An Analytical Framework for Studying Small-Number Effects in Catalytic Reaction Networks: A Probability Generating Function Approach to Chemical Master Equations

PubMed Central

Nakagawa, Masaki; Togashi, Yuichi

2016-01-01

Cell activities primarily depend on chemical reactions, especially those mediated by enzymes, and this has led to these activities being modeled as catalytic reaction networks. Although deterministic ordinary differential equations of concentrations (rate equations) have been widely used for modeling purposes in the field of systems biology, it has been pointed out that these catalytic reaction networks may behave in a way that is qualitatively different from such deterministic representation when the number of molecules for certain chemical species in the system is small. Apart from this, representing these phenomena by simple binary (on/off) systems that omit the quantities would also not be feasible. As recent experiments have revealed the existence of rare chemical species in cells, the importance of being able to model potential small-number phenomena is being recognized. However, most preceding studies were based on numerical simulations, and theoretical frameworks to analyze these phenomena have not been sufficiently developed. Motivated by the small-number issue, this work aimed to develop an analytical framework for the chemical master equation describing the distributional behavior of catalytic reaction networks. For simplicity, we considered networks consisting of two-body catalytic reactions. We used the probability generating function method to obtain the steady-state solutions of the chemical master equation without specifying the parameters. We obtained the time evolution equations of the first- and second-order moments of concentrations, and the steady-state analytical solution of the chemical master equation under certain conditions. These results led to the rank conservation law, the connecting state to the winner-takes-all state, and analysis of 2-molecules M-species systems. A possible interpretation of the theoretical conclusion for actual biochemical pathways is also discussed. PMID:27047384

Dicamba Monooxygenase: Structural Insights into a Dynamic Rieske Oxygenase that Catalyzes an Exocyclic Monooxygenation

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

D'Ordine, Robert L.; Rydel, Timothy J.; Storek, Michael J.

2009-09-08

Dicamba (2-methoxy-3,6-dichlorobenzoic acid) O-demethylase (DMO) is the terminal Rieske oxygenase of a three-component system that includes a ferredoxin and a reductase. It catalyzes the NADH-dependent oxidative demethylation of the broad leaf herbicide dicamba. DMO represents the first crystal structure of a Rieske non-heme iron oxygenase that performs an exocyclic monooxygenation, incorporating O{sub 2} into a side-chain moiety and not a ring system. The structure reveals a 3-fold symmetric trimer ({alpha}{sub 3}) in the crystallographic asymmetric unit with similar arrangement of neighboring inter-subunit Rieske domain and non-heme iron site enabling electron transport consistent with other structurally characterized Rieske oxygenases. While themore » Rieske domain is similar, differences are observed in the catalytic domain, which is smaller in sequence length than those described previously, yet possessing an active-site cavity of larger volume when compared to oxygenases with larger substrates. Consistent with the amphipathic substrate, the active site is designed to interact with both the carboxylate and aromatic ring with both key polar and hydrophobic interactions observed. DMO structures were solved with and without substrate (dicamba), product (3,6-dichlorosalicylic acid), and either cobalt or iron in the non-heme iron site. The substitution of cobalt for iron revealed an uncommon mode of non-heme iron binding trapped by the non-catalytic Co{sup 2+}, which, we postulate, may be transiently present in the native enzyme during the catalytic cycle. Thus, we present four DMO structures with resolutions ranging from 1.95 to 2.2 {angstrom}, which, in sum, provide a snapshot of a dynamic enzyme where metal binding and substrate binding are coupled to observed structural changes in the non-heme iron and catalytic sites.« less

Process to convert biomass and refuse derived fuel to ethers and/or alcohols

DOEpatents

Diebold, James P.; Scahill, John W.; Chum, Helena L.; Evans, Robert J.; Rejai, Bahman; Bain, Richard L.; Overend, Ralph P.

1996-01-01

A process for conversion of a feedstock selected from the group consisting of biomass and refuse derived fuel (RDF) to provide reformulated gasoline components comprising a substantial amount of materials selected from the group consisting of ethers, alcohols, or mixtures thereof, comprising: drying said feedstock; subjecting said dried feedstock to fast pyrolysis using a vortex reactor or other means; catalytically cracking vapors resulting from said pyrolysis using a zeolite catalyst; condensing any aromatic byproduct fraction; catalytically alkylating any benzene present in said vapors after condensation; catalytically oligomerizing any remaining ethylene and propylene to higher olefins; isomerizing said olefins to reactive iso-olefins; and catalytically reacting said iso-olefins with an alcohol to form ethers or with water to form alcohols.

