergetic effect between catalytic reaction and electric field, revealing strengthened water pressure dependence of the reaction rate when applying an electric field, with one-third the apparent activation energy at the lower reaction temperature range. Operando–IR measurements revealed that proton conduction via adsorbed water on the catalyst surface occurred during electric field application. Methane was activated by proton collision at the Pd–CeO2 interface, based on the inverse kinetic isotope effect. Proton conduction on the catalyst surface plays an important role in methane activation at low temperature. This report is the first describing promotion of the catalytic reaction by surface protonics. PMID:27905505

Effect of dipolar fields, surface termination, and surface orientation on photochemical reactions on transition metal oxides

NASA Astrophysics Data System (ADS)

Giocondi, Jennifer Lynn

Experiments have been conducted to determine the effects of dipolar fields, surface termination, and surface orientation on the photochemical reactivity of several transition metal oxides. These compounds include BaTiO3, SrTiO3, BaTi4O9, Sr2Nb2O 7, and Sr2Ta2O7 which were studied as polycrystalline ceramics, single crystals, micron-sized faceted particles, or some combination of these forms. The reduction of Ag+ from an aqueous AgNO3 solution (Ag0 product) and the oxidation of Pb2+ from an aqueous lead acetate solution (PbO 2 product) were selected as probe reactions because they leave insoluble products on the oxide surfaces. The reactivity of ferroelectric BaTiO3 was dominated by the effect of dipolar fields on the transport of photogenerated charge carriers. Silver was reduced on domains with a positive surface charge while lead was oxidized on domains with a negative surface charge. This reactivity implies that the dipolar field in individual domains drives photogenerated charge carriers to oppositely charged surfaces. This reaction mechanism results in a physical separation of the photogenerated charge carriers and the locations of the oxidation and reduction half reactions on the catalyst surface. Experiments performed on polycrystalline ceramics, single crystals, and micron-sized particles all showed this domain specific reactivity. SrTiO3 has the ideal cubic perovskite structure from which the tetragonally distorted ferroelectric BaTiO3 phase is derived. Polished and annealed surfaces of randomly oriented grain surfaces were bound by some combination of the following three planes: {110}, {111}, and a complex facet inclined approximately 24° from {100}. Surfaces with the complex {100} facet were found to be the most active for Ag reduction. Single crystal studies also showed that the nonpolar (100) surface is the most reactive and that the composition of the termination layer does not influence this reaction. However, the polar (111) and (110) surfaces had a non-uniform distribution of reaction products. For these orientations, the location of the reduction and oxidation reactions is determined by the chemical and charge terminations of the different terraces or facets. The reactivity for silver reduction on the faceted particles is ranked as (100) > (111) > (110) while the (100) surface was least reactive for lead oxidation. Overall, these results show that the photochemical reactivity of SrTiO3 is anisotropic and that on polar surfaces, dipolar fields arising from charged surface domains influence the transport of photogenerated charge carriers and promote spatially selective oxidation and reduction reactions. (Abstract shortened by UMI.)

Development and design of nanomaterial reagents in conjunction with new methods for their synthetic applications

NASA Astrophysics Data System (ADS)

Kwaramba, Farai Brian

This Ph.D. deals with the integration of nanotechnology with organometallic/ organic synthetic technologies. The first part of this research sought to develop a library of novel molecular gears programmed to exploit photo-switching and electrostatic repulsion to control the molecular rotation of covalently linked triptypyrazines. Incorporation of these two modes allows for control of triptycene based gear systems using unexplored external methods. The triptypyrazine was an attractive scaffold because of its intrinsic pH and electrochemical activity, thus providing a novel construct for controlling molecular motion. This design finds relevance in the fabrication of nano-electromechanical devices and understanding controlled molecular motion. This Ph.D. also sought to address the need to generate and recycle low cost hydrosilylation catalysts. Metal nanoparticle catalysts can potentially meet this need due to their high surface area and reactivity. Their morphology and surface texture provide avenues for selectivity in reactions. Metal-nanoparticles on a silicon matrix can be formed by reducing metal salts with silicon hydrides. Investigations towards iron-nanoparticle catalyzed hydrosilylation of unsaturated bonds were conducted. Furthermore, this research sought to develop highly functionalized silanes, as guiding scaffolds for generating chiral silicon hydrides. Fabrication of metal-nanoparticle catalysts with the same, could install surface definition on these heterogeneous green catalysts, thus allowing selectivity in their catalysis. A bottom up approach to nanofabrication, started with the generation of a library of highly functionalized alkynyl-silane building blocks using the hydrosilylation reaction. Hydrosilylation of carbon-carbon and carbon-heteroatom unsaturated bonds has proven to be an important reaction in organic syntheses. Additionally, silicon tethers have been utilized in complex organic syntheses as a way to increase reaction rates, and selectivity. The most commonly employed silicon tethers have been disiloxanes followed by siloxanes, then silanes. Of these methods the synthesis and utilization of tethered silyl-alkynes was limited. To address this gap, this work developed methodology to prepare tethered silyl alkynes through a hydrosilylation reaction. It was established that [IrCl(COD)]2 in the presence of excess COD can selectively catalyze the hydrosilylation of alkenes with alkynyl-silanes. This approach overrides traditional hydrosilylation catalysts' reactivity trends.

Structural identification of Zn xZr yO z catalysts for Cascade aldolization and self-deoxygenation reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baylon, Rebecca A. L.; Sun, Junming; Kovarik, Libor

Complementary characterizations, such as nitrogen sorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), visible Raman, scanning transmission electron microscopy (STEM) coupled with elemental mapping, NH3/CO2 temperature programmed desorption (NH3/CO2-TPD), infrared spectroscopic analysis of adsorbed pyridine (Py-IR), and CO2-IR, have been employed to identify the structure and surface chemistry (i.e., acid-base) of mixed Zn xZr yO z oxide catalysts of varied ratios of Zn/Zr. Atomically dispersed Zn2+ species are present in the framework within a thin surface shell (1.5-2.0 nm) of ZrO2 particles when the Zn/Zr ratio is smaller than 1/10; when the ratio is above this, both atomically dispersed Zn2+more » and ZnO clusters coexist in mixed Zn xZr yO z oxide catalysts. The presence of ZnO clusters shows no significant side effect but only a slight increase of selectivity to CO2, caused by steam reforming. The incorporation of atomic Zn2+ into the ZrO2 framework was found to not only passivate strong Lewis acid sites (i.e., Zr-O-Zr) on ZrO2, but to also generate new Lewis acid-base site pairs with enhanced Lewis basicity on the bridged O (i.e., ). In the mixed ketone (i.e., acetone and methyl ethyl ketone (MEK)) reactions, while the passivation of strong acid sites can be correlated to the inhibition of side reactions, such as ketone decomposition and coking, the new Lewis acid-base pairs introduced enhance the cascade aldolization and self-deoxygenation reactions involved in olefin (C3=-C6=) production. More importantly, the surface acid-base properties change with varying Zn/Zr ratios, which in turn affect the cross- and self-condensation reactivity and subsequent distribution of olefins.« less

Structural Identification of Zn xZr yO z Catalysts for Cascade Aldolization and Self-Deoxygenation Reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baylon, Rebecca A. L.; Sun, Junming; Kovarik, Libor

Here, complementary characterizations, such as nitrogen sorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), visible Raman, scanning transmission electron microscopy (STEM) coupled with elemental mapping, NH 3/CO 2 temperature programmed desorption (NH 3/CO 2-TPD), infrared spectroscopic analysis of adsorbed pyridine (Py-IR), and CO 2-IR, have been employed to identify the structure and surface chemistry (i.e., acid-base) of mixed Zn xZr yO z oxide catalysts of varied ratios of Zn/Zr. Atomically dispersed Zn 2+ species are present in the framework within a thin surface shell (1.5-2.0 nm) of ZrO 2 particles when the Zn/Zr ratio is smaller than 1/10; when the ratio is above this, both atomically dispersed Zn 2+ and ZnO clusters coexist in mixed Zn xZr yO z oxide catalysts. The presence of ZnO clusters shows no significant side effect but only a slight increase of selectivity to CO 2, caused by steam reforming. The incorporation of atomic Zn 2+ into the ZrO 2 framework was found to not only passivate strong Lewis acid sites (i.e., Zr-O-Zr) on ZrO 2, but to also generate new Lewis acid-base site pairs with enhanced Lewis basicity on the bridged O (i.e., Zr—omore » $$\\curvearrowleft\\atop{e\\atop—}$$Zn). In the mixed ketone (i.e., acetone and methyl ethyl ketone (MEK)) reactions, while the passivation of strong acid sites can be correlated to the inhibition of side reactions, such as ketone decomposition and coking, the new Lewis acid-base pairs introduced enhance the cascade aldolization and self-deoxygenation reactions involved in olefin (C 3 =-C 6 =) production. More importantly, the surface acid-base properties change with varying Zn/Zr ratios, which in turn affect the cross- and self-condensation reactivity and subsequent distribution of olefins.« less

Structural Identification of Zn xZr yO z Catalysts for Cascade Aldolization and Self-Deoxygenation Reactions

DOE PAGES

Baylon, Rebecca A. L.; Sun, Junming; Kovarik, Libor; ...

2018-04-22

Here, complementary characterizations, such as nitrogen sorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), visible Raman, scanning transmission electron microscopy (STEM) coupled with elemental mapping, NH 3/CO 2 temperature programmed desorption (NH 3/CO 2-TPD), infrared spectroscopic analysis of adsorbed pyridine (Py-IR), and CO 2-IR, have been employed to identify the structure and surface chemistry (i.e., acid-base) of mixed Zn xZr yO z oxide catalysts of varied ratios of Zn/Zr. Atomically dispersed Zn 2+ species are present in the framework within a thin surface shell (1.5-2.0 nm) of ZrO 2 particles when the Zn/Zr ratio is smaller than 1/10; when the ratio is above this, both atomically dispersed Zn 2+ and ZnO clusters coexist in mixed Zn xZr yO z oxide catalysts. The presence of ZnO clusters shows no significant side effect but only a slight increase of selectivity to CO 2, caused by steam reforming. The incorporation of atomic Zn 2+ into the ZrO 2 framework was found to not only passivate strong Lewis acid sites (i.e., Zr-O-Zr) on ZrO 2, but to also generate new Lewis acid-base site pairs with enhanced Lewis basicity on the bridged O (i.e., Zr—omore » $$\\curvearrowleft\\atop{e\\atop—}$$Zn). In the mixed ketone (i.e., acetone and methyl ethyl ketone (MEK)) reactions, while the passivation of strong acid sites can be correlated to the inhibition of side reactions, such as ketone decomposition and coking, the new Lewis acid-base pairs introduced enhance the cascade aldolization and self-deoxygenation reactions involved in olefin (C 3 =-C 6 =) production. More importantly, the surface acid-base properties change with varying Zn/Zr ratios, which in turn affect the cross- and self-condensation reactivity and subsequent distribution of olefins.« less

78 FR 71615 - Agency Forms Undergoing Paperwork Reduction Act Review

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-29

...TM Program (Hands-on, Online, Blended models). Trainee Reaction Survey-- 180 1 15/60 Hands-On Model. Trainee Reaction Survey-- 180 1 15/60 Online Model. Trainee Reaction Survey-- 180 1 15/60 Blended Model... Program (Train-the- Participant Survey. Trainer model). Trainee Reaction Survey-- 30 1 15/60 Train-the...

Reflectance-difference spectroscopy of GaAs crystal growth by OMCVD

NASA Astrophysics Data System (ADS)

Colas, Etienne G.; Aspnes, David E.; Bhat, Rajaram J.; Studna, A. A.; Koza, M. A.; Keramidas, Vassilis G.

1990-02-01

This paper summarizes results of our investigations of growth on (001) and (110) GaAs by atmospheric-pressure organometallic chemical vapor deposition (OMCVD). We follow evolutions of surface species to a sensitivity of 0.01 monolayer (ML) on a time scale of 0.1 s under alternating flows of trimethylgallium (TMG) and arsine (AsH3) as functions of partial pressure, sample temperature, and surface orienta-tion. The reaction of TMG with an AsH3-saturated (001) surface is rate-limited by com-petition between desorption and decomposition of TMG molecules chemisorbed to surface lattice sites via an excluded-volume mechanism, while the reaction of AsH3 with the TMG-saturated (001) surface is essentially instantaneous. In contrast, TMG reacts essentially instantaneously with the AsH3 -saturated (110) surface while the AsH3 reaction with the TMG-saturated (110) surface is the rate-limiting step. However, the latter rate is not intrinsic to the AsH3-surface reaction but appears to be determined by desorption of adsorbed species that block active sites.

Pulse electrochemical meso/micro/nano ultraprecision machining technology.

PubMed

Lee, Jeong Min; Kim, Young Bin; Park, Jeong Woo

2013-11-01

This study demonstrated meso/micro/nano-ultraprecision machining through electrochemical reactions using intermittent DC pulses. The experiment focused on two machining methods: (1) pulse electrochemical polishing (PECP) of stainless steel, and (2) pulse electrochemical nano-patterning (PECNP) on a silicon (Si) surface, using atomic force microscopy (AFM) for fabrication. The dissolution reaction at the stainless steel surface following PECP produced a very clean, smooth workpiece. The advantages of the PECP process included improvements in corrosion resistance, deburring of the sample surface, and removal of hydrogen from the stainless steel surface as verified by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). In PECNP, the electrochemical reaction generated within water molecules produced nanoscale oxide textures on a Si surface. Scanning probe microscopy (SPM) was used to evaluate nanoscale-pattern processing on a Si wafer surface produced by AFM-PECNP For both processes using pulse electrochemical reactions, three-dimensional (3-D) measurements and AFM were used to investigate the changes on the machined surfaces. Preliminary results indicated the potential for advancing surface polishing techniques and localized micro/nano-texturing technology using PECP and PECNP processes.

Bio-inspired immobilization of metal oxides on monolithic microreactor for continuous Knoevenagel reaction.

PubMed

Song, Wentong; Shi, Da; Tao, Shengyang; Li, Zhaoliang; Wang, Yuchao; Yu, Yongxian; Qiu, Jieshan; Ji, Min; Wang, Xinkui

2016-11-01

A facile method is reported to construct monolithic microreactor with high catalytic performance for Knoevenagel reaction. The microreactor is based on hierarchically porous silica (HPS) which has interconnected macro- and mesopores. Then the HPS is surface modified by pyrogallol (PG) polymer. Al(NO3)3 and Mg(NO3)2 are loaded on the surface of HPS through coordination with -OH groups of PG. After thermal treatment, Al(NO3)3 and Mg(NO3)2 are converted Al2O3 and MgO. The as-synthesized catalytic microreactor shows a high and stable performance in Knoevenagel reaction. The microreactor possess large surface area and interconnected pore structures which are beneficial for reactions. Moreover, this economic, facile and eco-friendly surface modification method can be used in loading more metal oxides for more reactions. Copyright © 2016 Elsevier Inc. All rights reserved.

Surface Cracking and Interface Reaction Associated Delamination Failure of Thermal and Environmental Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dong-Ming; Choi, Sung R.; Eldridge, Jeffrey I.; Lee, Kang N.; Miller, Robert A.

2003-01-01

In this paper, surface cracking and interface reactions of a BSAS coating and a multi-layer ZrO2-8wt%Y2O3 and mullite/BSAS/Si thermal and environmental barrier coating system on SiC/SiC ceramic matrix composites were characterized after long-term combined laser thermal gradient and furnace cyclic tests in a water vapor containing environment. The surface cracking was analyzed based on the coating thermal gradient sintering behavior and thermal expansion mismatch stress characteristics under the thermal cyclic conditions. The interface reactions, which were largely enhanced by the coating surface cracking in the water vapor environment, were investigated in detail, and the reaction phases were identified for the coating system after the long-term exposure. The accelerated coating delamination failure was attributed to the increased delamination driving force under the thermal gradient cyclic loading and the reduced interface adhesion due to the detrimental interface reactions.

Surface Cracking and Interface Reaction Associated Delamination Failure of Thermal and Environmental Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Choi, Sung R.; Eldridge, Jeffrey I.; Lee, Kang N.; Miller, Robert A.

2003-01-01

In this paper, surface cracking and interface reactions of a BSAS coating and a multi-layer ZTO2-8wt%Y2O3 and mullite/BSAS/Si thermal and environmental barrier coating system on SiC/SiC ceramic matrix composites were characterized after long-term combined laser thermal gradient and furnace cyclic tests in a water vapor containing environment. The surface cracking was analyzed based on the coating thermal gradient sintering behavior and thermal expansion mismatch stress characteristics under the thermal cyclic conditions. The interface reactions, which were largely enhanced by the coating surface cracking in the water vapor environment, were investigated in detail, and the reaction phases were identified for the coating system after the long- term exposure. The accelerated coating delamination failure was attributed to the increased delamination driving force under the thermal gradient cyclic loading and the reduced interface adhesion due to the detrimental interface reactions.

Theoretical determination of chemical rate constants using novel time-dependent methods

NASA Technical Reports Server (NTRS)

Dateo, Christopher E.

1994-01-01

The work completed within the grant period 10/1/91 through 12/31/93 falls primarily in the area of reaction dynamics using both quantum and classical mechanical methodologies. Essentially four projects have been completed and have been or are in preparation of being published. The majority of time was spent in the determination of reaction rate coefficients in the area of hydrocarbon fuel combustion reactions which are relevant to NASA's High Speed Research Program (HSRP). These reaction coefficients are important in the design of novel jet engines with low NOx emissions, which through a series of catalytic reactions contribute to the deterioration of the earth's ozone layer. A second area of research studied concerned the control of chemical reactivity using ultrashort (femtosecond) laser pulses. Recent advances in pulsed-laser technologies have opened up a vast new field to be investigated both experimentally and theoretically. The photodissociation of molecules adsorbed on surfaces using novel time-independent quantum mechanical methods was a third project. And finally, using state-of-the-art, high level ab initio electronic structure methods in conjunction with accurate quantum dynamical methods, the rovibrational energy levels of a triatomic molecule with two nonhydrogen atoms (HCN) were calculated to unprecedented levels of agreement between theory and experiment.

Surface CHEMKIN (Version 4. 0): A Fortran package for analyzing heterogeneous chemical kinetics at a solid-surface---gas-phase interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coltrin, M.E.; Kee, R.J.; Rupley, F.M.

1991-07-01

Heterogeneous reaction at the interface between a solid surface and adjacent gas is central to many chemical processes. Our purpose for developing the software package SURFACE CHEMKIN was motivated by our need to understand the complex surface chemistry in chemical vapor deposition systems involving silicon, silicon nitride, and gallium arsenide. However, we have developed the approach and implemented the software in a general setting. Thus, we expect it will find use in such diverse applications as chemical vapor deposition, chemical etching, combustion of solids, and catalytic processes, and for a wide range of chemical systems. We believe that it providesmore » a powerful capability to help model, understand, and optimize important industrial and research chemical processes. The SURFACE CHEMKIN software is designed to work in conjunction with the CHEMKIN-2 software, which handles the chemical kinetics in the gas phase. It may also be used in conjunction with the Transport Property Package, which provides information about molecular diffusion. Thus, these three packages provide a foundation on which a user can build applications software to analyze gas-phase and heterogeneous chemistry in flowing systems. These packages should not be considered programs'' in the ordinary sense. That is, they are not designed to accept input, solve a particular problem, and report the answer. Instead, they are software tools intended to help a user work efficiently with large systems of chemical reactions and develop Fortran representations of systems of equations that define a particular problem. It is up the user to solve the problem and interpret the answer. 11 refs., 15 figs., 5 tabs.« less

Development of a constant surface pressure penetration langmuir balance based on axisymmetric drop shape analysis.

PubMed

Wege, H A; Holgado-Terriza, J A; Cabrerizo-Vílchez, M A

2002-05-15

A new constant pressure pendant-drop penetration surface balance has been developed combining a pendant-drop surface balance, a rapid-subphase-exchange technique, and a fuzzy logic control algorithm. Beside the determination of insoluble monolayer compression-expansion isotherms, it allows performance of noninvasive kinetic studies of the adsorption of surfactants added to the new subphase onto the free surface and of the adsorption/penetration/reaction of the former onto/into/with surface layers, respectively. The interfacial pressure pi is a fundamental parameter in these studies: by working at constant pi one controls the height of the energy barrier to adsorption/penetration and can select different regimes and steps of the adsorption/penetration process. In our device a solution drop is formed at the tip of a coaxial double capillary, connected to a double microinjector. Drop profiles are extracted from digital drop micrographs and fitted to the equation of capillarity, yielding pi, the drop volume V, and the interfacial area A. pi is varied changing V (and hence A) with the microinjector. Control is based on a case-adaptable modulated fuzzy-logic PID algorithm able to maintain constant pi (or A) under a wide range of experimental conditions. The drop subphase liquid can be exchanged quantitatively by the coaxial capillaries. The adsorption/penetration/reaction kinetics at constant pi are then studied monitoring A(t), i.e., determining the relative area change necessary at each instant to compensate the pressure variation due to the interaction of the surfactant in the subsurface with the surface layer. A fully Windows-integrated program manages the whole setup. Examples of experimental protein adsorption and monolayer penetration kinetics are presented.

The passivation of uranium metal surfaces by nitrogen bombardment — the formation of uranium nitride

NASA Astrophysics Data System (ADS)

Allen, Geoffrey C.; Holmes, Nigel R.

1988-05-01

As part of a detailed investigation of the behaviour of metallic uranium in various atmospheres, we have examined the reaction between nitrogen gas and uranium metal. At room temperature there was no evidence of reaction between nitrogen gas and a clean metal surface; the only changes observed could be attributed to reaction between the metal and traces of oxygen (less than 0.1 ppm) in the nitrogen gas. Reaction between the metal and nitrogen was induced, however, by accelerating nitrogen towards the surface using a fast atom gun. The resulting nitrided surface was characterized by X-ray photoelectron spectroscopy, and its oxidation behaviour was monitored over an extended period in UHV and in air.

Etude de l'electrocatalyse de la reduction de l'oxygene sur des alliages de palladium cuivre

NASA Astrophysics Data System (ADS)

Fouda-Onana, Frederic

This thesis is on the development of the ORR on Pd-Cu alloys in acid medium. Density Functional Theory (DFT) was used to determine the intrinsic properties of the alloys. The alloys were fabricated by RF sputtering on glassy carbon support and chemical salt reduction on carbon support. They characterised by electrochemical methods and correlations were made between the intrinsic properties and the experimental electrochemical parameters. These correlations were used to explain the electrocatalytic performance of the ORR on these aklooys and to determine the mechanism of this reaction on these electrocatalysts. Accordingly the following aspects were studied in details. In the first step, ab initio investigations of the effect of the intermediate adsorption on the variation of the reversible potential of the ORR on Pt(100) was shown. Density Functional Theory (DFT) was used to determine the energies and the geometry parameters of the intermediates which can be adsorbed on Pt(100) during the oxygen reduction reaction (ORR) and their effect on the . The Comparison of these energies and parameters using the Bridge or the Griffiths sites adsorption mechanism suggests that the two paths are feasible. In both mechanisms, the total adsorption energies of the intermediates species continuously decrease. Moreover, according to the geometry analysis, the O-O bond distance in H2O2 is higher in both (Bridge and Griffiths) processes compared to the gas phase. Such a result suggests a dissociative H2O2 adsorption whatever the type of the involved mechanism involved. In the second step, the Oxygen reduction reaction (ORR) on palladium-copper alloys was studied through two approaches. The first one is based on the correlations between the surface chemical composition and the kinetics parameters of the ORR. The second approach is focused on the correlations between the adsorption energies of O2 and OH of Pd-Cu(111) surfaces and the electronic properties of the alloys. The adsorbtion energy calculations are based on on ab initio calculation using the program VASP (Vienna ab initio program) in a MeDeA environnement (software purchased from Materials Design, Inc. The studies of the oxygen reduction reaction were performed in an acidic media on Palladium-Copper alloys as catalyst. The variation of the intrinsic metal surface properties (lattice parameter, binding energy, work function (Wf), d-band filling and d-band center epsilond) and O2 and OH adsorption energies of on (111) Pd-Cu surface alloys were determined using ab initio program. Calculations of these parameters were based on plane waves approach on slab system with density functional theory (DFT) using the Vienna ab initio simulation program (VASP). It was shown that insertion of Cu atoms in Pd lattice affects geometric and electronic properties of Pd. These changes influence significantly O2 and OH adsorption. In the third step, the oxygen reduction reaction (ORR) on Pd-Cu catalyst has been studied in acidic media. The palladium alloys were prepared by RF magnetron using a palladium and a copper wafer as targets on the glassy carbon substrate. The dual sputtering we used allowed the deposition of about 1micrometer thin film of Pd-Cu on glassy carbon (GC). The ORR kinetics was studied on these catalysts in 0,1M HClO4. Cyclic voltammetry (CV) was used to determine the electrochemical active surface area (Sa). An increase in Sa with the Cu content in the alloy was observed for the alloys containing more than 50% in Cu. The Pd-Cu alloys containing more than 50% in Cu exhibits a constant value of 23 cm2 for Sa. It was further shown that the ORR on the Pd-Cu alloys proceeds through the 4 electrons transfer mechanism and a Tafel slope of 60 mV/dec. The Pd 50Cu50 exhibits the highest activity for this reaction. The enhancement of the electro catalytic activity is attributed to an optimal d band property that makes easier the OOH dissociative adsorption which is considered as chemical rate determining step (RDS) for the ORR. It was also found that all the Pd-Cu alloys exhibited better electrocatalystic performances for the ORR than Pd or Cu alone. From the polarisation of the ORR in 0,1 M HClO4 it was shown that the curve of the Pd electrode was shifted to the lower potentials than those of the Pd-Cu alooys. In addition, the variation of the kinetic current of the ORR at 0,6 V vs. SCE (0,841 V vs. RHE) on the Pd-Cu alloys with the composition of in Cu content exhibited a volcano-shape. (Abstract shortened by UMI.)

First principles study of the atomic layer deposition of alumina by TMA-H2O-process.

PubMed

Weckman, Timo; Laasonen, Kari

2015-07-14

Atomic layer deposition (ALD) is a coating technology used to produce highly uniform thin films. Aluminiumoxide, Al2O3, is mainly deposited using trimethylaluminium (TMA) and water as precursors and is the most studied ALD-process to date. However, only few theoretical studies have been reported in the literature. The surface reaction mechanisms and energetics previously reported focus on a gibbsite-like surface model but a more realistic description of the surface can be achieved when the hydroxylation of the surface is taken into account using dissociatively adsorbed water molecules. The adsorbed water changes the structure of the surface and reaction energetics change considerably when compared to previously studied surface model. Here we have studied the TMA-H2O process using density functional theory on a hydroxylated alumina surface and reproduced the previous results for comparison. Mechanisms and energetics during both the TMA and the subsequent water pulse are presented. TMA is found to adsorb exothermically onto the surface. The reaction barriers for the ligand-exchange reactions between the TMA and the surface hydroxyl groups were found to be much lower compared to previously presented results. TMA dissociation on the surface is predicted to saturate at monomethylaluminium. Barriers for proton diffusion between surface sites are observed to be low. TMA adsorption was also found to be cooperative with the formation of methyl bridges between the adsorbants. The water pulse was studied using single water molecules reacting with the DMA and MMA surface species. Barriers for these reactions were found to reasonable in the process conditions. However, stabilizing interactions amongst water molecules were found to lower the reaction barriers and the dynamical nature of water is predicted to be of importance. It is expected that these calculations can only set an upper limit for the barriers during the water pulse.

Ceramic surfaces, interfaces and solid-state reactions

NASA Astrophysics Data System (ADS)

Heffelfinger, Jason Roy

Faceting, the decomposition of a surface into two or more surfaces of different orientation, is studied as a function of annealing time for ceramic surfaces. Single-crystals of Alsb2Osb3\\ (alpha-Alsb2Osb3 or corundum structure) are carefully prepared and characterized by atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The mechanisms by which the originally smooth vicinal surface transforms into either a hill-and-valley or a terrace-and-step structure have been characterized. The progression of faceting is found to have a series of stages: surface smoothing, nucleation and growth of individual facets, formation of facet domains, coalescence of individual and facet domains and facet coarsening. These stages provide a model for the mechanisms of how other ceramic surfaces may facet into hill-and-valley and terrace-and-step surface microstructures. The well characterized Alsb2Osb3 surfaces provide excellent substrates by which to study the effect of surface structure on thin-film growth. Pulsed-laser deposition was used to grow thin films of yttria stabilized zirconia (YSZ) and Ysb2Osb3 onto annealed Alsb2Osb3 substrates. The substrate surface structure, such as surface steps and terraces, was found to have several effects on thin-film growth. Thin-films grown onto single-crystal substrates serve as a model geometry for studying thin-film solid-state reactions. Here, the reaction sequence and orientation relationship between thin films of Ysb2Osb3 and an Alsb2Osb3 substrate were characterized for different reaction temperatures. In a system were multiple reaction phases can form, the yttria aluminum monoclinic phase (YAM) was found to form prior to formation of other phases in this system. In a second system, a titanium alloy was reacted with single crystal Alsb2Osb3 in order to study phase formation in an intermetallic system. Both Tisb3Al and TiAl were found to form as reaction products and their orientation relationships with the Alsb2Osb3 are discussed.

Contrast reaction training in US radiology residencies: a COARDRI study.

PubMed

LeBedis, Christina A; Rosenkrantz, Andrew B; Otero, Hansel J; Decker, Summer J; Ward, Robert J

To perform a survey-based assessment of current contrast reaction training in US diagnostic radiology residency programs. An electronic survey was distributed to radiology residency program directors from 9/2015-11/2015. 25.7% of programs responded. 95.7% of those who responded provide contrast reaction management training. 89.4% provide didactic lectures (occurring yearly in 71.4%). 37.8% provide hands-on simulation training (occurring yearly in 82.3%; attended by both faculty and trainees in 52.9%). Wide variability in contrast reaction education in US diagnostic radiology residency programs reveals an opportunity to develop and implement a national curriculum. Copyright © 2017 Elsevier Inc. All rights reserved.

Reactions of water and C1 molecules on carbide and metal-modified carbide surfaces

DOE PAGES

Wan, Weiming; Tackett, Brian M.; Chen, Jingguang G.

2017-02-23

The formation of carbides can significantly modify the physical and chemical properties of the parent metals. In the current review, we summarize the general trends in the reactions of water and C1 molecules over transition metal carbide (TMC) and metal-modified TMC surfaces and thin films. Although the primary focus of the current review is on the theoretical and experimental studies of reactions of C1 molecules (CO, CO 2, CH 3OH, etc.), the reactions of water will also be reviewed because water plays an important role in many of the C1 transformation reactions. This review is organized by discussing separately thermalmore » reactions and electrochemical reactions, which provides insights into the application of TMCs in heterogeneous catalysis and electrocatalysis, respectively. In thermal reactions, we discuss the thermal decomposition of water and methanol, as well as the reactions of CO and CO 2 over TMC surfaces. In electrochemical reactions, we summarize recent studies in the hydrogen evolution reaction, electrooxidation of methanol and CO, and electroreduction of CO 2. Lastly, future research opportunities and challenges associated with using TMCs as catalysts and electrocatalysts are also discussed.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Luan; Tao, Franklin, E-mail: franklin.tao.2011@gmail.com; Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, Kansas 66045

Tracking surface chemistry of a catalyst during catalysis is significant for fundamental understanding of catalytic performance of the catalyst since it allows for establishing an intrinsic correlation between surface chemistry of a catalyst at its working status and its corresponding catalytic performance. Ambient pressure X-ray photoelectron spectroscopy can be used for in-situ studies of surfaces of different materials or devices in a gas. To simulate the gaseous environment of a catalyst in a fixed-bed a flowing gaseous environment of reactants around the catalyst is necessary. Here, we report the development of a new flowing reaction cell for simulating in-situ studymore » of a catalyst surface under a reaction condition in gas of one reactant or during catalysis in a mixture of reactants of a catalytic reaction. The homemade reaction cell is installed in a high vacuum (HV) or ultrahigh vacuum (UHV) environment of a chamber. The flowing gas in the reaction cell is separated from the HV or UHV environment through well sealings at three interfaces between the reaction cell and X-ray window, sample door and aperture of front cone of an energy analyzer. Catalyst in the cell is heated through infrared laser beam introduced through a fiber optics interfaced with the reaction cell through a homemade feedthrough. The highly localized heating on the sample holder and Au-passivated internal surface of the reaction cell effectively minimizes any unwanted reactions potentially catalyzed by the reaction cell. The incorporated laser heating allows a fast heating and a high thermal stability of the sample at a high temperature. With this cell, a catalyst at 800 °C in a flowing gas can be tracked readily.« less

Mechanism of atomic layer deposition of SiO2 on the silicon (100)-2×1 surface using SiCl4 and H2O as precursors

NASA Astrophysics Data System (ADS)

Kang, Jeung Ku; Musgrave, Charles B.

2002-03-01

We use density functional theory to investigate atomic layer deposition (ALD) mechanism of silicon dioxide on the Si(100)-2×1 surface from the precursors SiCl4 and H2O. First, we explore the reaction mechanism of water with the bare Si(100)-2×1 surface to produce surface hydroxyl groups. We find that this reaction proceeds through a two-step pathway with an overall barrier of 33.3 kcal/mol. Next, we investigate the ALD mechanism for the binary reaction sequence: the SiCl4 half reaction and the H2O half reaction. For the SiCl4 half reaction, SiCl4 first forms a σ-bond with the oxygen of the surface OH group and then releases an HCl molecule. The predicted barrier for this process is 15.8 kcal/mol. Next, adsorbed SiCl3 reacts with a neighboring OH group to form bridged SiCl2 with a barrier of 22.6 kcal/mol. The H2O half reaction also proceeds through two sequential steps with an overall barrier of 19.1 kcal/mol for the reaction of H2O with bridged SiCl2 to form bridged Si(OH)2. The predicted barrier of 22.6 kcal/mol for the rate-limiting step of the ALD binary reaction mechanism is consistent with the experimental value of 22.0 kcal/mol. In addition, we find that the calculated frequencies are in good agreement with the experimentally measured IR spectra.

Development of Airport Surface Required Navigation Performance (RNP)

NASA Technical Reports Server (NTRS)

Cassell, Rick; Smith, Alex; Hicok, Dan

1999-01-01

The U.S. and international aviation communities have adopted the Required Navigation Performance (RNP) process for defining aircraft performance when operating the en-route, approach and landing phases of flight. RNP consists primarily of the following key parameters - accuracy, integrity, continuity, and availability. The processes and analytical techniques employed to define en-route, approach and landing RNP have been applied in the development of RNP for the airport surface. To validate the proposed RNP requirements several methods were used. Operational and flight demonstration data were analyzed for conformance with proposed requirements, as were several aircraft flight simulation studies. The pilot failure risk component was analyzed through several hypothetical scenarios. Additional simulator studies are recommended to better quantify crew reactions to failures as well as additional simulator and field testing to validate achieved accuracy performance, This research was performed in support of the NASA Low Visibility Landing and Surface Operations Programs.

Coadsorbed species explain the mechanism of methanol temperature-desorption on CeO 2(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sutton, Jonathan E.; Steven H. Overbury; Beste, Ariana

2016-03-24

Here, we have used density functional theory calculations to investigate the temperature-programmed desorption (TPD) of methanol from CeO 2(111). For the first time, low-temperature water formation and high-temperature methanol desorption are explained by our calculations. High coverages of methanol, which correspond to experimental conditions, are required to properly describe these features of the TPD spectrum. We identify a mechanism for the low-temperature formation of water involving the dissociation of two methanol molecules on the same surface O atom and filling of the resulting surface vacancy with one of the methoxy products. After water desorption, methoxy groups are stabilized on themore » surface and react at higher temperatures to form methanol and formaldehyde by a disproportionation mechanism. Alternatively, the stabilized methoxy groups undergo sequential C–H scission reactions to produce formaldehyde. Calculated energy requirements and methanol/formaldehyde selectivity agree with the experimental data.« less

Reactions of Microsolvated Organic Compounds at Ambient Surfaces: Droplet Velocity, Charge State, and Solvent Effects

NASA Astrophysics Data System (ADS)

Badu-Tawiah, Abraham K.; Campbell, Dahlia I.; Cooks, R. Graham

2012-06-01

The exposure of charged microdroplets containing organic ions to solid-phase reagents at ambient surfaces results in heterogeneous ion/surface reactions. The electrosprayed droplets were driven pneumatically in ambient air and then electrically directed onto a surface coated with reagent. Using this reactive soft landing approach, acid-catalyzed Girard condensation was achieved at an ambient surface by directing droplets containing Girard T ions onto a dry keto-steroid. The charged droplet/surface reaction was much more efficient than the corresponding bulk solution-phase reaction performed on the same scale. The increase in product yield is ascribed to solvent evaporation, which causes moderate pH values in the starting droplet to reach extreme values and increases reagent concentrations. Comparisons are made with an experiment in which the droplets were pneumatically accelerated onto the ambient surface (reactive desorption electrospray ionization, DESI). The same reaction products were observed but differences in spatial distribution were seen associated with the "splash" of the high velocity DESI droplets. In a third type of experiment, the reactions of charged droplets with vapor phase reagents were examined by allowing electrosprayed droplets containing a reagent to intercept the headspace vapor of an analyte. Deposition onto a collector surface and mass analysis showed that samples in the vapor phase were captured by the electrospray droplets, and that instantaneous derivatization of the captured sample is possible in the open air. The systems examined under this condition included the derivatization of cortisone vapor with Girard T and that of 4-phenylpyridine N-oxide and 2-phenylacetophenone vapors with ethanolamine.

SS/RCS surface tension propellant acquisition/expulsion tankage technology program

NASA Technical Reports Server (NTRS)

1974-01-01

An evaluation of published propellant physical property data together with bubble point tests of fine-mesh screen in propellants, was conducted. The effort consisted of: (1) the collection and evaluation of pertinent physical property data for hydrazine (N2H4), monomethylhydrazine (MMH), and nitrogen tetroxide (N2O4); (2) testing to determine the effect of dissolved pressurant gas, temperature, purity, and system cleanliness or contamination on system bubble point, and (3) the compilation and publishing of both the literature and test results. The space shuttle reaction control system (SS/RCS) is a bipropellant system using N2O4 and MMH, while the auxiliary power system (SS/APU) employs monopropellant N2H4. Since both the RCS and the APU use a surface tension device for propellant acquisition, the propellant properties of interest are those which impact the design and operation of surface tension systems. Information on propellant density, viscosity, surface tension, and contact angle was collected, compiled, and evaluated.

Surface-active ionic liquids in micellar catalysis: impact of anion selection on reaction rates in nucleophilic substitutions† †Electronic supplementary information (ESI) available: Formulae for calculating aggregation parameters and fitting of kinetic constants and copies of NMR spectra. See DOI: 10.1039/c6cp00493h Click here for additional data file.

PubMed Central

Cognigni, Alice; Gaertner, Peter; Zirbs, Ronald; Peterlik, Herwig; Prochazka, Katharina; Schröder, Christian

2016-01-01

A series of surface-active ionic liquids based on the 1-dodecyl-3-methylimidazolium cation and different anions such as halides and alkylsulfates was synthesized. The aggregation behavior of these ionic liquids in water was characterized by surface tension, conductivity measurements and UV-Vis spectroscopy in order to determine the critical micelle concentration (CMC) and to provide aggregation parameters. The determination of surface activity and aggregation properties of amphiphilic ionic liquids was accompanied by SAXS studies on selected surface-active ionic liquids. The application of these surface-active ionic liquids with different anions was tested in nucleophilic substitution reactions for the degradation of organophosphorus compounds. Kinetic studies via UV-Vis spectrophotometry showed a strong acceleration of the reaction in the micellar system compared to pure water. In addition, an influence of the anion was observed, resulting in a correlation between the anion binding to the micelle and the reaction rate constants, indicating that the careful choice of the surface-active ionic liquid can considerably affect the outcome of reactions. PMID:27121134

The Effect of Simulated Microgravity Environment of RWV Bioreactors on Surface Reactions and Adsorption of Serum Proteins on Bone-bioactive Microcarriers

NASA Technical Reports Server (NTRS)

Radin, Shula; Ducheyne, P.; Ayyaswamy, P. S.

2003-01-01

Biomimetically modified bioactive materials with bone-like surface properties are attractive candidates for use as microcarriers for 3-D bone-like tissue engineering under simulated microgravity conditions of NASA designed rotating wall vessel (RWV) bioreactors. The simulated microgravity environment is attainable under suitable parametric conditions of the RWV bioreactors. Ca-P containing bioactive glass (BG), whose stimulatory effect on bone cell function had been previously demonstrated, was used in the present study. BG surface modification via reactions in solution, resulting formation of bone-like minerals at the surface and adsorption of serum proteins is critical for obtaining the stimulatory effect. In this paper, we report on the major effects of simulated microgravity conditions of the RWV on the BG reactions surface reactions and protein adsorption in physiological solutions. Control tests at normal gravity were conducted at static and dynamic conditions. The study revealed that simulated microgravity remarkably enhanced reactions involved in the BG surface modification, including BG dissolution, formation of bone-like minerals at the surface and adsorption of serum proteins. Simultaneously, numerical models were developed to simulate the mass transport of chemical species to and from the BG surface under normal gravity and simulated microgravity conditions. The numerical results showed an excellent agreement with the experimental data at both testing conditions.

Poly(L-lysine) Interfaces via Dual Click Reactions on Surface-Bound Custom-Designed Dithiol Adsorbates.

PubMed

Shakiba, Amin; Jamison, Andrew C; Lee, T Randall

2015-06-09

Surfaces modified with poly(L-lysine) can be used to immobilize selected biomolecules electrostatically. This report describes the preparation of a set of self-assembled monolayers (SAMs) from three different azide-terminated adsorbates as platforms for performing controlled surface attachments and as a means of determining the parameters that afford stable poly(L-lysine)-modified SAM surfaces having controlled packing densities. A maleimide-terminated alkyne linker was "clicked" to the azide-terminated surfaces via a copper-catalyzed cycloaddition reaction to produce the attachment sites for the polypeptides. A thiol-Michael addition was then used to immobilize cysteine-terminated poly(L-lysine) moieties on the gold surface, avoiding adsorbate self-reactions with this two-step procedure. Each step in this process was analyzed by ellipsometry, X-ray photoelectron spectroscopy, polarization modulation infrared reflection-absorption spectroscopy, and contact angle goniometry to determine which adsorbate structure most effectively produced the targeted polypeptide interface. Additionally, a series of mixed SAMs using an azidoalkanethiol in combination with a normal alkanethiol having an equivalent alkyl chain were prepared to provide data to determine how dilution of the azide reactive site on the SAM surface influences the initial click reaction. Overall, the collected data demonstrate the advantages of an appropriately designed bidentate absorbate and its potential to form effective platforms for biomolecule surface attachment via click reactions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Zongyuan; Duchoň, Tomáš; Wang, Huanru

We have studied the reaction of ethanol and water over Ni–CeO 2-x(111) model surfaces to elucidate the mechanistic steps associated with the ethanol steam reforming (ESR) reaction. Our results provide insights about the importance of hydroxyl groups to the ESR reaction over Ni-based catalysts. Systematically, we have investigated the reaction of ethanol on Ni–CeO 2-x(111) at varying Ce³⁺ concentrations (CeO 1.8–2.0) with absence/presence of water using a combination of soft X-ray photoelectron spectroscopy (sXPS) and temperature-programmed desorption (TPD). Consistent with previous reports, upon annealing, metallic Ni formed on reduced ceria while NiO was the main component on fully oxidized ceria.more » Ni⁰ is the active phase leading to both the C–C and C–H cleavage of ethanol but is also responsible for carbon accumulation or coking. We have identified a Ni₃C phase that formed prior to the formation of coke. At temperatures above 600K, the lattice oxygen from ceria and the hydroxyl groups from water interact cooperatively in the removal of coke, likely through a strong metal–support interaction between nickel and ceria that facilitates oxygen transfer.« less

Synthesis of waste cooking oil based biodiesel via ferric-manganese promoted molybdenum oxide / zirconia nanoparticle solid acid catalyst: influence of ferric and manganese dopants.

PubMed

Alhassan, Fatah H; Rashid, Umer; Taufiq-Yap, Yun Hin

2015-01-01

The utilization of ferric-manganese promoted molybdenum oxide/zirconia (Fe-Mn- MoO3/ZrO2) (FMMZ) solid acid catalyst for production of biodiesel was demonstrated. FMMZ is produced through impregnation reaction followed by calcination at 600°C for 3 h. The characterization of FMMZ had been done using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), temperature programmed desorption of NH3 (TPD-NH3), transmission electron microscopy(TEM) and Brunner-Emmett-Teller (BET) surface area measurement. The effect of waste cooking oil methyl esters (WCOME's) yield on the reactions variables such as reaction temperature, catalyst loading, molar ratio of methanol/oil and reusability were also assessed. The catalyst was used to convert the waste cooking oil into corresponding methyl esters (95.6%±0.15) within 5 h at 200℃ reaction temperature, 600 rpm stirring speed, 1:25 molar ratio of oil to alcohol and 4% w/w catalyst loading. The reported catalyst was successfully recycled in six connective experiments without loss in activity. Moreover, the fuel properties of WCOME's were also reported using ASTM D 6751 methods.

Propagation of a Chemical Reaction through Heterogeneous Lithium- Polytetrafluoroethylene Mixtures

DTIC Science & Technology

1975-12-11

Condensed Phases ........... ............... 9 1.2.1 Lithium-Gas Surface Reactions. .......... 10 1.2.2 Composite Solid Propellant Combustion. . .. 13...f:- the o:cu:=ence _A a surface reaction was developed, but no analyti7al reaction zate model was presented- 1.2.2 Composite S’-lid Propellant...Combustion Composite solid propellants are plastic-like materials consisting of small oxidizer particles embedded in a fuel matrix. Ammonium perchlorate is

Role of a Streambed's Benthic Biolayer in Enhancing Chemical Reactions in Hyporheic Flow

NASA Astrophysics Data System (ADS)

Harvey, J. W.

2016-12-01

Chemical processing of metals, nutrients, and organic compounds occurs throughout natural waters, however the rate of reactions often is greater at the streambed interface compared with surface water or deeper groundwater. Hydrologic exchange across the sediment interface brings reactive solutes and fine particulate organic matter from surface waters into contact with the streambed biolayer, a zone with algae and other living microflora and fauna, microbial communities, and reactive geochemical coatings on granular sediments. Compared with surface water or deeper hyporheic sediments, the intrinsic rate of reactions may be stimulated in biolayers because of higher rates of metabolic processing and associated redox reactions. Also, hydrologic transport may enhance reaction rates by relieving potential transport limitations through the re-supply of reactive substrates from surface water. As a result the chemical processing that occurs in the biolayer may far exceed processing that occurs in deeper hyporheic flow. Here I highlight new understanding of enhancement of reaction rates and their hydrologic and biogeochemical controls in streambed biolayers compared with hyporheic flow as a whole. The approach distinguishes and quantifies reaction limitation and transport limitation both at the centimeter-scale within the hyporheic zone and at the river network scale where the effect of streambed reactions accumulates and influences downstream water quality.

Rayleigh surface acoustic wave as an efficient heating system for biological reactions: investigation of microdroplet temperature uniformity.

PubMed

Roux-Marchand, Thibaut; Beyssen, Denis; Sarry, Frederic; Elmazria, Omar

2015-04-01

When a microdroplet is put on the Rayleigh surface acoustic wave path, longitudinal waves are radiated into the liquid and induce several phenomena such as the wellknown surface acoustic wave streaming. At the same time, the temperature of the microdroplet increases as it has been shown. In this paper, we study the temperature uniformity of a microdroplet heated by Rayleigh surface acoustic wave for discrete microfluidic applications such as biological reactions. To precisely ascertain the temperature uniformity and not interfere with the biological reaction, we used an infrared camera. We then tested the temperature uniformity as a function of three parameters: the microdroplet volume, the Rayleigh surface acoustic wave frequency, and the continuous applied radio frequency power. Based on these results, we propose a new device structure to develop a future lab on a chip based on reaction temperatures.

The surface sulfur doping induced enhanced performance of cobalt catalysts in oxygen evolution reactions.

PubMed

Al-Mamun, Mohammad; Zhu, Zhengju; Yin, Huajie; Su, Xintai; Zhang, Haimin; Liu, Porun; Yang, Huagui; Wang, Dan; Tang, Zhiyong; Wang, Yun; Zhao, Huijun

2016-08-04

A novel surface sulfur (S) doped cobalt (Co) catalyst for the oxygen evolution reaction (OER) is theoretically designed through the optimisation of the electronic structure of highly reactive surface atoms which is also validated by electrocatalytic OER experiments.

Effect of Electronic Excitation on Hydrogen Atom Transfer (Tautomerization) Reactions for the DNA Base Adenine

NASA Technical Reports Server (NTRS)

Chaban, Galina M.; Salter, Latasha M.; Kwak, Dochan (Technical Monitor)

2002-01-01

Geometrical structures and energetic properties for four different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest single excited state potential energy surface are studied. The energetic order of the tautomers on the ground state potential surface is 9H less than 7H less than 3H less than 1H, while on the excited state surface this order is found to be different: 3H less than 1H less than 9H less than 7H. Minimum energy reaction paths are obtained for hydrogen atom transfer (9 yields 3 tautomerization) reactions in the ground and the lowest excited electronic state. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic state, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. The barrier for this reaction in the excited state may become very low in the presence of water or other polar solvent molecules, and therefore such tautomerization reaction may play an important role in the solution phase photochemistry of adenine.

Nonenzymatic Reactions above Phospholipid Surfaces of Biological Membranes: Reactivity of Phospholipids and Their Oxidation Derivatives

PubMed Central

Solís-Calero, Christian; Ortega-Castro, Joaquín; Frau, Juan; Muñoz, Francisco

2015-01-01

Phospholipids play multiple and essential roles in cells, as components of biological membranes. Although phospholipid bilayers provide the supporting matrix and surface for many enzymatic reactions, their inherent reactivity and possible catalytic role have not been highlighted. As other biomolecules, phospholipids are frequent targets of nonenzymatic modifications by reactive substances including oxidants and glycating agents which conduct to the formation of advanced lipoxidation end products (ALEs) and advanced glycation end products (AGEs). There are some theoretical studies about the mechanisms of reactions related to these processes on phosphatidylethanolamine surfaces, which hypothesize that cell membrane phospholipids surface environment could enhance some reactions through a catalyst effect. On the other hand, the phospholipid bilayers are susceptible to oxidative damage by oxidant agents as reactive oxygen species (ROS). Molecular dynamics simulations performed on phospholipid bilayers models, which include modified phospholipids by these reactions and subsequent reactions that conduct to formation of ALEs and AGEs, have revealed changes in the molecular interactions and biophysical properties of these bilayers as consequence of these reactions. Then, more studies are desirable which could correlate the biophysics of modified phospholipids with metabolism in processes such as aging and diseases such as diabetes, atherosclerosis, and Alzheimer's disease. PMID:25977746

The dissolution of calcite in CO2-saturated solutions at 25°C and 1 atmosphere total pressure

USGS Publications Warehouse

Plummer, Niel; Wigley, T.M.L.

1976-01-01

The dissolution of Iceland spar in CO2-saturated solutions at 25°C and 1 atm total pressure has been followed by measurement of pH as a function of time. Surface concentrations of reactant and product species have been calculated from bulk fluid data using mass transport theory and a model that accounts for homogeneous reactions in the bulk fluid. The surface concentrations are found to be close to bulk solution values. This indicates that calcite dissolution under the experimental conditions is controlled by the kinetics of surface reaction. The rate of calcite dissolution follows an empirical second order relation with respect to calcium and hydrogen ion from near the initial condition (pH 3.91) to approximately pH 5.9. Beyond pH 5.9 the rate of surface reaction is greatly reduced and higher reaction orders are observed. Calculations show that the rate of calcite dissolution in natural environments may be influenced by both transport and surface-reaction processes. In the absence of inhibition, relatively short times should be sufficient to establish equilibrium.

The Role of Grain Surface Reactions in the Chemistry of Star Forming Regions

NASA Technical Reports Server (NTRS)

Kress, M. E.; Tielens, A. G. G. M.; Roberge, W. G.

1998-01-01

The importance of reactions at the surfaces of dust grains has long been recognized to be one of the two main chemical processes that form molecules in cold, dark interstellar clouds where simple, saturated (fully-hydrogenated) molecules such as H2 water, methanol, H2CO, H2S, ammonia and CH4 are present in quantities far too high to be consistent with their extremely low gas phase formation rates. In cold dark regions of interstellar space, dust grains provide a substrate onto which gas-phase species can accrete and react. Grains provide a "third body" or a sink for the energy released in the exothermic reactions that form chemical bonds. In essence, the surfaces of dust grains open up alternative reaction pathways to form observed molecules whose abundances cannot be explained with gas-phase chemistry alone. This concept is taken one step further in this work: instead of merely acting as a substrate onto which radicals and molecules may physically adsorb, some grains may actively participate in the reaction itself, forming chemical bonds with the accreting species. Until recently, surface chemical reactions had not been thought to be important in warm circumstellar media because adspecies rapidly desorb from grains at very low temperatures; thus, the residence times of molecules and radicals on the surface of grains at all but the lowest temperatures are far too short to allow these reactions to occur. However, if the adspecies could adsorb more strongly, via a true chemical bond with surfaces of some dust grains, then grain surface reactions will play an important role in warm circumstellar regions as well. In this work, the surface-catalyzed reaction CO + 3 H2 yields CH4 + H2O is studied in the context that it may be very effective at converting the inorganic molecule CO into the simplest organic compound, methane. H2 and CO are the most abundant molecules in space, and the reaction converting them to methane, while kinetically inhibited in the gas phase under most astrophysical conditions, is catalyzed by iron, an abundant constituent of interstellar dust. At temperatures between 600 and 1000 K, which occur in the outflows from red giants and near luminous young stars, this reaction readily proceeds in the presence of an iron catalyst. Iron is one of the more abundant elements composing interstellar dust. Its abundance relative to hydrogen is almost that of silicon, and both of these heavy elements are primarily locked up in dust at all but the hottest regions of interstellar space.

Physical and chemical properties and adsorption type of activated carbon prepared from plum kernels by NaOH activation.

PubMed

Tseng, Ru-Ling

2007-08-25

Activated carbon was prepared from plum kernels by NaOH activation at six different NaOH/char ratios. The physical properties including the BET surface area, the total pore volume, the micropore ratio, the pore diameter, the burn-off, and the scanning electron microscope (SEM) observation as well as the chemical properties, namely elemental analysis and temperature programmed desorption (TPD), were measured. The results revealed a two-stage activation process: stage 1 activated carbons were obtained at NaOH/char ratios of 0-1, surface pyrolysis being the main reaction; stage 2 activated carbons were obtained at NaOH/char ratios of 2-4, etching and swelling being the main reactions. The physical properties of stage 2 activated carbons were similar, and specific area was from 1478 to 1887m(2)g(-1). The results of reaction mechanism of NaOH activation revealed that it was apparently because of the loss ratio of elements C, H, and O in the activated carbon, and the variations in the surface functional groups and the physical properties. The adsorption of the above activated carbons on phenol and three kinds of dyes (MB, BB1, and AB74) were used for an isotherm equilibrium adsorption study. The data fitted the Langmuir isotherm equation. Various kinds of adsorbents showed different adsorption types; separation factor (R(L)) was used to determine the level of favorability of the adsorption type. In this work, activated carbons prepared by NaOH activation were evaluated in terms of their physical properties, chemical properties, and adsorption type; and activated carbon PKN2 was found to have most application potential.

A computation study on the interplay between surface morphology and electrochemical performance of patterned thin film electrodes for Li-ion batteries

NASA Astrophysics Data System (ADS)

Gur, Sourav; Frantziskonis, George N.; Aifantis, Katerina E.

2017-08-01

Recent experiments illustrate that the morphology of the electrode surface impacts the voltage - capacity curves and long term cycling performance of Li-ion batteries. The present study systematically explores the role of the electrode surface morphology and uncertainties in the reactions that occur during electrochemical cycling, by performing kinetic Monte Carlo (kMC) simulations using the lattice Boltzmann method (LBM). This allows encoding of the inherent stochasticity at discrete microscale reaction events over the deterministic mean field reaction dynamics that occur in Li-ion cells. The electrodes are taken to be dense thin films whose surfaces are patterned with conical, trapezoidal, dome-shaped, or pillar-shaped structures. It is shown that the inherent perturbations in the reactions together with the characteristics of the electrode surface configuration can significantly improve battery performance, mainly because patterned surfaces, as opposed to flat surfaces, result in a smaller voltage drop. The most efficient pattern was the trapezoidal, which is consistent with experimental evidence on Si patterned electrodes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Runhong; Fung, Victor; Zhang, Yafen

Perovskites are interesting materials for catalysis due to their great tunability. However, the correlation of many reaction processes to the termination of a perovskite surface is still unclear. In this paper, we use the methanol coupling reaction on the SrTiO 3(100) surface as a probe reaction to investigate direct C–C coupling from a computational perspective. We use density functional theory to assess methanol adsorption, C–H activation, and direct C–C coupling reactions on the SrTiO 3(100) surface of different terminations. We find that, although methanol molecules dissociatively adsorb on both A and B terminations with similar strength, the dehydrogenation and C–Cmore » coupling reactions have significantly lower activation energies on the B termination than on the A termination. The predicted formation of methoxy and acetate on the SrTiO 3(100) B termination can well explain the ambient-pressure XPS data of methanol on the single-crystal SrTiO 3(100) surface at 250 °C. Finally, this work suggests that a choice of B termination of perovskites would be beneficial for the C–C coupling reaction of methanol.« less

Computed Potential Energy Surfaces and Minimum Energy Pathways for Chemical Reactions

NASA Technical Reports Server (NTRS)

Walch, Stephen P.; Langhoff, S. R. (Technical Monitor)

1994-01-01

Computed potential energy surfaces are often required for computation of such parameters as rate constants as a function of temperature, product branching ratios, and other detailed properties. For some dynamics methods, global potential energy surfaces are required. In this case, it is necessary to obtain the energy at a complete sampling of all the possible arrangements of the nuclei, which are energetically accessible, and then a fitting function must be obtained to interpolate between the computed points. In other cases, characterization of the stationary points and the reaction pathway connecting them is sufficient. These properties may be readily obtained using analytical derivative methods. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method to obtain accurate energetics, gives usefull results for a number of chemically important systems. The talk will focus on a number of applications including global potential energy surfaces, H + O2, H + N2, O(3p) + H2, and reaction pathways for complex reactions, including reactions leading to NO and soot formation in hydrocarbon combustion.

Fundamental insights into interfacial catalysis.

PubMed

Gong, Jinlong; Bao, Xinhe

2017-04-03

Surface and interfacial catalysis plays a vital role in chemical industries, electrochemistry and photochemical reactions. The challenges of modern chemistry are to optimize the chemical reaction processes and understand the detailed mechanism of chemical reactions. Since the early 1960s, the foundation of surface science systems has allowed the study of surface and interfacial phenomena on atomic/molecular level, and thus brought a number of significant developments to fundamental and technological processes, such as catalysis, material science and biochemistry, just to name a few. This themed issue describes the recent advances and developments in the fundamental understanding of surface and interfacial catalysis, encompassing areas of knowledge from metal to metal oxide, carbide, graphene, hexagonal boron nitride, and transition metal dichalcogenides under ultrahigh vacuum conditions, as well as under realistic reaction conditions.

Chip PCR. I. Surface passivation of microfabricated silicon-glass chips for PCR.

PubMed Central

Shoffner, M A; Cheng, J; Hvichia, G E; Kricka, L J; Wilding, P

1996-01-01

The microreaction volumes of PCR chips (a microfabricated silicon chip bonded to a piece of flat glass to form a PCR reaction chamber) create a relatively high surface to volume ratio that increases the significance of the surface chemistry in the polymerase chain reaction (PCR). We investigated several surface passivations in an attempt to identify 'PCR friendly' surfaces and used those surfaces to obtain amplifications comparable with those obtained in conventional PCR amplification systems using polyethylene tubes. Surface passivations by a silanization procedure followed by a coating of a selected protein or polynucleotide and the deposition of a nitride or oxide layer onto the silicon surface were investigated. Native silicon was found to be an inhibitor of PCR and amplification in an untreated PCR chip (i.e. native slicon) had a high failure rate. A silicon nitride (Si(3)N(4) reaction surface also resulted in consistent inhibition of PCR. Passivating the PCR chip using a silanizing agent followed by a polymer treatment resulted in good amplification. However, amplification yields were inconsistent and were not always comparable with PCR in a conventional tube. An oxidized silicon (SiO(2) surface gave consistent amplifications comparable with reactions performed in a conventional PCR tube. PMID:8628665

Thermo-chemical Ice Penetrator for Icy Moons

NASA Astrophysics Data System (ADS)

Arenberg, J. W.; Lee, G.; Harpole, G.; Zamel, J.; Sen, B.; Ross, F.; Retherford, K. D.

2016-12-01

The ability to place sensors or to take samples below the ice surface enables a wide variety of potential scientific investigations. Penetrating an ice cap can be accomplished via a mechanical drill, laser drill, kinetic impactor, or heated penetrator. This poster reports on the development of technology for the latter most option, namely a self-heated probe driven by an exothermic chemical reaction: a Thermo-chemical ice penetrator (TChIP). Our penetrator design employs a eutectic mix of alkali metals that produce an exothermic reaction upon contact with an icy surface. This reaction increases once the ice starts melting, so no external power is required. This technology is inspired by a classified Cold-War era program developed at Northrop Grumman for the US Navy. Terrestrial demonstration of this technology took place in the Arctic; however, this device cannot be considered high TRL for application at the icy moons of the solar system due to the environmental differences between Earth's Arctic and the icy moons. These differences demand a TChIP design specific to these cold, low mass, airless worlds. It is expected that this model of TChIP performance will be complex, incorporating all of the forces on the penetrator, gravity, the thermo-chemistry at the interface between penetrator and ice, and multi-phase heat and mass transport, and hydrodynamics. Our initial efforts are aimed at the development of a validated set of tools and simulations to predict the performance of the penetrator for both the environment found on these icy moons and for a terrestrial environment. The purpose of the inclusion of the terrestrial environment is to aid in model validation. Once developed and validated, our models will allow us to design penetrators for a specific scientific application on a specific body. This poster discusses the range of scientific investigations that are enabled by TChIP. We also introduce the development plan to advance TChIP to the point where it can be considered for infusion into a program.

Technology for a Thermo-chemical Ice Penetrator for Icy Moons

NASA Astrophysics Data System (ADS)

Arenberg, Jonathan; Harpole, George; Zamel, James; Sen, Bashwar; Lee, Greg; Ross, Floyd; Retherford, Kurt D.

2016-10-01

The ability to place sensors or to take samples below the ice surface enables a wide variety of potential scientific investigations. Penetrating an ice cap can be accomplished via a mechanical drill, laser drill, kinetic impactor, or heated penetrator. This poster reports on the development of technology for the latter most option, namely a self-heated probe driven by an exothermic chemical reaction: a Thermo-chemical ice penetrator (TChIP). Our penetrator design employs a eutectic mix of alkali metals that produce an exothermic reaction upon contact with an icy surface. This reaction increases once the ice starts melting, so no external power is required. This technology is inspired by a classified Cold-War era program developed at Northrop Grumman for the US Navy. Terrestrial demonstration of this technology took place in the Arctic; however, this device cannot be considered high TRL for application at the icy moons of the solar system due to the environmental differences between Earth's Arctic and the icy moons. These differences demand a TChIP design specific to these cold, low mass, airless worlds. It is expected that this model of TChIP performance will be complex, incorporating all of the forces on the penetrator, gravity, the thermo-chemistry at the interface between penetrator and ice, and multi-phase heat and mass transport, and hydrodynamics. Our initial efforts are aimed at the development of a validated set of tools and simulations to predict the performance of the penetrator for both the environment found on these icy moons and for a terrestrial environment. The purpose of the inclusion of the terrestrial environment is to aid in model validation. Once developed and validated, our models will allow us to design penetrators for a specific scientific application on a specific body. This poster discusses the range of scientific investigations that are enabled by TChIP. We also introduce the development plan to advance TChIP to the point where it can be considered for infusion into a program.

Modeling of hydrogen evolution reaction on the surface of GaInP2

NASA Astrophysics Data System (ADS)

Choi, Woon Ih; Wood, Brandon; Schwegler, Eric; Ogitsu, Tadashi

2012-02-01

GaInP2 is promising candidate material for hydrogen production using sunlight. It reduces solvated proton into hydrogen molecule using light-induced excited electrons in the photoelectrochemical cell. However, it is challenging to model hydrogen evolution reaction (HER) using first-principles molecular dynamics. Instead, we use Anderson-Newns model and generalized solvent coordinate in Marcus-Hush theory to describe adiabatic free energy surface of HER. Model parameters are fitted from the DFT calculations. We model Volmer-Heyrovsky reaction path on the surfaces of CuPt phase of GaInP2. We also discuss effects of surface oxide and catalyst atoms that exist on top of bare surfaces in experimental circumstances.

Reduction of chlorine radical chemical etching of GaN under simultaneous plasma-emitted photon irradiation

NASA Astrophysics Data System (ADS)

Liu, Zecheng; Imamura, Masato; Asano, Atsuki; Ishikawa, Kenji; Takeda, Keigo; Kondo, Hiroki; Oda, Osamu; Sekine, Makoto; Hori, Masaru

2017-08-01

Surface chemical reactions on the GaN surface with Cl radicals are thermally enhanced in the high-temperature Cl2 plasma etching of GaN, resulting in the formation of etch pits and thereby, a roughened surface. Simultaneous irradiation of ultraviolet (UV) photons in Cl2 plasma emissions with wavelengths of 258 and 306 nm reduces the surface chemical reactions because of the photodissociation of both Ga and N chlorides, which leads to a suppression of the increase in surface roughness. Compared with Si-related materials, we point out that photon-induced reactions should be taken into account during the plasma processing of wide-bandgap semiconductors.

Atomic-Scale Design of Iron Fischer-Tropsch Catalysts: A Combined Computational Chemistry, Experimental, and Microkinetic Modeling Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manos Mavrikakis; James A. Dumesic; Amit A. Gokhale

2006-03-03

Efforts during this second year focused on four areas: (1) continued searching and summarizing of published Fischer-Tropsch synthesis (FTS) mechanistic and kinetic studies of FTS reactions on iron catalysts; (2) investigation of CO adsorption/desorption and temperature programmed hydrogenation (TPH) of carbonaceous species after FTS on unsupported iron and alumina-supported iron catalysts; (3) activity tests of alumina-supported iron catalysts in a fixed bed reactor; (4) sequential design of experiments, for the collection of rate data in a Berty CSTR reactor, and nonlinear-regression analysis to obtain kinetic parameters. Literature sources describing mechanistic and kinetic studies of Fischer-Tropsch synthesis on iron catalysts weremore » compiled in a review. Temperature-programmed desorption/reaction methods (the latter using mass-spectrometry detection and also thermogravimetric analyzer (TGA)) were utilized to study CO adsorption/-desorption on supported and unsupported iron catalysts. Molecular and dissociative adsorptions of CO occur on iron catalysts at 25-150 C. The amounts adsorbed and bond strengths of adsorption are influenced by supports and promoters. That CO adsorbs dissociatively on polycrystalline Fe at temperatures well below those of FT reaction indicates that CO dissociation is facile and unlikely to be the rate-limiting step during FTS. Carbonaceous species formed after FT reaction for only 5 minutes at 200 C were initially hydrogenated under mild, isothermal condition (200 C and 1 atm), followed by TPH to 800 C. During the mild, isothermal hydrogenation, only about 0.1-0.2 mL of atomic carbon is apparently removed, while during TPH to 800 C multilayer equivalents of atomic, polymeric, carbidic, and graphitic carbons are removed. Rates of CO conversion on alumina-supported iron catalysts at 220-260 C and 20 atm are correlated well by a Langmuir-Hinshelwood expression, derived assuming carbon hydrogenation to CH and OH recombination to water to be rate-determining steps. In the coming year, studies will focus on quantitative determination of the rates of kinetically-relevant elementary steps on Fe catalysts with/without K and Pt promoters and at various levels of Al{sub 2}O{sub 3} support, providing a database for understanding (1) effects of promoter and support on elementary kinetic parameters and (2) for validation of computational models that incorporate effects of surface structure and promoters. Kinetic parameters will be incorporated into a microkinetics model, enabling prediction of rate without invoking assumptions, e.g. of a rate-determining step or a most-abundant surface intermediate. Calculations using periodic, self-consistent Density Functional Theory (DFT) methods were performed on two model surfaces: (1) Fe(110) with 1/4 ML subsurface carbon, and (2) Fe(110) with 1/4 ML Pt adatoms. Reaction networks for FTS on these systems were characterized in full detail by evaluating the thermodynamics and kinetics of each elementary step. We discovered that subsurface C stabilizes all the reactive intermediates, in contrast to Pt, which destabilizes most of them. A comparative study of the reactivities of the modified-Fe surfaces against pure Fe is expected to yield a more comprehensive understanding of promotion mechanisms for FTS on Fe.« less

Method of inducing surface ensembles on a metal catalyst

DOEpatents

Miller, Steven S.

1989-01-01

A method of inducing surface ensembles on a transition metal catalyst used in the conversion of a reactant gas or gas mixture, such as carbon monoxide and hydrogen into hydrocarbons (the Fischer-Tropsch reaction) is disclosed which comprises adding a Lewis base to the syngas (CO+H.sub.2) mixture before reaction takes place. The formation of surface ensembles in this manner restricts the number and types of reaction pathways which will be utilized, thus greatly narrowing the product distribution and maximizing the efficiency of the Fischer-Tropsch reaction. Similarly, amines may also be produced by the conversion of reactant gas or gases, such as nitrogen, hydrogen, or hydrocarbon constituents.

Method of inducing surface ensembles on a metal catalyst

DOEpatents

Miller, S.S.

1987-10-02

A method of inducing surface ensembles on a transition metal catalyst used in the conversion of a reactant gas or gas mixture, such as carbon monoxide and hydrogen into hydrocarbons (the Fischer-Tropsch reaction) is disclosed which comprises adding a Lewis base to the syngas (CO + H/sub 2/) mixture before reaction takes place. The formation of surface ensembles in this manner restricts the number and types of reaction pathways which will be utilized, thus greatly narrowing the product distribution and maximizing the efficiency of the Fischer-Tropsch reaction. Similarly, amines may also be produced by the conversion of reactant gas or gases, such as nitrogen, hydrogen, or hydrocarbon constituents.

Three pillars for achieving quantum mechanical molecular dynamics simulations of huge systems: Divide-and-conquer, density-functional tight-binding, and massively parallel computation.

PubMed

Nishizawa, Hiroaki; Nishimura, Yoshifumi; Kobayashi, Masato; Irle, Stephan; Nakai, Hiromi

2016-08-05

The linear-scaling divide-and-conquer (DC) quantum chemical methodology is applied to the density-functional tight-binding (DFTB) theory to develop a massively parallel program that achieves on-the-fly molecular reaction dynamics simulations of huge systems from scratch. The functions to perform large scale geometry optimization and molecular dynamics with DC-DFTB potential energy surface are implemented to the program called DC-DFTB-K. A novel interpolation-based algorithm is developed for parallelizing the determination of the Fermi level in the DC method. The performance of the DC-DFTB-K program is assessed using a laboratory computer and the K computer. Numerical tests show the high efficiency of the DC-DFTB-K program, a single-point energy gradient calculation of a one-million-atom system is completed within 60 s using 7290 nodes of the K computer. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Inclusion of Ti and Zr species on clay surfaces and their effect on the interaction with organic molecules

NASA Astrophysics Data System (ADS)

Rangel-Rivera, Pedro; Bachiller-Baeza, María Belén; Galindo-Esquivel, Ignacio; Rangel-Porras, Gustavo

2018-07-01

The interactions between the clay surface and the organic molecules play an important role in the efficient of these materials in adsorption and catalytic processes. These materials are often modified with the inclusion of other catalytic particles for the purpose of enhancing the activity. In this study, commercial clay K10 was modified with the particles inclusion of titanium and zirconium. The solid surfaces were examined by infrared spectroscopy, scanning electron microscopy (SEM) coupled to an energy-dispersive X-ray spectroscopy device (EDS), and X-ray photoelectron spectroscopy (XPS). Temperature programmed desorption of ammonia (TPD-NH3) and propan-2-ol decomposition test reaction were performed to probe the acid properties. The adsorption of acetic acid, ethanol, and propan-2-ol on the surface of each solid and their thermal stability were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). Finally, these materials were used in the esterification of acetic acid with penta-1-ol. The real effect over the incorporation of titanium species and zirconium species on clay surface for interacting with the organic molecules was discussed.

Adjusting the surface areal density of click-reactive azide groups by kinetic control of the azide substitution reaction on bromine-functional SAMs.

PubMed

Zhang, Shuo; Maidenberg, Yanir; Luo, Kai; Koberstein, Jeffrey T

2014-06-03

Azide-alkyne click chemistry has emerged as an important and versatile means for tethering a wide variety of guest molecules to virtually any substrate. In many of these applications, it is important to exercise control over the areal density of surface functional groups to achieve a desired areal density of the tethered guest molecule of interest. We demonstrate herein that the areal density of surface azide groups on flat germanium surfaces and nanoparticle substrates (silica and iron oxide) can be controlled kinetically by appropriately timed quenching of the S(N)2 substitution reaction of bromo-alkane-silane monolayers induced by the addition of sodium azide. The kinetics of the azide substitution reaction on monolayers formed on flat Ge substrates, determined by attenuated total reflection infrared spectroscopy (ATR-IR), are found to be identical to those for monolayers formed on both silica and iron oxide nanoparticles, the latter determined by transmission infrared spectroscopy. To validate the method, the percentages of surface bromine groups converted to azide groups after various reaction times were measured by quenching the S(N)2 reaction followed by analysis with ATR-IR (for Ge) and thermogravimetric analysis (after a subsequent click reaction with an alkyne-terminal polymer) for the nanoparticle substrates. The conversions found after quenching agree well with those expected from the standard kinetic curves. The latter result suggests that the kinetic method for the control of azide group areal density is a versatile means for functionalizing substrates with a prescribed areal density of azide groups for subsequent click reactions, and that the method is universal for any substrate, flat or nanoparticle, that can be modified with bromo-alkane-silane monolayers. Regardless of the surface geometry, we find that the azide substitution reaction is complete within 2-3 h, in sharp contrast to previous reports that indicate times of 48-60 h required for completion of the reaction.

Beyond the conventional understanding of water-rock reactivity

NASA Astrophysics Data System (ADS)

Fischer, Cornelius; Luttge, Andreas

2017-01-01

A common assumption is that water-rock reaction rates should converge to a mean value. There is, however, an emerging consensus on the genuine nature of reaction rate variations under identical chemical conditions. Thus, the further use of mean reaction rates for the prediction of material fluxes is environmentally and economically risky, manifest for example in the management of nuclear waste or the evolution of reservoir rocks. Surface-sensitive methods and resulting information about heterogeneous surface reactivity illustrate the inherent rate variability. Consequently, a statistical analysis was developed in order to quantify the heterogeneity of surface rates. We show how key components of the rate combine to give an overall rate and how the identification of those individual rate contributors provide mechanistic insight into complex heterogeneous reactions. This generates a paradigm change by proposing a new pathway to reaction model parameterization and for the prediction of reaction rates.

Characterization of the reactivity of a silica derived from acid activation of sepiolite with silane by 29Si and 13C solid-state NMR.

PubMed

Valentín, J L; López-Manchado, M A; Posadas, P; Rodríguez, A; Marcos-Fernández, A; Ibarra, L

2006-06-15

The mechanism of the reaction between a silica sample coming from acid treatment of sepiolite (denominated Silsep) and an organosilane, namely bis(triethoxysilylpropyl)tetrasulfane (TESPT), has been evaluated by solid state NMR spectroscopy, being compared with the silanization reaction of a commercial silica. The effect of the silane concentration and temperature on the course of the reaction was considered. Experimental results indicate that the silanization reaction is more effective in the case of Silsep, favoring both the reaction of silane molecules with the filler surface and the reaction between neighboring silane molecules. This different behavior is attributed to structural factors, moisture, and number of acid centers on silica surface. Environmental scanning electron microscopy (ESEM) was used to deposit micrometric water drops on the surface of these samples and to evaluate the proportion and distribution of the organophylization process.

Kinetic study on the H + SiH4 abstraction reaction using an ab initio potential energy surface.

PubMed

Cao, Jianwei; Zhang, Zhijun; Zhang, Chunfang; Bian, Wensheng; Guo, Yin

2011-01-14

Variational transition state theory calculations with the correction of multidimensional tunneling are performed on a 12-dimensional ab initio potential energy surface for the H + SiH(4) abstraction reaction. The surface is constructed using a dual-level strategy. For the temperature range 200-1600 K, thermal rate constants are calculated and kinetic isotope effects for various isotopic species of the title reaction are investigated. The results are in very good agreement with available experimental data.

Chemoselective phototransformation of C-H bonds on a polymer surface through a photoinduced cerium recycling redox reaction.

PubMed

Huang, Zhenhua; Wu, Zhengfang; Yang, Peng; Yang, Wantai

2014-09-01

It is generally accepted that Ce(4+) is unable to directly oxidize unreactive alkyl C-H bonds without the assistance of adjacent polar groups. Herein, we demonstrate in our newly developed confined photochemical reaction system that this recognized issue may be challenged. As we found, when a thin layer of a CeCl(3)/HCl aqueous solution was applied to a polymeric substrate and the substrate subjected to UV irradiation, Ce(3+) was first photooxidized to form Ce(4+) in the presence of H(+), and the in situ formed Ce(4+) then performs an oxidation reaction on the C-H bonds of the polymer surface to form surface-carbon radicals for radical graft polymerization reactions and functional-group transformations, while reducing to Ce(3+) and releasing H(+) in the process. This photoinduced cerium recycling redox (PCRR) reaction behaved as a biomimetic system in an artificial recycling reaction, leading to a sustainable chemical modification strategy for directly transforming alkyl C-H bonds on polymer surfaces into small-molecule groups and polymer brushes. This method is expected to provide a green and economical tool for industrial applications of polymer-surface modification. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Superior long-term activity for a Pt-Re alloy compared to Pt in methanol oxidation reactions

NASA Astrophysics Data System (ADS)

Duke, Audrey S.; Xie, Kangmin; Monnier, John R.; Chen, Donna A.