A novel enzymatic bioelectrode system combining a redox hydrogel with a carbon NanoWeb.

PubMed

Little, Shannon J; Ralph, Stephen F; Mano, Nicolas; Chen, Jun; Wallace, Gordon G

2011-08-21

A novel bioelectrode system has been prepared in which an enzyme and a conducting polymer hydrogel are combined in a nanostructured scaffold. The latter consists of fibres of carbon NanoWeb, grown by chemical vapour deposition onto reticulated vitreous carbon (RVC). The catalytic currents produced by this new bioelectrode system are significantly larger than those obtained using conventional electrodes. This journal is © The Royal Society of Chemistry 2011

Stabilized tin-oxide-based oxidation/reduction catalysts

NASA Technical Reports Server (NTRS)

Watkins, Anthony Neal (Inventor); Oglesby, Donald M. (Inventor); Gulati, Suresh T. (Inventor); Summers, Jerry C. (Inventor); Schryer, David R. (Inventor); Davis, Patricia P. (Inventor); Leighty, Bradley D. (Inventor); Jordan, Jeffrey D. (Inventor); Schryer, Jacqueline L. (Inventor)

2008-01-01

The invention described herein involves a novel approach to the production of oxidation/reduction catalytic systems. The present invention serves to stabilize the tin oxide reducible metal-oxide coating by co-incorporating at least another metal-oxide species, such as zirconium. In one embodiment, a third metal-oxide species is incorporated, selected from the group consisting of cerium, lanthanum, hafnium, and ruthenium. The incorporation of the additional metal oxide components serves to stabilize the active tin-oxide layer in the catalytic process during high-temperature operation in a reducing environment (e.g., automobile exhaust). Moreover, the additional metal oxides are active components due to their oxygen-retention capabilities. Together, these features provide a mechanism to extend the range of operation of the tin-oxide-based catalyst system for automotive applications, while maintaining the existing advantages.

A dual-catalysis approach to enantioselective [2 + 2] photocycloadditions using visible light.

PubMed

Du, Juana; Skubi, Kazimer L; Schultz, Danielle M; Yoon, Tehshik P

2014-04-25

In contrast to the wealth of catalytic systems that are available to control the stereochemistry of thermally promoted cycloadditions, few similarly effective methods exist for the stereocontrol of photochemical cycloadditions. A major unsolved challenge in the design of enantioselective catalytic photocycloaddition reactions has been the difficulty of controlling racemic background reactions that occur by direct photoexcitation of substrates while unbound to catalyst. Here, we describe a strategy for eliminating the racemic background reaction in asymmetric [2 + 2] photocycloadditions of α,β-unsaturated ketones to the corresponding cyclobutanes by using a dual-catalyst system consisting of a visible light-absorbing transition-metal photocatalyst and a stereocontrolling Lewis acid cocatalyst. The independence of these two catalysts enables broader scope, greater stereochemical flexibility, and better efficiency than previously reported methods for enantioselective photochemical cycloadditions.

Method of producing pyrolysis gases from carbon-containing materials

DOEpatents

Mudge, Lyle K.; Brown, Michael D.; Wilcox, Wayne A.; Baker, Eddie G.

1989-01-01

A gasification process of improved efficiency is disclosed. A dual bed reactor system is used in which carbon-containing feedstock materials are first treated in a gasification reactor to form pyrolysis gases. The pyrolysis gases are then directed into a catalytic reactor for the destruction of residual tars/oils in the gases. Temperatures are maintained within the catalytic reactor at a level sufficient to crack the tars/oils in the gases, while avoiding thermal breakdown of the catalysts. In order to minimize problems associated with the deposition of carbon-containing materials on the catalysts during cracking, a gaseous oxidizing agent preferably consisting of air, oxygen, steam, and/or mixtures thereof is introduced into the catalytic reactor at a high flow rate in a direction perpendicular to the longitudinal axis of the reactor. This oxidizes any carbon deposits on the catalysts, which would normally cause catalyst deactivation.