2017-03-01

Pt-Re bimetallic catalysts have shown enhanced activity compared to pure Pt for reactions involving oxidation, but the origins of this improved activity are not fully understood. Methanol oxidation on a Pt-Re alloy surface and pure Pt foil was studied in a microreactor coupled to an ultrahigh vacuum chamber. For reaction at 60 °C, the Pt-Re alloy surface exhibits superior long-term activity over a 24 h reaction period compared to pure Pt. The initial activity of Pt is 10-15% higher than on Pt-Re; however, the Pt surface gradually loses activity after 10 h online, whereas the activity of Pt-Re does not diminish. Post-reaction XPS shows that more carbon accumulates on the Pt than on Pt-Re, and the improved long-term activity is attributed to a greater ability of Pt-Re to oxidize the carbonaceous intermediates that eventually poison active sites. Both Pt and Pt-Re surfaces have almost no activity for methanol oxidation until a minimum coverage of oxygen is achieved from O2 dissociation. A comparison with methanol oxidation studies on Pt and Pt-Re in a pressure regime that is 150 times lower than in this work demonstrates that more carbon and less oxygen accumulate on the surfaces during reaction at the lower pressures.

Surface-induced dissociation and chemical reactions of C2D4(+) on stainless steel, carbon (HOPG), and two different diamond surfaces.

PubMed

Feketeová, Linda; Zabka, Jan; Zappa, Fabio; Grill, Verena; Scheier, Paul; Märk, Tilmann D; Herman, Zdenek

2009-06-01

Surface-induced interactions of the projectile ion C(2)D(4)(+) with room-temperature (hydrocarbon covered) stainless steel, carbon highly oriented pyrolytic graphite (HOPG), and two different types of diamond surfaces (O-terminated and H-terminated) were investigated over the range of incident energies from a few eV up to 50 eV. The relative abundance of the product ions in dependence on the incident energy of the projectile ion [collision-energy resolved mass spectra, (CERMS) curves] was determined. The product ion mass spectra contained ions resulting from direct dissociation of the projectile ions, from chemical reactions with the hydrocarbons on the surface, and (to a small extent) from sputtering of the surface material. Sputtering of the surface layer by low-energy Ar(+) ions (5-400 eV) indicated the presence of hydrocarbons on all studied surfaces. The CERMS curves of the product ions were analyzed to obtain both CERMS curves for the products of direct surface-induced dissociation of the projectile ion and CERMS curves of products of surface reactions. From the former, the fraction of energy converted in the surface collision into the internal excitation of the projectile ion was estimated as 10% of the incident energy. The internal energy of the surface-excited projectile ions was very similar for all studied surfaces. The H-terminated room-temperature diamond surface differed from the other surfaces only in the fraction of product ions formed in H-atom transfer surface reactions (45% of all product ions formed versus 70% on the other surfaces).

Use of Ambient Ionization High-Resolution Mass Spectrometry for the Kinetic Analysis of Organic Surface Reactions.

PubMed

Sen, Rickdeb; Escorihuela, Jorge; Smulders, Maarten M J; Zuilhof, Han

2016-04-12

In contrast to homogeneous systems, studying the kinetics of organic reactions on solid surfaces remains a difficult task due to the limited availability of appropriate analysis techniques that are general, high-throughput, and capable of offering quantitative, structural surface information. Here, we demonstrate how direct analysis in real time mass spectrometry (DART-MS) complies with above considerations and can be used for determining interfacial kinetic parameters. The presented approach is based on the use of a MS tag that--in principle--allows application to other reactions. To show the potential of DART-MS, we selected the widely applied strain-promoted alkyne-azide cycloaddition (SPAAC) as a model reaction to elucidate the effects of the nanoenvironment on the interfacial reaction rate.

Effects of Si/Al Ratio on Cu/SSZ-13 NH3-SCR Catalysts: Implications for the active Cu species and the Roles of Brønsted Acidity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Feng; Washton, Nancy M.; Wang, Yilin

2015-09-03

Cu/SSZ-13 catalysts with three Si/Al ratios of 6, 12 and 35 were synthesized with Cu incorporation via solution ion exchange. The implications of varying Si/Al ratios on the nature of the multiple Cu species that can be present in the SSZ-13 zeolite are a major focus of this work, as highlighted by the results of a variety of catalyst characterization and reaction kinetics measurements. Specifically, catalysts were characterized with surface area/pore volume measurements, temperature programmed reduction by H2 (H2-TPR), NH3 temperature programmed desorption (NH3-TPD), and DRIFTS and solid-state nuclear magnetic resonance (NMR) spectroscopies. Catalytic properties were examined using NO oxidation,more » ammonia oxidation, and standard ammonia selective catalytic reduction (NH3-SCR) reactions on selected catalysts under differential conditions. Besides indicating possible variably active multiple Cu species for these reactions, the measurements are also used to untangle some of the complexities caused by the interplay between redox of Cu ion centers and Brønsted acidity. All three reactions appear to follow a redox reaction mechanism, yet the roles of Brønsted acidity are quite different. For NO oxidation, increasing Si/Al ratio lowers Cu redox barriers, thus enhancing reaction rates. Brønsted acidity appears to play essentially no role for this reaction. For standard NH3-SCR, residual Brønsted acidity plays a significant beneficial role at both low- and high-temperature regimes. For NH3 oxidation, no clear trend is observed suggesting both Cu ion center redox and Brønsted acidity play important and perhaps competing roles. The authors gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.« less

NO 2 oxidation reactivity and burning mode of diesel particulates

DOE PAGES

Strzelec, Andrea; Vander Wal, Randy L.; Thompson, Thomas N.; ...

2016-03-24

The NO 2 oxidation kinetics and burning mode for diesel particulate from light-duty and medium-duty engines fueled with either ultra low sulfur diesel or soy methyl ester biodiesel blends have been investigated and are shown to be significantly different from oxidation by O 2. Oxidation kinetics were measured using a flow-through packed bed microreactor for temperature programmed reactions and isothermal differential pulsed oxidation reactions. The burning mode was evaluated using the same reactor system for flowing BET specific surface area measurements and HR-TEM with fringe analysis to evaluate the nanostructure of the nascent and partially oxidized particulates. The low activationmore » energy measured, specific surface area progression with extent of oxidation, HR-TEM images and difference plots of fringe length and tortuosity paint a consistent picture of higher reactivity for NO 2, which reacts indiscriminately immediately upon contact with the surface, leading to the Zone I or shrinking core type oxidation. In comparison, O 2 oxidation is shown to have relatively lower reactivity, preferentially attacking highly curved lamella, which are more reactive due to bond strain, and short lamella, which have a higher proportion of more reactive edge sites. Furthermore, this preferential oxidation leads to Zone II type oxidation, where solid phase diffusion of oxygen via pores contributes significantly to slowing the overall oxidation rate, by comparison.« less

Thermal induced BCN nanosheets evolution and its usage as metal-free catalyst in ethylbenzene dehydrogenation

NASA Astrophysics Data System (ADS)

Wang, Liancheng; Wang, Conghui; Zhang, Zhenwei; Wu, Jianghong; Ding, Ruimin; Lv, Baoliang

2017-11-01

Compared with mushroomed progress in metal-free C-rich BCN catalysts, little is known about the BN-rich BCN or even BN ones. Its related study has drawn great interest recently but still in its infancy stage. In this study, three kinds of BCN nanosheets (NSs) with tuned surface carbon contents (5.5-14.3%), specific surface area (SSA, 82-290 m2/g) and morphologies (ultrathin nanosheets, triangular plates) were fabricated through a solid state reaction by simply adjusting the reaction temperature, and those effects on the ethylbenzene dehydrogenation performances were studied in CO2 atmosphere. The morphology evolution of BCN NSs from ultrathin nanosheets to the triangular plates was observed and control experiments were carried out. The BCN nanosheets show relatively strong interaction with CO2 and distinct CO2 absorption properties. The CO2 temperature programmed desorption also indicates that the desorption peaks of CO2 are above 400 °C, enabling them potential CO2 utilization catalysts. A weak association was found between the surface C contents and the catalytic performance as it normalized with SSA, and the B-O species could be taken as an active site in CO2 atmosphere. Though much progress still needed, it is convincing that the BCN catalyst could be a promising metal-free catalyst in dehydrogenation beyond carbocatalyst.

Ultrathin Bi2WO6 nanosheet decorated with Pt nanoparticles for efficient formaldehyde removal at room temperature

NASA Astrophysics Data System (ADS)

Sun, Dong; Le, Yao; Jiang, Chuanjia; Cheng, Bei

2018-05-01

Two-dimensional (2D) ultrathin bismuth tungstate (Bi2WO6) nanosheets (BWO-NS) with a thickness of approximately 4.0 nm were synthesized by a one-step hydrothermal method, and decorated with platinum (Pt) nanoparticles (NPs) via an impregnation/borohydride-reduction approach. The as-prepared ultrathin Pt-BWO-NS exhibited superior catalytic activity for removing gaseous formaldehyde (HCHO) at ambient temperature, in comparison with bulk counterpart with Bi2WO6 sheet thickness of tens of nanometers. The ultrathin structure endowed the Pt-BWO-NS sample with larger specific surface area, which can provide abundant surface active sites for HCHO adsorption and facilitate the homogeneous dispersion of Pt NPs. X-ray photoelectron spectroscopy and hydrogen temperature-programmed reduction analyses revealed the interaction between the Bi2WO6 support and Pt species, which is crucial for activating surface oxygen atoms to participate in the catalytic HCHO oxidation process. By conducting in situ diffuse reflectance infrared Fourier transform spectroscopy under different atmospheres, i.e., gaseous HCHO in nitrogen or oxygen (O2), the reaction mechanism and the role of O2 were elucidated, with dioxymethylene, formate and linearly adsorbed carbon monoxide identified as the main reaction intermediates. This study may provide new enlightenment on fabricating novel 2D nanomaterials for efficient indoor air purification and potentially other environmental applications.

[Degradation of m-Cresol with Fe-MCM-41 in Catalytic Ozonation].

PubMed

Sun, Wen-jing; Wang, Ya-min; Wei, Huang-zhao; Wang, Sen; Li, Xu-ning; Li, Jing-mei; Sun, Cheng-lin; An, Lu-yang

2015-04-01

Fe-MCM-41 was first used for the treatment of m-cresol in catalytic ozonation. The effect of the percentage of Fe dopping mass, catalyst dosage and the natural concentration of substrate on m-cresol conversion and TOC removal were studied. The structural property of Fe-MCM-41 was characterized by X-ray diffraction, temperature-programmed reduction, Mössbauer spectra and BET of catalysts. The results showed that Fe dopping mass had a great effect on the catalytic activity of Fe-MCM-41 in catalytic ozonation and the optimal percentage of dopping mass was 4.4% (wt). The results showed that with Fe dopping mass increase, the degree of crystallinity became weaker, the crystal surface distance reduced, as well as the specific surface area, pore volume and aperture. γ-Fe2O3 was the only form staying on the surface of MCM-41, and the catalyst had good ferromagnetism and stability. Ozonation played a role of both direct oxidation and indirect oxidation in the reaction, approximately the same ratio. Under the experimental condition of the natural pH of model wastewater,using 4.4% (wt) Fe-MCM-41 as catalyst, natural concentration of m-cresol 500 mg x L(-1), catalyst dosage 0.1 g x L(-1) and reaction time 30 min, m-cresol conversion and TOC removal were 100% and 26.8%, respectively.

Elementary Chemical Reactions in Surface Photocatalysis

NASA Astrophysics Data System (ADS)

Guo, Qing; Zhou, Chuanyao; Ma, Zhibo; Ren, Zefeng; Fan, Hongjun; Yang, Xueming

2018-04-01

Photocatalytic hydrogen evolution and organic degradation on oxide materials have been extensively investigated in the last two decades. Great efforts have been dedicated to the study of photocatalytic reaction mechanisms of a variety of molecules on TiO2 surfaces by using surface science methods under ultra-high vacuum (UHV) conditions, providing fundamental understanding of surface chemical reactions in photocatalysis. In this review, we summarize the recent progress in the study of photocatalysis of several important species (water, methanol, and aldehydes) on different TiO2 surfaces. The results of these studies have provided us deep insights into the elementary processes of surface photocatalysis and stimulated a new frontier of research in this area. Based on the results of these studies, a new dynamics-based photocatalysis model is also discussed.

Engineering surfaces for bioconjugation: developing strategies and quantifying the extent of the reactions.

PubMed

Gauvreau, Virginie; Chevallier, Pascale; Vallières, Karine; Petitclerc, Eric; Gaudreault, René C; Laroche, Gaétan

2004-01-01

This study presents two-step and multistep reactions for modifying the surface of plasma-functionalized poly(tetrafluoroethylene) (PTFE) surfaces for subsequent conjugation of biologically relevant molecules. First, PTFE films were treated by a radiofrequency glow discharge (RFGD) ammonia plasma to introduce amino groups on the fluoropolymer surface. This plasma treatment is well optimized and allows the incorporation of a relative surface concentration of approximately 2-3.5% of amino groups, as assessed by chemical derivatization followed by X-ray photoelectron spectroscopy (XPS). In a second step, these amino groups were further reacted with various chemical reagents to provide the surface with chemical functionalities such as maleimides, carboxylic acids, acetals, aldehydes, and thiols, that could be used later on to conjugate a wide variety of biologically relevant molecules such as proteins, DNA, drugs, etc. In the present study, glutaric and cis-aconitic anhydrides were evaluated for their capability to provide carboxylic functions to the PTFE plasma-treated surface. Bromoacetaldehyde diethylacetal was reacted with the aminated PTFE surface, providing a diethylacetal function, which is a latent form of aldehyde functionality. Reactions with cross-linkers such as sulfo-succinimidyl derivatives (sulfo-SMCC, sulfo-SMPB) were evaluated to provide a highly reactive maleimide function suitable for further chemical reactions with thiolated molecules. Traut reagent (2-iminothiolane) was also conjugated to introduce a thiol group onto the fluoropolymer surface. PTFE-modified surfaces were analyzed by XPS with a particular attention to quantify the extent of the reactions that occurred on the polymer. Finally, surface immobilization of fibronectin performed using either glutaric anhydride or sulfo-SMPB activators demonstrated the importance of selecting the appropriate conjugation strategy to retain the protein biological activity.

Dynamical importance of van der Waals saddle and excited potential surface in C(1D)+D2 complex-forming reaction

PubMed Central

Shen, Zhitao; Ma, Haitao; Zhang, Chunfang; Fu, Mingkai; Wu, Yanan; Bian, Wensheng; Cao, Jianwei

2017-01-01

Encouraged by recent advances in revealing significant effects of van der Waals wells on reaction dynamics, many people assume that van der Waals wells are inevitable in chemical reactions. Here we find that the weak long-range forces cause van der Waals saddles in the prototypical C(1D)+D2 complex-forming reaction that have very different dynamical effects from van der Waals wells at low collision energies. Accurate quantum dynamics calculations on our highly accurate ab initio potential energy surfaces with van der Waals saddles yield cross-sections in close agreement with crossed-beam experiments, whereas the same calculations on an earlier surface with van der Waals wells produce much smaller cross-sections at low energies. Further trajectory calculations reveal that the van der Waals saddle leads to a torsion then sideways insertion reaction mechanism, whereas the well suppresses reactivity. Quantum diffraction oscillations and sharp resonances are also predicted based on our ground- and excited-state potential energy surfaces. PMID:28094253

In situ formation of the active sites in Pd-Au bimetallic nanocatalysts for CO oxidation: NAP (near ambient pressure) XPS and MS study.

PubMed

Bukhtiyarov, A V; Prosvirin, I P; Saraev, A A; Klyushin, A Yu; Knop-Gericke, A; Bukhtiyarov, V I

2018-06-07

Model bimetallic Pd-Au/HOPG catalysts have been investigated in the CO oxidation reaction using a combination of NAP XPS and MS techniques. The samples have shown catalytic activity at temperatures above 150 °C. The redistribution of Au and Pd on the surface depending on the reaction conditions has been demonstrated using NAP XPS. The Pd enrichment of the bimetallic particles' surface under reaction gas mixture has been shown. Apparently, CO adsorption induces Pd segregation on the surface. Heating the sample under reaction conditions above 150 °C decomposes the Pd-CO state due to CO desorption and reaction and simultaneous Pd-Au alloy formation on the surface takes place. Cooling back down to RT results in reversible Pd segregation due to Pd-CO formation and the sample becomes inactive. It has been shown that in situ studies are necessary for investigation of the active sites in Pd-Au bimetallic systems.

Hydrogen-assisted versus hydroxyl-assisted CO dissociation over Co-doped Cu(111): A DFT study

NASA Astrophysics Data System (ADS)

Zha, Hao; Dong, Xiuqin; Yu, Yingzhe; Zhang, Minhua

2018-03-01

First principle based density functional theory (DFT) was used to calculate the step-by-step hydrogenation and dissociation reaction network of carbon monoxide (CO) over Co-doped Cu(111) surface as a model for understanding the lateral interaction of surface hydroxyl species (OH) on these reactions. We discussed the Csbnd O bond length and the adsorption energy changes of reaction intermediates under different adsorption circumstances for purpose of making out the effect of surface hydroxyl on the reaction selectivity. Reaction intermediates co-adsorbed with H atom and hydroxyl could undergo H-assisted or OH-assisted routes. The calculations show that the OH-assisted route prefers with the formation of COH, CHOH and CH2OH while general H-assisted route prefers with the formation of HCO, CH2O and CH3O. Considering the rather low activation barrier of COH, CHOH and CH2OH to form CHX, the existence of hydroxyl on the surface is in favor of boosting the CHX and suppressing the methanol.

Modeling sorption of divalent metal cations on hydrous manganese oxide using the diffuse double layer model

USGS Publications Warehouse

Tonkin, J.W.; Balistrieri, L.S.; Murray, J.W.

2004-01-01

Manganese oxides are important scavengers of trace metals and other contaminants in the environment. The inclusion of Mn oxides in predictive models, however, has been difficult due to the lack of a comprehensive set of sorption reactions consistent with a given surface complexation model (SCM), and the discrepancies between published sorption data and predictions using the available models. The authors have compiled a set of surface complexation reactions for synthetic hydrous Mn oxide (HMO) using a two surface site model and the diffuse double layer SCM which complements databases developed for hydrous Fe (III) oxide, goethite and crystalline Al oxide. This compilation encompasses a range of data observed in the literature for the complex HMO surface and provides an error envelope for predictions not well defined by fitting parameters for single or limited data sets. Data describing surface characteristics and cation sorption were compiled from the literature for the synthetic HMO phases birnessite, vernadite and ??-MnO2. A specific surface area of 746 m2g-1 and a surface site density of 2.1 mmol g-1 were determined from crystallographic data and considered fixed parameters in the model. Potentiometric titration data sets were adjusted to a pH1EP value of 2.2. Two site types (???XOH and ???YOH) were used. The fraction of total sites attributed to ???XOH (??) and pKa2 were optimized for each of 7 published potentiometric titration data sets using the computer program FITEQL3.2. pKa2 values of 2.35??0.077 (???XOH) and 6.06??0.040 (???YOH) were determined at the 95% confidence level. The calculated average ?? value was 0.64, with high and low values ranging from 1.0 to 0.24, respectively. pKa2 and ?? values and published cation sorption data were used subsequently to determine equilibrium surface complexation constants for Ba2+, Ca2+, Cd 2+, Co2+, Cu2+, Mg2+, Mn 2+, Ni2+, Pb2+, Sr2+ and Zn 2+. In addition, average model parameters were used to predict additional sorption data for which complementary titration data were not available. The two-site model accounts for variability in the titration data and most metal sorption data are fit well using the pKa2 and ?? values reported above. A linear free energy relationship (LFER) appears to exist for some of the metals; however, redox and cation exchange reactions may limit the prediction of surface complexation constants for additional metals using the LFER. ?? 2003 Elsevier Ltd. All rights reserved.

A monolayer of hierarchical silver hemi-mesoparticles with tunable surface topographies for highly sensitive surface-enhanced Raman spectroscopy

NASA Astrophysics Data System (ADS)

Zhu, Shuangmei; Fan, Chunzhen; Mao, Yanchao; Wang, Junqiao; He, Jinna; Liang, Erjun; Chao, Mingju

2016-02-01

We proposed a facile green synthesis system to synthesize large-scale Ag hemi-mesoparticles monolayer on Cu foil. Ag hemi-mesoparticles have different surface morphologies on their surfaces, including ridge-like, meatball-like, and fluffy-like shapes. In the reaction, silver nitrate was reduced by copper at room temperature in dimethyl sulfoxide via the galvanic displacement reaction. The different surface morphologies of the Ag hemi-mesoparticles were adjusted by changing the reaction time, and the hemi-mesoparticle surface formed fluffy-spherical nanoprotrusions at longer reaction time. At the same time, we explored the growth mechanism of silver hemi-mesoparticles with different surface morphologies. With 4-mercaptobenzoic acid as Raman probe molecules, the fluffy-like silver hemi-mesoparticles monolayer with the best activity of surface enhanced Raman scattering (SERS), the enhancement factor is up to 7.33 × 107 and the detection limit can reach 10-10M. SERS measurements demonstrate that these Ag hemi-mesoparticles can serve as sensitive SERS substrates. At the same time, using finite element method, the distribution of the localized electromagnetic field near the particle surface was simulated to verify the enhanced mechanism. This study helps us to understand the relationship between morphology Ag hemi-mesoparicles and the properties of SERS.

A monolayer of hierarchical silver hemi-mesoparticles with tunable surface topographies for highly sensitive surface-enhanced Raman spectroscopy.

PubMed

Zhu, Shuangmei; Fan, Chunzhen; Mao, Yanchao; Wang, Junqiao; He, Jinna; Liang, Erjun; Chao, Mingju

2016-02-21

We proposed a facile green synthesis system to synthesize large-scale Ag hemi-mesoparticles monolayer on Cu foil. Ag hemi-mesoparticles have different surface morphologies on their surfaces, including ridge-like, meatball-like, and fluffy-like shapes. In the reaction, silver nitrate was reduced by copper at room temperature in dimethyl sulfoxide via the galvanic displacement reaction. The different surface morphologies of the Ag hemi-mesoparticles were adjusted by changing the reaction time, and the hemi-mesoparticle surface formed fluffy-spherical nanoprotrusions at longer reaction time. At the same time, we explored the growth mechanism of silver hemi-mesoparticles with different surface morphologies. With 4-mercaptobenzoic acid as Raman probe molecules, the fluffy-like silver hemi-mesoparticles monolayer with the best activity of surface enhanced Raman scattering (SERS), the enhancement factor is up to 7.33 × 10(7) and the detection limit can reach 10(-10)M. SERS measurements demonstrate that these Ag hemi-mesoparticles can serve as sensitive SERS substrates. At the same time, using finite element method, the distribution of the localized electromagnetic field near the particle surface was simulated to verify the enhanced mechanism. This study helps us to understand the relationship between morphology Ag hemi-mesoparicles and the properties of SERS.

Predictive Finite Rate Model for Oxygen-Carbon Interactions at High Temperature

NASA Astrophysics Data System (ADS)

Poovathingal, Savio

An oxidation model for carbon surfaces is developed to predict ablation rates for carbon heat shields used in hypersonic vehicles. Unlike existing empirical models, the approach used here was to probe gas-surface interactions individually and then based on an understanding of the relevant fundamental processes, build a predictive model that would be accurate over a wide range of pressures and temperatures, and even microstructures. Initially, molecular dynamics was used to understand the oxidation processes on the surface. The molecular dynamics simulations were compared to molecular beam experiments and good qualitative agreement was observed. The simulations reproduced cylindrical pitting observed in the experiments where oxidation was rapid and primarily occurred around a defect. However, the studies were limited to small systems at low temperatures and could simulate time scales only of the order of nanoseconds. Molecular beam experiments at high surface temperature indicated that a majority of surface reaction products were produced through thermal mechanisms. Since the reactions were thermal, they occurred over long time scales which were computationally prohibitive for molecular dynamics to simulate. The experiments provided detailed dynamical data on the scattering of O, O2, CO, and CO2 and it was found that the data from molecular beam experiments could be used directly to build a model. The data was initially used to deduce surface reaction probabilities at 800 K. The reaction probabilities were then incorporated into the direct simulation Monte Carlo (DSMC) method. Simulations were performed where the microstructure was resolved and dissociated oxygen convected and diffused towards it. For a gas-surface temperature of 800 K, it was found that despite CO being the dominant surface reaction product, a gas-phase reaction forms significant CO2 within the microstructure region. It was also found that surface area did not play any role in concentration of reaction products because the reaction probabilities were in the diffusion dominant regime. The molecular beam data at different surface temperatures was then used to build a finite rate model. Each reaction mechanism and all rate parameters of the new model were determined individually based on the molecular beam data. Despite the experiments being performed at near vacuum conditions, the finite rate model developed using the data could be used at pressures and temperatures relevant to hypersonic conditions. The new model was implemented in a computational fluid dynamics (CFD) solver and flow over a hypersonic vehicle was simulated. The new model predicted similar overall mass loss rates compared to existing models, however, the individual species production rates were completely different. The most notable difference was that the new model (based on molecular beam data) predicts CO as the oxidation reaction product with virtually no CO2 production, whereas existing models predict the exact opposite trend. CO being the dominant oxidation product is consistent with recent high enthalpy wind tunnel experiments. The discovery that measurements taken in molecular beam facilities are able to determine individual reaction mechanisms, including dependence on surface coverage, opens up an entirely new way of constructing ablation models.

Scanning tunnelling microscope for boron surface studies

NASA Astrophysics Data System (ADS)

Trenary, Michael

1990-10-01

The equipment purchased is to be used in an experimental study of the relationship between atomic structure and chemical reactivity for boron and carbon surfaces. This research is currently being supported by grant AFOSR-88-0111. A renewal proposal is currently pending with AFOSR to continue these studies. Carbon and boron are exceptionally stable, covalently bonded solids with highly unique crystal structures. The specific reactions to be studied are loosely related to the problems of oxidation and oxidation inhibition of carbon/carbon composites. The main experimental instrument to be used is a scanning tunneling microscope (STM) purchased under grant number AFSOR-89-0146. Other techniques to be used include Auger electron spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), low energy electron diffraction (LEED), temperature programmed desorption (TPD) and scanning tunneling microscopy (STM).

Adsorption of acrylonitrile on diamond and silicon (001)-(2 x 1) surfaces: effects of dimer structure on reaction pathways and product distributions.

PubMed

Schwartz, Michael P; Barlow, Daniel E; Russell, John N; Butler, James E; D'Evelyn, Mark P; Hamers, Robert J

2005-06-15

Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) are used to compare the reaction of acrylonitrile with Si(001) and C(001) (diamond) surfaces. Our results show that reaction with Si(001) and C(001) yield very different product distributions that result from fundamental differences in the ionic character of these surfaces. While acrylonitrile reacts with the C(001) surface via a [2 + 2] cycloaddition reaction in a manner similar to nonpolar molecules such as alkenes and disilenes, reaction with the Si(001) surface occurs largely through the nitrile group. This work represents the first experimental example of how differences in dimer structure lead to very different chemistry for C(001) compared to that for Si(001). The fact that Si(001) reacts with the strongly polar nitrile group of acrylonitrile indicates that the zwitterionic character of this surface controls its reactivity. C(001) dimers, on the other hand, behave more like a true molecular double bond, albeit a highly strained one. Consequently, while alternative strategies will be necessary for chemical modification of Si(001), traditional schemes from organic chemistry for functionalization of alkenes and disilenes may be available for building molecular layers on C(001).

Direct Measurements of Half-Cycle Reaction Heats during Atomic Layer Deposition by Calorimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lownsbury, James M.; Gladden, James A.; Campbell, Charles T.

We introduce a new high-temperature adsorption calorimeter that approaches the ideal limit of a heat detector whereby the signal at any time is proportional to the heat power being delivered to the sample and prove its sensitivity for measuring pulse-to-pulse heats of half-reactions during atomic layer deposition (ALD) at 400 K. The heat dynamics of amorphous Al2O3 growth via sequential self-limiting surface reaction of trimethylaluminum (TMA) and H2O is clearly resolved. Calibration enables quantitation of the exothermic TMA and H2O half-reactions with high precision, -343 kJ/mol TMA and -251 kJ/mol H2O, respectively. A time resolution better than 1 ms ismore » demonstrated, allowing for the deconvolution of at least two distinct surface reactions during TMA microdosing. It is further demonstrated that this method can provide the heat of reaction versus extent of reaction during each precursors half-reaction, thus providing even richer mechanistic information on the surface processes involved. The broad applicability of this novel calorimeter is demonstrated through excellent signal-to-noise ratios of less exothermic ALD half-reactions to produce TiO2 and MnO.« less

In situ loading of well-dispersed silver nanoparticles on nanocrystalline magnesium oxide for real-time monitoring of catalytic reactions by surface enhanced Raman spectroscopy.

PubMed

Zhang, Kaige; Li, Gongke; Hu, Yuling

2015-10-28

The surface-enhanced Raman spectroscopy (SERS) technique is of great importance for insight into the transient reaction intermediates and mechanistic pathways involved in heterogeneously catalyzed chemical reactions under actual reaction conditions, especially in water. Herein, we demonstrate a facile method for in situ synthesis of nanocrystalline magnesium oxide-Ag(0) (nano MgO-Ag(0)) hybrid nanomaterials with dispersed Ag nanoparticles (Ag NPs) on the surface of nanocrystalline magnesium oxide (nano MgO) via Sn(2+) linkage and reduction. As a benefit from the synergy effect of nano MgO and Ag NPs, the nano MgO-Ag(0) exhibited both excellent SERS and catalytic activities for the reduction of 4-nitrothiophenol in the presence of NaBH4. The nano MgO-Ag(0) was used for real-time monitoring of the catalytic reaction process of 4-nitrothiophenol to 4-aminothiophenol in an aqueous medium by observing the SERS signals of the reactant, intermediate and final products. The intrinsic reaction kinetics and reaction mechanism of this reaction were also investigated. This SERS-based synergy technique provides a novel approach for quantitative in situ monitoring of catalytic chemical reaction processes.

Direct Measurements of Half-Cycle Reaction Heats during Atomic Layer Deposition by Calorimetry

DOE PAGES

Lownsbury, James M.; Gladden, James A.; Campbell, Charles T.; ...

2017-10-05

We introduce a new high-temperature adsorption calorimeter that approaches the ideal limit of a heat detector whereby the signal at any time is proportional to the heat power being delivered to the sample and prove its sensitivity for measuring pulse-to-pulse heats of half-reactions during atomic layer deposition (ALD) at 400 K. The heat dynamics of amorphous Al2O3 growth via sequential self-limiting surface reaction of trimethylaluminum (TMA) and H2O is clearly resolved. Calibration enables quantitation of the exothermic TMA and H2O half-reactions with high precision, -343 kJ/mol TMA and -251 kJ/mol H2O, respectively. A time resolution better than 1 ms ismore » demonstrated, allowing for the deconvolution of at least two distinct surface reactions during TMA microdosing. It is further demonstrated that this method can provide the heat of reaction versus extent of reaction during each precursors half-reaction, thus providing even richer mechanistic information on the surface processes involved. The broad applicability of this novel calorimeter is demonstrated through excellent signal-to-noise ratios of less exothermic ALD half-reactions to produce TiO2 and MnO.« less

Heterogeneous polymer modification: Polyolefin maleation in supercritical carbon dioxide and amorphous fluoropolymer surface modification

NASA Astrophysics Data System (ADS)

Hayes, Heather J.

1999-11-01

Three distinct heterogeneous polymer modification reactions are explored in this work. The first is a bulk reaction commonly conducted on polyolefins---the free radical addition of maleic anhydride. This reaction was run using supercritical carbon dioxide (SC CO2) as the solvent. The second was the chemical surface modification of an amorphous fluorocopolymer of tetrafluoroethylene and a perfluorodioxole monomer (Teflon AF). Several reactions were explored to reduce the surface of the fluorocopolymer for the enhancement of wettability. The last modification was also on Teflon AF and involved the physical modification of the surface through the transport polymerization of xylylene in order to synthesize a novel bilayer membrane. The bulk maleation of poly-4-methyl-1-pentene (PMP) was the focus of the first project. SC CO2 was utilized as both solvent and swelling agent to promote this heterogeneous reaction and led to successful grafting of anhydride groups on both PMP and linear low density polyethylene. Varying the reaction conditions and reagent concentrations allowed optimization of the reaction. The grafted anhydride units were found to exist as single maleic and succinic grafts, and the PMP became crosslinked upon maleation. The surface of a fluoropolymer can be difficult to alter. An examination of three reactions was made to determine the reactivity of Teflon AF: sodium naphthalenide treatment (Na-Nap), aluminum metal modification through deposition and dissolution, and mercury/ammonia photosensitization. The fluorocopolymer with the lower perfluorodioxole percentage was found to be more reactive towards modification with the Na-Nap treatment. The other modification reactions appeared to be nearly equally reactive toward both fluorocopolymers. The functionality of the Na-Nap-treated surface was examined in detail with the use of several derivatization reactions. In the final project, an asymmetric gas separation membrane was synthesized using Teflon AF as the highly permeable support layer and chemical vapor deposited poly(p-xylylene) (PPX) as the thin selective layer. This bilayer membrane has oxygen and nitrogen permeability values close to those predicted by the series resistance model. To enhance the weak adhesive bond between Teflon AF and PPX, Na-Nap reduction was used to modify the Teflon AF surface prior to the vapor deposition polymerization of di-p-xylylene monomer.

Surface Modifications during a Catalytic Reaction: A Combined APT and FIB/SEM Analysis of Surface Segregation

DOE PAGES

Barroo, Cedric; Janvelyan, Nare; Zugic, Branko; ...

2016-07-25

To improve the understanding of catalytic processes, the surface structure and composition of the active materials need to be determined before and after reaction. Morphological changes may occur under reaction conditions and can dramatically influence the reactivity and/or selectivity of a catalyst. Goldbased catalysts with different architectures are currently being developed for selective oxidation reactions at low temperatures. Specifically, nanoporous Au (npAu) with a composition of Au 97-Ag 3 is obtained by dealloying a Ag 70-Au 30 bulk alloy. Recent studies highlight the efficiency of npAu catalysts for methanol oxidation using ozone to activate the catalysts before methanol oxidation. Inmore » this paper, we studied the morphological and compositional changes occurring at the surface of Au-based catalysts in certain conditions.« less

Elucidating the alkaline oxygen evolution reaction mechanism on platinum

DOE PAGES

Favaro, M.; Valero-Vidal, C.; Eichhorn, J.; ...

2017-03-07

Understanding the interplay between surface chemistry, electronic structure, and reaction mechanism of the catalyst at the electrified solid/liquid interface will enable the design of more efficient materials systems for sustainable energy production. The substantial progress in operando characterization, particularly using synchrotron based X-ray spectroscopies, provides the unprecedented opportunity to uncover surface chemical and structural transformations under various (electro)chemical reaction environments. In this work, we study a polycrystalline platinum surface under oxygen evolution conditions in an alkaline electrolyte by means of ambient pressure X-ray photoelectron spectroscopy performed at the electrified solid/liquid interface. We elucidate previously inaccessible aspects of the surface chemistrymore » and structure as a function of the applied potential, allowing us to propose a reaction mechanism for oxygen evolution on a platinum electrode in alkaline solutions.« less

Adsorption and ring-opening of lactide on the chiral metal surface Pt(321)S studied by density functional theory

NASA Astrophysics Data System (ADS)

Franke, J.-H.; Kosov, D. S.

2015-01-01

We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321)S. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

NO oxidation on Zeolite Supported Cu Catalysts: Formation and Reactivity of Surface Nitrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Hai-Ying; Wei, Zhehao; Kollar, Marton

2016-04-18

The comparative activities of a small-pore Cu-CHA and a large-pore Cu-BEA catalyst for the selective catalytic reduction (SCR) of NOx with NH3, and for the oxidation of NO to NO2 and the subsequent formation of surface nitrates were investigated. Although both catalysts are highly active in SCR reactions, they exhibit very low NO oxidation activity. Furthermore, Cu-CHA is even less active than Cu-BEA in catalyzing NO oxidation but is clearly more active for SCR reactions. Temperature-programed desorption (TPD) experiments following the adsorption of (NO2 + NO + O2) with different NO2:NO ratios reveal that the poor NO oxidation activity ofmore » the two catalysts is not due to the formation of stable surface nitrates. On the contrary, NO is found to reduce and decompose the surface nitrates on both catalysts. To monitor the reaction pathways, isotope exchange experiments were conducted by using 15NO to react with 14N-nitrate covered catalyst surfaces. The evolution of FTIR spectra during the isotope exchange process demonstrates that 14N-nitrates are simply displaced with no formation of 15N-nitrates on the Cu-CHA sample, which is clearly different from that observed on the Cu-BEA sample where formation of 15N-nitrates is apparent. The results suggest that the formal oxidation state of N during the NO oxidation on Cu-CHA mainly proceeds from its original +2 to a +3 oxidation state, whereas reaching a higher oxidation state for N, such as +4 or +5, is possible on Cu-BEA. The authors at PNNL gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.« less

On the adsorption/reaction of acetone on pure and sulfate-modified zirconias.

PubMed

Crocellà, Valentina; Cerrato, Giuseppina; Morterra, Claudio

2013-08-28

In situ FTIR spectroscopy was employed to investigate some aspects of the ambient temperature (actually, IR-beam temperature) adsorption of acetone on various pure and sulfate-doped zirconia specimens. Acetone uptake yields, on all examined systems and to a variable extent, different types of specific molecular adsorption, depending on the kind/population of available surface sites: relatively weak H-bonding interaction(s) with surface hydroxyls, medium-strong coordinative interaction with Lewis acidic sites, and strong H-bonding interaction with Brønsted acidic centres. Moreover acetone, readily and abundantly adsorbed in molecular form, is able to undergo the aldol condensation reaction (yielding, as the main reaction product, adsorbed mesityl oxide) only if the adsorbing material possesses some specific surface features. The occurrence/non-occurrence of the acetone self-condensation reaction is discussed, and leads to conclusions concerning the sites that catalyze the condensation reaction that do not agree with either of two conflicting interpretations present in the literature of acetone uptake/reaction on, mainly, zeolitic systems. In particular, what turns out to be actually necessary for the acetone aldol condensation reaction to occur on the examined zirconia systems is the presence of coordinatively unsaturated O(2-) surface sites of basicity sufficient to lead to the extraction of a proton from one of the CH3 groups of adsorbed acetone.

Mechanisms and energetics of hydride dissociation reactions on surfaces of plasma-deposited silicon thin films

NASA Astrophysics Data System (ADS)

Singh, Tejinder; Valipa, Mayur S.; Mountziaris, T. J.; Maroudas, Dimitrios

2007-11-01

We report results from a detailed analysis of the fundamental silicon hydride dissociation processes on silicon surfaces and discuss their implications for the surface chemical composition of plasma-deposited hydrogenated amorphous silicon (a-Si:H) thin films. The analysis is based on a synergistic combination of first-principles density functional theory (DFT) calculations of hydride dissociation on the hydrogen-terminated Si(001)-(2×1) surface and molecular-dynamics (MD) simulations of adsorbed SiH3 radical precursor dissociation on surfaces of MD-grown a-Si :H films. Our DFT calculations reveal that, in the presence of fivefold coordinated surface Si atoms, surface trihydride species dissociate sequentially to form surface dihydrides and surface monohydrides via thermally activated pathways with reaction barriers of 0.40-0.55eV. The presence of dangling bonds (DBs) results in lowering the activation barrier for hydride dissociation to 0.15-0.20eV, but such DB-mediated reactions are infrequent. Our MD simulations on a-Si :H film growth surfaces indicate that surface hydride dissociation reactions are predominantly mediated by fivefold coordinated surface Si atoms, with resulting activation barriers of 0.35-0.50eV. The results are consistent with experimental measurements of a-Si :H film surface composition using in situ attenuated total reflection Fourier transform infrared spectroscopy, which indicate that the a-Si :H surface is predominantly covered with the higher hydrides at low temperatures, while the surface monohydride, SiH(s ), becomes increasingly more dominant as the temperature is increased.

Influence of surface properties on the mechanism of H2S removal by alkaline activated carbons.

PubMed

Yan, Rong; Chin, Terence; Ng, Yuen Ling; Duan, Huiqi; Liang, David Tee; Tay, Joo Hwa

2004-01-01

Alkaline activated carbons are widely used as adsorbents of hydrogen sulfide (H2S), one of the major odorous compounds arising from sewage treatment facilities. Although a number of studies have explored the effects of various parameters, mechanisms of H2S adsorption by alkaline carbons are not yet fully understood. The major difficulty seems to lie in the fact that little is known with certainty about the predominant reactions occurring on the carbon surface. In this study, the surface properties of alkaline activated carbons were systematically investigated to further exploit and better understand the mechanisms of H2S adsorption by alkaline activated carbons. Two commercially available alkaline activated carbons and their representative exhausted samples (8 samples collected at different height of the column after H2S breakthrough tests) were studied. The 8 portions of the exhausted carbon were used to represent the H2S/carbon reaction process. The surface properties of both the original and the exhausted carbons were characterized using the sorption of nitrogen (BET test), surface pH, Boehm titration, thermal and FTIR analysis. Porosity and surface area provide detailed information about the pore structure of the exhausted carbons with respect to the reaction extent facilitating the understanding of potential pore blockages. Results of Boehm titration and FTIR both demonstrate the significant effects of surface functional groups, and identification of oxidation products confirmed the different mechanisms involved with the two carbons. From the DTG curves of thermal analysis, two well-defined peaks representing two products of surface reactions (i.e., sulfur and sulfuric acid) were observed from the 8 exhausted portions with gradually changing patterns coinciding with the extent of the reaction. Surface pH values of the exhausted carbons show a clear trend of pH drop along the reaction extent, while pH around 2 was observed for the bottom of the bed indicating sulfuric acid as the predominant products. Although both carbons are coal-based and of KOH impregnated type, performances of different carbons differ significantly. A correlation is well established to link the reaction extent with various surface properties. In summary, not only the homogeneous alkali impregnation and physical porosity but also the carbon surface chemistry are significant factors influencing the performances of alkaline activated carbons as H2S adsorbents.

Simulations of the thermodynamics and kinetics of NH3 at the RuO2 (110) surface

NASA Astrophysics Data System (ADS)

Erdtman, Edvin; Andersson, Mike; Lloyd Spetz, Anita; Ojamäe, Lars

2017-02-01

Ruthenium(IV)oxide (RuO2) is a material used for various purposes. It acts as a catalytic agent in several reactions, for example oxidation of carbon monoxide. Furthermore, it is used as gate material in gas sensors. In this work theoretical and computational studies were made on adsorbed molecules on RuO2 (110) surface, in order to follow the chemistry on the molecular level. Density functional theory calculations of the reactions on the surface have been performed. The calculated reaction and activation energies have been used as input for thermodynamic and kinetics calculations. A surface phase diagram was calculated, presenting the equilibrium composition of the surface at different temperature and gas compositions. The kinetics results are in line with the experimental studies of gas sensors, where water has been produced on the surface, and hydrogen is found at the surface which is responsible for the sensor response.

Surface- and Tip-Enhanced Raman Spectroscopy in Catalysis

PubMed Central

2016-01-01

Surface- and tip-enhanced Raman spectroscopy (SERS and TERS) techniques exhibit highly localized chemical sensitivity, making them ideal for studying chemical reactions, including processes at catalytic surfaces. Catalyst structures, adsorbates, and reaction intermediates can be observed in low quantities at hot spots where electromagnetic fields are the strongest, providing ample opportunities to elucidate reaction mechanisms. Moreover, under ideal measurement conditions, it can even be used to trigger chemical reactions. However, factors such as substrate instability and insufficient signal enhancement still limit the applicability of SERS and TERS in the field of catalysis. By the use of sophisticated colloidal synthesis methods and advanced techniques, such as shell-isolated nanoparticle-enhanced Raman spectroscopy, these challenges could be overcome. PMID:27075515

Comparative investigation of two methods for Acetylcholinesterase enzyme immobilization on modified porous silicon

NASA Astrophysics Data System (ADS)

Khaldi, Khadidja; Sam, Sabrina; Lounas, Amel; Yaddaden, Chafiaa; Gabouze, Noure-Eddine

2017-11-01

In this work, Acetylcholinesterase enzyme (AChE) was immobilized on porous silicon (PSi) surface using two strategies. In the first method, acid chains were covalently grafted on the hydrogenated PSi by hydrosilylation reaction. The obtained acid-terminated surface was activated by a reaction with N-hydroxysuccinimide (NHS) in the presence of a peptide-coupling agent N-ethyl-N‧-(3-dimethylaminopropyl)-carbodiimide (EDC), and then reacted with the amino linker of the lysine residues AChE to anchor the enzyme by a covalent amide bond. In the second procedure, the PSi surface was first hydroxylated in piranha solution, followed by a silanization reaction with 3-aminopropyltriethoxysilane (APTES) to form amine-terminated surface. Finally, AChE was attached to the terminal amine groups by an aminolysis reaction with carboxylic acid groups of AChE in the presence of NHS/EDC mixture. Fourier transform infrared spectroscopy (FTIR) confirmed the efficiency of the surface modifications. The enzymatic activity of immobilized AChE was determined by means of a colorimetric test and was discussed according to the enzyme orientation on the surface which was revealed by contact angle measurements.

Rapid Covalent Modification of Silicon Oxide Surfaces through Microwave-Assisted Reactions with Alcohols.

PubMed

Lee, Austin W H; Gates, Byron D

2016-07-26

We demonstrate the method of a rapid covalent modification of silicon oxide surfaces with alcohol-containing compounds with assistance by microwave reactions. Alcohol-containing compounds are prevalent reagents in the laboratory, which are also relatively easy to handle because of their stability against exposure to atmospheric moisture. The condensation of these alcohols with the surfaces of silicon oxides is often hindered by slow reaction kinetics. Microwave radiation effectively accelerates this condensation reaction by heating the substrates and/or solvents. A variety of substrates were modified in this demonstration, such as silicon oxide films of various thicknesses, glass substrates such as microscope slides (soda lime), and quartz. The monolayers prepared through this strategy demonstrated the successful formation of covalent surface modifications of silicon oxides with water contact angles of up to 110° and typical hysteresis values of 2° or less. An evaluation of the hydrolytic stability of these monolayers demonstrated their excellent stability under acidic conditions. The techniques introduced in this article were successfully applied to tune the surface chemistry of silicon oxides to achieve hydrophobic, oleophobic, and/or charged surfaces.

Novel pathways for elimination of chlorine atoms from growing Si(100) surfaces in CVD reactors

NASA Astrophysics Data System (ADS)

Kunioshi, Nílson; Hagino, Sho; Fuwa, Akio; Yamaguchi, Katsunori

2018-05-01

Reactions leading to elimination of chlorine atoms from growing Si(100) surfaces were simulated using clusters of silicon atoms of different sizes and shapes, and at the UB3LYP/6-31 g(d,p) level of theory. The reactions of type SiCl2(s) + 2 H2(g), where (s) indicates an adsorbed species at the surface and (g) a gas-phase species, were found to proceed in two steps: SiCl2(s) + H2(g) → SiHCl(s) + HCl(g) and SiHCl(s) + H2(g) → SiH2(s) + HCl(g), each having activation energies around 55 kcal/mol, a value which is comparable to experimental values published in the literature. In addition, the results suggested that H-passivation of Si(100) surfaces support reactions leading to canonical epitaxial growth, providing a plausible explanation for the convenience of passivating the surfaces prior to silicon deposition. The reactions analyzed here can therefore be seen as important steps in the mechanism of epitaxial growth of Si(100) surfaces.

Boundary Control of Linear Uncertain 1-D Parabolic PDE Using Approximate Dynamic Programming.

PubMed

Talaei, Behzad; Jagannathan, Sarangapani; Singler, John

2018-04-01

This paper develops a near optimal boundary control method for distributed parameter systems governed by uncertain linear 1-D parabolic partial differential equations (PDE) by using approximate dynamic programming. A quadratic surface integral is proposed to express the optimal cost functional for the infinite-dimensional state space. Accordingly, the Hamilton-Jacobi-Bellman (HJB) equation is formulated in the infinite-dimensional domain without using any model reduction. Subsequently, a neural network identifier is developed to estimate the unknown spatially varying coefficient in PDE dynamics. Novel tuning law is proposed to guarantee the boundedness of identifier approximation error in the PDE domain. A radial basis network (RBN) is subsequently proposed to generate an approximate solution for the optimal surface kernel function online. The tuning law for near optimal RBN weights is created, such that the HJB equation error is minimized while the dynamics are identified and closed-loop system remains stable. Ultimate boundedness (UB) of the closed-loop system is verified by using the Lyapunov theory. The performance of the proposed controller is successfully confirmed by simulation on an unstable diffusion-reaction process.

Dissociation mechanisms of HFO-1336mzz(Z) on Cu(1 1 1), Cu(1 1 0) and Cu(1 0 0) surfaces: A density functional theory study

NASA Astrophysics Data System (ADS)

Huo, Erguang; Liu, Chao; Xu, Xiaoxiao; Li, Qibin; Dang, Chaobin

2018-06-01

The catalytic effect of Cu(1 1 1), Cu(1 1 0) and Cu(1 0 0) surfaces on the decomposition of HFO-1336mzz(Z) have been investigated by using Density Functional Theory (DFT) calculations. On the basis of adsorption energy analysis, the most stable adsorption energies of HFO-1336mzz(Z) and relevant products on Cu(1 1 1), Cu(1 1 0) and Cu(1 0 0) surfaces were studied, respectively, and the co-adsorption structures of relevant species were obtained. Finally, four initiation decomposition reactions of HFO-1336mzz(Z) on Cu(1 1 1), Cu(1 1 0) and Cu(1 0 0) surfaces were proposed and investigated, respectively. At the same time, the four similar homolytic reactions of free HFO-1336mzz(Z) molecular were calculated to compare with the dissociation reactions occurred on Cu(1 1 1), Cu(1 1 0) and Cu(1 0 0) surfaces and illuminate the catalytic effect of Cu(1 1 1), Cu(1 1 0) and Cu(1 0 0) surfaces on the HFO-1336mzz(Z) decomposition. The results indicated that Cu(1 1 1), Cu(1 1 0) and Cu(1 0 0) surfaces had a good catalytic effect on the decomposition of HFO-1336mzz(Z). The fracture reactions of Cdbnd C bonds on Cu(1 1 1), Cu(1 1 0) and Cu(1 0 0) surfaces were easier to occur than that of other reactions. Cu(1 0 0) surface had the highest catalytic activity and the lowest for Cu(1 1 1) surface.

From petal effect to lotus effect: a facile solution immersion process for the fabrication of super-hydrophobic surfaces with controlled adhesion.

PubMed

Cheng, Zhongjun; Du, Ming; Lai, Hua; Zhang, Naiqing; Sun, Kening

2013-04-07

In this paper, a convenient approach based on the reaction between an alkyl thiol and hierarchical structured Cu(OH)2 substrates is reported for the fabrication of super-hydrophobic surfaces with controlled adhesion. This reaction can etch the Cu(OH)2 microstructures and simultaneously introduce a coating with low surface energy. By simply controlling the reaction time or the chain length of the thiol, super-hydrophobic surfaces with controlled adhesion can be achieved, and the adhesive force between the surface and the water droplet can be adjusted from extreme low (∼14 μN) to very high (∼65 μN). The tunable effect of the adhesion is ascribed to the different wetting states for the droplet on the surface that results from the change of the morphology and microstructure scale after the thiolate reaction. Noticeably, the as-prepared surfaces are acid/alkali-resisting; the acidic and basic water droplets have similar contact angles and adhesive forces to that of the neutral water droplet. Moreover, we demonstrate a proof of water droplet transportation for application in droplet-based microreactors via our surfaces. We believe that the results reported here would be helpful for the further understanding of the effect of wetting states on the surface adhesion and the fabrication principle for a super-hydrophobic surface with controlled adhesion.

Allylic ionic liquid electrolyte-assisted electrochemical surface passivation of LiCoO2 for advanced, safe lithium-ion batteries.

PubMed

Mun, Junyoung; Yim, Taeeun; Park, Jang Hoon; Ryu, Ji Heon; Lee, Sang Young; Kim, Young Gyu; Oh, Seung M

2014-08-29

Room-temperature ionic liquid (RTIL) electrolytes have attracted much attention for use in advanced, safe lithium-ion batteries (LIB) owing to their nonvolatility, high conductivity, and great thermal stability. However, LIBs containing RTIL-electrolytes exhibit poor cyclability because electrochemical side reactions cause problematic surface failures of the cathode. Here, we demonstrate that a thin, homogeneous surface film, which is electrochemically generated on LiCoO2 from an RTIL-electrolyte containing an unsaturated substituent on the cation (1-allyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide, AMPip-TFSI), can avert undesired side reactions. The derived surface film comprised of a high amount of organic species from the RTIL cations homogenously covered LiCoO2 with a <25 nm layer and helped suppress unfavorable thermal reactions as well as electrochemical side reactions. The superior performance of the cell containing the AMPip-TFSI electrolyte was further elucidated by surface, electrochemical, and thermal analyses.

Allylic ionic liquid electrolyte-assisted electrochemical surface passivation of LiCoO2 for advanced, safe lithium-ion batteries

NASA Astrophysics Data System (ADS)

Mun, Junyoung; Yim, Taeeun; Park, Jang Hoon; Ryu, Ji Heon; Lee, Sang Young; Kim, Young Gyu; Oh, Seung M.

2014-08-01

Room-temperature ionic liquid (RTIL) electrolytes have attracted much attention for use in advanced, safe lithium-ion batteries (LIB) owing to their nonvolatility, high conductivity, and great thermal stability. However, LIBs containing RTIL-electrolytes exhibit poor cyclability because electrochemical side reactions cause problematic surface failures of the cathode. Here, we demonstrate that a thin, homogeneous surface film, which is electrochemically generated on LiCoO2 from an RTIL-electrolyte containing an unsaturated substituent on the cation (1-allyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide, AMPip-TFSI), can avert undesired side reactions. The derived surface film comprised of a high amount of organic species from the RTIL cations homogenously covered LiCoO2 with a <25 nm layer and helped suppress unfavorable thermal reactions as well as electrochemical side reactions. The superior performance of the cell containing the AMPip-TFSI electrolyte was further elucidated by surface, electrochemical, and thermal analyses.

Effect of atmospheric oxidative plasma treatments on polypropylenic fibers surface: Characterization and reaction mechanisms

NASA Astrophysics Data System (ADS)

Nisticò, Roberto; Magnacca, Giuliana; Faga, Maria Giulia; Gautier, Giovanna; D'Angelo, Domenico; Ciancio, Emanuele; Lamberti, Roberta; Martorana, Selanna

2013-08-01

Atmospheric pressure plasma-dielectric barrier discharge (APP-DBD, open chamber configuration) was used to functionalize polypropylene (PP) fibers surface in order to generate oxidized-reactive groups such as hydroperoxides, alcohols and carbonyl species (i.e. ketones and others). Such a species increased the surface polarity, without causing material degradation. Three different types of plasma mixture (He, He/O2, He/O2/H2O) under three different values of applied power (750, 1050, 1400 W) were investigated. The formed plasma species (O2+, O single atom and OH radical) and their distribution were monitored via optical emission spectrometry (OES) measurements, and the plasma effects on PP surface species formation were followed by X-ray photoemission spectroscopy (XPS). Results allowed to better understand the reaction pathways between plasma phase and PP fibers. In fact, two reaction mechanisms were proposed, the first one concerning the plasma phase reactions and the second one involving material surface modifications.

Allylic ionic liquid electrolyte-assisted electrochemical surface passivation of LiCoO2 for advanced, safe lithium-ion batteries

PubMed Central

Mun, Junyoung; Yim, Taeeun; Park, Jang Hoon; Ryu, Ji Heon; Lee, Sang Young; Kim, Young Gyu; Oh, Seung M.

2014-01-01

Room-temperature ionic liquid (RTIL) electrolytes have attracted much attention for use in advanced, safe lithium-ion batteries (LIB) owing to their nonvolatility, high conductivity, and great thermal stability. However, LIBs containing RTIL-electrolytes exhibit poor cyclability because electrochemical side reactions cause problematic surface failures of the cathode. Here, we demonstrate that a thin, homogeneous surface film, which is electrochemically generated on LiCoO2 from an RTIL-electrolyte containing an unsaturated substituent on the cation (1-allyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide, AMPip-TFSI), can avert undesired side reactions. The derived surface film comprised of a high amount of organic species from the RTIL cations homogenously covered LiCoO2 with a <25 nm layer and helped suppress unfavorable thermal reactions as well as electrochemical side reactions. The superior performance of the cell containing the AMPip-TFSI electrolyte was further elucidated by surface, electrochemical, and thermal analyses. PMID:25168309

Laboratory Studies of Atmospheric Heterogeneous Chemistry

NASA Technical Reports Server (NTRS)

Keyser, L. F.; Leu, M-T.

1993-01-01

In the laboratory, ice films formed by freezing from the liquid or more frequently by deposition from the vapor phase have been used to simulate stratospheric cloud surfaces for measurements of reaction and uptake rates. To obtain intrinsic surface reaction probabilities that can be used in atmospheric models, the area of the film surface that actually takes part in the reaction must be known. It is important to know not only the total surface area but also the film morphology in order to determine where and how the surface is situated and, thus, what fraction of it is available for reaction. Information on the structure of these ice films has been obtained by using several experimental methods. In the sections that follow, these methods will be discussed, then the results will be used to construct a working model of the ice films, and finally the model will be applied to an experimental study of HC1 uptake by H_2O ice.

Rapid pathogen detection with bacterial-assembled magnetic mesoporous silica.

PubMed

Lee, Soo Youn; Lee, Jiho; Lee, Hye Sun; Chang, Jeong Ho

2014-03-15

We report rapid and accurate pathogen detection by coupling with high efficiency magnetic separation of pathogen by Ni(2+)-heterogeneous magnetic mesoporous silica (Ni-HMMS) and real time-polymerase chain reaction (RT-PCR) technique. Ni-HMMS was developed with a significant incorporation of Fe particles within the silica mesopores by programmed thermal hydrogen reaction and functionalized with Ni(2+) ion on the surface by the wet impregnation process. High abundant Ni(2+) ions on the Ni-HMMS surface were able to assemble with cell wall component protein NikA (nickel-binding membrane protein), which contains several pathogenic bacteria including Escherichia coli O157:H7. NikA protein expression experiment showed the outstanding separation rate of the nikA gene-overexpressed E. coli (pSY-Nik) when comparing with wild-type E. coli (44.5 ± 13%) or not over-expressed E. coli (pSY-Nik) (53.2 ± 2.7%). Moreover, Ni-HMMS showed lower obstacle effect by large reaction volume (10 mL) than spherical core/shell-type silica magnetic nanoparticles functionalized with Ni(2+) (ca. 40 nm-diameters). Finally, the Ni-HMMS was successfully assessed to separate pathogenic E. coli O157:H7 and applied to direct and rapid RT-PCR to quantitative detection at ultralow concentration (1 Log10 cfu mL(-1)) in the real samples (milk and Staphylococcus aureus culture broth) without bacterial amplification and DNA extraction step. © 2013 Elsevier B.V. All rights reserved.

kmos: A lattice kinetic Monte Carlo framework

NASA Astrophysics Data System (ADS)

Hoffmann, Max J.; Matera, Sebastian; Reuter, Karsten

2014-07-01

Kinetic Monte Carlo (kMC) simulations have emerged as a key tool for microkinetic modeling in heterogeneous catalysis and other materials applications. Systems, where site-specificity of all elementary reactions allows a mapping onto a lattice of discrete active sites, can be addressed within the particularly efficient lattice kMC approach. To this end we describe the versatile kmos software package, which offers a most user-friendly implementation, execution, and evaluation of lattice kMC models of arbitrary complexity in one- to three-dimensional lattice systems, involving multiple active sites in periodic or aperiodic arrangements, as well as site-resolved pairwise and higher-order lateral interactions. Conceptually, kmos achieves a maximum runtime performance which is essentially independent of lattice size by generating code for the efficiency-determining local update of available events that is optimized for a defined kMC model. For this model definition and the control of all runtime and evaluation aspects kmos offers a high-level application programming interface. Usage proceeds interactively, via scripts, or a graphical user interface, which visualizes the model geometry, the lattice occupations and rates of selected elementary reactions, while allowing on-the-fly changes of simulation parameters. We demonstrate the performance and scaling of kmos with the application to kMC models for surface catalytic processes, where for given operation conditions (temperature and partial pressures of all reactants) central simulation outcomes are catalytic activity and selectivities, surface composition, and mechanistic insight into the occurrence of individual elementary processes in the reaction network.

Core-level photoemission investigation of atomic-fluorine adsorption on GaAs(110)

NASA Astrophysics Data System (ADS)

McLean, A. B.; Terminello, L. J.; McFeely, F. R.

1989-12-01

The adsorption of atomic F on the cleaved GaAs(110) surface has been studied with use of high-resolution core-level photoelectron spectroscopy by exposing the GaAs(110) surfaces to XeF2, which adsorbs dissociatively, leaving atomic F behind. This surface reaction produces two chemically shifted components in the Ga 3d core-level emission which are attributed to an interfacial monofluoride and a stable trifluoride reaction product, respectively. The As 3d core level develops only one chemically shifted component and from its exposure-dependent behavior it is attributed to an interfacial monofluoride. Least-squares analysis of the core-level line shapes revealed that (i) the F bonds to both the anion and the cation , (ii) the GaF3 component (characteristic of strong interfacial reaction) and the surface core-level shifted component (characteristic of a well ordered, atomically clean surface) are present together over a relatively large range of XeF2 exposures, and (iii) it is the initial disruption of the GaAs(110) surface that is the rate-limiting step in this surface reaction. These results are compared with similar studies of Cl and O adsorption on GaAs(110).

Surface characterization studies of walnut-shell biochar catalysts for simultaneously removing of organic sulfur from yellow phosphorus tail gas

NASA Astrophysics Data System (ADS)

Song, Xin; Li, Kai; Ning, Ping; Wang, Chi; Sun, Xin; Tang, Lihong; Ruan, Haotian; Han, Shuang

2017-12-01

The influences of different preparation conditions for surface characteristics on removing organic sulfur were studied. From BET, XRD, FTIR, DRIFTS, TG/DTA, CO2-TPD results, it can be seen that these preparation conditions had great influences on the pore structure, specific surface area, crystal structure and surface functional groups. The micropore volume, amorphous structure and alkalinity site strength played major roles in desulfurization process. H2S was oxidized by oxygen containing functional groups, such as sbnd COO, sbnd Cdbnd O. H2O molecule could be converted into some groups, such as sbnd CH and Csbnd OH groups, and promoted the hydrolysis reaction. The strong alkalinity site was the key factor for chemical adsorption and hydrolysis. H2O molecule, sbnd CH, Csbnd OH groups promoted the hydrolysis reaction and sbnd COO, sbnd Cdbnd O groups promoted the oxidation of H2S on the surface of WSB. Meanwhile, the main desulfurization process over WSB after carbonization was adsorption and it changed to hydrolysis reaction after activation on the surface of WSB. Furthermore, the reaction mechanism was investigated by DRIFTS measurement according to the change of surface functional groups.

Dimensional accuracy and surface property of titanium casting using gypsum-bonded alumina investment.

PubMed

Yan, Min; Takahashi, Hidekazu; Nishimura, Fumio

2004-12-01

The aim of the present study was to evaluate the dimensional accuracy and surface property of titanium casting obtained using a gypsum-bonded alumina investment. The experimental gypsum-bonded alumina investment with 20 mass% gypsum content mixed with 2 mass% potassium sulfate was used for five cp titanium castings and three Cu-Zn alloy castings. The accuracy, surface roughness (Ra), and reaction layer thickness of these castings were investigated. The accuracy of the castings obtained from the experimental investment ranged from -0.04 to 0.23%, while surface roughness (Ra) ranged from 7.6 to 10.3microm. A reaction layer of about 150 microm thickness under the titanium casting surface was observed. These results suggested that the titanium casting obtained using the experimental investment was acceptable. Although the reaction layer was thin, surface roughness should be improved.

Using the Training Reactions Questionnaire to Analyze the Reactions of University Students Undergoing Career-Related Training in Jordan: A Prospective Human Resource Development Approach

ERIC Educational Resources Information Center

Khasawneh, Samer; Al-Zawahreh, Abdelghafour

2015-01-01

The primary purpose of the present study was to validate Morgan and Casper's training reactions questionnaire (TRQ) for use in Jordan. The study also investigated the reactions of university students to career-related training programs. Another purpose of the study was to determine the impact of certain aspects of training programs on the overall…

Metal Catalyzed Fusion: Nuclear Active Environment vs. Process

NASA Astrophysics Data System (ADS)

Chubb, Talbot

2009-03-01

To achieve radiationless dd fusion and/or other LENR reactions via chemistry: some focus on environment of interior or altered near-surface volume of bulk metal; some on environment inside metal nanocrystals or on their surface; some on the interface between nanometal crystals and ionic crystals; some on a momentum shock-stimulation reaction process. Experiment says there is also a spontaneous reaction process.

Oil-encapsulated nanodroplet array for bio-molecular detection.

PubMed

Qiao, Wen; Zhang, Tiantian; Yen, Tony; Ku, Ti-Hsuan; Song, Junlan; Lian, Ian; Lo, Yu-Hwa

2014-09-01

Detection of low abundance biomolecules is challenging for biosensors that rely on surface chemical reactions. For surface reaction based biosensors, it require to take hours or even days for biomolecules of diffusivities in the order of 10(-10-11) m2/s to reach the surface of the sensors by Brownian motion. In addition, often times the repelling Coulomb interactions between the molecules and the probes further defer the binding process, leading to undesirably long detection time for applications such as point-of-care in vitro diagnosis. In this work, we designed an oil encapsulated nanodroplet array microchip utilizing evaporation for pre-concentration of the targets to greatly shorten the reaction time and enhance the detection sensitivity. The evaporation process of the droplets is facilitated by the superhydrophilic surface and resulting nanodroplets are encapsulated by oil drops to form stable reaction chamber. Using this method, desirable droplet volumes, concentrations of target molecules, and reaction conditions (salt concentrations, reaction temperature, etc.) in favour of fast and sensitive detection are obtained. A linear response over 2 orders of magnitude in target concentration was achieved at 10 fM for protein targets and 100 fM for miRNA mimic oligonucleotides.

Understanding Methanol Coupling on SrTiO 3 from First Principles

DOE PAGES

Huang, Runhong; Fung, Victor; Zhang, Yafen; ...

2018-03-19

Perovskites are interesting materials for catalysis due to their great tunability. However, the correlation of many reaction processes to the termination of a perovskite surface is still unclear. In this paper, we use the methanol coupling reaction on the SrTiO 3(100) surface as a probe reaction to investigate direct C–C coupling from a computational perspective. We use density functional theory to assess methanol adsorption, C–H activation, and direct C–C coupling reactions on the SrTiO 3(100) surface of different terminations. We find that, although methanol molecules dissociatively adsorb on both A and B terminations with similar strength, the dehydrogenation and C–Cmore » coupling reactions have significantly lower activation energies on the B termination than on the A termination. The predicted formation of methoxy and acetate on the SrTiO 3(100) B termination can well explain the ambient-pressure XPS data of methanol on the single-crystal SrTiO 3(100) surface at 250 °C. Finally, this work suggests that a choice of B termination of perovskites would be beneficial for the C–C coupling reaction of methanol.« less

Dynamical resonances in the fluorine atom reaction with the hydrogen molecule.

PubMed

Yang, Xueming; Zhang, Dong H

2008-08-01

[Reaction: see text]. The concept of transition state has played a crucial role in the field of chemical kinetics and reaction dynamics. Resonances in the transition state region are important in many chemical reactions at reaction energies near the thresholds. Detecting and characterizing isolated reaction resonances, however, have been a major challenge in both experiment and theory. In this Account, we review the most recent developments in the study of reaction resonances in the benchmark F + H 2 --> HF + H reaction. Crossed molecular beam scattering experiments on the F + H 2 reaction have been carried out recently using the high-resolution, highly sensitive H-atom Rydberg tagging technique with HF rovibrational states almost fully resolved. Pronounced forward scattering for the HF (nu' = 2) product has been observed at the collision energy of 0.52 kcal/mol in the F + H 2 (j = 0) reaction. Quantum dynamical calculations based on two new potential energy surfaces, the Xu-Xie-Zhang (XXZ) surface and the Fu-Xu-Zhang (FXZ) surface, show that the observed forward scattering of HF (nu' = 2) in the F + H 2 reaction is caused by two Feshbach resonances (the ground resonance and first excited resonance). More interestingly, the pronounced forward scattering of HF (nu' = 2) at 0.52 kcal/mol is enhanced considerably by the constructive interference between the two resonances. In order to probe the resonance potential more accurately, the isotope substituted F + HD --> HF + D reaction has been studied using the D-atom Rydberg tagging technique. A remarkable and fast changing dynamical picture has been mapped out in the collision energy range of 0.3-1.2 kcal/mol for this reaction. Quantum dynamical calculations based on the XXZ surface suggest that the ground resonance on this potential is too high in comparison with the experimental results of the F + HD reaction. However, quantum scattering calculations on the FXZ surface can reproduce nearly quantitatively the resonance picture of the F + HD reaction observed in the experiment. It is clear that the dynamics of the F + HD reaction below the threshold was dominated by the ground resonance state. Furthermore, the forward scattering HF (nu' = 3) channel from the F + H 2 ( j = 0) reaction was investigated and was attributed mainly to a slow-down mechanism over the centrifugal exit barrier, with small contributions from a shape resonance mechanism in a narrow collision energy range. A striking effect of the reagent rotational excitation on resonance was also observed in F + H 2 ( j = 1), in comparison with F + H 2 ( j = 0). From these concerted experimental and theoretical studies, a clear physical picture of the reaction resonances in this benchmark reaction has emerged, providing a textbook example of dynamical resonances in elementary chemical reactions.

Bifurcations on Potential Energy Surfaces of Organic Reactions

PubMed Central

Ess, Daniel H.; Wheeler, Steven E.; Iafe, Robert G.; Xu, Lai; Çelebi-Ölçüm, Nihan; Houk, K. N.

2009-01-01

A single transition state may lead to multiple intermediates or products if there is a post-transition state reaction path bifurcation. These bifurcations arise when there are sequential transition states with no intervening energy minimum. For such systems, the shape of the potential energy surface and dynamic effects control selectivity rather than transition state energetics. This minireview covers recent investigations of organic reactions exhibiting reaction pathway bifurcations. Such phenomena are surprisingly general and affect experimental observables such as kinetic isotope effects and product distributions. PMID:18767086

The spectroscopic chemical and photophysical properties of Martian soils and their analogs

NASA Technical Reports Server (NTRS)

Coyne, Lelia M.

1987-01-01

The program of research outlined should advance significantly the understanding of the spectral signal of montmorillonites in general and the variations produced in it by structural and surface ferric and ferrous iron and interlayer water as a function of several environmental conditions that are different between Earth and Mars. In addition, an extensive data base was collected providing spectral characterization of several features (iron, both surface and structural, OH-groups, both structural and from adsorbed water and O(-) centers) that are known, or thought to be, influential in directing the surface activity of these important materials. With this data base with which to assess the results of the Viking labeled release simulation studies, it should be possible to gain important insights into the mechanisms of surface reactivity for this important chemical reaction. The results to be gained from these studies will provide a significant body of ground base truth from which to assess: the presence of smectite clays on Mars; the mineralogical form in which the Martian iron is bound; establish upper limits on the present surface water content of Martian soils; perhaps provide insights on the Martian surface radiation history; and to make strong predictions about the nature of surface chemistry on Mars, if iron-bearing clays are a significant component of the surface mineralogical assemblage.

Chemical reactions in low-g

NASA Technical Reports Server (NTRS)

Grodzka, P. G.; Facemire, B. R.

1978-01-01

The Apollo-Soyuz flight experiment, 'Chemical Foams' demonstrated that foams and air/liquid dispersions are much more stable in low-gravity than on the ground. It thus should be possible to conduct unique chemical reactions in space foams. The low-g results and subsequent ground work on the formaldehyde clock reaction indicate that the reaction is strongly influenced by (1) dissociated and undissociated solution species being adsorbed at solid/liquid and gas/liquid surfaces and (2) chemical reaction rates apparently being affected by long-range forces determined by the liquid mass and the extent and nature of all surface interfaces.

Ab initio study of C + H3+ reactions

NASA Technical Reports Server (NTRS)

Talbi, D.; DeFrees, D. J.

1991-01-01

The reaction C + H3+ --> CH(+) + H2 is frequently used in models of dense interstellar cloud chemistry with the assumption that it is fast, i.e. there are no potential energy barriers inhibiting it. Ab initio molecular orbital study of the triplet CH3+ potential energy surface (triplet because the reactant carbon atom is a ground state triplet) supports this hypothesis. The reaction product is 3 pi CH+; the reaction is to exothermic even though the product is not in its electronic ground state. No path has been found on the potential energy surface for C + H3+ --> CH2(+) + H reaction.

Experimental Studies of Hydrogenation and Other Reactions on Surfaces Under Astrophysically Relevant Conditions

NASA Technical Reports Server (NTRS)

Vidali, Gianfranco

1998-01-01

The goal of our project is to study hydrogen recombination reactions on solid surfaces under conditions that are relevant in astrophysics. Laboratory experiments were conducted using low-flux, cold atomic H and D beams impinging on a sample kept under ultra high vacuum conditions. Realistic analogues of interstellar dust grains were used. Our results show that current models for hydrogen recombination reactions have to be modified to take into account the role of activated diffusion of H on surfaces even at low temperature.

Toward a Role of Light Absorption in Initiation Chemistry of Shocked HMX single Crystals and Crystalline High Explosives

NASA Astrophysics Data System (ADS)

Plaksin, Igor; Rodrigues, L.

2013-06-01

Question which mechanism is driving radiation-induced reactions, thermal or athermal becomes a subject of conflicting discussions. Major challenge of this work is to identify at micro- (sub-granular), meso- (grain level) and macro-scale roles of these two mechanisms in triggering initiation chemistry in HMX-based HEs. Four acceptor-patterns were tested at 20 GPa input pressure: single HMX crystal-in-water, HMX/water-slurry, PBX(HMX/HTPB) & inert PBX-simulant (HMX-particles replaced by crystalline sucrose). Scenario of reaction onset-localizations-dissipation was spatially resolved using Multi-Channel Optical Analyzer MCOA-UC (96 channels, 100um-spatial accuracy, 0.2ns-timeresolution, 450-850 nm-spectral range) through real-time panoramic recording emitted reaction light and shock field in standard optic monitor. Experiments reveal a dual nature of initiation chemistry: athermal and thermal. Single-crystal tests disclose origination of photo-induced reactions downstream of emitting reaction spot due to intensified radiation absorption in surface micro-defects. Polycrystalline samples reveal cyclic reproducibility of radiation-induced thermal precursors in which radiation absorption causes thermal expansion/phase-changes of HMX-grains resulting in oscillating detonation. Work was supported by the Office of Naval Research under the ONR and ONR Global Grants N00014-12-1-0477 and N62909-12-1-7131 with Drs. Cliff Bedford and Shawn Thorne Program Managers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franke, J.-H.; Kosov, D. S.

We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321){sup S}. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with amore » functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.« less

Role of graphene on the surface chemical reactions of BiPO4-rGO with low OH-related defects.

PubMed

Gao, Erping; Wang, Wenzhong

2013-11-21

Graphene has been widely introduced into photocatalysis to enhance photocatalytic performance due to its unique physical and chemical properties. However, the effect of graphene on the surface chemical reactions of photocatalysis has not been clearly researched, which is important for photocatalysis because photocatalytic reactions ultimately occur on the catalyst surface. Herein, a two-step solution-phase reaction has been designed to synthesize quasi-core-shell structured BiPO4-rGO cuboids and the role of graphene on the surface chemical reactions was investigated in detail. It was found that the introduced graphene modified the process and the mechanism of the surface chemical reactions. The change mainly originates from the interaction between graphene and the adsorbed O2 molecule. Due to the electron transfer from graphene to adsorbed O2, graphene could tune the interfacial charge transport and efficiently activate molecular oxygen to form O2˙(-) anions as the major oxidation species instead of ˙OH. In addition, the two-step synthesis approach could efficiently suppress the formation of OH-related defects in the lattice. As a result, the BiPO4-rGO composite exhibited superior photocatalytic activity to BiPO4 and P25, about 4.3 times that of BiPO4 and 6.9 times that of P25.

Numerical simulation of hydrogen-air reacting flows in rectangular channels with catalytic surface reactions

NASA Astrophysics Data System (ADS)

Amano, Ryoichi S.; Abou-Ellail, Mohsen M.; Elhaw, Samer; Saeed Ibrahim, Mohamed

2013-09-01

In this work a prediction was numerically modeled for a catalytically stabilized thermal combustion of a lean homogeneous mixture of air and hydrogen. The mixture flows in a narrow rectangular channel lined with a thin coating of platinum catalyst. The solution using an in-house code is based on the steady state partial differential continuity, momentum and energy conservation equations for the mixture and species involved in the reactions. A marching technique is used along the streamwise direction to solve the 2-D plane-symmetric laminar flow of the gas. Two chemical kinetic reaction mechanisms were included; one for the gas phase reactions consisting of 17 elementary reactions; of which 7 are forward-backward reactions while the other mechanism is for the surface reactions—which are the prime mover of the combustion under a lean mixture condition—consisting of 16 elementary reactions. The results were compared with a former congruent experimental work where temperature was measured using thermocouples, while using PLIF laser for measuring water and hydrogen mole fractions. The comparison showed good agreement. More results for the velocities, mole fractions of other species were carried out across the transverse and along the streamwise directions providing a complete picture of overall mechanism—gas and surface—and on the production, consumptions and travel of the different species. The variations of the average OH mole fraction with the streamwise direction showed a sudden increase in the region where the ignition occurred. Also the rate of reactions of the entire surface species were calculated along the streamwise direction and a surface water production flux equation was derived by calculating the law of mass action's constants from the concentrations of hydrogen, oxygen and the rate of formation of water near the surface.

Skating on thin ice: surface chemistry under interstellar conditions

NASA Astrophysics Data System (ADS)

Fraser, H.; van Dishoeck, E.; Tielens, X.