New, efficient and viable system for ethanol fuel utilization on combined electric/internal combustion engine vehicles

NASA Astrophysics Data System (ADS)

Sato, André G.; Silva, Gabriel C. D.; Paganin, Valdecir A.; Biancolli, Ana L. G.; Ticianelli, Edson A.

2015-10-01

Although ethanol can be directly employed as fuel on polymer-electrolyte fuel cells (PEMFC), its low oxidation kinetics in the anode and the crossover to the cathode lead to a substantial reduction of energy conversion efficiency. However, when fuel cell driven vehicles are considered, the system may include an on board steam reformer for converting ethanol into hydrogen, but the hydrogen produced contains carbon monoxide, which limits applications in PEMFCs. Here, we present a system consisting of an ethanol dehydrogenation catalytic reactor for producing hydrogen, which is supplied to a PEMFC to generate electricity for electric motors. A liquid by-product effluent from the reactor can be used as fuel for an integrated internal combustion engine, or catalytically recycled to extract more hydrogen molecules. Power densities comparable to those of a PEMFC operating with pure hydrogen are attained by using the hydrogen rich stream produced by the ethanol dehydrogenation reactor.

Lignases and aldo-keto reductases for conversion of lignin-containing materials to fermentable products

DOEpatents

Scharf, Michael; Sethi, Amit

2016-09-13

Termites have specialized digestive systems that overcome the lignin barrier in wood to release fermentable simple sugars. Using the termite Reticulitermes flavipes and its gut symbionts, high-throughput titanium pyrosequencing and proteomics approaches experimentally compared the effects of lignin-containing diets on host-symbiont digestome composition. Proteomic investigations and functional digestive studies with recombinant lignocellulases conducted in parallel provided strong evidence of congruence at the transcription and translational levels and provide enzymatic strategies for overcoming recalcitrant lignin barriers in biofuel feedstocks. Briefly described, therefore, the disclosure provides a system for generating a fermentable product from a lignified plant material, the system comprising a cooperating series of at least two catalytically active polypeptides, where said catalytically active polypeptides are selected from the group consisting of: cellulase Cell-1, .beta.-glu cellulase, an aldo-keto-reductase, a catalase, a laccase, and an endo-xylanase.

Oxygen-Dependent Photocatalytic Water Reduction with a Ruthenium(imidazolium) Chromophore and a Cobaloxime Catalyst.

PubMed

Petermann, Lydia; Staehle, Robert; Pfeifer, Maxim; Reichardt, Christian; Sorsche, Dieter; Wächtler, Maria; Popp, Jürgen; Dietzek, Benjamin; Rau, Sven

2016-06-06

Detailed investigations of a photocatalytic system capable of producing hydrogen under pre-catalytic aerobic conditions are reported. This system consists of the NHC precursor chromophore [Ru(tbbpy)2 (RR'ip)][PF6 ]3 (abbreviated as Ru(RR'ip)[PF6 ]3 ; tbbpy=4,4'-di-tert-butyl-2,2'-bipyridine, RR'ip=1,3-disubstituted-1H-imidazo[4,5-f][1,10]phenanthrolinium), the reduction catalyst Co(dmgH)2 (dmgH=dimethylglyoximato), and the electron donor ascorbic acid (AA). Screening studies with respect to solvent, cobaloxime catalyst, electron donor, pH, and concentrations of the individual components yielded optimized photocatalytic conditions. The system shows high activity based on Ru, with turnover numbers up to 2000 under oxygen-free and pre-catalytic aerobic conditions. The turnover frequency in the latter case was even higher than that for the oxygen-free catalyst system. The Ru complexes show high photostability and their first excited state is primarily located on the RR'ip ligand. X-ray crystallographic analysis of the rigid cyclophane-type ligand dd(ip)2 (Br)2 (dd(ip)2 =1,1',3,3'-bis(2,3,5,6-tetramethyl-1,4-phenylene)bis(methylene)bis(1H-imidazo[4,5-f][1,10]phenanthrolinium)) and the catalytic activity of its Ru complex [{(tbbpy)2 Ru}2 (μ-dd(ip)2 )][PF6 ]6 (abbreviated as Ru2 (dd(ip)2 )[PF6 ]6 ) suggest an intermolecular catalytic cycle. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Process to convert biomass and refuse derived fuel to ethers and/or alcohols

DOEpatents

Diebold, J.P.; Scahill, J.W.; Chum, H.L.; Evans, R.J.; Rejai, B.; Bain, R.L.; Overend, R.P.