Solid CO2 has been observed towards both active star forming regions and quiescent clouds (Gerakines et. al. (1999)). The high abundance of CO2 in the solid phase, and its low abundance in the gas phase, support the idea that CO2 is almost exclusively formed in the solid state. Several possible formation mechanisms have been postulated (Ruffle &Herbst (2001): Charnley &Kaufman (2000)), and the detection of CO2 towards quiescent sources such as Elias 16 (Whittet et. al. (1998)) clearly suggests that CO2 can be produced in the absence of UV or electron mediated processes. The most likely route is via the surface reactions between O atoms, or OH radicals, and CO. The tools of modern surface- science offer us the potential to determine many of the physical and chemical attributes of icy interstellar grain mantles under highly controlled conditions, that closely mimic interstellar environments. The Leiden Surface Reaction Simulation Device ( urfreside) combines UHV (UltraS High Vacuum) surface science techniques with an atomic beam to study chemical reactions occurring on the SURFACE and in the BULK of interstellar ice grain mimics. By simultaneously combining two or more surface analysis techniques, the chemical kinetics, reaction mechanisms and activation energies can be determined directly. The experiment is aimed at identifying the key barrierless reactions and desorption pathways on and in H2 O and CO ices under interstellar conditions. The results from traditional HV (high vacuum) and UHV studies of the CO + O and CO + OH reactions will be presented in this paper. Charnley, S.B., & Kaufman, M.J., 2000, ApJ, 529, L111 Gerakines, P.A., 1999, ApJ, 522, 357 Ruffle, D.P., & Herbst, E., 2001, MNRAS, 324, 1054 Whittet, D.C.B., et.al., 1998, ApJ, 498, L159

The influence of Pilates exercises on body balance in the standing position of hearing impaired people.

PubMed

Walowska, Jagoda; Bolach, Bartosz; Bolach, Eugeniusz

2017-11-13

Hearing impairment may affect the body posture maintenance. The aim of the study was to evaluate the effect of modified Pilates exercise program on the body posture maintenance in hearing impaired people. Eighty students (aged 13-24) were enrolled and randomly allocated into two groups: test group (n = 41) which attended an original program based on modified Pilates exercises and control group (n = 39) which attended standard physical education classes. Stabilographic tests were conducted at baseline and after 6-week training program. Both groups showed improved control of body balance in a standing position manifested in reductions of the length of path, surface area, and speed of deflection. Modified Pilates program was significantly more effective in improving body balance control in relaxed posture and with feet together than standard physical education classes. The greater efficiency of the modified Pilates program was expressed in a significant improvement in balance control parameters, i.e., path length, surface area, and speed of deflection. The modified Pilates program was more effective in improving body balance control in the hearing impaired people than standard physical education classes. Modification of physical activity recommendations for hearing impaired students may be considered; however, further research is required. Implications for Rehabilitation Hearing impairment impacts the mental, social and, physical spheres of life as well as deteriorates equivalent reactions and the way body posture is maintained. In hearing impaired people, control of body balance and muscle coordination is often disturbed, thus more attention should be paid to exercises associated with balance which may improve the ability to learn and develop motor skills. Modified Pilates program was significantly more effective in improving body balance control than standard physical education classes in hearing impaired people.

Surface complexation modeling

USDA-ARS?s Scientific Manuscript database

Adsorption-desorption reactions are important processes that affect the transport of contaminants in the environment. Surface complexation models are chemical models that can account for the effects of variable chemical conditions, such as pH, on adsorption reactions. These models define specific ...

Carbide and carbonitride surface treatment method for refractory metals

DOEpatents

Meyer, G.A.; Schildbach, M.A.

1996-12-03

A carbide and carbonitride surface treatment method for refractory metals is provided, in steps including, heating a part formed of boron, chromium, hafnium, molybdenum, niobium, tantalum, titanium, tungsten or zirconium, or alloys thereof, in an evacuated chamber and then introducing reaction gases including nitrogen and hydrogen, either in elemental or water vapor form, which react with a source of elemental carbon to form carbon-containing gaseous reactants which then react with the metal part to form the desired surface layer. Apparatus for practicing the method is also provided, in the form of a carbide and carbonitride surface treatment system including a reaction chamber, a source of elemental carbon, a heating subassembly and a source of reaction gases. Alternative methods of providing the elemental carbon and the reaction gases are provided, as well as methods of supporting the metal part, evacuating the chamber with a vacuum subassembly and heating all of the components to the desired temperature. 5 figs.

Study of Pt-Rh/CeO2-ZrO2-MxOy (M = Y, La)/Al2O3 three-way catalysts

NASA Astrophysics Data System (ADS)

Jiaxiu, Guo; Zhonghua, Shi; Dongdong, Wu; Huaqiang, Yin; Maochu, Gong; Yaoqiang, Chen

2013-05-01

CeO2-ZrO2-MxOy (M = Y; La) mixed oxides, prepared by co-precipitation method and characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Raman spectra (RM) and oxygen pulse reaction, were comparatively investigated to elucidate the combinational effects of Y and/or La oxide promoters on the catalytic activity and anti-aging performance of monolithic cordierite honeycomb catalysts with low Pt and Rh content. The catalytic activities, water-gas shift (WGS) and steam reforming reaction (SR) were studied under a simulated gas mixture. The catalysts were also characterized by H2-temperature-programmed reduction (H2-TPR) and O2-temperature-programmed desorption (O2-TPD). The results showed that the prepared CeO2-ZrO2-MxOy oxides have a face-centered cubic fluorite structure and are nanosize. La3+ ions can significantly improve thermal stability and efficiently retard CeO2-ZrO2 crystal sintering and growth. Doped CeO2-ZrO2 with Y3+ and La3+ has 105 and 60 m2/g surface area and 460 and 390 μmol/g OSC before and after aging. The T50 of fresh Pt-Rh/CZYL/LA is 170 °C for CO, 222 °C for C3H8 and 189 °C for NO, and shift to 205, 262 and 228 °C after hydrothermal aging, which are better than those of Pt-Rh/CZY/LA or Pt-Rh/CZL/LA. WGS and SR are relate to the OSC of oxygen storage materials and absorbed oxygen species on the catalyst surface and affect the three-way catalytic activities of catalysts. The reductive property of noble metals and the dissociatively adsorbed O2 on the surface of catalysts are closely related to the catalytic activities.

The reaction mechanism with free energy barriers at constant potentials for the oxygen evolution reaction at the IrO 2 (110) surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ping, Yuan; Nielsen, Robert J.; Goddard, William A.

How to efficiently oxidize H 2O to O 2 (oxygen evolution reaction, OER) in photoelectrochemical cells (PEC) is a great challenge due to its complex charge transfer process, high overpotential, and corrosion. So far no OER mechanism has been fully explained atomistically with both thermodynamic and kinetics. IrO 2 is the only known OER catalyst with both high catalytic activity and stability in acidic conditions. This is important because PEC experiments often operate at extreme pH conditions. In this work, we performed first-principles calculations integrated with implicit solvation at constant potentials to examine the detailed atomistic reaction mechanism of OERmore » at the IrO 2 (110) surface. We determined the surface phase diagram, explored the possible reaction pathways including kinetic barriers, and computed reaction rates based on the microkinetic models. Furthermore, this allowed us to resolve several long-standing puzzles about the atomistic OER mechanism.« less

The reaction mechanism with free energy barriers at constant potentials for the oxygen evolution reaction at the IrO 2 (110) surface

DOE PAGES

Ping, Yuan; Nielsen, Robert J.; Goddard, William A.

2016-12-09

How to efficiently oxidize H 2O to O 2 (oxygen evolution reaction, OER) in photoelectrochemical cells (PEC) is a great challenge due to its complex charge transfer process, high overpotential, and corrosion. So far no OER mechanism has been fully explained atomistically with both thermodynamic and kinetics. IrO 2 is the only known OER catalyst with both high catalytic activity and stability in acidic conditions. This is important because PEC experiments often operate at extreme pH conditions. In this work, we performed first-principles calculations integrated with implicit solvation at constant potentials to examine the detailed atomistic reaction mechanism of OERmore » at the IrO 2 (110) surface. We determined the surface phase diagram, explored the possible reaction pathways including kinetic barriers, and computed reaction rates based on the microkinetic models. Furthermore, this allowed us to resolve several long-standing puzzles about the atomistic OER mechanism.« less

Low-energy electron-induced reactions in condensed matter

NASA Astrophysics Data System (ADS)

Arumainayagam, Christopher R.; Lee, Hsiao-Lu; Nelson, Rachel B.; Haines, David R.; Gunawardane, Richard P.

2010-01-01

The goal of this review is to discuss post-irradiation analysis of low-energy (≤50 eV) electron-induced processes in nanoscale thin films. Because electron-induced surface reactions in monolayer adsorbates have been extensively reviewed, we will instead focus on low-energy electron-induced reactions in multilayer adsorbates. The latter studies, involving nanoscale thin films, serve to elucidate the pivotal role that the low-energy electron-induced reactions play in high-energy radiation-induced chemical reactions in condensed matter. Although electron-stimulated desorption (ESD) experiments conducted during irradiation have yielded vital information relevant to primary or initial electron-induced processes, we wish to demonstrate in this review that analyzing the products following low-energy electron irradiation can provide new insights into radiation chemistry. This review presents studies of electron-induced reactions in nanoscale films of molecular species such as oxygen, nitrogen trifluoride, water, alkanes, alcohols, aldehydes, ketones, carboxylic acids, nitriles, halocarbons, alkane and phenyl thiols, thiophenes, ferrocene, amino acids, nucleotides, and DNA using post-irradiation techniques such as temperature-programmed desorption (TPD), reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), gel electrophoresis, and microarray fluorescence. Post-irradiation temperature-programmed desorption, in particular, has been shown to be useful in identifying labile radiolysis products as demonstrated by the first identification of methoxymethanol as a reaction product of methanol radiolysis. Results of post-irradiation studies have been used not only to identify radiolysis products, but also to determine the dynamics of electron-induced reactions. For example, studies of the radiolysis yield as a function of incident electron energy have shown that dissociative electron attachment plays an important role in the electron-induced single strand breaks in DNA leading to mutagenic damage. Studies such as these not only provide insight into the fundamentals of electron-molecule interactions in the condensed phase but also may provide information valuable to (a) furthering cost-efficient destruction of hazardous chemicals, (b) understanding the electron-induced decomposition of feed gases used in the plasma processing of semiconductor devices, (c) clarifying the role, if any, of low-energy electrons, produced by cosmic rays, contributing to the formation of the ozone hole by interacting with halocarbons and producing Cl atoms, (d) illuminating the dynamics of electron-induced oligomerization and/or polymerization, and (e) explicating the astrochemistry of icy grains.

Near-infrared continuous-wave light driving a two-photon photochromic reaction with the assistance of localized surface plasmon.

PubMed

Tsuboi, Yasuyuki; Shimizu, Ryosuke; Shoji, Tatsuya; Kitamura, Noboru

2009-09-09

We demonstrate that a photochromic reaction can be driven by irradiation from a weak, near-infrared continuous-wave (NIR-CW) laser light. A two-photon ring-opening photochromic reaction of a diarylethene (DE) derivative can be induced by irradiation with a NIR-CW laser light (lambda = 808 nm). An ultrathin polymer film doped with DE in its closed form was coated onto a gold-nanoparticle-integrated glass substrate. Upon irradiation of the sample with a CW laser at low fluence (0.1-4.0 W/cm(2)), we could clearly observe bleaching of the DE (ring-opening reaction). Following the IR irradiation, the bleached absorption could be reversibly recovered by applying UV irradiation (ring-closing reaction). We verified that the yield of the photochromic ring-opening reaction of the DE was proportional to the square of the irradiation fluence. The origin of this NIR-CW-induced two-photon photochromic reaction is an "enhancing effect" that acts on the electromagnetic field (localized surface plasmon) of the gold nanoparticles. The DE interacts with the surface plasmon and receives energy from two photons, which excites it to a state from which the ring-opening reaction can be initiated.

Effect of hydrogen coverage on hydrogenation of o-cresol on Pt(111)

NASA Astrophysics Data System (ADS)

Li, Yaping; Liu, Zhimin; Crossley, Steven P.; Jentoft, Friederike C.; Wang, Sanwu

2018-06-01

The conversion of phenolics over metal catalysts is an important process for upgrading biofuels. With density functional calculations, hydrogenation of o-cresol on the hydrogen-covered Pt(111) surface was investigated. The results show that the coverage of hydrogen plays a significant role in the reaction rate while it does not affect the reaction selectivity. The reaction barriers of the hydrogenation process leading to the formation of both 2-methyl-cyclohexanone (the intermediate product) and 2-methyl-cyclohexanol (the final product) at high H coverages (∼1 ML) are found to be smaller by 0.14-0.69 eV than those at lower H coverages (∼1/25 ML). After both hydrogen and cresol are adsorbed on Pt(111) from their initial gas phase state, the reaction energy of each hydrogenation step on the surface is also dependent on the hydrogen coverage. On the H-covered Pt(111) surface, most steps of hydrogenation involve exothermic reactions when the hydrogen coverage is high while they are endothermic reactions at low hydrogen coverages. The differences in reaction rate and reaction energy between high and low H coverages can be understood with the coverage-dependent bonding strength and configurations.

Chemistry of acetylene on platinum (111) and (100) surfaces

PubMed Central

Muetterties, E. L.; Tasi, M.-C.; Kelemen, S. R.

1981-01-01

An ultra-high vacuum experimental study of acetylene chemisorption on Pt(111) and Pt(100) and of the reaction of hydrogen with the acetylene adsorbate has established distinguishing features of carbon-hydrogen bond breaking and making processes as a function of pressure, temperature, and surface crystallography. The rates for both processes are substantially higher on the Pt(100) surface. Net acetylene-hydrogen processes, in the temperature range of 20°C to ≈130°C, are distinctly different on the two surfaces: on Pt(100) the net reaction is hydrogen exchange (1H-2H exchange) and on Pt(111) the only detectable reaction is hydrogenation. Stereochemical differences in the acetylene adsorbate structure are considered to be a contributing factor to the differences in acetylene chemistry on these two surfaces. Images PMID:16593110

Effects of space environment on structural materials - A preliminary study and development of materials characterization protocols

NASA Technical Reports Server (NTRS)

Miglionico, C.; Stein, C.; Murr, L. E.

1991-01-01

A preliminary study of materials exposed in space in LEO for nearly six years in the NASA Long-Duration Exposure Facility is presented. It is demonstrated that it will be necessary to isolate surface debris and reaction products from materials exposed in space. Replication techniques originally designed for electron microscopy examination of surfaces can be applied to lift off and isolate such surface features. Debris and reaction products were examined through a variety of analytical techniques, including the surface morphology by SEM, and internal microstructures by STEM and TEM, EDS, and SAD. The results illustrate the role that atomic oxygen and micrometeorites play in surface alteration and reaction in LEO space environments, as well as the role of debris created from other proximate materials.

A BASIC program for the removal of noise from reaction traces using Fourier filtering.

PubMed

Brittain, T

1989-04-01

Software for the removal of noise from reaction curves using the principle of Fourier filtering has been written in BASIC to execute on a PC. The program inputs reaction traces which are subjected to a rotation-inversion process, to produce functions suitable for Fourier analysis. Fourier transformation into the frequency domain is followed by multiplication of the transform by a rectangular filter function, to remove the noise frequencies. Inverse transformation then yields a noise-reduced reaction trace suitable for further analysis. The program is interactive at each stage and could easily be modified to remove noise from a range of input data types.

Black silicon with self-cleaning surface prepared by wetting processes

PubMed Central

2013-01-01

This paper reports on a simple method to prepare a hydrophobic surface on black silicon, which is fabricated by metal-assisted wet etching. To increase the reaction rate, the reaction device was placed in a heat collection-constant temperature type magnetic stirrer and set at room temperature. It was demonstrated that the micro- and nanoscale spikes on the black silicon made the surface become hydrophobic. As the reaction rate increases, the surface hydrophobicity becomes more outstanding and presents self-cleaning until the very end. The reflectance of the black silicon is drastically suppressed over a broad spectral range due to the unique geometry, which is effective for the enhancement of absorption. PMID:23941184

Long Term Degradation of Resin for High Temperature Composites

NASA Technical Reports Server (NTRS)

Patekar, Kaustubh A.

2000-01-01

The durability of polymer matrix composites exposed to harsh environments is a major concern. Surface degradation and damage are observed in polyimide composites used in air at 125 to 300 C. It is believed that diffusion of oxygen into the material and oxidative chemical reactions in the matrix are responsible. Previous work has characterized and modeled diffusion behavior, and thermogravimetric analyses (TGAs) have been carried out in nitrogen, air, and oxygen to provide quantitative information on thermal and oxidative reactions. However, the model developed using these data was not able to capture behavior seen in isothermal tests, especially those of long duration. A test program that focuses on lower temperatures and makes use of isothermal tests was undertaken to achieve a better understanding of the degradation reactions under use conditions. A new low-cost technique was developed to collect chemical degradation data for isothermal tests lasting over 200 hr in the temperature range 125 to 300 C. Results indicate complex behavior not captured by the previous TGA tests, including the presence of weight-adding reactions. Weight gain reactions dominated in the 125 to 225 C temperature range, while weight loss reactions dominated beyond 225 C. The data obtained from isothermal tests was used to develop a new model of the material behavior. This model was able to fully capture the behavior seen in the tests up to 275 C. Correlation of the current model with both isothermal data at 300 C and high rate TGA test data is mediocre. At 300 C and above, the reaction mechanisms appear to change. Attempts (which failed) to measure non-oxidative degradation indicate that oxidative reactions dominate the degradation at low temperatures. Based on this work, long term isothermal testing in an oxidative atmosphere is recommended for studying the degradation behavior of this class of materials.

Aluminum/water reactions under extreme conditions

NASA Astrophysics Data System (ADS)

Hooper, Joseph

2013-03-01

We discuss mechanisms that may control the reaction of aluminum and water under extreme conditions. We are particularly interested in the high-temperature, high-strain regime where the native oxide layer is destroyed and fresh aluminum is initially in direct contact with liquid or supercritical water. Disparate experimental data over the years have suggested rapid oxidation of aluminum is possible in such situations, but no coherent picture has emerged as to the basic oxidation mechanism or the physical processes that govern the extent of reaction. We present theoretical and computational analysis of traditional metal/water reaction mechanisms that treat diffusion through a dynamic oxide layer or reaction limited by surface kinetics. Diffusion through a fresh solid oxide layer is shown to be far too slow to have any effect on the millisecond timescale (even at high temperatures). Quantum molecular dynamics simulations of liquid Al and water surface reactions show rapid water decomposition at the interface, catalyzed by adjacent water molecules in a Grotthus-like relay mechanism. The surface reaction barriers are far too low for this to be rate-limiting in any way. With these straightforward mechanisms ruled out, we investigate two more complex possibilities for the rate-limiting factor; first, we explore the possibility that newly formed oxide remains a metastable liquid well below its freezing point, allowing for diffusion-limited reactions through the oxide shell but on a much faster timescale. The extent of reaction would then be controlled by the solidification kinetics of alumina. Second, we discuss preliminary analysis on surface erosion and turbulent mixing, which may play a prominent role during hypervelocity penetration of solid aluminum projectiles into water.

Formation of the prebiotic molecule NH2CHO on astronomical amorphous solid water surfaces: accurate tunneling rate calculations.

PubMed

Song, Lei; Kästner, Johannes

2016-10-26

Investigating how formamide forms in the interstellar medium is a hot topic in astrochemistry, which can contribute to our understanding of the origin of life on Earth. We have constructed a QM/MM model to simulate the hydrogenation of isocyanic acid on amorphous solid water surfaces to form formamide. The binding energy of HNCO on the ASW surface varies significantly between different binding sites, we found values between ∼0 and 100 kJ mol -1 . The barrier for the hydrogenation reaction is almost independent of the binding energy, though. We calculated tunneling rate constants of H + HNCO → NH 2 CO at temperatures down to 103 K combining QM/MM with instanton theory. Tunneling dominates the reaction at such low temperatures. The tunneling reaction is hardly accelerated by the amorphous solid water surface compared to the gas phase for this system, even though the activation energy of the surface reaction is lower than the one of the gas-phase reaction. Both the height and width of the barrier affect the tunneling rate in practice. Strong kinetic isotope effects were observed by comparing to rate constants of D + HNCO → NHDCO. At 103 K we found a KIE of 231 on the surface and 146 in the gas phase. Furthermore, we investigated the gas-phase reaction NH 2 + H 2 CO → NH 2 CHO + H and found it unlikely to occur at cryogenic temperatures. The data of our tunneling rate constants are expected to significantly influence astrochemical models.

Direct instrumental identification of catalytically active surface sites

NASA Astrophysics Data System (ADS)

Pfisterer, Jonas H. K.; Liang, Yunchang; Schneider, Oliver; Bandarenka, Aliaksandr S.

2017-09-01

The activity of heterogeneous catalysts—which are involved in some 80 per cent of processes in the chemical and energy industries—is determined by the electronic structure of specific surface sites that offer optimal binding of reaction intermediates. Directly identifying and monitoring these sites during a reaction should therefore provide insight that might aid the targeted development of heterogeneous catalysts and electrocatalysts (those that participate in electrochemical reactions) for practical applications. The invention of the scanning tunnelling microscope (STM) and the electrochemical STM promised to deliver such imaging capabilities, and both have indeed contributed greatly to our atomistic understanding of heterogeneous catalysis. But although the STM has been used to probe and initiate surface reactions, and has even enabled local measurements of reactivity in some systems, it is not generally thought to be suited to the direct identification of catalytically active surface sites under reaction conditions. Here we demonstrate, however, that common STMs can readily map the catalytic activity of surfaces with high spatial resolution: we show that by monitoring relative changes in the tunnelling current noise, active sites can be distinguished in an almost quantitative fashion according to their ability to catalyse the hydrogen-evolution reaction or the oxygen-reduction reaction. These data allow us to evaluate directly the importance and relative contribution to overall catalyst activity of different defects and sites at the boundaries between two materials. With its ability to deliver such information and its ready applicability to different systems, we anticipate that our method will aid the rational design of heterogeneous catalysts.

Production of Organic Grain Coatings by Surface-Mediated Reactions and the Consequences of This Process for Meteoritic Constituents

NASA Technical Reports Server (NTRS)

Nuth, Joseph A., III; Johnson, Natasha M.

2011-01-01

When hydrogen, nitrogen and CO are exposed to amorphous iron silicate surfaces at temperatures between 500 - 900K, a carbonaceous coating forms via Fischer-Tropsch type reactions. Under normal circumstances such a catalytic coating would impede or stop further reaction. However, we find that this coating is a better catalyst than the amorphous iron silicates that initiate these reactions. The formation of a self-perpetuating catalytic coating on grain surfaces could explain the rich deposits of macromolecular carbon found in primitive meteorites and would imply that protostellar nebulae should be rich in organic material. Many more experiments are needed to understand this chemical system and its application to protostellar nebulae.

Oxidation of dissolved iron under warmer, wetter conditions on Mars: Transitions to present-day arid environments

NASA Technical Reports Server (NTRS)

Burns, R. G.

1993-01-01

The copious deposits of ferric-iron assemblages littering the surface of bright regions of Mars indicate that efficient oxidative weathering reactions have taken place during the evolution of the planet. Because the kinetics of atmosphere-surface (gas-solid) reactions are considerably slower than chemical weathering reactions involving an aqueous medium, most of the oxidation products now present in the martian regolith probably formed when groundwater flowed near the surface. This paper examines how chemical weathering reactions were effected by climatic variations when warm, wet environments became arid on Mars. Analogies are drawn with hydrogeochemical and weathering environments on the Australian continent where present-day oxidation of iron is occurring in acidic ground water under arid conditions.

Unravelling Site-Specific Photo-Reactions of Ethanol on Rutile TiO2(110)

PubMed Central

Hansen, Jonas Ø.; Bebensee, Regine; Martinez, Umberto; Porsgaard, Soeren; Lira, Estephania; Wei, Yinying; Lammich, Lutz; Li, Zheshen; Idriss, Hicham; Besenbacher, Flemming; Hammer, Bjørk; Wendt, Stefan

2016-01-01

Finding the active sites of catalysts and photo-catalysts is crucial for an improved fundamental understanding and the development of efficient catalytic systems. Here we have studied the photo-activated dehydrogenation of ethanol on reduced and oxidized rutile TiO2(110) in ultrahigh vacuum conditions. Utilizing scanning tunnelling microscopy, various spectroscopic techniques and theoretical calculations we found that the photo-reaction proceeds most efficiently when the reactants are adsorbed on regular Ti surface sites, whereas species that are strongly adsorbed at surface defects such as O vacancies and step edges show little reaction under reducing conditions. We propose that regular Ti surface sites are the most active sites in photo-reactions on TiO2. PMID:26915303

Membrane Fusion Promoted by Increasing Surface Densities of the Paramyxovirus F and HN Proteins: Comparison of Fusion Reactions Mediated by Simian Virus 5 F, Human Parainfluenza Virus Type 3 F, and Influenza Virus HA

PubMed Central

Dutch, Rebecca Ellis; Joshi, Sangeeta Bagai; Lamb, Robert A.

1998-01-01

The membrane fusion reaction promoted by the paramyxovirus simian virus 5 (SV5) and human parainfluenza virus type 3 (HPIV-3) fusion (F) proteins and hemagglutinin-neuraminidase (HN) proteins was characterized when the surface densities of F and HN were varied. Using a quantitative content mixing assay, it was found that the extent of SV5 F-mediated fusion was dependent on the surface density of the SV5 F protein but independent of the density of SV5 HN protein, indicating that HN serves only a binding function in the reaction. However, the extent of HPIV-3 F protein promoted fusion reaction was found to be dependent on surface density of HPIV-3 HN protein, suggesting that the HPIV-3 HN protein is a direct participant in the fusion reaction. Analysis of the kinetics of lipid mixing demonstrated that both initial rates and final extents of fusion increased with rising SV5 F protein surface densities, suggesting that multiple fusion pores can be active during SV5 F protein-promoted membrane fusion. Initial rates and extent of lipid mixing were also found to increase with increasing influenza virus hemagglutinin protein surface density, suggesting parallels between the mechanism of fusion promoted by these two viral fusion proteins. PMID:9733810

Evidence of a reduction reaction of oxidized iron/cobalt by boron atoms diffused toward naturally oxidized surface of CoFeB layer during annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sato, Soshi, E-mail: sato.soshi@cies.tohoku.ac.jp; Honjo, Hiroaki; Niwa, Masaaki

2015-04-06

We have investigated the redox reaction on the surface of Ta/CoFeB/MgO/CoFeB magnetic tunnel junction stack samples after annealing at 300, 350, and 400 °C for 1 h using angle-resolved X-ray photoelectron spectroscopy for precise analysis of the chemical bonding states. At a capping tantalum layer thickness of 1 nm, both the capping tantalum layer and the surface of the underneath CoFeB layer in the as-deposited stack sample were naturally oxidized. By comparison of the Co 2p and Fe 2p spectra among the as-deposited and annealed samples, reduction of the naturally oxidized cobalt and iron atoms occurred on the surface of the CoFeB layer.more » The reduction reaction was more significant at higher annealing temperature. Oxidized cobalt and iron were reduced by boron atoms that diffused toward the surface of the top CoFeB layer. A single CoFeB layer was prepared on SiO{sub 2}, and a confirmatory evidence of the redox reaction with boron diffusion was obtained by angle-resolved X-ray photoelectron spectroscopy analysis of the naturally oxidized surface of the CoFeB single layer after annealing. The redox reaction is theoretically reasonable based on the Ellingham diagram.« less

Plasmonic Imaging of Electrochemical Reactions of Single Nanoparticles.

PubMed

Fang, Yimin; Wang, Hui; Yu, Hui; Liu, Xianwei; Wang, Wei; Chen, Hong-Yuan; Tao, N J

2016-11-15

Electrochemical reactions are involved in many natural phenomena, and are responsible for various applications, including energy conversion and storage, material processing and protection, and chemical detection and analysis. An electrochemical reaction is accompanied by electron transfer between a chemical species and an electrode. For this reason, it has been studied by measuring current, charge, or related electrical quantities. This approach has led to the development of various electrochemical methods, which have played an essential role in the understanding and applications of electrochemistry. While powerful, most of the traditional methods lack spatial and temporal resolutions desired for studying heterogeneous electrochemical reactions on electrode surfaces and in nanoscale materials. To overcome the limitations, scanning probe microscopes have been invented to map local electrochemical reactions with nanometer resolution. Examples include the scanning electrochemical microscope and scanning electrochemical cell microscope, which directly image local electrochemical reaction current using a scanning electrode or pipet. The use of a scanning probe in these microscopes provides high spatial resolution, but at the expense of temporal resolution and throughput. This Account discusses an alternative approach to study electrochemical reactions. Instead of measuring electron transfer electrically, it detects the accompanying changes in the reactant and product concentrations on the electrode surface optically via surface plasmon resonance (SPR). SPR is highly surface sensitive, and it provides quantitative information on the surface concentrations of reactants and products vs time and electrode potential, from which local reaction kinetics can be analyzed and quantified. The plasmonic approach allows imaging of local electrochemical reactions with high temporal resolution and sensitivity, making it attractive for studying electrochemical reactions in biological systems and nanoscale materials with high throughput. The plasmonic approach has two imaging modes: electrochemical current imaging and interfacial impedance imaging. The former images local electrochemical current associated with electrochemical reactions (faradic current), and the latter maps local interfacial impedance, including nonfaradic contributions (e.g., double layer charging). The plasmonic imaging technique can perform voltammetry (cyclic or square wave) in an analogous manner to the traditional electrochemical methods. It can also be integrated with bright field, dark field, and fluorescence imaging capabilities in one optical setup to provide additional capabilities. To date the plasmonic imaging technique has found various applications, including mapping of heterogeneous surface reactions, analysis of trace substances, detection of catalytic reactions, and measurement of graphene quantum capacitance. The plasmonic and other emerging optical imaging techniques (e.g., dark field and fluorescence microscopy), together with the scanning probe-based electrochemical imaging and single nanoparticle analysis techniques, provide new capabilities for one to study single nanoparticle electrochemistry with unprecedented spatial and temporal resolutions. In this Account, we focus on imaging of electrochemical reactions at single nanoparticles.

Adsorption Isotherms and Surface Reaction Kinetics

ERIC Educational Resources Information Center

Lobo, L. S.; Bernardo, C. A.

1974-01-01

Explains an error that occurs in calculating the conditions for a maximum value of a rate expression for a bimolecular reaction. The rate expression is derived using the Langmuir adsorption isotherm to relate gas pressures and corresponding surface coverages. (GS)

Reaction Mechanisms on Multiwell Potential Energy Surfaces in Combustion (and Atmospheric) Chemistry

DOE PAGES

Osborn, David L.

2017-03-15

Chemical reactions occurring on a potential energy surface with multiple wells are ubiquitous in low temperature combustion and the oxidation of volatile organic compounds in earth’s atmosphere. The rich variety of structural isomerizations that compete with collisional stabilization make characterizing such complex-forming reactions challenging. This review describes recent experimental and theoretical advances that deliver increasingly complete views of their reaction mechanisms. New methods for creating reactive intermediates coupled with multiplexed measurements provide many experimental observables simultaneously. Automated methods to explore potential energy surfaces can uncover hidden reactive pathways, while master equation methods enable a holistic treatment of both sequential andmore » well-skipping pathways. Our ability to probe and understand nonequilibrium effects and reaction sequences is increasing. These advances provide the fundamental science base for predictive models of combustion and the atmosphere that are crucial to address global challenges.« less

Theoretical Study of Tautomerization Reactions for the Ground and First Excited Electronic States of Adenine

NASA Technical Reports Server (NTRS)

Salter, Latasha M.; Chaban, Galina M.; Kwak, Dochan (Technical Monitor)

2002-01-01

Geometrical structures and energetic properties for different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest singlet excited state potential energy surfaces are studied. Four tautomeric forms are considered, and their energetic order is found to be different on the ground and the excited state potential energy surfaces. Minimum energy reaction paths are obtained for hydrogen atom transfer (tautomerization) reactions in the ground and the lowest excited electronic states. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic states, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. This tautomerization process should become possible in the presence of water or other polar solvent molecules and should play an important role in the photochemistry of adenine.

Reaction Mechanisms on Multiwell Potential Energy Surfaces in Combustion (and Atmospheric) Chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osborn, David L.

Chemical reactions occurring on a potential energy surface with multiple wells are ubiquitous in low temperature combustion and the oxidation of volatile organic compounds in earth’s atmosphere. The rich variety of structural isomerizations that compete with collisional stabilization make characterizing such complex-forming reactions challenging. This review describes recent experimental and theoretical advances that deliver increasingly complete views of their reaction mechanisms. New methods for creating reactive intermediates coupled with multiplexed measurements provide many experimental observables simultaneously. Automated methods to explore potential energy surfaces can uncover hidden reactive pathways, while master equation methods enable a holistic treatment of both sequential andmore » well-skipping pathways. Our ability to probe and understand nonequilibrium effects and reaction sequences is increasing. These advances provide the fundamental science base for predictive models of combustion and the atmosphere that are crucial to address global challenges.« less

Hydrogen isotopic substitution of solid methylamine through atomic surface reactions at low temperatures: A potential contribution to the D/H ratio of methylamine in molecular clouds

NASA Astrophysics Data System (ADS)

Oba, Yasuhiro; Chigai, Takeshi; Osamura, Yoshihiro; Watanabe, Naoki; Kouchi, Akira

2014-01-01

We experimentally studied hydrogen (H)-deuterium (D) substitution reactions of solid methylamine (CH3NH2) under astrophysically relevant conditions. We also calculated the potential energy surface for the H-D substitution reactions of methylamine isotopologues using quantum chemical methods. Despite the relatively large energy barrier of more than 18 kJ mol-1, CH3NH2 reacted with D atoms to yield deuterated methylamines at 10 K, suggesting that the H-D substitution reaction proceeds through quantum tunneling. Deuterated methylamines reacted with H atoms as well. On the basis of present results, we propose that methylamine has potential for D enrichment through atomic surface reactions on interstellar grains at very low temperatures in molecular clouds. D enrichment would occur in particular in the methyl group of methylamine.

Porous silicon structures with high surface area/specific pore size

DOEpatents

Northrup, M.A.; Yu, C.M.; Raley, N.F.

1999-03-16

Fabrication and use of porous silicon structures to increase surface area of heated reaction chambers, electrophoresis devices, and thermopneumatic sensor-actuators, chemical preconcentrates, and filtering or control flow devices. In particular, such high surface area or specific pore size porous silicon structures will be useful in significantly augmenting the adsorption, vaporization, desorption, condensation and flow of liquids and gases in applications that use such processes on a miniature scale. Examples that will benefit from a high surface area, porous silicon structure include sample preconcentrators that are designed to adsorb and subsequently desorb specific chemical species from a sample background; chemical reaction chambers with enhanced surface reaction rates; and sensor-actuator chamber devices with increased pressure for thermopneumatic actuation of integrated membranes. Examples that benefit from specific pore sized porous silicon are chemical/biological filters and thermally-activated flow devices with active or adjacent surfaces such as electrodes or heaters. 9 figs.

Porous silicon structures with high surface area/specific pore size

DOEpatents

Northrup, M. Allen; Yu, Conrad M.; Raley, Norman F.

1999-01-01

Fabrication and use of porous silicon structures to increase surface area of heated reaction chambers, electrophoresis devices, and thermopneumatic sensor-actuators, chemical preconcentrates, and filtering or control flow devices. In particular, such high surface area or specific pore size porous silicon structures will be useful in significantly augmenting the adsorption, vaporization, desorption, condensation and flow of liquids and gasses in applications that use such processes on a miniature scale. Examples that will benefit from a high surface area, porous silicon structure include sample preconcentrators that are designed to adsorb and subsequently desorb specific chemical species from a sample background; chemical reaction chambers with enhanced surface reaction rates; and sensor-actuator chamber devices with increased pressure for thermopneumatic actuation of integrated membranes. Examples that benefit from specific pore sized porous silicon are chemical/biological filters and thermally-activated flow devices with active or adjacent surfaces such as electrodes or heaters.

High Chemical Activity of a Perovskite Surface: Reaction of CO with Sr3Ru2O7

NASA Astrophysics Data System (ADS)

Stöger, Bernhard; Hieckel, Marcel; Mittendorfer, Florian; Wang, Zhiming; Fobes, David; Peng, Jin; Mao, Zhiqiang; Schmid, Michael; Redinger, Josef; Diebold, Ulrike

2014-09-01

Adsorption of CO at the Sr3Ru2O7(001) surface was studied with low-temperature scanning tunneling microscopy (STM) and density functional theory. In situ cleaved single crystals terminate in an almost perfect SrO surface. At 78 K, CO first populates impurities and then adsorbs above the apical surface O with a binding energy Eads=-0.7 eV. Above 100 K, this physisorbed CO replaces the surface O, forming a bent CO2 with the C end bound to the Ru underneath. The resulting metal carboxylate (Ru-COO) can be desorbed by STM manipulation. A low activation (0.2 eV) and high binding (-2.2 eV) energy confirm a strong reaction between CO and regular surface sites of Sr3Ru2O7; likely, this reaction causes the "UHV aging effect" reported for this and other perovskite oxides.

Rapid Surface Functionalization of Hydrogen-Terminated Silicon by Alkyl Silanols.

PubMed

Escorihuela, Jorge; Zuilhof, Han

2017-04-26

Surface functionalization of inorganic semiconductor substrates, particularly silicon, has focused attention toward many technologically important applications, involving photovoltaic energy, biosensing and catalysis. For such modification processes, oxide-free (H-terminated) silicon surfaces are highly required, and different chemical approaches have been described in the past decades. However, their reactivity is often poor, requiring long reaction times (2-18 h) or the use of UV light (10-30 min). Here, we report a simple and rapid surface functionalization for H-terminated Si(111) surfaces using alkyl silanols. This catalyst-free surface reaction is fast (15 min at room temperature) and can be accelerated with UV light irradiation, reducing the reaction time to 1-2 min. This grafting procedure leads to densely packed organic monolayers that are hydrolytically stable (even up to 30 days at pH 3 or 11) and can display excellent antifouling behavior against a range of organic polymers.

Rapid Surface Functionalization of Hydrogen-Terminated Silicon by Alkyl Silanols

PubMed Central

2017-01-01

Surface functionalization of inorganic semiconductor substrates, particularly silicon, has focused attention toward many technologically important applications, involving photovoltaic energy, biosensing and catalysis. For such modification processes, oxide-free (H-terminated) silicon surfaces are highly required, and different chemical approaches have been described in the past decades. However, their reactivity is often poor, requiring long reaction times (2–18 h) or the use of UV light (10–30 min). Here, we report a simple and rapid surface functionalization for H-terminated Si(111) surfaces using alkyl silanols. This catalyst-free surface reaction is fast (15 min at room temperature) and can be accelerated with UV light irradiation, reducing the reaction time to 1–2 min. This grafting procedure leads to densely packed organic monolayers that are hydrolytically stable (even up to 30 days at pH 3 or 11) and can display excellent antifouling behavior against a range of organic polymers. PMID:28409624

Mechanistic Insights of Ethanol Steam Reforming over Ni–CeO x (111): The Importance of Hydroxyl Groups for Suppressing Coke Formation

DOE PAGES

Liu, Zongyuan; Duchoň, Tomáš; Wang, Huanru; ...

2015-07-30

We have studied the reaction of ethanol and water over Ni–CeO 2-x(111) model surfaces to elucidate the mechanistic steps associated with the ethanol steam reforming (ESR) reaction. Our results provide insights about the importance of hydroxyl groups to the ESR reaction over Ni-based catalysts. Systematically, we have investigated the reaction of ethanol on Ni–CeO 2-x(111) at varying Ce³⁺ concentrations (CeO 1.8–2.0) with absence/presence of water using a combination of soft X-ray photoelectron spectroscopy (sXPS) and temperature-programmed desorption (TPD). Consistent with previous reports, upon annealing, metallic Ni formed on reduced ceria while NiO was the main component on fully oxidized ceria.more » Ni⁰ is the active phase leading to both the C–C and C–H cleavage of ethanol but is also responsible for carbon accumulation or coking. We have identified a Ni₃C phase that formed prior to the formation of coke. At temperatures above 600K, the lattice oxygen from ceria and the hydroxyl groups from water interact cooperatively in the removal of coke, likely through a strong metal–support interaction between nickel and ceria that facilitates oxygen transfer.« less

Structure and chemistry of model catalysts in ultrahigh vacuum

NASA Astrophysics Data System (ADS)

Walker, Joshua D.

The study of catalysis is a key area of focus not only in the industrial sector but also in the nature and biological systems. The market for catalysis is a multi-billion dollar industry. Many of the materials and products we use on a daily basis are formed through a catalytic process. The quest to understanding and improving catalytic mechanisms is ongoing. Many model catalysts use transition metals as a support for chemical reactions to take place due to their selectivity and activity. Palladium, gold, and copper metals are studied in this work and show the ability to be catalytically reactive. It is important to understand the characteristics and properties of these surfaces. A well-known example of catalysis is the conversion of carbon monoxide (CO), a very harmful gas to carbon dioxide (CO2) which is less harmful. This reaction is mainly seen in the automotive industry. This reaction is investigated in this work on a Au(111) single crystal, which is normally inert but becomes reactivity with the adsorption of oxygen on the surface. Temperature Programmed Desorption (TPD) is used to understand some of the chemistry and effects with and without the addition of H2O. The oxidation of CO is shown to be enhanced by the addition of water, but warrants further analysis too fully understand the different mechanisms and reaction pathways existing. The field of nano-electronics is rapidly growing as technology continues to challenge scientists to create innovative ideas. The trend to produce smaller electronic products is increasing as consumer demands persist. It has been shown previously that 1,4-phenlyene diisocyanobenzene (1,4-PDI) on Au(111) react to form one-dimensional oligomer chains comprising alternating gold and 1,4-PDI units on the Au(111) surface. A similar compound 1,3-phenlyene diisocyanobenzene (1,3-PDI) was studied in order to investigate whether the oligomerization found for 1,4-PDI is a general phenomenon and to ultimately explore the effect of molecular geometry on electron transport using a range of surface-sensitive techniques. Sulfur-containing molecules, in particular those with sulfur-sulfur linkages, are used as lubricant additives for ferrous surfaces [1-14] so that dialkyl disulfides have been used as simple model compounds to explore the surface and tribological chemistry on iron [15,16] where they react at the high temperatures attained at the interface during rubbing to deposit a ferrous sulfide film. However, the tribological chemistry can depend critically on the nature of the substrate so that a good lubricant additive for one type of surface may not be applicable to another. In particular, the lubrication of sliding copper-copper interfaces in electrical motors [17-20] provides a particular challenge. To study this system surface sensitive techniques Low energy electron diffraction (LEED) and TPD surface analysis was employed. LEED experiments suggest that tribological experiments can be conducted on copper foils rather than copper single crystals and produce comparable results. The ability to produce ideal model catalysts is very important in the Surface science field. To enhance catalytic performance of these catalysts, various strategies can be used in the preparation process. One approach in this quest is to produce an alloy surface that increases the activity of the surface. The process of developing and understanding the chemistry of AuPd alloys was probed in detail using TPD, LEED and Density Functional Theory (DFT).

Computer modeling of a hot filament diamond deposition reactor

NASA Technical Reports Server (NTRS)

Kuczmarski, Maria A.; Washlock, Paul A.; Angus, John C.

1991-01-01

A commercial fluid mechanics program, FLUENT, has been applied to the modeling of a hot-filament diamond deposition reactor. Streamlines and contours of constant temperature and species concentrations are obtained for practical reactor geometries and conditions. The modeling is presently restricted to two-dimensional simulations and to a chemical mechanism of ten independent homogeneous and surface reactions. Comparisons are made between predicted power consumption, substrate temperature, and concentrations of atomic hydrogen and methyl-radical with values taken from the literature. The results to date indicate that the modeling can aid in the rational design and analysis of practical reactor configurations.

Kinetics of liquid-solid reactions in naphthenic acid conversion and Kraft pulping

NASA Astrophysics Data System (ADS)

Yang, Ling

Two liquid-solid reactions, in which the morphology of the solid changes as the reactions proceeds, were examined. One is the NA conversion in oil by decarboxylation on metal oxides and carbonates, and the other is the Kraft pulping in which lignin removal by delignification reaction. In the study of the NA conversion, CaO was chosen as the catalyst for the kinetic study from the tested catalysts based on NA conversion. Two reaction mixtures, carrier oil plus commercial naphthenic acids and heavy vacuum gas oil (HVGO) from Athabasca bitumen, were applied in the kinetic study. The influence of TAN, temperature, and catalyst loading on the NA conversion and decarboxylation were studied systematically. The results showed that the removal rate of TAN and the decarboxylation of NA were both independent of the concentration of NA over the range studied, and significantly dependent on reaction temperature. The data from analyzing the spent catalyst demonstrated that calcium naphthenate was an intermediate of the decarboxylation reaction of NA, and the decomposition of calcium naphthenate was a rate-determining step. In the study on the delignification of the Kraft pulping, a new mechanism was proposed for the heterogeneous delignification reaction during the Kraft pulping process. In particular, the chemical reaction mechanism took into account the heterogeneous nature of Kraft pulping. Lignin reacted in parallel with sodium hydroxide and sodium sulfide. The mechanism consists of three key kinetic steps: (1) adsorption of hydroxide and hydrosulfide ions on lignin; (2) surface reaction on the solid surface to produce degraded lignin products; and (3) desorption of degradation products from the solid surface. The most important step for the delignification process is the surface reaction, rather than the reactions occurring in the liquid phase. A kinetic model has, thus, been developed based on the proposed mechanism. The derived kinetic model showed that the mechanism could be employed to predict the pulping behavior under a variety of conditions with good accuracy.

Critical Role of Water and Oxygen Defects in C-O Scission during CO2 Reduction on Zn2GeO4(010).

PubMed

Yang, Jing; Li, Yanlu; Zhao, Xian; Fan, Weiliu

2018-03-27

Exploration of catalyst structure and environmental sensitivity for C-O bond scission is essential for improving the conversion efficiency because of the inertness of CO 2 . We performed density functional theory calculations to understand the influence of the properties of adsorbed water and the reciprocal action with oxygen vacancy on the CO 2 dissociation mechanism on Zn 2 GeO 4 (010). When a perfect surface was hydrated, the introduction of H 2 O was predicted to promote the scission step by two modes based on its appearance, with the greatest enhancement from dissociative adsorbed H 2 O. The dissociative H 2 O lowers the barrier and reaction energy of CO 2 dissociation through hydrogen bonding to preactivate the C-O bond and assisted scission via a COOH intermediate. The perfect surface with bidentate-binding H 2 O was energetically more favorable for CO 2 dissociation than the surface with monodentate-binding H 2 O. Direct dissociation was energetically favored by the former, whereas monodentate H 2 O facilitated the H-assisted pathway. The defective surface exhibited a higher reactivity for CO 2 decomposition than the perfect surface because the generation of oxygen vacancies could disperse the product location. When the defective surface was hydrated, the reciprocal action for vacancy and surface H 2 O on CO 2 dissociation was related to the vacancy type. The presence of H 2 O substantially decreased the reaction energy for the direct dissociation of CO 2 on O 2c1 - and O 3c2 -defect surfaces, which converts the endoergic reaction to an exoergic reaction. However, the increased decomposition barrier made the step kinetically unfavorable and reduced the reaction rate. When H 2 O was present on the O 2c2 -defect surface, both the barrier and reaction energy for direct dissociation were invariable. This result indicated that the introduction of H 2 O had little effect on the kinetics and thermodynamics. Moreover, the H-assisted pathway was suppressed on all hydrated defect surfaces. These results provide a theoretical perspective for the design of highly efficient catalysts.

Adsorption and electron-induced polymerization of methyl methacrylate on Ru(101xAF0)

NASA Astrophysics Data System (ADS)

Hedhili, M. N.; Yakshinskiy, B. V.; Wasielewski, R.; Ciszewski, A.; Madey, T. E.

2008-05-01

The adsorption and electron irradiation of methyl methacrylate (MMA) on a Ru(101¯0) surface have been studied using x-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and low energy ion scattering. TPD analysis indicates that a monolayer of MMA chemisorbs and dissociates on the Ru(101¯0) surface. The reaction products observed upon heating include H2, CO, CO2, and a small amount of MMA. Physisorbed multilayers of MMA desorb at temperatures around 170K. Electron irradiation of physisorbed MMA at 140K leads to a modification of the MMA film: The XPS spectra show an increase in thermal stability of the film with retention of the MMA structure, and indicate that electron irradiation induces polymerization. An increase in the electron bombardment fluence induces a degradation of the formed polymerized species and leads to the accumulation of carbon on the Ru surface. These results are relevant to the accumulation of carbon on surfaces of Ru films that serve as capping layers on Mo /Si multilayer mirrors used in extreme ultraviolet lithography.

A study of diazonium couplings with aromatic nucleophiles both in solution and on a polymer surface

NASA Astrophysics Data System (ADS)

Chng, Shuyun; Parker, Emily M.; Griffiths, Jon-Paul; Moloney, Mark G.; Wu, Linda Y. L.

2017-04-01

Diazonium coupling is a technique finding wider application to materials and biological science, for hybridization and linking processes, and for the construction of responsive surface functionality. For this reason, detailed examination of solution and surface processes was warranted, and results of such a study are reported here. The modification of polystyrene surfaces was examined as a model, and the process compared to a solution mimic using N,N-dimethylaniline. It was confirmed that solution and solid surface reactions proceed in a similar manner in terms of the chemical functionality generated, but with lower chemical efficiency and reaction times slower for the latter, in a reaction which was pH dependent. The solution process was shown to give only the trans-azo para- coupled products. Whilst there are clear similarities between the solution and surface chemistry, the efficiency of coupling at a surface is not necessarily replicated in the chemical yield of the mimicking solution processes, but nonetheless provides an alternative to other Click-type surface modifications. It should not be assumed that such couplings occur with quantitative efficiency at the surface.

Changes Found on Run-In and Scuffed Surfaces of Steel Chrome Plate, and Cast Iron

NASA Technical Reports Server (NTRS)

Good, J. N.; Godfrey, Douglas

1947-01-01

A study was made of run-in and scuffed steel, chrome-plate, and cast-iron surfaces. X-ray and electron diffraction techniques, micro-hardness determinations, and microscopy were used. Surface changes varied and were found to include three classes: chemical reaction, hardening, and crystallite-size alteration. The principal chemical reactions were oxidation and carburization.

Acetone and Water on TiO₂(110): H/D Exchange

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henderson, Michael A.

2005-04-12

Isotopic H/D exchange between coadsorbed acetone and water on the TiO?(110) surface was examined using temperature programmed desorption (TPD) as a function of coverage and two surface pretreatments (oxidation and reduction). Coadsorbed acetone and water interact repulsively on reduced TiO?(110) based on results from the companion paper to this study, with water exerting a greater influence in destabilizing acetone and acetone having only a nominal influence on water. Despite the repulsive interaction between these coadsorbates, about 0.02 ML of a 1 ML d6-acetone on the reduced surface exhibits H/D exchange with coadsorbed water, with the exchange occurring exclusively in themore » high temperature region of the d?-acetone TPD spectrum at {approx}340 K. The effect was confirmed with combinations of d?-acetone and D?O. The extent of exchange decreased on the reduced surface with water coverages above {approx}0.3 ML due to the ability of water to displace coadsorbed acetone from first layer sites to the multilayer. In contrast, the extent of exchange increased by a factor of 3 when the surface was pre-oxidized prior to coadsorption. In this case, there was no evidence for the negative influence of high water coverages on the extent of H/D exchange. Comparison of the TPD spectra from the exchange products (either d?- or d?-acetone depending on the coadsorption pairing) suggests that, in addition to the 340 K exchange process seen on the reduced surface, a second exchange process was observed on the oxidized surface at {approx}390 K. In both cases (oxidized and reduced), desorption of the H/D exchange products appeared to be reaction limited and to involve the influence of OH/OD groups (or water formed during recombinative desorption of OH/OD groups) instead of molecularly adsorbed water. The 340 K exchange process is assigned to reaction at step sites and the 390 K exchange process is attributed to the influence of oxygen adatoms deposited during surface oxidation. The H/D exchange mechanism likely involves an enolate or propenol surface intermediate formed transiently during the desorption of oxygen-stabilized acetone molecules.« less

Si1-yCy/Si(001) gas-source molecular beam epitaxy from Si2H6 and CH3SiH3: Surface reaction paths and growth kinetics

NASA Astrophysics Data System (ADS)

Foo, Y. L.; Bratland, K. A.; Cho, B.; Desjardins, P.; Greene, J. E.

2003-04-01

In situ surface probes and postdeposition analyses were used to follow surface reaction paths and growth kinetics of Si1-yCy alloys grown on Si(001) by gas-source molecular-beam epitaxy from Si2H6/CH3SiH3 mixtures as a function of C concentration y (0-2.6 at %) and temperature Ts (500-600 °C). High-resolution x-ray diffraction reciprocal lattice maps show that all layers are in tension and fully coherent with their substrates. Film growth rates R decrease with both y and Ts, and the rate of decrease in R as a function of y increases rapidly with Ts. In situ isotopically tagged D2 temperature-programmed desorption (TPD) measurements reveal that C segregation during steady-state Si1-yCy(001) growth results in charge transfer from Si surface dangling bonds to second-layer C atoms, which have a higher electronegativity than Si. From the TPD results, we obtain the coverage θSi*(y,Ts) of Si* surface sites with C backbonds as well as H2 desorption energies Ed from both Si and Si* surface sites. θSi* increases with increasing y and Ts in the kinetically limited segregation regime while Ed decreases from 2.52 eV for H2 desorption from Si surface sites with Si back bonds to 2.22 eV from Si* surface sites. This leads to an increase in the H2 desorption rate, and hence should yield higher film deposition rates, with increasing y and/or Ts during Si1-yCy(001) growth. The effect, however, is more than offset by the decrease in Si2H6 reactive sticking probabilities at Si* surface sites. Film growth rates R(Ts,JSi2H6,JCH3SiH3) calculated using a simple transition-state kinetic model, together with measured kinetic parameters, were found to be in excellent agreement with the experimental data.

Silver Nanoparticles with Surface-Bonded Oxygen for Highly Selective CO 2 Reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Kun; Kharel, Priti; Peng, Yande

Here, the surface electronic structures of catalysts need to be carefully engineered in CO 2 reduction reaction (CO 2RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lows the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO 2RR reaction intermediates, which may significantly improve the catalyst activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO 2RR performances. A comparative investigation on air-annealedmore » Ag (Air-Ag) catalyst with or without the post-treatment of H 2 thermal annealing (H 2-Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O-Ag δ+) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rather than H 2 in CO 2RR electrolysis. As a result, while the maximal CO Faradaic efficiency of H 2-Ag is at ~ 30 %, the Air-Ag catalyst presented a high CO selectivity of more than 90 % under a current density of ~ 21 mA/cm 2.« less

A Semi-Empirical Two Step Carbon Corrosion Reaction Model in PEM Fuel Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, Alan; Colbow, Vesna; Harvey, David

2013-01-01

The cathode CL of a polymer electrolyte membrane fuel cell (PEMFC) was exposed to high potentials, 1.0 to 1.4 V versus a reversible hydrogen electrode (RHE), that are typically encountered during start up/shut down operation. While both platinum dissolution and carbon corrosion occurred, the carbon corrosion effects were isolated and modeled. The presented model separates the carbon corrosion process into two reaction steps; (1) oxidation of the carbon surface to carbon-oxygen groups, and (2) further corrosion of the oxidized surface to carbon dioxide/monoxide. To oxidize and corrode the cathode catalyst carbon support, the CL was subjected to an accelerated stressmore » test cycled the potential from 0.6 VRHE to an upper potential limit (UPL) ranging from 0.9 to 1.4 VRHE at varying dwell times. The reaction rate constants and specific capacitances of carbon and platinum were fitted by evaluating the double layer capacitance (Cdl) trends. Carbon surface oxidation increased the Cdl due to increased specific capacitance for carbon surfaces with carbon-oxygen groups, while the second corrosion reaction decreased the Cdl due to loss of the overall carbon surface area. The first oxidation step differed between carbon types, while both reaction rate constants were found to have a dependency on UPL, temperature, and gas relative humidity.« less

Activating Aluminum Reactivity with Fluoropolymer Coatings for Improved Energetic Composite Combustion.

PubMed

McCollum, Jena; Pantoya, Michelle L; Iacono, Scott T

2015-08-26

Aluminum (Al) particles are passivated by an aluminum oxide (Al2O3) shell. Energetic blends of nanometer-sized Al particles with liquid perfluorocarbon-based oxidizers such as perfluoropolyethers (PFPE) excite surface exothermic reaction between fluorine and the Al2O3 shell. The surface reaction promotes Al particle reactivity. Many Al-fueled composites use solid oxidizers that induce no Al2O3 surface exothermicity, such as molybdenum trioxide (MoO3) or copper oxide (CuO). This study investigates a perfluorinated polymer additive, PFPE, incorporated to activate Al reactivity in Al-CuO and Al-MoO3. Flame speeds, differential scanning calorimetry (DSC), and quadrupole mass spectrometry (QMS) were performed for varying percentages of PFPE blended with Al/MoO3 or Al/CuO to examine reaction kinetics and combustion performance. X-ray photoelectron spectroscopy (XPS) was performed to identify product species. Results show that the performance of the thermite-PFPE blends is highly dependent on the bond dissociation energy of the metal oxide. Fluorine-Al-based surface reaction with MoO3 produces an increase in reactivity, whereas the blends with CuO show a decline when the PFPE concentration is increased. These results provide new evidence that optimizing Al combustion can be achieved through activating exothermic Al surface reactions.

Silver Nanoparticles with Surface-Bonded Oxygen for Highly Selective CO 2 Reduction

DOE PAGES

Jiang, Kun; Kharel, Priti; Peng, Yande; ...

2017-09-12

Here, the surface electronic structures of catalysts need to be carefully engineered in CO 2 reduction reaction (CO 2RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lows the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO 2RR reaction intermediates, which may significantly improve the catalyst activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO 2RR performances. A comparative investigation on air-annealedmore » Ag (Air-Ag) catalyst with or without the post-treatment of H 2 thermal annealing (H 2-Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O-Ag δ+) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rather than H 2 in CO 2RR electrolysis. As a result, while the maximal CO Faradaic efficiency of H 2-Ag is at ~ 30 %, the Air-Ag catalyst presented a high CO selectivity of more than 90 % under a current density of ~ 21 mA/cm 2.« less

Surface Proton Transfer Promotes Four-Electron Oxygen Reduction on Gold Nanocrystal Surfaces in Alkaline Solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Fang; Zhang, Yu; Liu, Shizhong

Four-electron oxygen reduction reaction (4e-ORR), as a key pathway in energy conversion, is preferred over the two-electron reduction pathway that falls short in dissociating dioxygen molecules. Gold (Au) surfaces exhibit high sensitivity of the ORR pathway to its atomic structures. The long-standing puzzle remains unsolved why the Au surfaces with {100} sub-facets were exceptionally capable to catalyze the 4e-ORR in alkaline solution, though limited within a narrow potential window. Herein we report the discovery of a dominant 4e-ORR over the whole potential range on {310} surface of Au nanocrystal shaped as truncated ditetragonal prism (TDP). In contrast, ORR pathways onmore » single-crystalline facets of shaped nanoparticles, including {111} on nano-octahedra and {100} on nano-cubes, are similar to their single-crystal counterparts. Combining our experimental results with density functional theory calculations, we elucidate the key role of surface proton transfers from co-adsorbed H 2O molecules in activating the facet- and potential-dependent 4e ORR on Au in alkaline solutions. These results elucidate how surface atomic structures determine the reaction pathways via bond scission and formation among weakly adsorbed water and reaction intermediates. The new insight helps in developing facet-specific nanocatalysts for various reactions.« less

Surface Proton Transfer Promotes Four-Electron Oxygen Reduction on Gold Nanocrystal Surfaces in Alkaline Solution

DOE PAGES

Lu, Fang; Zhang, Yu; Liu, Shizhong; ...

2017-05-11

Four-electron oxygen reduction reaction (4e-ORR), as a key pathway in energy conversion, is preferred over the two-electron reduction pathway that falls short in dissociating dioxygen molecules. Gold (Au) surfaces exhibit high sensitivity of the ORR pathway to its atomic structures. The long-standing puzzle remains unsolved why the Au surfaces with {100} sub-facets were exceptionally capable to catalyze the 4e-ORR in alkaline solution, though limited within a narrow potential window. Herein we report the discovery of a dominant 4e-ORR over the whole potential range on {310} surface of Au nanocrystal shaped as truncated ditetragonal prism (TDP). In contrast, ORR pathways onmore » single-crystalline facets of shaped nanoparticles, including {111} on nano-octahedra and {100} on nano-cubes, are similar to their single-crystal counterparts. Combining our experimental results with density functional theory calculations, we elucidate the key role of surface proton transfers from co-adsorbed H 2O molecules in activating the facet- and potential-dependent 4e ORR on Au in alkaline solutions. These results elucidate how surface atomic structures determine the reaction pathways via bond scission and formation among weakly adsorbed water and reaction intermediates. The new insight helps in developing facet-specific nanocatalysts for various reactions.« less

Combined valence bond-molecular mechanics potential-energy surface and direct dynamics study of rate constants and kinetic isotope effects for the H + C2H6 reaction.

PubMed

Chakraborty, Arindam; Zhao, Yan; Lin, Hai; Truhlar, Donald G

2006-01-28

This article presents a multifaceted study of the reaction H+C(2)H(6)-->H(2)+C(2)H(5) and three of its deuterium-substituted isotopologs. First we present high-level electronic structure calculations by the W1, G3SX, MCG3-MPWB, CBS-APNO, and MC-QCISD/3 methods that lead to a best estimate of the barrier height of 11.8+/-0.5 kcal/mol. Then we obtain a specific reaction parameter for the MPW density functional in order that it reproduces the best estimate of the barrier height; this yields the MPW54 functional. The MPW54 functional, as well as the MPW60 functional that was previously parametrized for the H+CH(4) reaction, is used with canonical variational theory with small-curvature tunneling to calculate the rate constants for all four ethane reactions from 200 to 2000 K. The final MPW54 calculations are based on curvilinear-coordinate generalized-normal-mode analysis along the reaction path, and they include scaled frequencies and an anharmonic C-C bond torsion. They agree with experiment within 31% for 467-826 K except for a 38% deviation at 748 K; the results for the isotopologs are predictions since these rate constants have never been measured. The kinetic isotope effects (KIEs) are analyzed to reveal the contributions from subsets of vibrational partition functions and from tunneling, which conspire to yield a nonmonotonic temperature dependence for one of the KIEs. The stationary points and reaction-path potential of the MPW54 potential-energy surface are then used to parametrize a new kind of analytical potential-energy surface that combines a semiempirical valence bond formalism for the reactive part of the molecule with a standard molecular mechanics force field for the rest; this may be considered to be either an extension of molecular mechanics to treat a reactive potential-energy surface or a new kind of combined quantum-mechanical/molecular mechanical (QM/MM) method in which the QM part is semiempirical valence bond theory; that is, the new potential-energy surface is a combined valence bond molecular mechanics (CVBMM) surface. Rate constants calculated with the CVBMM surface agree with the MPW54 rate constants within 12% for 534-2000 K and within 23% for 200-491 K. The full CVBMM potential-energy surface is now available for use in variety of dynamics calculations, and it provides a prototype for developing CVBMM potential-energy surfaces for other reactions.

The effect of impurities and incident angle on the secondary electron emission of Ni(110)

NASA Astrophysics Data System (ADS)

Lazar, Hadar; Patino, Marlene; Raitses, Yevgeny; Koel, Bruce E.; Gentile, Charles; Feibush, Eliot

2015-11-01

The investigation of secondary electron emission (SEE) of conducting materials used for magnetic fusion devices and plasma thrusters is important for determining device lifetime and performance. Methods to quantify the secondary electron emission from conducting materials and to characterize the effects that impurities and incident angles have on secondary electron emission were developed using 4-grid low energy electron diffraction (LEED) optics. The total secondary electron yield from a Ni(110) surface was continuously measured from the sample current as surface contamination increased from reactions with background gases in the ultrahigh vacuum chamber. Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) were used to examine the composition and impurity levels on the Ni(110) surface. The total secondary electron yield was also measured at different incident angles. Thank you to the Princeton Plasma Physics Laboratory and the Department of Energy for the opportunity to work on this project through the Science Undergraduate Laboratory Internships.

Selective deoxygenation of aldehydes and alcohols on molybdenum carbide (Mo2C) surfaces

NASA Astrophysics Data System (ADS)

Xiong, Ke; Yu, Weiting; Chen, Jingguang G.

2014-12-01

The selective deoxygenation of aldehydes and alcohols without cleaving the Csbnd C bond is crucial for upgrading bio-oil and other biomass-derived molecules to useful fuels and chemicals. In this work, propanal, 1-propanol, furfural and furfuryl alcohol were selected as probe molecules to study the deoxygenation of aldehydes and alcohols on molybdenum carbide (Mo2C) prepared over a Mo(1 1 0) surface. The reaction pathways were investigated using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). The deoxygenation of propanal and 1-propanol went through a similar intermediate (propoxide or η2(C,O)-propanal) to produce propene. The deoxygenation of furfural and furfuryl alcohol produced a surface intermediate similar to adsorbed 2-methylfuran. The comparison of these results revealed the promising deoxygenation performance of Mo2C, as well as the effect of the furan ring on the selective deoxygenation of the Cdbnd O and Csbnd OH bonds.

Enhanced capture of elemental mercury by bamboo-based sorbents.

PubMed

Tan, Zengqiang; Xiang, Jun; Su, Sheng; Zeng, Hancai; Zhou, Changsong; Sun, Lushi; Hu, Song; Qiu, Jianrong

2012-11-15

To develop cost-effective sorbent for gas-phase elemental mercury removal, the bamboo charcoal (BC) produced from renewable bamboo and KI modified BC (BC-I) were used for elemental mercury removal. The effect of NO, SO2 on gas-phase Hg0 adsorption by KI modified BC was evaluated on a fixed bed reactor using an online mercury analyzer. BET surface area analysis, temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) were used to determine the pore structure and surface chemistry of the sorbents. The results show that KI impregnation reduced the sorbents' BET surface area and total pore volume compared with that of the original BC. But the BC-I has excellent adsorption capacity for elemental mercury at a relatively higher temperature of 140 °C and 180 °C. The presence of NO or SO2 could inhibit Hg0 capture, but BC-I has strong anti-poisoning ability. The specific reaction mechanism has been further analyzed. Copyright © 2012 Elsevier B.V. All rights reserved.

The effects of impurities and incidence angle on the secondary electron emission of Ni(110)

NASA Astrophysics Data System (ADS)

Lazar, Hadar; Patino, Marlene; Raitses, Yevgeny; Koel, Bruce; Gentile, Charles; Feibush, Eliot

The investigation of secondary electron emission (SEE) of conducting materials used for magnetic fusion devices and plasma thrusters is important for determining device lifetime and performance. Methods to quantify the secondary electron emission from conducting materials and to characterize the effects that impurities and incidence angles have on secondary electron emission were developed using 4-grid low energy electron diffraction (LEED) optics. The total secondary electron yield from a Ni(110) surface was continuously measured from the sample current as surface contamination increased from reactions with background gases in the ultrahigh vacuum chamber. Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) were used to examine the composition and impurity levels on the Ni(110) surface. The total secondary electron yield was also measured at different incidence angles. Thank you to the Princeton Plasma Physics Laboratory (PPPL) and the Department of Energy (DOE) for the opportunity to work on this project through the Science Undergraduate Laboratory Internships (SULI).

On-Surface Domino Reactions: Glaser Coupling and Dehydrogenative Coupling of a Biscarboxylic Acid To Form Polymeric Bisacylperoxides.

PubMed

Held, Philipp Alexander; Gao, Hong-Ying; Liu, Lacheng; Mück-Lichtenfeld, Christian; Timmer, Alexander; Mönig, Harry; Barton, Dennis; Neugebauer, Johannes; Fuchs, Harald; Studer, Armido

2016-08-08

Herein we report the on-surface oxidative homocoupling of 6,6'-(1,4-buta-1,3-diynyl)bis(2-naphthoic acid) (BDNA) via bisacylperoxide formation on different Au substrates. By using this unprecedented dehydrogenative polymerization of a biscarboxylic acid, linear poly-BDNA with a chain length of over 100 nm was prepared. It is shown that the monomer BDNA can be prepared in situ at the surface via on-surface Glaser coupling of 6-ethynyl-2-naphthoic acid (ENA). Under the Glaser coupling conditions, BDNA directly undergoes polymerization to give the polymeric peroxide (poly-BDNA) representing a first example of an on-surface domino reaction. It is shown that the reaction outcome varies as a function of surface topography (Au(111) or Au(100)) and also of the surface coverage, to give branched polymers, linear polymers, or 2D metal-organic networks. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of Hydrogen Sulfide Exposure on the Transport and Structural Properties of the Metal–Organic Framework ZIF-8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dutta, Akshita; Tymi?ska, Nina; Zhu, Guanghui

In this paper, the interaction between hydrogen sulfide and ZIF-8 was studied via structural characterizations and guest molecule diffusion measurements. It was found that hydrogen sulfide reacts with the ZIF-8 external particle surface to form a surface barrier that excludes the uptake of larger molecules (ethanol) and slows down the uptake of smaller molecules (carbon dioxide). Nonetheless, bulk transport properties were unaltered, as supported by pulsed field gradient nuclear magnetic resonance studies. Dispersion-corrected density functional theory calculations revealed that H 2S is consumed by reactions occurring at the ZIF external surface. These reactions result in water and defect formation, bothmore » of which were found to be exothermic and independent of both crystallographic facets ({001} and {110}) and surface termination. Finally, we concluded that these surface reactions lead to structural and chemical changes to the ZIF-8 external surface that generate surface barriers to molecular transport.« less

Influence of Hydrogen Sulfide Exposure on the Transport and Structural Properties of the Metal–Organic Framework ZIF-8

DOE PAGES

Dutta, Akshita; Tymi?ska, Nina; Zhu, Guanghui; ...

2018-03-09

In this paper, the interaction between hydrogen sulfide and ZIF-8 was studied via structural characterizations and guest molecule diffusion measurements. It was found that hydrogen sulfide reacts with the ZIF-8 external particle surface to form a surface barrier that excludes the uptake of larger molecules (ethanol) and slows down the uptake of smaller molecules (carbon dioxide). Nonetheless, bulk transport properties were unaltered, as supported by pulsed field gradient nuclear magnetic resonance studies. Dispersion-corrected density functional theory calculations revealed that H 2S is consumed by reactions occurring at the ZIF external surface. These reactions result in water and defect formation, bothmore » of which were found to be exothermic and independent of both crystallographic facets ({001} and {110}) and surface termination. Finally, we concluded that these surface reactions lead to structural and chemical changes to the ZIF-8 external surface that generate surface barriers to molecular transport.« less

Surface modifications of hydrogen storage alloy by heavy ion beams with keV to MeV irradiation energies

NASA Astrophysics Data System (ADS)

Abe, Hiroshi; Tokuhira, Shinnosuke; Uchida, Hirohisa; Ohshima, Takeshi

2015-12-01

This study deals with the effect of surface modifications induced from keV to MeV heavy ion beams on the initial reaction rate of a hydrogen storage alloy (AB5) in electrochemical process. The rare earth based alloys like this sample alloy are widely used as a negative electrode of Ni-MH (Nickel-Metal Hydride) battery. We aimed to improve the initial reaction rate of hydrogen absorption by effective induction of defects such as vacancies, dislocations, micro-cracks or by addition of atoms into the surface region of the metal alloys. Since defective layer near the surface can easily be oxidized, the conductive oxide layer is formed on the sample surface by O+ beams irradiation, and the conductive oxide layer might cause the improvement of initial reaction rate of hydriding. This paper demonstrates an effective surface treatment of heavy ion irradiation, which induces catalytic activities of rare earth oxides in the alloy surface.

Organelle-mimicking liposome dissociates G-quadruplexes and facilitates transcription

PubMed Central

Pramanik, Smritimoy; Tateishi-Karimata, Hisae; Sugimoto, Naoki

2014-01-01

Important biological reactions involving nucleic acids occur near the surface of membranes such as the nuclear membrane (NM) and rough endoplasmic reticulum (ER); however, the interactions between biomembranes and nucleic acids are poorly understood. We report here that transcription was facilitated in solution with liposomes, which mimic a biomembrane surface, relative to the reaction in a homogeneous aqueous solution when the template was able to form a G-quadruplex. The G-quadruplex is known to be an inhibitor of transcription, but the stability of the G-quadruplex was decreased at the liposome surface because of unfavourable enthalpy. The destabilization of the G-quadruplex was greater at the surface of NM- and ER-mimicking liposomes than at the surfaces of liposomes designed to mimic other organelles. Thermodynamic analyses revealed that the G-rich oligonucleotides adopted an extended structure at the liposome surface, whereas in solution the compact G-quadruplex was formed. Our data suggest that changes in structure and stability of nucleic acids regulate biological reactions at membrane surfaces. PMID:25336617

Multiscale atomistic simulation of metal-oxygen surface interactions: Methodological development, theoretical investigation, and correlation with experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Judith C.

The purpose of this grant is to develop the multi-scale theoretical methods to describe the nanoscale oxidation of metal thin films, as the PI (Yang) extensive previous experience in the experimental elucidation of the initial stages of Cu oxidation by primarily in situ transmission electron microscopy methods. Through the use and development of computational tools at varying length (and time) scales, from atomistic quantum mechanical calculation, force field mesoscale simulations, to large scale Kinetic Monte Carlo (KMC) modeling, the fundamental underpinings of the initial stages of Cu oxidation have been elucidated. The development of computational modeling tools allows for acceleratedmore » materials discovery. The theoretical tools developed from this program impact a wide range of technologies that depend on surface reactions, including corrosion, catalysis, and nanomaterials fabrication.« less

Treatment and Managing Reactions

MedlinePlus

... of reactions. Learn more here. Milk Egg Peanut Tree Nuts Soy Wheat Fish Shellfish Sesame Other Food Allergens Allergy Alerts Research Programs Research Programs We are the world’s largest private source of food allergy research funding. ...

Topology of Surface Ligands on Liposomes: Characterization Based on the Terms, Incorporation Ratio, Surface Anchor Density, and Reaction Yield.

PubMed

Lee, Shang-Hsuan; Sato, Yusuke; Hyodo, Mamoru; Harashima, Hideyoshi

2016-01-01

The surface topology of ligands on liposomes is an important factor in active targeting in drug delivery systems. Accurately evaluating the density of anchors and bioactive functional ligands on a liposomal surface is critical for ensuring the efficient delivery of liposomes. For evaluating surface ligand density, it is necessary to clarify that on the ligand-modified liposomal surfaces, some anchors are attached to ligands but some are not. To distinguish between these situations, a key parameter, surface anchor density, was introduced to specify amount of total anchors on the liposomal surface. Second, the parameter reaction yield was introduced to identify the amount of ligand-attached anchors among total anchors, since the conjugation efficiency is not always the same nor 100%. Combining these independent parameters, we derived: incorporation ratio=surface anchor density×reaction yield. The term incorporation ratio defines the surface ligand density. Since the surface anchor density represents the density of polyethylene glycol (PEG) on the surfaces in most cases, it also determines liposomal function. It is possible to accurately characterize various PEG and ligand densities and to define the surface topologies. In conclusion, this quantitative methodology can standardize the liposome preparation process and qualify the modified liposomal surfaces.

Novel duplex vapor-electrochemical method for silicon solar cells

NASA Technical Reports Server (NTRS)

Nanis, L.; Sanjurjo, A.; Westphal, S.

1979-01-01

Optimization studies were carried out for the SiF4-Na reaction with solid Na feed. The goals of the study were the consistent production of high purity reaction products and the gathering of relevant information needed to scale-up the reactor. Parameters studied include: (1) effect of surface to volume ratio of Na slices on the extent of reaction; (2) effect of Na surface oxidation on the extent of reaction; (3) effect of external heating on the extent of SiF4-Na reaction; (4) effect of Na slice addition rate on extent of the reaction; and (5) SiF4-Na reaction - high pressure experiments. An investigation was also made of the possible role played by NaF as a fluxing agent during the separation of silicon by melting of the reaction product (Si + NaF) mixture. Since silicon can be produced by the thermite reaction between Na2SiF6 and Na, studies were initiated to gather information on parameters which control the efficiency of the thermite reaction.

A Mechanistic Study of CO 2 Reduction at the Interface of a Gallium Phosphide (GaP) Surface using Core-level Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flynn, Kristen

2015-08-18

Carbon dioxide (CO 2) emission into the atmosphere has increased tremendously through burning of fossil fuels, forestry, etc.. The increased concentration has made CO 2 reductions very attractive though the reaction is considered uphill. Utilizing the sun as a potential energy source, CO 2 has the possibility to undergo six electron and four proton transfers to produce methanol, a useable resource. This reaction has been shown to occur selectively in an aqueous pyridinium solution with a gallium phosphide (GaP) electrode. Though this reaction has a high faradaic efficiency, it was unclear as to what role the GaP surface played duringmore » the reaction. In this work, we aim to address the fundamental role of GaP during the catalytic conversion, by investigating the interaction between a clean GaP surface with the reactants, products, and intermediates of this reaction using X-ray photoelectron spectroscopy. We have determined a procedure to prepare atomically clean GaP and our initial CO 2 adsorption studies have shown that there is evidence of chemisorption and reaction to form carbonate on the clean surface at LN2 temperatures (80K), in contrast to previous theoretical calculations. These findings will enable future studies on CO 2 catalysis.« less

A Mechanistic Study of CO 2 Reduction at the Interface of a Gallium Phosphide (GaP) Surface using Core-level Spectroscopy - Oral Presentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flynn, Kristen

2015-08-19

Carbon dioxide (CO 2) emission into the atmosphere has increased tremendously through burning of fossil fuels, forestry, etc.. The increased concentration has made CO 2 reductions very attractive though the reaction is considered uphill. Utilizing the sun as a potential energy source, CO 2 has the possibility to undergo six electron and four proton transfers to produce methanol, a useable resource. This reaction has been shown to occur selectively in an aqueous pyridinium solution with a gallium phosphide (GaP) electrode. Though this reaction has a high faradaic efficiency, it was unclear as to what role the GaP surface played duringmore » the reaction. In this work, we aim to address the fundamental role of GaP during the catalytic conversion, by investigating the interaction between a clean GaP surface with the reactants, products, and intermediates of this reaction using X-ray photoelectron spectroscopy. We have determined a procedure to prepare atomically clean GaP and our initial CO 2 adsorption studies have shown that there is evidence of chemisorption and reaction to form carbonate on the clean surface at LN2 temperatures (80K), in contrast to previous theoretical calculations. These findings will enable future studies on CO 2 catalysis.« less

Theory of vibrationally assisted tunneling for hydroxyl monomer flipping on Cu(110)

NASA Astrophysics Data System (ADS)

Gustafsson, Alexander; Ueba, Hiromu; Paulsson, Magnus

2014-10-01

To describe vibrationally mediated configuration changes of adsorbates on surfaces we have developed a theory to calculate both reaction rates and pathways. The method uses the T-matrix to describe excitations of vibrational states by the electrons of the substrate, adsorbate, and tunneling electrons from a scanning tunneling probe. In addition to reaction rates, the theory also provides the reaction pathways by going beyond the harmonic approximation and using the full potential energy surface of the adsorbate which contains local minima corresponding to the adsorbates different configurations. To describe the theory, we reproduce the experimental results in [T. Kumagai et al., Phys. Rev. B 79, 035423 (2009), 10.1103/PhysRevB.79.035423], where the hydrogen/deuterium atom of an adsorbed hydroxyl (OH/OD) exhibits back and forth flipping between two equivalent configurations on a Cu(110) surface at T =6 K. We estimate the potential energy surface and the reaction barrier, ˜160 meV, from DFT calculations. The calculated flipping processes arise from (i) at low bias, tunneling of the hydrogen through the barrier, (ii) intermediate bias, tunneling electrons excite the vibrations increasing the reaction rate although over the barrier processes are rare, and (iii) higher bias, overtone excitations increase the reaction rate further.