1996-04-02

A process is described for conversion of a feedstock selected from the group consisting of biomass and refuse derived fuel (RDF) to provide reformulated gasoline components comprising a substantial amount of materials selected from the group consisting of ethers, alcohols, or mixtures thereof, comprising: drying said feedstock; subjecting said dried feedstock to fast pyrolysis using a vortex reactor or other means; catalytically cracking vapors resulting from said pyrolysis using a zeolite catalyst; condensing any aromatic byproduct fraction; catalytically alkylating any benzene present in said vapors after condensation; catalytically oligomerizing any remaining ethylene and propylene to higher olefins; isomerizing said olefins to reactive iso-olefins; and catalytically reacting said iso-olefins with an alcohol to form ethers or with water to form alcohols. 35 figs.

Solid strong base K-Pt/NaY zeolite nano-catalytic system for completed elimination of formaldehyde at room temperature

NASA Astrophysics Data System (ADS)

Song, Shaoqing; Wu, Xi; Lu, Changhai; Wen, Meicheng; Le, Zhanggao; Jiang, Shujuan

2018-06-01

Solid strong base nano-catalytic system of K-modification NaY zeolite supported 0.08% Pt (K-Pt/NaY) were constructed for eliminating HCHO at room temperature. In the catalytic process, activation energy over K-Pt/NaY nano-catalytic system was greatly decreased along with the enhanced reaction rate. Characterization and catalytic tests revealed the surface electron structure of K-Pt/NaY was improved, as reflected by the enhanced HCHO adsorption capability, high sbnd OH concentration, and low-temperature reducibility. Therefore, the optimal K-Pt/NaY showed high catalytic efficiency and strong H2O tolerance for HCHO elimination by directly promoting the reaction between active sbnd OH and formate species. These results may suggest a new way for probing the advanced solid strong base nano-catalytic system for the catalytic elimination of indoor HCHO.

Methodology for the effective stabilization of tin-oxide-based oxidation/reduction catalysts

NASA Technical Reports Server (NTRS)

Jordan, Jeffrey D. (Inventor); Schryer, David R. (Inventor); Leighty, Bradley D. (Inventor); Watkins, Anthony N. (Inventor); Summers, Jerry C. (Inventor); Davis, Patricia P. (Inventor); Oglesby, Donald M. (Inventor); Schryer, Jacqueline L. (Inventor); Gulati, Suresh T. (Inventor)

2011-01-01

The invention described herein involves a novel approach to the production of oxidation/reduction catalytic systems. The present invention serves to stabilize the tin oxide reducible metal-oxide coating by co-incorporating at least another metal-oxide species, such as zirconium. In one embodiment, a third metal-oxide species is incorporated, selected from the group consisting of cerium, lanthanum, hafnium, and ruthenium. The incorporation of the additional metal oxide components serves to stabilize the active tin-oxide layer in the catalytic process during high-temperature operation in a reducing environment (e.g., automobile exhaust). Moreover, the additional metal oxides are active components due to their oxygen-retention capabilities. Together, these features provide a mechanism to extend the range of operation of the tin-oxide-based catalyst system for automotive applications, while maintaining the existing advantages.

A Dual-Catalysis Approach to Enantioselective [2+2] Photocycloadditions Using Visible Light

PubMed Central

Du, Juana; Skubi, Kazimer L.; Schultz, Danielle M.; Yoon, Tehshik P.

2015-01-01

In contrast to the wealth of catalytic systems that are available to control the stereochemistry of thermally promoted cycloadditions, few similarly effective methods exist for the stereocontrol of photochemical cycloadditions. A major unsolved challenge in the design of enantioselective catalytic photocycloaddition reactions has been the difficulty of controlling racemic background reactions that occur by direct photoexcitation of substrates while unbound to catalyst. Here we describe a strategy for eliminating the racemic background reaction in asymmetric [2+2] photocycloadditions of α,β-unsaturated ketones to the corresponding cyclobutanes by employing a dual-catalyst system consisting of a visible light-absorbing transition metal photocatalyst and a stereocontrolling Lewis acid co-catalyst. The independence of these two catalysts enables broader scope, greater stereochemical flexibility, and better efficiency than previously reported methods for enantioselective photochemical cycloadditions. PMID:24763585

A review of tin oxide-based catalytic systems: Preparation, characterization and catalytic behavior

NASA Technical Reports Server (NTRS)

Hoflund, Gar B.