Nanocatalytic growth of Si nanowires from Ni silicate coated SiC nanoparticles on Si solar cell.

PubMed

Parida, Bhaskar; Choi, Jaeho; Ji, Hyung Yong; Park, Seungil; Lim, Gyoungho; Kim, Keunjoo

2013-09-01

We investigated the nanocatalytic growth of Si nanowires on the microtextured surface of crystalline Si solar cell. 3C-SiC nanoparticles have been used as the base for formation of Ni silicate layer in a catalytic reaction with the Si melt under H2 atmosphere at an annealing temperature of 1100 degrees C. The 10-nm thick Ni film was deposited after the SiC nanoparticles were coated on the microtextured surface of the Si solar cell by electron-beam evaporation. SiC nanoparticles form a eutectic alloy surface of Ni silicate and provide the base for Si supersaturation as well as the Ni-Si alloy layer on Si substrate surface. This bottom reaction mode for the solid-liquid-solid growth mechanism using a SiC nanoparticle base provides more stable growth of nanowires than the top reaction mode growth mechanism in the absence of SiC nanoparticles. Thermally excited Ni nanoparticle forms the eutectic alloy and provides collectively excited electrons at the alloy surface, which reduces the activation energy of the nanocatalytic reaction for formation of nanowires.

Molecular dynamics simulation of sodium aluminosilicate glass structures and glass surface-water reactions using the reactive force field (ReaxFF)

NASA Astrophysics Data System (ADS)

Dongol, R.; Wang, L.; Cormack, A. N.; Sundaram, S. K.

2018-05-01

Reactive potentials are increasingly used to study the properties of glasses and glass water reactions in a reactive molecular dynamics (MD) framework. In this study, we have simulated a ternary sodium aluminosilicate glass and investigated the initial stages of the glass surface-water reactions at 300 K using reactive force field (ReaxFF). On comparison of the simulated glass structures generated using ReaxFF and classical Buckingham potentials, our results show that the atomic density profiles calculated for the surface glass structures indicate a bond-angle distribution dependency. The atomic density profiles also show higher concentrations of non-bridging oxygens (NBOs) and sodium ions at the glass surface. Additionally, we present our results of formation of silanol species and the diffusion of water molecules at the glass surface using ReaxFF.

Surface modification of Cu metal particles by the chemical reaction between the surface oxide layer and a halogen surfactant

NASA Astrophysics Data System (ADS)

Yokoyama, Shun; Takahashi, Hideyuki; Itoh, Takashi; Motomiya, Kenichi; Tohji, Kazuyuki

2014-01-01

Surface oxides on small (2-5 μm) copper metal particles can be removed by chemical reaction with tris(2,3-dibromopropyl) isocyanurate (TIC) in diethylene glycol mono-n-hexyl ether (DGHE) solution under mild conditions where metal particles are not damaged. Surface oxides convert to copper bromide species and subsequently dissolve into the solvent. It was found that resultant surface species are resistant to re-oxidation due to remaining surface bromides. This finding opens up a possibility to create microclines based on cheap copper nanoparticles.

Energy partitioning in polyatomic chemical reactions: Quantum state resolved studies of highly exothermic atom abstraction reactions from molecules in the gas phase and at the gas-liquid interface

NASA Astrophysics Data System (ADS)

Zolot, Alexander M.

This thesis recounts a series of experiments that interrogate the dynamics of elementary chemical reactions using quantum state resolved measurements of gas-phase products. The gas-phase reactions F + HCl → HF + Cl and F + H2O → HF + OH are studied using crossed supersonic jets under single collision conditions. Infrared (IR) laser absorption probes HF product with near shot-noise limited sensitivity and high resolution, capable of resolving rovibrational states and Doppler lineshapes. Both reactions yield inverted vibrational populations. For the HCl reaction, strongly bimodal rotational distributions are observed, suggesting microscopic branching of the reaction mechanism. Alternatively, such structure may result from a quantum-resonance mediated reaction similar to those found in the well-characterized F + HD system. For the H2O reaction, a small, but significant, branching into v = 2 is particularly remarkable because this manifold is accessible only via the additional center of mass collision energy in the crossed jets. Rotationally hyperthermal HF is also observed. Ab initio calculations of the transition state geometry suggest mechanisms for both rotational and vibrational excitation. Exothermic chemical reaction dynamics at the gas-liquid interface have been investigated by colliding a supersonic jet of F atoms with liquid squalane (C30H62), a low vapor pressure hydrocarbon compatible with the high vacuum environment. IR spectroscopy provides absolute HF( v,J) product densities and Doppler resolved velocity component distributions perpendicular to the surface normal. Compared to analogous gas-phase F + hydrocarbon reactions, the liquid surface is a more effective "heat sink," yet vibrationally excited populations reveal incomplete thermal accommodation with the surface. Non-Boltzmann J-state populations and hot Doppler lineshapes that broaden with HF excitation indicate two competing scattering mechanisms: (i) a direct reactive scattering channel, whereby newly formed molecules leave the surface without equilibrating, and (ii) a partially accommodated fraction that shares vibrational, rotational, and translational energy with the liquid surface before returning to the gas phase. Finally, a velocity map ion imaging apparatus has been implemented to investigate reaction dynamics in crossed molecular beams. Resonantly enhanced multiphoton ionization (REMPI) results in rotational, vibrational, and electronic state selectivity. Velocity map imaging measurements provide differential cross sections and information about the internal energy distribution of the undetected collision partner.

Surface-catalyzed air oxidation reactions of hydrazines: Tubular reactor studies

NASA Technical Reports Server (NTRS)

Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

1988-01-01

The surface-catalyzed air oxidation reactions of hydrazine, monomethylhydrazine, unsymmetrical dimethylhydrazine, symmetrical dimethylhydrazine, trimethylhydrazine and tetramethylhydrazine were investigated in a metal-powder packed turbular flow reactor at 55 plus or minus 3 C. Hydrazine was completely reacted on all surfaces studied. The major products of monomethylhydrazine (MMH) oxidation were methanol, methane and methyldiazene. The di-, tri- and tetra-methyl hydrazines were essentially unreactive under these conditions. The relative catalytic reactivities toward MMH are: Fe greater than Al2O3 greater than Ti greater than Zn greater than 316 SS greater than Cr greater than Ni greater than Al greater than 304L SS. A kinetic scheme and mechanism involving adsorption, oxidative dehydrogenation and reductive elimination reactions on a metal oxide surface are proposed.

Plasma-catalyzed fuel reformer

DOEpatents

Hartvigsen, Joseph J.; Elangovan, S.; Czernichowski, Piotr; Hollist, Michele

2013-06-11

A reformer is disclosed that includes a plasma zone to receive a pre-heated mixture of reactants and ionize the reactants by applying an electrical potential thereto. A first thermally conductive surface surrounds the plasma zone and is configured to transfer heat from an external heat source into the plasma zone. The reformer further includes a reaction zone to chemically transform the ionized reactants into synthesis gas comprising hydrogen and carbon monoxide. A second thermally conductive surface surrounds the reaction zone and is configured to transfer heat from the external heat source into the reaction zone. The first thermally conductive surface and second thermally conductive surface are both directly exposed to the external heat source. A corresponding method and system are also disclosed and claimed herein.

DYNAMICS OF MINERAL STRUCTURES AND THE FATE OF METALS IN SOILS AND SEDIMENTS

EPA Science Inventory

Significant progress has been made in elucidating sorption reactions that control the partitioning of metals from solution to mineral surfaces in contaminated soil/sediment systems. Surface complexation models have been developed to quantify the forward reaction with reasonable ...

Diffusion and Surface Reaction in Heterogeneous Catalysis

ERIC Educational Resources Information Center

Baiker, A.; Richarz, W.

1978-01-01

Ethylene hydrogenation on a platinum catalyst, electrolytically applied to a tube wall, is a good system for the study of the interactions between diffusion and surface reaction in heterogeneous catalysis. Theoretical background, apparatus, procedure, and student performance of this experiment are discussed. (BB)

Lateral uniformity in chemical composition along a buried reaction front in polymers using off-specular reflectivity.

PubMed

Lavery, Kristopher A; Prabhu, Vivek M; Satija, Sushil; Wu, Wen-Li

2010-12-01

Off-specular neutron reflectometry was applied to characterize the form and amplitude of lateral compositional variations at a buried reaction-diffusion front. In this work, off-specular neutron measurements were first calibrated using off-specular x-ray reflectivity and atomic force microscopy via a roughened glass surface, both as a free surface and as a buried interface that was prepared by spin coating thin polymer films upon the glass surface. All three methods provided consistent roughness values despite the difference in their detection mechanism. Our neutron results demonstrated, for the first time, that the compositional heterogeneity at a buried reaction front can be measured; the model system used in this study mimics the deprotection reaction that occurs during the photolithographic process necessary for manufacturing integrated circuits.

Label-free electrical detection of pyrophosphate generated from DNA polymerase reactions on field-effect devices.

PubMed

Credo, Grace M; Su, Xing; Wu, Kai; Elibol, Oguz H; Liu, David J; Reddy, Bobby; Tsai, Ta-Wei; Dorvel, Brian R; Daniels, Jonathan S; Bashir, Rashid; Varma, Madoo

2012-03-21

We introduce a label-free approach for sensing polymerase reactions on deoxyribonucleic acid (DNA) using a chelator-modified silicon-on-insulator field-effect transistor (SOI-FET) that exhibits selective and reversible electrical response to pyrophosphate anions. The chemical modification of the sensor surface was designed to include rolling-circle amplification (RCA) DNA colonies for locally enhanced pyrophosphate (PPi) signal generation and sensors with immobilized chelators for capture and surface-sensitive detection of diffusible reaction by-products. While detecting arrays of enzymatic base incorporation reactions is typically accomplished using optical fluorescence or chemiluminescence techniques, our results suggest that it is possible to develop scalable and portable PPi-specific sensors and platforms for broad biomedical applications such as DNA sequencing and microbe detection using surface-sensitive electrical readout techniques.

Reactions of Ground State Nitrogen Atoms N(4S) with Astrochemically-Relevant Molecules on Interstellar Dusts

NASA Astrophysics Data System (ADS)

Krim, Lahouari; Nourry, Sendres

2015-06-01

In the last few years, ambitious programs were launched to probe the interstellar medium always more accurately. One of the major challenges of these missions remains the detection of prebiotic compounds and the understanding of reaction pathways leading to their formation. These complex heterogeneous reactions mainly occur on icy dust grains, and their studies require the coupling of laboratory experiments mimicking the extreme conditions of extreme cold and dilute media. For that purpose, we have developed an original experimental approach that combine the study of heterogeneous reactions (by exposing neutral molecules adsorbed on ice to non-energetic radicals H, OH, N...) and a neon matrix isolation study at very low temperatures, which is of paramount importance to isolate and characterize highly reactive reaction intermediates. Such experimental approach has already provided answers to many questions raised about some astrochemically-relevant reactions occurring in the ground state on the surface of dust grain ices in dense molecular clouds. The aim of this new present work is to show the implication of ground state atomic nitrogen on hydrogen atom abstraction reactions from some astrochemically-relevant species, at very low temperatures (3K-20K), without providing any external energy. Under cryogenic temperatures and with high barrier heights, such reactions involving N(4S) nitrogen atoms should not occur spontaneously and require an initiating energy. However, the detection of some radicals species as byproducts, in our solid samples left in the dark for hours at 10K, proves that hydrogen abstraction reactions involving ground state N(4S) nitrogen atoms may occur in solid phase at cryogenic temperatures. Our results show the efficiency of radical species formation stemming from non-energetic N-atoms and astrochemically-relevant molecules. We will then discuss how such reactions, involving nitrogen atoms in their ground states, might be the first key step towards complex organic molecules production in the interstellar medium.

3rd hand smoking; heterogeneous oxidation of nicotine and secondary aerosol formation in the indoor environment

NASA Astrophysics Data System (ADS)

Petrick, Lauren; Dubowski, Yael

2010-05-01

Tobacco smoking is well known as a significant source of primary indoor air pollutants. However, only recently has it been recognized that the impact of Tobacco smoking may continue even after the cigarette has been extinguished (i.e., third hand smoke) due to the effect of indoor surfaces. These surfaces may affect the fate of tobacco smoke in the form of secondary reactions and pollutants, including secondary organic aerosol (SOA) formation. Fourier Transform Infrared spectrometry with Attenuated Total Reflection (FTIR-ATR) in tandem with a Scanning Mobility Particle Sizing (SMPS) system was used to monitor the ozonation of cellulose sorbed nicotine and resulting SOA formation. SOA formation began at onset of ozone introduction ([O3] = 60 ± 5 ppb) with a size distribution of dp ≤ 25 nm, and was determined to be a result of heterogeneous reaction (opposed to homogeneous). SOA yield from reacted surface nicotine was on the order of 10 %. Simultaneous to SOA monitoring, FTIR-ATR spectra showed surface changes in the nicotine film as the reaction progressed, revealing a pseudo first-order surface reaction rate of 0.0026 ± 0.0008 min-1. Identified surface oxidation products included: cotinine, myosmine, methylnicotinamide and nicotyrine. Surface reaction rate was found to be partially inhibited at high relative humidity. Given the toxicity of some of the identified products (e.g., cotinine has shown potential mutagenicity and teratogenicity) and that small particles may contribute to adverse health effects, the present study indicates that exposure to 3rd hand smoke ozonation products may pose additional health risks.

Design study for a magnetically supported reaction wheel

NASA Technical Reports Server (NTRS)

Stocking, G.; Dendy, J.; Sabnis, A.

1974-01-01

Results are described of a study program in which the characteristics of a magnetically supported reaction wheel are defined. Tradeoff analyses are presented for the principal components, which are then combined in several reaction wheel design concepts. A preliminary layout of the preferred configuration is presented along with calculated design and performance parameters. Recommendations are made for a prototype development program.

Towards a Model of Reactive-Cracking: the Role of Reactions, Elasticity and Surface Energy Driven Flow in Poro-elastic Media

NASA Astrophysics Data System (ADS)

Evans, O.; Spiegelman, M. W.; Wilson, C. R.; Kelemen, P. B.

2016-12-01

Many critical processes can be described by reactive fluid flow in brittle media, including hydration/alteration of oceanic plates near spreading ridges, chemical weathering, and dehydration/decarbonation of subducting plates. Such hydration reactions can produce volume changes that may induce stresses large enough to drive fracture in the rock, in turn exposing new reactive surface and modifying the permeability. A better understanding of this potentially rich feedback could also be critical in the design of engineered systems for geologic carbon sequestration. To aid understanding of these processes we have developed a macroscopic continuum description of reactive fluid flow in an elastically deformable porous media. We explore the behaviour of this model by considering a simplified hydration reaction (e.g. olivine + H20 -> serpentine + brucite). In a closed system, these hydration reactions will continue to consume available fluids until the permeability reaches zero, leaving behind it a highly stressed residuum. Our model demonstrates this limiting behaviour, and that the elastic stresses generated are large enough to cause failure/fracture of the host rock. Whilst it is understood that `reactive fracture' is an important mechanism for the continued evolution of this process, it is also proposed that imbibition/surface energy driven flow may play a role. Through a simplified set of computational experiments, we investigate the relative roles of elasticity and surface energy in both a non-reactive purely poro-elastic framework, and then in the presence of reaction. We demonstrate that surface energy can drive rapid diffusion of porosity, thus allowing the reaction to propagate over larger areas. As we expect both surface energy and fracture/failure to be of importance in these processes, we plan to integrate the current model into one that allows for fracture once critical stresses are exceeded.

The role of defective silica surfaces in exogenous delivery of prebiotic compounds: clues from first principles calculations.

PubMed

Rimola, Albert; Ugliengo, Piero

2009-04-14

The reaction of glycine (Gly) with a strained (SiO)(2) four-membered ring defect (D2) at the surface of an interstellar silica grain dust has been studied at ONIOM2[B3LYP/6-31+G(d,p):MNDO] level within a cluster approach in the context of hypothetical reactions occurring in the interstellar medium. The D2 opens up exothermically for reaction with Gly (Delta(r)U(0)=-26.3 kcal mol(-1)) to give a surface mixed anhydride S(surf)-O-C([double bond, length as m-dash]O)-CH(2)NH(2) as a product. The reaction barriers, DeltaU( not equal)(0), are 0.1 and 10.4 kcal mol(-1) for reactive channels involving COOH and NH(2) as attacking groups, respectively. Calculations show the surface mixed anhydride to be rather stable under the action of interstellar processes, such as reactions with isolated H(2)O and NH(3) molecules or the exposure to cosmic rays and UV radiation. The hydrolysis of the surface mixed anhydride to release again Gly was modelled by microsolvation (from 1 to 4 H(2)O molecules) mimicking what could have happened to the interstellar dust after seeding the primordial ocean in the early Earth. Results for these calculations show that the reaction is exergonic and activated, the Delta(r)G(298) becoming more negative and the DeltaG( not equal)(298) being dramatically reduced as a function of increasing number of H(2)O molecules. The present results are relevant because they show that defects present at interstellar dust surfaces could have played a significant role in capturing, protecting and delivering essential prebiotic compounds on the early Earth.

Organic chemistry on solid surfaces

NASA Astrophysics Data System (ADS)

Ma, Zhen; Zaera, Francisco

2006-07-01

Chemistry on solid surfaces is central to many areas of practical interest such as heterogeneous catalysis, tribology, electrochemistry, and materials processing. With the development of many surface-sensitive analytical techniques in the past decades, great advances have been possible in our understanding of such surface chemistry at the molecular level. Earlier studies with model systems, single crystals in particular, have provided rich information about the adsorption and reaction kinetics of simple inorganic molecules. More recently, the same approach has been expanded to the study of the surface chemistry of relatively complex organic molecules, in large measure in connection with the selective synthesis of fine chemicals and pharmaceuticals. In this report, the chemical reactions of organic molecules and fragments on solid surfaces, mainly on single crystals of metals but also on crystals of metal oxides, carbides, nitrides, phosphides, sulfides and semiconductors as well as on more complex models such as bimetallics, alloys, and supported particles, are reviewed. A scheme borrowed from the organometallic and organic chemistry literature is followed in which key examples of representative reactions are cited first, and general reactivity trends in terms of both the reactants and the nature of the surface are then identified to highlight important mechanistic details. An attempt has been made to emphasize recent advances, but key earlier examples are cited as needed. Finally, correlations between surface and organometallic and organic chemistry, the relevance of surface reactions to applied catalysis and materials functionalization, and some promising future directions in this area are briefly discussed.

Collisions of slow polyatomic ions with surfaces: dissociation and chemical reactions of C2H2+*, C2H3+, C2H4+*, C2H5+, and their deuterated variants C2D2+* and C2D4+* on room-temperature and heated carbon surfaces.

PubMed

Jasík, Juraj; Zabka, Jan; Feketeova, Linda; Ipolyi, Imre; Märk, Tilmann D; Herman, Zdenek

2005-11-17

Interaction of C2Hn+ (n = 2-5) hydrocarbon ions and some of their isotopic variants with room-temperature and heated (600 degrees C) highly oriented pyrolytic graphite (HOPG) surfaces was investigated over the range of incident energies 11-46 eV and an incident angle of 60 degrees with respect to the surface normal. The work is an extension of our earlier research on surface interactions of CHn+ (n = 3-5) ions. Mass spectra, translational energy distributions, and angular distributions of product ions were measured. Collisions with the HOPG surface heated to 600 degrees C showed only partial or substantial dissociation of the projectile ions; translational energy distributions of the product ions peaked at about 50% of the incident energy. Interactions with the HOPG surface at room temperature showed both surface-induced dissociation of the projectiles and, in the case of radical cation projectiles C2H2+* and C2H4+*, chemical reactions with the hydrocarbons on the surface. These reactions were (i) H-atom transfer to the projectile, formation of protonated projectiles, and their subsequent fragmentation and (ii) formation of a carbon chain build-up product in reactions of the projectile ion with a terminal CH3-group of the surface hydrocarbons and subsequent fragmentation of the product ion to C3H3+. The product ions were formed in inelastic collisions in which the translational energy of the surface-excited projectile peaked at about 32% of the incident energy. Angular distributions of reaction products showed peaking at subspecular angles close to 68 degrees (heated surfaces) and 72 degrees (room-temperature surfaces). The absolute survival probability at the incident angle of 60 degrees was about 0.1% for C2H2+*, close to 1% for C2H4+* and C2H5+, and about 3-6% for C2H3+.

Reaction of a phospholipid monolayer with gas-phase ozone at the air-water interface: measurement of surface excess and surface pressure in real time.

PubMed

Thompson, Katherine C; Rennie, Adrian R; King, Martin D; Hardman, Samantha J O; Lucas, Claire O M; Pfrang, Christian; Hughes, Brian R; Hughes, Arwel V

2010-11-16

The reaction between gas-phase ozone and monolayers of the unsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, on aqueous solutions has been studied in real time using neutron reflection and surface pressure measurements. The reaction between ozone and lung surfactant, which contains POPC, leads to decreased pulmonary function, but little is known about the changes that occur to the interfacial material as a result of oxidation. The results reveal that the initial reaction of ozone with POPC leads to a rapid increase in surface pressure followed by a slow decrease to very low values. The neutron reflection measurements, performed on an isotopologue of POPC with a selectively deuterated palmitoyl strand, reveal that the reaction leads to loss of this strand from the air-water interface, suggesting either solubilization of the product lipid or degradation of the palmitoyl strand by a reactive species. Reactions of (1)H-POPC on D(2)O reveal that the headgroup region of the lipids in aqueous solution is not dramatically perturbed by the reaction of POPC monolayers with ozone supporting degradation of the palmitoyl strand rather than solubilization. The results are consistent with the reaction of ozone with the oleoyl strand of POPC at the air-water interface leading to the formation of OH radicals. The highly reactive OH radicals produced can then go on to react with the saturated palmitoyl strands leading to the formation of oxidized lipids with shorter alkyl tails.

Methanol synthesis on ZnO(0001{sup ¯}). IV. Reaction mechanisms and electronic structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frenzel, Johannes, E-mail: johannes.frenzel@theochem.rub.de; Marx, Dominik

2014-09-28

Methanol synthesis from CO and H{sub 2} over ZnO, which requires high temperatures and high pressures giving rise to a complex interplay of physical and chemical processes over this heterogeneous catalyst surface, is investigated using ab initio simulations. The redox properties of the surrounding gas phase are known to directly impact on the catalyst properties and thus, set the overall catalytic reactivity of this easily reducible oxide material. In Paper III of our series [J. Kiss, J. Frenzel, N. N. Nair, B. Meyer, and D. Marx, J. Chem. Phys. 134, 064710 (2011)] we have qualitatively shown that for the partiallymore » hydroxylated and defective ZnO(0001{sup ¯}) surface there exists an intricate network of surface chemical reactions. In the present study, we employ advanced molecular dynamics techniques to resolve in detail this reaction network in terms of elementary steps on the defective surface, which is in stepwise equilibrium with the gas phase. The two individual reduction steps were investigated by ab initio metadynamics sampling of free energy landscapes in three-dimensional reaction subspaces. By also sampling adsorption and desorption processes and thus molecular species that are in the gas phase but close to the surface, our approach successfully generated several alternative pathways of methanol synthesis. The obtained results suggest an Eley-Rideal mechanism for both reduction steps, thus involving “near-surface” molecules from the gas phase, to give methanol preferentially over a strongly reduced catalyst surface, while important side reactions are of Langmuir-Hinshelwood type. Catalyst re-reduction by H{sub 2} stemming from the gas phase is a crucial process after each reduction step in order to maintain the catalyst's activity toward methanol formation and to close the catalytic cycle in some reaction channels. Furthermore, the role of oxygen vacancies, side reactions, and spectator species is investigated and mechanistic details are discussed based on extensive electronic structure analysis.« less

Electromagnetic field redistribution induced selective plasmon driven surface catalysis in metal nanowire-film systems

PubMed Central

Pan, Liang; Huang, Yingzhou; Yang, Yanna; Xiong, Wen; Chen, Guo; Su, Xun; Wei, Hua; Wang, Shuxia; Wen, Weijia

2015-01-01

For the novel interpretation of Raman spectrum from molecule at metal surface, the plasmon driven surface catalysis (PDSC) reactions have become an interesting topic in the research field of surface enhanced Raman scattering (SERS). In this work, the selective PDSC reactions of p,p’-dimercaptoazobenzene (DMAB) produced from para-aminothiophenol (PATP) or 4-nitrobenzenethiol (4NBT) were demonstrated in the Ag nanowires dimer-Au film systems. The different SERS spectra collected at individual part and adjacent part of the same nanowire-film system pointed out the importance of the electromagnetic field redistribution induced by image charge on film in this selective surface catalysis, which was confirmed by the simulated electromagnetic simulated electro- magnetic field distributions. Our result indicated this electromagnetic field redistribution induced selective surface catalysis was largely affected by the polarization and wavelength of incident light but slightly by the difference in diameters between two nanowires. Our work provides a further understanding of PDSC reaction in metal nanostructure and could be a deep support for the researches on surface catalysis and surface analysis. PMID:26601698

Selective C-O Hydrogenolysis and Decarboxylation of Biomass-Derived Heterocyclic Compounds over Heterogeneous Catalysts

NASA Astrophysics Data System (ADS)

Chia, Mei

The catalytic deoxygenation of biomass-derived compounds through selective C-O hydrogenolysis, catalytic transfer hydrogenation and lactonization, and decarboxylation to value-added chemicals over heterogeneous catalysts was examined under liquid phase reaction conditions. The reactions studied involve the conversion or production of heterocyclic compounds, specifically, cyclic ethers, lactones, and 2-pyrones. A bimetallic RhRe/C catalyst was found to be selective for the hydrogenolysis of secondary C-O bonds for a broad range cyclic ethers and polyols. Results from experimentally-observed reactivity trends, NH3 temperature-programmed desorption, fructose dehydration reaction studies, and first-principles density functional theory (DFT) calculations are consistent with the hypothesis of a bifunctional catalyst which facilitates acid-catalyzed ring-opening and dehydration coupled with metal-catalyzed hydrogenation. C-O hydrogenolysis and fructose dehydration activities were observed to decrease with an increase in reduction temperature and a decrease in the number of surface metallic Re atoms measured by in situ X-ray absorption spectroscopy. No C-O hydrogenolysis activity was detected over RhRe/C under water-free conditions. The activation of water molecules by Re atoms on the surface of metallic Rh is suggested to result in the formation of Bronsted acidity over RhRe/C. The catalytic transfer hydrogenation and lactonization of levulinic acid and its esters to gamma-valerolactone was accomplished through the Meerwein-Ponndorf-Verley reaction over metal oxide catalysts using secondary alcohols as the hydrogen donor. ZrO2 was a highly active material for CTH under batch and continuous flow reaction conditions; the initial activity of the catalyst was repeatedly regenerable by calcination in air, with no observable loss in catalytic activity. Lastly, the 2-pyrone, triacetic acid lactone, is shown to be a promising biorenewable platform chemical from which a wide range of chemical intermediates and end products can be obtained using heterogeneous catalysts or by thermal decomposition. Mechanistic insights from experimentally-observed reactivity trends and results from DFT calculations indicate that 2-pyrones undergo reactions unique to their structure such as keto-enol tautomerization, retro Diels-Alder, and nucleophilic attack by water. Ring-opening and decarboxylation reactions were found to be governed by key structural features such as the degree of saturation in the ring (e.g., C4=C5 bond), nature of the solvent, and presence of an acid catalyst.

Some reflections on the understanding of the oxygen reduction reaction at Pt(111)

PubMed Central

Gómez-Marín, Ana M; Rizo, Ruben

2013-01-01

Summary The oxygen reduction reaction (ORR) is a pivotal process in electrochemistry. Unfortunately, after decades of intensive research, a fundamental knowledge about its reaction mechanism is still lacking. In this paper, a global and critical view on the most important experimental and theoretical results regarding the ORR on Pt(111) and its vicinal surfaces, in both acidic and alkaline media, is taken. Phenomena such as the ORR surface structure sensitivity and the lack of a reduction current at high potentials are discussed in the light of the surface oxidation and disordering processes and the possible relevance of the hydrogen peroxide reduction and oxidation reactions in the ORR mechanism. The necessity to build precise and realistic reaction models, which are deducted from reliable experimental results that need to be carefully taken under strict working conditions is shown. Therefore, progress in the understanding of this important reaction on a molecular level, and the choice of the right approach for the design of the electrocatalysts for fuel-cell cathodes is only possible through a cooperative approach between theory and experiments. PMID:24455454

Some reflections on the understanding of the oxygen reduction reaction at Pt(111).

PubMed

Gómez-Marín, Ana M; Rizo, Ruben; Feliu, Juan M

2013-12-27

The oxygen reduction reaction (ORR) is a pivotal process in electrochemistry. Unfortunately, after decades of intensive research, a fundamental knowledge about its reaction mechanism is still lacking. In this paper, a global and critical view on the most important experimental and theoretical results regarding the ORR on Pt(111) and its vicinal surfaces, in both acidic and alkaline media, is taken. Phenomena such as the ORR surface structure sensitivity and the lack of a reduction current at high potentials are discussed in the light of the surface oxidation and disordering processes and the possible relevance of the hydrogen peroxide reduction and oxidation reactions in the ORR mechanism. The necessity to build precise and realistic reaction models, which are deducted from reliable experimental results that need to be carefully taken under strict working conditions is shown. Therefore, progress in the understanding of this important reaction on a molecular level, and the choice of the right approach for the design of the electrocatalysts for fuel-cell cathodes is only possible through a cooperative approach between theory and experiments.

Solar-Powered Plasmon-Enhanced Heterogeneous Catalysis

NASA Astrophysics Data System (ADS)

Naldoni, Alberto; Riboni, Francesca; Guler, Urcan; Boltasseva, Alexandra; Shalaev, Vladimir M.; Kildishev, Alexander V.

2016-06-01

Photocatalysis uses semiconductors to convert sunlight into chemical energy. Recent reports have shown that plasmonic nanostructures can be used to extend semiconductor light absorption or to drive direct photocatalysis with visible light at their surface. In this review, we discuss the fundamental decay pathway of localized surface plasmons in the context of driving solar-powered chemical reactions. We also review different nanophotonic approaches demonstrated for increasing solar-to-hydrogen conversion in photoelectrochemical water splitting, including experimental observations of enhanced reaction selectivity for reactions occurring at the metalsemiconductor interface. The enhanced reaction selectivity is highly dependent on the morphology, electronic properties, and spatial arrangement of composite nanostructures and their elements. In addition, we report on the particular features of photocatalytic reactions evolving at plasmonic metal surfaces and discuss the possibility of manipulating the reaction selectivity through the activation of targeted molecular bonds. Finally, using solar-to-hydrogen conversion techniques as an example, we quantify the efficacy metrics achievable in plasmon-driven photoelectrochemical systems and highlight some of the new directions that could lead to the practical implementation of solar-powered plasmon-based catalytic devices.

Quantum Molecular Dynamics Simulations of Nanotube Tip Assisted Reactions

NASA Technical Reports Server (NTRS)

Menon, Madhu

1998-01-01

In this report we detail the development and application of an efficient quantum molecular dynamics computational algorithm and its application to the nanotube-tip assisted reactions on silicon and diamond surfaces. The calculations shed interesting insights into the microscopic picture of tip surface interactions.

SURFACE REACTIONS OF OXIDES OF SULFUR

EPA Science Inventory

Surface reactions of several sulfur-containing molecules have been studied in order to understand the mechanism by which sulfate ions are formed on atmospheric aerosols. At 25C the heterogeneous oxidation of SO2 by NO2 to sulfuric acid and sulfate ions occurred on hydrated silica...

The use of surface enhanced absorption, scattering and catalytic properties of gold nanoparticles in some bio- and biomedical applications

NASA Astrophysics Data System (ADS)

Huang, Xiaohua; El-Sayed, Ivan H.; El-Sayed, Mostafa A.

2005-08-01

Gold nanoparticles with unique optical properties offer useful applications in biotechnology. In this article two applications that we have developed are summarized, in one they are used in cancer cell diagnostics and in the other they are found to have catalytic property for the NADH oxidation reaction which is important in ATP formations. By conjugation with anti-EGFR antibodies which specifically target EGFR that are usually overexpressed on most cancer cells, gold nanoparticles are used as a molecular contrast agent for cancer cell diagnostics using their both strong surface plasmon absorption and efficient Mie scattering properties. Au nanoparticles are also good catalysts for many reactions due to their high surface to volume ratio. Au nanoparticles are found to be the catalyst for the NADH oxidation reaction. This was studied by monitoring the effect of the nanoparticles on NADH fluorescence intensity and lifetime as well as the change of the surface plasmon absorption band during the reaction.

Electrocatalytic oxidation of cellulose at a gold electrode.

PubMed

Sugano, Yasuhito; Latonen, Rose-Marie; Akieh-Pirkanniemi, Marceline; Bobacka, Johan; Ivaska, Ari

2014-08-01

The electrochemical properties of cellulose dissolved in NaOH solution at a Au surface were investigated by cyclic voltammetry, FTIR spectroscopy, the electrochemical quartz crystal microbalance technique, and electrochemical impedance spectroscopy. The reaction products were characterized by SEM, TEM, and FTIR and NMR spectroscopy. The results imply that cellulose is irreversibly oxidized. Adsorption and desorption of hydroxide ions at the Au surface during potential cycling have an important catalytic role in the reaction (e.g., approach of cellulose to the electrode surface, electron transfer, adsorption/desorption of the reaction species at the electrode surface). Moreover, two types of cellulose derivatives were obtained as products. One is a water-soluble cellulose derivative in which some hydroxyl groups are oxidized to carboxylic groups. The other derivative is a water-insoluble hybrid material composed of cellulose and Au nanoparticles (≈4 nm). Furthermore, a reaction scheme of the electrocatalytic oxidation of cellulose at a gold electrode in a basic medium is proposed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Amorphous nickel boride membrane on a platinum-nickel alloy surface for enhanced oxygen reduction reaction.

PubMed

He, Daping; Zhang, Libo; He, Dongsheng; Zhou, Gang; Lin, Yue; Deng, Zhaoxiang; Hong, Xun; Wu, Yuen; Chen, Chen; Li, Yadong

2016-08-09

The low activity of the oxygen reduction reaction in polymer electrolyte membrane fuel cells is a major barrier for electrocatalysis, and hence needs to be optimized. Tuning the surface electronic structure of platinum-based bimetallic alloys, a promising oxygen reduction reaction catalyst, plays a key role in controlling its interaction with reactants, and thus affects the efficiency. Here we report that a dealloying process can be utilized to experimentally fabricate the interface between dealloyed platinum-nickel alloy and amorphous nickel boride membrane. The coating membrane works as an electron acceptor to tune the surface electronic structure of the platinum-nickel catalyst, and this composite catalyst composed of crystalline platinum-nickel covered by amorphous nickel boride achieves a 27-times enhancement in mass activity relative to commercial platinum/carbon at 0.9 V for the oxygen reduction reaction performance. Moreover, this interactional effect between a crystalline surface and amorphous membrane can be readily generalized to facilitate the 3-times higher catalytic activity of commercial platinum/carbon.

A Monte Carlo Sensitivity Analysis of CF2 and CF Radical Densities in a c-C4F8 Plasma

NASA Technical Reports Server (NTRS)

Bose, Deepak; Rauf, Shahid; Hash, D. B.; Govindan, T. R.; Meyyappan, M.

2004-01-01

A Monte Carlo sensitivity analysis is used to build a plasma chemistry model for octacyclofluorobutane (c-C4F8) which is commonly used in dielectric etch. Experimental data are used both quantitatively and quantitatively to analyze the gas phase and gas surface reactions for neutral radical chemistry. The sensitivity data of the resulting model identifies a few critical gas phase and surface aided reactions that account for most of the uncertainty in the CF2 and CF radical densities. Electron impact dissociation of small radicals (CF2 and CF) and their surface recombination reactions are found to be the rate-limiting steps in the neutral radical chemistry. The relative rates for these electron impact dissociation and surface recombination reactions are also suggested. The resulting mechanism is able to explain the measurements of CF2 and CF densities available in the literature and also their hollow spatial density profiles.

Carbide and carbonitride surface treatment method for refractory metals

DOEpatents

Meyer, Glenn A.; Schildbach, Marcus A.

1996-01-01

A carbide and carbonitride surface treatment method for refractory metals is provided, in steps including, heating a part formed of boron, chromium, hafnium, molybdenum, niobium, tantalum, titanium, tungsten or zirconium, or alloys thereof, in an evacuated chamber and then introducing reaction gases including nitrogen and hydrogen, either in elemental or water vapor form, which react with a source of elemental carbon to form carbon-containing gaseous reactants which then react with the metal part to form the desired surface layer. Apparatus for practicing the method is also provided, in the form of a carbide and carbonitride surface treatment system (10) including a reaction chamber (14), a source of elemental carbon (17), a heating subassembly (20) and a source of reaction gases (23). Alternative methods of providing the elemental carbon (17) and the reaction gases (23) are provided, as well as methods of supporting the metal part (12), evacuating the chamber (14) with a vacuum subassembly (18) and heating all of the components to the desired temperature.

Mass spectrometric studies of phosphine pyrolysis and OMVPE growth of InP. [organometallic vapor phase epitaxy

NASA Technical Reports Server (NTRS)

Larsen, C. A.; Buchan, N. I.; Stringfellow, G. B.

1987-01-01

The mechanism of PH3 decomposition was studied by using D2 as a carrier gas and analyzing the reaction products with a mass spectrometer. The effects of InP and silica surfaces were investigated. The only gaseous product below 600 C is H2. Since any gas-phase H atoms would produce HD, the reaction occurs entirely on the surface. The slow step is the unimolecular removal of the first hydrogen atom, with an activation energy of 36.0 kcal/mole on InP surfaces. The reaction on InP is first-order for PH3 concentrations as high as 15 percent, so the surface is not saturated at those conditions. When trimethylindium (TMIn) is added to the gas mixture, the mechanism changes dramatically, probably proceeding via an unstable intermediate adduct of TMIn and PH3 which eliminates CH4 upon formation. This concerted reaction lowers the pyrolysis temperatures of both PH3 and TMIn.

Kinetics of the heterogeneous photo oxidation of the pesticide bupirimate by OH-radicals and ozone under atmospheric conditions.

PubMed

Bouya, H; Errami, M; Chakir, A; Roth, E

2015-09-01

This article is concerned with the study of the photochemical degradation of bupirimate adsorbed on a quartz surface by atmospheric oxidants, namely ozone and OH radicals. OH oxidation experiments were conducted relative to two reference compounds, terbuthylazine and (4-chlorophenyl)(3,4-dimethoxyphenyl) methanone. Meanwhile, ozone oxidation experiments were performed in the absolute mode and were interpreted by both, the Surface Layer Reaction and the Gas Surface Reaction models of heterogeneous reactions. The obtained results show that the rate constants for the reactions between bupirimate and OH radicals and ozone are (cm(3)molecule(-1)s(-1)): (1.06 ± 0.87) × 10(-12) and (5.4 ± 0.3) × 10(-20), respectively. As a consequence, for the experimental conditions used in this study, the lifetime of bupirimate at quartz like surface/atmosphere interfaces is several months against ozone and a tenth of days against OH-radical. Copyright © 2015 Elsevier Ltd. All rights reserved.

Catalysts for electrochemical generation of oxygen

NASA Technical Reports Server (NTRS)

Hagans, P.; Yeager, E.

1979-01-01

Several aspects of the electrolytic evolution of oxygen for use in life support systems are analyzed including kinetic studies of various metal and nonmetal electrode materials, the formation of underpotential films on electrodes, and electrode surface morphology and the use of single crystal metals. In order to investigate the role of surface morphology to electrochemical reactions, a low energy electron diffraction and an Auger electron spectrometer are combined with an electrochemical thin-layer cell allowing initial characterization of the surface, reaction run, and then a comparative surface analysis.

Chemical treatment for silica-containing glass surfaces

DOEpatents

Grabbe, Alexis; Michalske, Terry Arthur; Smith, William Larry

1999-01-01

Dehydroxylated, silica-containing, glass surfaces are known to be at least partially terminated by strained siloxane rings. According to the invention, a surface of this kind is exposed to a selected silane compound or mixture of silane compounds under reaction-promoting conditions. The ensuing reaction results in opening of the strained siloxane rings, and termination of surface atoms by chemical species, such as organic or organosilicon species, having desirable properties. These species can be chosen to provide qualities such as hydrophobicity, or improved coupling to a polymeric coating.

Chemical treatment for silica-containing glass surfaces

DOEpatents

Grabbe, Alexis; Michalske, Terry Arthur; Smith, William Larry

1998-01-01

Dehydroxylated, silica-containing, glass surfaces are known to be at least partially terminated by strained siloxane rings. According to the invention, a surface of this kind is exposed to a selected silane compound or mixture of silane compounds under reaction-promoting conditions. The ensuing reaction results in opening of the strained siloxane rings, and termination of surface atoms by chemical species, such as organic or organosilicon species, having desirable properties. These species can be chosen to provide qualities such as hydrophobicity, or improved coupling to a polymeric coating.

Chemical treatment for silica-containing glass surfaces

DOEpatents

Grabbe, Alexis; Michalske, Terry Arthur; Smith, William Larry

1999-01-01

Dehydroxylated, silica-containing, glass surfaces are known to be at least partially terminated by strained siloxane rings. According to the invention, a surface of this kind is exposed to a selected silane compound or mixture of silane compounds under reaction-promoting conditons. The ensuing reaction results in opening of the strained siloxane rings, and termination of surface atoms by chemical species, such as organic or organosilicon species, having desirable properties. These species can be chosen to provide qualities such as hydrophobicity, or improved coupling to a polymeric coating.

Theory of Reactions at a Solid Surface.

DTIC Science & Technology

1983-03-01

vibrational and rotational motions of X2 and X are separable even at small distances away from the surface, and that the lattice vibra- tions do not...volume of the clean surface, and o(X) is the reaction cross section of X atoms with lattice atoms M. Rearranging Eq. (28), we ,can write d[n(M) - an(R...positions of only a small number, n, of local surface atoms. We designate these as the "primary lattice atoms". The remaining N-n solid atoms serve

Detailed surface reaction mechanism in a three-way catalyst.

PubMed

Chatterjee, D; Deutschmann, O; Warnatz, J

2001-01-01

Monolithic three-way catalysts are applied to reduce the emission of combustion engines. The design of such a catalytic converter is a complex process involving the optimization of different physical and chemical parameters (in the simplest case, e.g., length, cell densities or metal coverage of the catalyst). Numerical simulation can be used as an effective tool for the investigation of the catalytic properties of a catalytic converter and for the prediction of the performance of the catalyst. To attain this goal, a two-dimensional flow-field description is coupled with a detailed surface reaction model (gas-phase reactions can be neglected in three-way catalysts). This surface reaction mechanism (with C3H6 taken as representative of unburnt hydrocarbons) was developed using sub-mechanisms recently developed for hydrogen, carbon monoxide and methane oxidation, literature values for C3H6 oxidation, and estimates for the remaining unknown reactions. Results of the simulation of a monolithic single channel are used to validate the surface reaction mechanism. The performance of the catalyst was simulated under lean, nearly stoichiometric and rich conditions. For these characteristic conditions, the oxidation of propene and carbon monoxide and the reduction of NO on a typical Pt/Rh coated three-way catalyst were simulated as a function of temperature. The numerically predicted conversion data are compared with experimentally measured data. The simulation further reveals the coupling between chemical reactions and transport processes within the monolithic channel.

Reactor design for uniform chemical vapor deposition-grown films without substrate rotation

DOEpatents

Wanlass, M.

1985-02-19

A quartz reactor vessel for growth of uniform semiconductor films includes a vertical, cylindrical reaction chamber in which a substrate-supporting pedestal provides a horizontal substrate-supporting surface spaced on its perimeter from the chamber wall. A cylindrical confinement chamber of smaller diameter is disposed coaxially above the reaction chamber and receives reaction gas injected at a tangent to the inside chamber wall, forming a helical gas stream that descends into the reaction chamber. In the reaction chamber, the edge of the substrate-supporting pedestal is a separation point for the helical flow, diverting part of the flow over the horizontal surface of the substrate in an inwardly spiraling vortex.

Reactor design for uniform chemical vapor deposition-grown films without substrate rotation

DOEpatents

Wanlass, Mark

1987-01-01

A quartz reactor vessel for growth of uniform semiconductor films includes a vertical, cylindrical reaction chamber in which a substrate-supporting pedestal provides a horizontal substrate-supporting surface spaced on its perimeter from the chamber wall. A cylindrical confinement chamber of smaller diameter is disposed coaxially above the reaction chamber and receives reaction gas injected at a tangent to the inside chamber wall, forming a helical gas stream that descends into the reaction chamber. In the reaction chamber, the edge of the substrate-supporting pedestal is a separation point for the helical flow, diverting part of the flow over the horizontal surface of the substrate in an inwardly spiraling vortex.

Methanol Adsorption and Reaction on Samaria Thin Films on Pt(111).

PubMed

Jhang, Jin-Hao; Schaefer, Andreas; Zielasek, Volkmar; Weaver, Jason F; Bäumer, Marcus

2015-09-17

We investigated the adsorption and reaction of methanol on continuous and discontinuous films of samarium oxide (SmO x ) grown on Pt(111) in ultrahigh vacuum. The methanol decomposition was studied by temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS), while structural changes of the oxide surface were monitored by low-energy electron diffraction (LEED). Methanol dehydrogenates to adsorbed methoxy species on both the continuous and discontinuous SmO x films, eventually leading to the desorption of CO and H₂ which desorbs at temperatures in the range 400-600 K. Small quantities of CO₂ are also detected mainly on as-prepared Sm₂O₃ thin films, but the production of CO₂ is limited during repeated TPD runs. The discontinuous film exhibits the highest reactivity compared to the continuous film and the Pt(111) substrate. The reactivity of methanol on reduced and reoxidized films was also investigated, revealing how SmO x structures influence the chemical behavior. Over repeated TPD experiments, a SmO x structural/chemical equilibrium condition is found which can be approached either from oxidized or reduced films. We also observed hydrogen absence in TPD which indicates that hydrogen is stored either in SmO x films or as OH groups on the SmO x surfaces.

Methanol Adsorption and Reaction on Samaria Thin Films on Pt(111)

PubMed Central

Jhang, Jin-Hao; Schaefer, Andreas; Zielasek, Volkmar; Weaver, Jason F.; Bäumer, Marcus

2015-01-01

We investigated the adsorption and reaction of methanol on continuous and discontinuous films of samarium oxide (SmOx) grown on Pt(111) in ultrahigh vacuum. The methanol decomposition was studied by temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS), while structural changes of the oxide surface were monitored by low-energy electron diffraction (LEED). Methanol dehydrogenates to adsorbed methoxy species on both the continuous and discontinuous SmOx films, eventually leading to the desorption of CO and H2 which desorbs at temperatures in the range 400–600 K. Small quantities of CO2 are also detected mainly on as-prepared Sm2O3 thin films, but the production of CO2 is limited during repeated TPD runs. The discontinuous film exhibits the highest reactivity compared to the continuous film and the Pt(111) substrate. The reactivity of methanol on reduced and reoxidized films was also investigated, revealing how SmOx structures influence the chemical behavior. Over repeated TPD experiments, a SmOx structural/chemical equilibrium condition is found which can be approached either from oxidized or reduced films. We also observed hydrogen absence in TPD which indicates that hydrogen is stored either in SmOx films or as OH groups on the SmOx surfaces. PMID:28793562

Catalytic Hydrogenation and Hydrodeoxygenation of Furfural over Pt(111): A Model System for the Rational Design and Operation of Practical Biomass Conversion Catalysts.

PubMed

Taylor, Martin J; Jiang, Li; Reichert, Joachim; Papageorgiou, Anthoula C; Beaumont, Simon K; Wilson, Karen; Lee, Adam F; Barth, Johannes V; Kyriakou, Georgios

2017-04-20

Furfural is a key bioderived platform chemical whose reactivity under hydrogen atmospheres affords diverse chemical intermediates. Here, temperature-programmed reaction spectrometry and complementary scanning tunneling microscopy (STM) are employed to investigate furfural adsorption and reactivity over a Pt(111) model catalyst. Furfural decarbonylation to furan is highly sensitive to reaction conditions, in particular, surface crowding and associated changes in the adsorption geometry: furfural adopts a planar geometry on clean Pt(111) at low coverage, tilting at higher coverage to form a densely packed furfural adlayer. This switch in adsorption geometry strongly influences product selectivity. STM reveals the formation of hydrogen-bonded networks for planar furfural, which favor decarbonylation on clean Pt(111) and hydrogenolysis in the presence of coadsorbed hydrogen. Preadsorbed hydrogen promotes furfural hydrogenation to furfuryl alcohol and its subsequent hydrogenolysis to methyl furan, while suppressing residual surface carbon. Furfural chemistry over Pt is markedly different from that over Pd, with weaker adsorption over the former affording a simpler product distribution than the latter; Pd catalyzes a wider range of chemistry, including ring-opening to form propene. Insight into the role of molecular orientation in controlling product selectivity will guide the design and operation of more selective and stable Pt catalysts for furfural hydrogenation.

Electron-stimulated reactions in nanoscale water films adsorbed on (alpha)-Al2O3(0001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrik, Nikolay G.; Kimmel, Gregory A.

2018-05-11

The radiation-induced decomposition and desorption of nanoscale amorphous solid water (D2O) films adsorbed on -Al2O3(0001) surface was studied at low temperature in ultrahigh vacuum using temperature programmed desorption (TPD) and electron stimulated desorption (ESD) with a mono-energetic, low energy electron source. ESD yields of molecular products ( D2, O2 and D¬2O) and the total sputtering yield increased with increasing D2O coverage up to ~15 water monolayers (i.e. ~15 1015 cm-2) to a coverage-independent level for thicker water films. Experiments with isotopically-layered water films (D2O and H2O) demonstrated that the highest water decomposition yields occurred at the interfaces of the nanoscalemore » water films with the alumina substrate and vacuum. However, the increased reactivity of the water/alumina interface is relatively small compared to the enhancements in the non-thermal reactions previously observed at the water/Pt(111) and water/TiO2(110) interfaces. We propose that the relatively low activity of Al2O3(0001) for the radiation-induced production of molecular hydrogen is associated with lower reactivity of this surface with hydrogen atoms, which are likely precursors for the molecular hydrogen.« less

Catalytic Hydrogenation and Hydrodeoxygenation of Furfural over Pt(111): A Model System for the Rational Design and Operation of Practical Biomass Conversion Catalysts

PubMed Central

2017-01-01

Furfural is a key bioderived platform chemical whose reactivity under hydrogen atmospheres affords diverse chemical intermediates. Here, temperature-programmed reaction spectrometry and complementary scanning tunneling microscopy (STM) are employed to investigate furfural adsorption and reactivity over a Pt(111) model catalyst. Furfural decarbonylation to furan is highly sensitive to reaction conditions, in particular, surface crowding and associated changes in the adsorption geometry: furfural adopts a planar geometry on clean Pt(111) at low coverage, tilting at higher coverage to form a densely packed furfural adlayer. This switch in adsorption geometry strongly influences product selectivity. STM reveals the formation of hydrogen-bonded networks for planar furfural, which favor decarbonylation on clean Pt(111) and hydrogenolysis in the presence of coadsorbed hydrogen. Preadsorbed hydrogen promotes furfural hydrogenation to furfuryl alcohol and its subsequent hydrogenolysis to methyl furan, while suppressing residual surface carbon. Furfural chemistry over Pt is markedly different from that over Pd, with weaker adsorption over the former affording a simpler product distribution than the latter; Pd catalyzes a wider range of chemistry, including ring-opening to form propene. Insight into the role of molecular orientation in controlling product selectivity will guide the design and operation of more selective and stable Pt catalysts for furfural hydrogenation. PMID:29225721

Electron-stimulated reactions in nanoscale water films adsorbed on α-Al 2 O 3 (0001)

DOE PAGES

Petrik, Nikolay G.; Kimmel, Greg A.

2018-04-11

The radiation-induced decomposition and desorption of nanoscale amorphous solid water (D 2O) films adsorbed on an α-Al 2O 3(0001) surface was studied at low temperature in ultrahigh vacuum using temperature programmed desorption (TPD) and electron stimulated desorption (ESD) with a mono-energetic, low energy electron source. ESD yields of molecular products (D 2, O 2 and D 2O) and the total sputtering yield increased with increasing D 2O coverage up to ~15 water monolayers (i.e. ~15 x 10 15 cm -2) to a coverage-independent level for thicker water films. Experiments with isotopically-layered water films (D 2O and H 2O) demonstrated thatmore » the highest water decomposition yields occurred at the interfaces of the nanoscale water films with the alumina substrate and vacuum. However, the increased reactivity of the water/alumina interface is relatively small compared to the enhancements in the non-thermal reactions previously observed at the water/Pt(111) and water/TiO 2(110) interfaces. Here, we propose that the relatively low activity of Al 2O 3(0001) for the radiation-induced production of molecular hydrogen is associated with lower reactivity of this surface with hydrogen atoms, which are likely precursors for the formation of molecular hydrogen.« less

Electron-stimulated reactions in nanoscale water films adsorbed on α-Al 2 O 3 (0001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrik, Nikolay G.; Kimmel, Greg A.

The radiation-induced decomposition and desorption of nanoscale amorphous solid water (D 2O) films adsorbed on an α-Al 2O 3(0001) surface was studied at low temperature in ultrahigh vacuum using temperature programmed desorption (TPD) and electron stimulated desorption (ESD) with a mono-energetic, low energy electron source. ESD yields of molecular products (D 2, O 2 and D 2O) and the total sputtering yield increased with increasing D 2O coverage up to ~15 water monolayers (i.e. ~15 x 10 15 cm -2) to a coverage-independent level for thicker water films. Experiments with isotopically-layered water films (D 2O and H 2O) demonstrated thatmore » the highest water decomposition yields occurred at the interfaces of the nanoscale water films with the alumina substrate and vacuum. However, the increased reactivity of the water/alumina interface is relatively small compared to the enhancements in the non-thermal reactions previously observed at the water/Pt(111) and water/TiO 2(110) interfaces. Here, we propose that the relatively low activity of Al 2O 3(0001) for the radiation-induced production of molecular hydrogen is associated with lower reactivity of this surface with hydrogen atoms, which are likely precursors for the formation of molecular hydrogen.« less

Insights into Acetone Photochemistry on Rutile TiO2(110). 1. Off-Normal CH3 Ejection from Acetone Diolate.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrik, Nikolay G.; Henderson, Michael A.; Kimmel, Gregory A.

2015-06-04

Thermal- and photon-stimulated reactions of acetone co-adsorbed with oxygen on rutile TiO2(110) surface are studied with infrared reflection-adsorption spectroscopy (IRAS) combined with temperature programmed desorption and angle-resolved photon stimulated desorption. IRAS results show that n2-acetone diolate ((CH3)2COO) is produced via thermally-activated reactions between the chemisorbed oxygen with co-adsorbed acetone. Formation of acetone diolate is also consistent with 18O / 16O isotopic exchange experiments. During UV irradiation at 30 K, CH3 radicals are ejected from the acetone diolate with a distribution that is peaked at .-. +- 66 degrees from the surface normal along the azimuth (i.e. perpendicular to the rowsmore » of bridging oxygen and Ti5c ions). This distribution is also consistent with the orientation of the C–CH3 bonds in the n2-acetone diolate on TiO2(110). The acetone diolate peaks disappear from the IRAS spectra after UV irradiation and new peaks are observed and associated with n2-acetate. The data presented here demonstrate direct signatures of the proposed earlier 2-step mechanism for acetone photooxidation on TiO2(110)« less

Enhanced Colloidal Stability of CeO2 Nanoparticles by Ferrous Ions: Adsorption, Redox Reaction, and Surface Precipitation.

PubMed

Liu, Xuyang; Ray, Jessica R; Neil, Chelsea W; Li, Qingyun; Jun, Young-Shin

2015-05-05

Due to the toxicity of cerium oxide (CeO2) nanoparticles (NPs), a better understanding of the redox reaction-induced surface property changes of CeO2 NPs and their transport in natural and engineered aqueous systems is needed. This study investigates the impact of redox reactions with ferrous ions (Fe2+) on the colloidal stability of CeO2 NPs. We demonstrated that under anaerobic conditions, suspended CeO2 NPs in a 3 mM FeCl2 solution at pH 4.8 were much more stable against sedimentation than those in the absence of Fe2+. Redox reactions between CeO2 NPs and Fe2+ lead to the formation of 6-line ferrihydrite on the CeO2 surfaces, which enhanced the colloidal stability by increasing the zeta potential and hydrophilicity of CeO2 NPs. These redox reactions can affect the toxicity of CeO2 NPs by increasing cerium dissolution, and by creating new Fe(III) (hydr)oxide reactive surface layers. Thus, these findings have significant implications for elucidating the phase transformation and transport of redox reactive NPs in the environment.

Enhanced Fe2O3 Reducibility via Surface Modification with Pd: Characterizing the Synergy within Pd/Fe Catalysts for Hydrodeoxygenation Reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hensley, Alyssa; Hong, Yongchun; Zhang, Renqin

2014-10-03

The synergistic catalysis in the hydrodeoxygenation of phenolic compounds over a Pd/Fe bimetallic surface has been well established. However, the nature of this synergy is still in part a mystery. In this work, we used a combined experimental and theoretical approach to understand a potential function of the surface Pd in the reduction of Pd/Fe2O3. This function of Pd was investigated via the comparison of the reduction properties as well as other physicochemical properties of samples synthesized by the reduction of Fe2O3 nanoparticles with and without surface Pd. Temperature-programmed reduction studies demonstrated the remarkable facilitation of reduction by addition ofmore » Pd, evidenced by a 150 degrees C shift toward lower temperature of the reduction peak of Fe3+. From X-ray photoelectron spectroscopy and theoretical calculation results, the interaction between Pd and the Fe2O3 surface occurs through the exchange of electrons with both the surface Fe and O atoms. This bonding between the Pd and surface oxide elements causes the Pd to partially donate electrons to the oxide surface, making the surface electrons more delocalized. This electron delocalization stabilizes the reduced oxide surfaces, as suggested by the TPR results and theoretical prediction. Therefore, the stabilization of the reduced Fe surface as well as the facilitated water formation by introduction of Pd is expected to significantly contribute to the Pd-Fe synergy in hydrodeoxygenation catalysis.« less

Chemical surface deposition of ultra-thin semiconductors

DOEpatents

McCandless, Brian E.; Shafarman, William N.

2003-03-25

A chemical surface deposition process for forming an ultra-thin semiconducting film of Group IIB-VIA compounds onto a substrate. This process eliminates particulates formed by homogeneous reactions in bath, dramatically increases the utilization of Group IIB species, and results in the formation of a dense, adherent film for thin film solar cells. The process involves applying a pre-mixed liquid coating composition containing Group IIB and Group VIA ionic species onto a preheated substrate. Heat from the substrate causes a heterogeneous reaction between the Group IIB and VIA ionic species of the liquid coating composition, thus forming a solid reaction product film on the substrate surface.

Interfaces in heterogeneous catalytic reactions: Ambient pressure XPS as a tool to unravel surface chemistry

DOE PAGES

Palomino, Robert M.; Hamlyn, Rebecca; Liu, Zongyuan; ...

2017-04-27

In this paper we provide a summary of the recent development of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and its application to catalytic surface chemistry. The methodology as well as significant advantages and challenges associated with this novel technique are described. Details about specific examples of using AP-XPS to probe surface chemistry under working reaction conditions for a number of reactions are explained: CO oxidation, water-gas shift (WGS), CO 2 hydrogenation, dry reforming of methane (DRM) and ethanol steam reforming (ESR). In conclusion, we discuss insights into the future development of the AP-XPS technique and its applications.

Interfaces in heterogeneous catalytic reactions: Ambient pressure XPS as a tool to unravel surface chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palomino, Robert M.; Hamlyn, Rebecca; Liu, Zongyuan

In this paper we provide a summary of the recent development of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and its application to catalytic surface chemistry. The methodology as well as significant advantages and challenges associated with this novel technique are described. Details about specific examples of using AP-XPS to probe surface chemistry under working reaction conditions for a number of reactions are explained: CO oxidation, water-gas shift (WGS), CO 2 hydrogenation, dry reforming of methane (DRM) and ethanol steam reforming (ESR). In conclusion, we discuss insights into the future development of the AP-XPS technique and its applications.

Process for forming a porous silicon member in a crystalline silicon member

DOEpatents

Northrup, M. Allen; Yu, Conrad M.; Raley, Norman F.

1999-01-01

Fabrication and use of porous silicon structures to increase surface area of heated reaction chambers, electrophoresis devices, and thermopneumatic sensor-actuators, chemical preconcentrates, and filtering or control flow devices. In particular, such high surface area or specific pore size porous silicon structures will be useful in significantly augmenting the adsorption, vaporization, desorption, condensation and flow of liquids and gasses in applications that use such processes on a miniature scale. Examples that will benefit from a high surface area, porous silicon structure include sample preconcentrators that are designed to adsorb and subsequently desorb specific chemical species from a sample background; chemical reaction chambers with enhanced surface reaction rates; and sensor-actuator chamber devices with increased pressure for thermopneumatic actuation of integrated membranes. Examples that benefit from specific pore sized porous silicon are chemical/biological filters and thermally-activated flow devices with active or adjacent surfaces such as electrodes or heaters.

Effects of surface poisons on the oxidation of binary alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagan, P.S.; Polizzotti, R.S.; Luckman, G.

1985-10-01

A system of reaction-diffusion equations describing the oxidation of binary alloys in environments containing small amounts of surface poisons is analyzed. These poisons reduce the oxygen flux into the alloy, which causes the alloy to oxidize in two stages.During the initial stage, the oxidation reaction occurs in a stationary boundary layer at the alloy surface. Consequently, a thin zone containing a very high concentration of the metal oxide is created at the alloy surface. During the second stage, the oxidation reaction occurs in a moving boundary layer. This leads to a Stefan problem, which is analyzed by using asymptotic andmore » numerical techniques. By comparing the solutions to those of alloys in unpoisoned environments, it is concluded that surface poisons can lead to the formation of protective external oxide scales in alloys which would not normally form such scales. 11 references.« less

Acetaldehyde Adsorption and Reaction onCeO2(100) Thin Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mullins, David R; Albrecht, Peter M

2013-01-01

This study reports and compares the adsorption and dissociation of acetaldehyde on oxidized and reduced CeOX(100) thin films. Acetaldehyde reacts and decomposes on fully oxidized CeO2(100) whereas it desorbs molecularly at low temperature on CeO2(111). The primary products are CO, CO2 and water along with trace amounts of crotonaldehyde and acetylene. The acetaldehyde adsorbs as the 2-acetaldehyde species, dioxyethylene. Decomposition proceeds by dehydrogenation through acetate and enolate intermediates. The reaction pathway is similar on the reduced CeO2-X(100) surface however the inability to react with surface O on the reduced surface results in H2 rather than H2O desorption and C ismore » left on the surface rather than producing CO and CO2. C-O bond cleavage in the enolate intermediate followed by reaction with surface H results in ethylene desorption.« less

Comprehensive mechanism and structure-sensitivity of ethanol oxidation on platinum: new transition-state searching method for resolving the complex reaction network.

PubMed

Wang, Hui-Fang; Liu, Zhi-Pan

2008-08-20

Ethanol oxidation on Pt is a typical multistep and multiselectivity heterogeneous catalytic process. A comprehensive understanding of this fundamental reaction would greatly benefit design of catalysts for use in direct ethanol fuel cells and the degradation of biomass-derived oxygenates. In this work, the reaction network of ethanol oxidation on different Pt surfaces, including close-packed Pt{111}, stepped Pt{211}, and open Pt{100}, is explored thoroughly with an efficient reaction path searching method, which integrates our new transition-state searching technique with periodic density functional theory calculations. Our new technique enables the location of the transition state and saddle points for most surface reactions simply and efficiently by optimization of local minima. We show that the selectivity of ethanol oxidation on Pt depends markedly on the surface structure, which can be attributed to the structure-sensitivity of two key reaction steps: (i) the initial dehydrogenation of ethanol and (ii) the oxidation of acetyl (CH3CO). On open surface sites, ethanol prefers C-C bond cleavage via strongly adsorbed intermediates (CH2CO or CHCO), which leads to complete oxidation to CO2. However, only partial oxidizations to CH3CHO and CH3COOH occur on Pt{111}. Our mechanism points out that the open surface Pt{100} is the best facet to fully oxidize ethanol at low coverages, which sheds light on the origin of the remarkable catalytic performance of Pt tetrahexahedra nanocrystals found recently. The physical origin of the structure-selectivity is rationalized in terms of both thermodynamics and kinetics. Two fundamental quantities that dictate the selectivity of ethanol oxidation are identified: (i) the ability of surface metal atoms to bond with unsaturated C-containing fragments and (ii) the relative stability of hydroxyl at surface atop sites with respect to other sites.

An improved reaction path optimization method using a chain of conformations

NASA Astrophysics Data System (ADS)

Asada, Toshio; Sawada, Nozomi; Nishikawa, Takuya; Koseki, Shiro

2018-05-01

The efficient fast path optimization (FPO) method is proposed to optimize the reaction paths on energy surfaces by using chains of conformations. No artificial spring force is used in the FPO method to ensure the equal spacing of adjacent conformations. The FPO method is applied to optimize the reaction path on two model potential surfaces. The use of this method enabled the optimization of the reaction paths with a drastically reduced number of optimization cycles for both potentials. It was also successfully utilized to define the MEP of the isomerization of the glycine molecule in water by FPO method.

Female Juvenile Delinquents' Reactions to a Reading Program: A Mixed Methods Study

ERIC Educational Resources Information Center

Sanger, Dixie; Ritzman, Mitzi; Schaefer, Lauren; Belau, Don

2010-01-01

Older students who struggle with reading are more motivated to participate in instructional intervention if they are interested in the program. This mixed methods study examined opinions and reactions of 41 female juvenile delinquents on a 1-hour demonstration of the START-IN (STudents Are Responding To INtervention) reading program. Following a…

Spiritual impacts of the space program on the world

NASA Technical Reports Server (NTRS)

Esch, M.

1972-01-01

The lessons learned from the space program in showing how fragile the environment is on earth are discussed. Examples are cited of the reactions of the astronauts to the unique features of earth. The reactions of the populace in seeking better living conditions and their concern with improving the environment are given as two outgrowths of the program.

Interfacial Reaction Studies Using ONIOM

NASA Technical Reports Server (NTRS)

Cardelino, Beatriz H.

2003-01-01

In this report, we focus on the calculations of the energetics and chemical kinetics of heterogeneous reactions for Organometallic vapor phase epitaxy (OMVPE). The work described in this report builds upon our own previous thermochemical and chemical kinetics studies. The first of these articles refers to the prediction of thermochemical properties, and the latter one deals with the prediction of rate constants for gaseous homolytic dissociation reactions. The calculations of this investigation are at the microscopic level. The systems chosen consisted of a gallium nitride (GaN) substrate, and molecular nitrogen (N2) and ammonia (NH3) as adsorbants. The energetics for the adsorption and the adsorbant dissociation processes were estimated, and reaction rate constants for the dissociation reactions of free and adsorbed molecules were predicted. The energetics for substrate decomposition was also computed. The ONIOM method, implemented in the Gaussian98 program, was used to perform the calculations. This approach has been selected since it allows dividing the system into two layers that can be treated at different levels of accuracy. The atoms of the substrate were modeled using molecular mechanics6 with universal force fields, whereas the adsorbed molecules were approximated using quantum mechanics, based on density functional theory methods with B3LYP functionals and 6-311G(d,p) basis sets. Calculations for the substrate were performed in slabs of several unit cells in each direction. The N2 and NH3 adsorbates were attached to a central location at the Ga-lined surface.

Effect of process conditions on the steam reforming of ethanol with a nano-Ni/SiO2 catalyst.

PubMed

Wu, C; Williams, P T

2012-01-01

In this paper, a nano-Ni/SiO2 catalyst was prepared by a sol-gel method and tested for hydrogen production from ethanol steam reforming using a two-stage fixed-bed reaction system. The reaction conditions, such as reaction temperature, water/ethanol ratio and sample feeding rate, were investigated with the prepared nano-Ni/SiO2 catalyst. Brunauer-Emmett-Teller surface area and porosity, temperature-programmed oxidation, X-ray diffraction and focused ion beam (FIB)/scanning electron microscopy were used in this work to analysis the fresh and/or reacted catalysts. An extended catalyst stability test for ethanol steam reforming with the Ni/SiO2 catalyst was carried out at a reaction temperature of 600 degrees C, when the water/ethanol ratio was kept at 3.5 and sample feeding rate was 4.74 g h(-1). The results showed that a stabilized gas and hydrogen production was obtained with a potential H2 production of about 40 wt.%. Increasing the reaction temperature during ethanol steam reforming with the Ni/SiO2 catalyst resulted in an increase of gas and hydrogen production. The gas yield was slightly reduced when the water/ethanol ratio was increased from 2.0 to 3.5. However, the potential H2 production was increased. The investigation of the sample feeding rate showed that the gas production per hour was increased due to the higher sample feeding rate, but the potential H2 production was reduced.

Enhanced Hydrodeoxygenation of m -Cresol over Bimetallic Pt–Mo Catalysts through an Oxophilic Metal-Induced Tautomerization Pathway

DOE PAGES

Robinson, Allison; Ferguson, Glen Allen; Gallagher, James R.; ...

2016-05-26

Supported bimetallic catalysts consisting of a noble metal (e.g., Pt) and an oxophilic metal (e.g., Mo) have received considerable attention for the hydrodeoxygenation of oxygenated aromatic compounds produced from biomass fast pyrolysis. Here, we report that PtMo can catalyze m-cresol deoxygenation via a pathway involving an initial tautomerization step. In contrast, the dominant mechanism on monometallic Pt/Al 2O 3 was found to be sequential Pt-catalyzed ring hydrogenation followed by dehydration on the support. Bimetallic Pt 10Mo 1 and Pt 1Mo 1 catalysts were found to produce the completely hydrogenated and deoxygenated product, methylcyclohexane (MCH), with much higher yields than monometallicmore » Pt catalysts with comparable metal loadings and surface areas. Over an inert carbon support, MCH formation was found to be slow over monometallic Pt catalysts, while deoxygenation was significant for PtMo catalysts even in the absence of an acidic support material. Experimental studies of m-cresol deoxygenation together with density functional theory calculations indicated that Mo sites on the PtMo bimetallic surface dramatically lower the barrier for m-cresol tautomerization and subsequent deoxygenation. The accessibility of this pathway arises from the increased interaction between the oxygen of m-cresol and the Mo sites in the Pt surface. This interaction significantly alters the configuration of the precursor and transition states for tautomerization. Lastly, a suite of catalyst characterization techniques including X-ray absorption spectroscopy (XAS) and temperature-programmed reduction (TPR) indicate that Mo was present in a reduced state on the bimetallic surface under conditions relevant for reaction. Overall, these results suggest that the use of bifunctional metal catalysts can result in new reaction pathways that are unfavorable on monometallic noble metal catalysts.« less

Ozone impacts of gas-aerosol uptake in global chemistry transport models

NASA Astrophysics Data System (ADS)

Stadtler, Scarlet; Simpson, David; Schröder, Sabine; Taraborrelli, Domenico; Bott, Andreas; Schultz, Martin

2018-03-01

The impact of six heterogeneous gas-aerosol uptake reactions on tropospheric ozone and nitrogen species was studied using two chemical transport models, the Meteorological Synthesizing Centre-West of the European Monitoring and Evaluation Programme (EMEP MSC-W) and the European Centre Hamburg general circulation model combined with versions of the Hamburg Aerosol Model and Model for Ozone and Related chemical Tracers (ECHAM-HAMMOZ). Species undergoing heterogeneous reactions in both models include N2O5, NO3, NO2, O3, HNO3, and HO2. Since heterogeneous reactions take place at the aerosol surface area, the modelled surface area density (Sa) of both models was compared to a satellite product retrieving the surface area. This comparison shows a good agreement in global pattern and especially the capability of both models to capture the extreme aerosol loadings in east Asia. The impact of the heterogeneous reactions was evaluated by the simulation of a reference run containing all heterogeneous reactions and several sensitivity runs. One reaction was turned off in each sensitivity run to compare it with the reference run. The analysis of the sensitivity runs confirms that the globally most important heterogeneous reaction is the one of N2O5. Nevertheless, NO2, HNO3, and HO2 heterogeneous reactions gain relevance particularly in east Asia due to the presence of high NOx concentrations and high Sa in the same region. The heterogeneous reaction of O3 itself on dust is of minor relevance compared to the other heterogeneous reactions. The impacts of the N2O5 reactions show strong seasonal variations, with the biggest impacts on O3 in springtime when photochemical reactions are active and N2O5 levels still high. Evaluation of the models with northern hemispheric ozone surface observations yields a better agreement of the models with observations in terms of concentration levels, variability, and temporal correlations at most sites when the heterogeneous reactions are incorporated. Our results are loosely consistent with results from earlier studies, although the magnitude of changes induced by N2O5 reaction is at the low end of estimates, which seems to fit a trend, whereby the more recent the study the lower the impacts of these reactions.

Adsorption, polymerization and decomposition of acetaldehyde on clean and carbon-covered Rh(111) surfaces

NASA Astrophysics Data System (ADS)

Kovács, Imre; Farkas, Arnold Péter; Szitás, Ádám; Kónya, Zoltán; Kiss, János

2017-10-01

The adsorption and dissociation of acetaldehyde were investigated on clean and carbon-covered Rh(111) single crystal surfaces by electron energy loss spectroscopy (EELS), temperature programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS) and work function (Δφ) measurements. Acetaldehyde is a starting material for the catalytic production of many important chemicals and investigation of its reactions motivated by environmental purposes too. The adsorption of acetaldehyde on clean Rh(111) surface produced various types of adsorption forms. η1-(O)-CH3CHOa and η2-(O,C)-CH3CHOa are developing and characterized by HREELS. η1-CH3CHOa partly desorbed at Tp = 150 K, another part of these species are incorporated in trimer and linear 2D polimer species. The desorption of trimers (at amu 132) were observed in TPD with a peak maximum at Tp = 225 K. Above this temperature acetaldehyde either desorbed or bonded as a stable surface intermediate (η2-CH3CHOa) on the rhodium surface. The molecules decomposed to adsorbed products, and only hydrogen and carbon monoxide were analyzed in TPD. Surface carbon decreased the uptake of adsorbed acetaldehyde, inhibited the formation of polymers, nevertheless, it induced the Csbnd O bond scission and CO formation with 40-50 K lower temperature after higher acetaldehyde exposure.

Dissociative adsorption of CCl 4 on the Fe 3O 4(1 1 1)-(2×2) selvedge of α-Fe 2O 3(0 0 0 1)

NASA Astrophysics Data System (ADS)

Adib, K.; Mullins, D. R.; Totir, G.; Camillone, N.; Fitts, J. P.; Rim, K. T.; Flynn, G. W.; Osgood, R. M.

2003-02-01

The surface reactions of CCl 4 with the Fe 3O 4(1 1 1)-(2×2) selvedge of naturally occurring α-Fe 2O 3(0 0 0 1) single-crystals have been investigated using synchrotron X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). CCl 4 was found to dissociate on the Fe 3O 4 surface at 100 K producing chemisorbed Cl and adsorbed CCl 2. TPD shows that the large majority of the dissociatively adsorbed CCl 2 fragments extract lattice oxygen and desorb as phosgene at >275 K. However, the XPS spectra show no evidence for the formation of surface-bound phosgene, at 100 K, indicating that its formation involves two steps. The first step, dissociation, is spontaneous at 100 K, whereas the second, oxygen atom abstraction to form phosgene, requires thermal excitation. Cl chemisorption yielded two separate species, the mono- and dichloride terminations of surface iron sites. The identification of these two surface terminations is based on the coverage dependence and the surface temperature history of their Cl 2p 3/2 peak intensity. For example, heating to >450 K allows the monochloride to transform into iron dichloride, indicating Cl adatom mobility at these temperatures.

Reactive Resonances in N+N2 Exchange Reaction

NASA Technical Reports Server (NTRS)

Wang, Dunyou; Huo, Winifred M.; Dateo, Christopher E.; Schwenke, David W.; Stallcop, James R.

2003-01-01

Rich reactive resonances are found in a 3D quantum dynamics study of the N + N2 exchange reaction using a recently developed ab initio potential energy surface. This surface is characterized by a feature in the interaction region called Lake Eyring , that is, two symmetric transition states with a shallow minimum between them. An L2 analysis of the quasibound states associated with the shallow minimum confirms that the quasibound states associated with oscillations in all three degrees of freedom in Lake Eyring are responsible for the reactive resonances in the state-to-state reaction probabilities. The quasibound states, mostly the bending motions, give rise to strong reasonance peaks, whereas other motions contribute to the bumps and shoulders in the resonance structure. The initial state reaction probability further proves that the bending motions are the dominating factors of the reaction probability and have longer life times than the stretching motions. This is the first observation of reactive resonances from a "Lake Eyring" feature in a potential energy surface.