1987-01-01

This paper reviews the important aspects of the preparation, characterization and catalytic behavior of tin oxide-based catalytic systems including doped tin oxide, mixed oxides which contain tin oxide, Pt supported on tin oxide and Pt/Sn supported on alumina. These systems have a broad range of applications and are continually increasing in importance. However, due to their complex nature, much remains to be understood concerning how they function catalytically.

Carbocation/Polyol Systems as Efficient Organic Catalysts for the Preparation of Cyclic Carbonates.

PubMed

Rulev, Yuri A; Gugkaeva, Zalina T; Lokutova, Anastasia V; Maleev, Victor I; Peregudov, Alexander S; Wu, Xiao; North, Michael; Belokon, Yuri N

2017-03-22

Carbocation/polyol systems are shown to be highly efficient catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 50 °C and 5 MPa CO 2 pressure. The best activity was shown by the combination of crystal violet and 1,1'-bi-2-naphthol (BINOL), which could be recycled five times with no loss of activity. The presence of specific interactions between the amino groups of the carbocation and the hydroxyl protons was confirmed by NMR experiments. The Job plots for the crystal violet iodide/BINOL and brilliant green iodide/BINOL systems showed that the catalytic systems consist of one molecule of the carbocation and one molecule of BINOL. Mechanistic studies using a deuterated epoxide indicate that there was some loss of epoxide stereochemistry during the reaction, but predominant retention of stereochemistry is observed. On this basis, a catalytic cycle is proposed. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Process of producing liquid hydrocarbon fuels from biomass

DOEpatents

Kuester, James L.

1987-07-07

A continuous thermochemical indirect liquefaction process to convert various biomass materials into diesel-type transportation fuels which fuels are compatible with current engine designs and distribution systems comprising feeding said biomass into a circulating solid fluidized bed gasification system to produce a synthesis gas containing olefins, hydrogen and carbon monoxide and thereafter introducing the synthesis gas into a catalytic liquefaction system to convert the synthesis gas into liquid hydrocarbon fuel consisting essentially of C.sub.7 -C.sub.17 paraffinic hydrocarbons having cetane indices of 50+.

Mechanism of Copper(I)/TEMPO-Catalyzed Aerobic Alcohol Oxidation

PubMed Central

Hoover, Jessica M.; Ryland, Bradford L.; Stahl, Shannon S.

2013-01-01

Homogeneous Cu/TEMPO catalyst systems (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) have emerged as some of the most versatile and practical catalysts for aerobic alcohol oxidation. Recently, we disclosed a (bpy)CuI/TEMPO/NMI catalyst system (NMI = N-methylimidazole) that exhibits fast rates and high selectivities, even with unactivated aliphatic alcohols. Here, we present a mechanistic investigation of this catalyst system, in which we compare the reactivity of benzylic and aliphatic alcohols. This work includes analysis of catalytic rates by gas-uptake and in situ IR kinetic methods and characterization of the catalyst speciation during the reaction by EPR and UV–visible spectroscopic methods. The data support a two-stage catalytic mechanism consisting of (1) “catalyst oxidation” in which CuI and TEMPO–H are oxidized by O2 via a binuclear Cu2O2 intermediate and (2) “substrate oxidation” mediated by CuII and the nitroxyl radical of TEMPO via a CuII-alkoxide intermediate. Catalytic rate laws, kinetic isotope effects, and spectroscopic data show that reactions of benzylic and aliphatic alcohols have different turnover-limiting steps. Catalyst oxidation by O2 is turnover limiting with benzylic alcohols, while numerous steps contribute to the turnover rate in the oxidation of aliphatic alcohols. PMID:23317450

Estimation of transient heat flux density during the heat supply of a catalytic wall steam methane reformer

NASA Astrophysics Data System (ADS)

Settar, Abdelhakim; Abboudi, Saïd; Madani, Brahim; Nebbali, Rachid

2018-02-01

Due to the endothermic nature of the steam methane reforming reaction, the process is often limited by the heat transfer behavior in the reactors. Poor thermal behavior sometimes leads to slow reaction kinetics, which is characterized by the presence of cold spots in the catalytic zones. Within this framework, the present work consists on a numerical investigation, in conjunction with an experimental one, on the one-dimensional heat transfer phenomenon during the heat supply of a catalytic-wall reactor, which is designed for hydrogen production. The studied reactor is inserted in an electric furnace where the heat requirement of the endothermic reaction is supplied by electric heating system. During the heat supply, an unknown heat flux density, received by the reactive flow, is estimated using inverse methods. In the basis of the catalytic-wall reactor model, an experimental setup is engineered in situ to measure the temperature distribution. Then after, the measurements are injected in the numerical heat flux estimation procedure, which is based on the Function Specification Method (FSM). The measured and estimated temperatures are confronted and the heat flux density which crosses the reactor wall is determined.

Development of a household waste treatment subsystem, volume 1. [with water conservation features

NASA Technical Reports Server (NTRS)

Gresko, T. M.; Murray, R. W.

1973-01-01

The domestic waste treatment subsystem was developed to process the daily liquid and non-metallic solid wastes provided by a family of four people. The subsystem was designed to be connected to the sewer line of a household which contained water conservation features. The system consisted of an evaporation technique to separate liquids from solids, an incineration technique for solids reduction, and a catalytic oxidizer for eliminating noxious gases from evaporation and incineration processes. All wastes were passed through a grinder which masticated the solids and deposited them in a settling tank. The liquids were transferred through a cleanable filter into a holding tank. From here the liquids were sprayed into an evaporator and a spray chamber where evaporation occurred. The resulting vapors were processed by catalytic oxidation. Water and latent energy were recovered in a combination evaporator/condenser heat exchanger. The solids were conveyed into an incinerator and reduced to ash while the incineration gases were passed through the catalytic oxidizer along with the processed water vapor.

Atomic-scale identification of Pd leaching in nanoparticle catalyzed C–C coupling: Effects of particle surface disorder

DOE PAGES

Briggs, Beverly D.; Bedford, Nicholas M.; Seifert, Soenke; ...

2015-07-23

C–C coupling reactions are of great importance in the synthesis of numerous organic compounds, where Pd nanoparticle catalyzed systems represent new materials to efficiently drive these reactions. Despite their pervasive utility, the catalytic mechanism of these particle-based reactions remains highly contested. Herein we present evidence of an atom leaching mechanism for Stille coupling under aqueous conditions using peptide-capped Pd nanoparticles. EXAFS analysis revealed Pd coordination changes in the nanoparticle consistent with Pd atom abstraction, where sizing analysis by SAXS confirmed particle size changes associated with a leaching process. It is likely that recently discovered highly disordered surface Pd atoms aremore » the favored catalytic active sites and are leached during oxidative addition, resulting in smaller particles. Thus, probing the mechanism of nanoparticle-driven C–C coupling reactions through structural analyses provides fundamental information concerning these active sites and their reactivity at the atomic-scale, which can be used to improve catalytic performance to meet important sustainability goals.« less

Invoking Direct Exciton-Plasmon Interactions by Catalytic Ag Deposition on Au Nanoparticles: Photoelectrochemical Bioanalysis with High Efficiency.

PubMed

Ma, Zheng-Yuan; Xu, Fei; Qin, Yu; Zhao, Wei-Wei; Xu, Jing-Juan; Chen, Hong-Yuan

2016-04-19

In this work, direct exciton-plasmon interactions (EPI) between CdS quantum dots (QDs) and Ag nanoparticles (NPs) were invoked ingeniously by catalytic Ag deposition on Au NPs for the stimulation of high efficient damping effect toward the excitonic responses in CdS QDs, on the basis of which a novel photoelectrochemical (PEC) bioanalytical format was achieved for sensitive microRNA detection. Specifically, upon the configurational change from the hairpin probe DNA to the "Y"-shaped ternary conjugate consisting of the original probe DNA, assistant DNA, and the target microRNA, the alkaline phosphatase (ALP) catalytic chemistry would then trigger the transition of the interparticle interplay from the CdS QDs-Au NPs to the CdS QDs-Ag NPs systems for the microRNA detection due to the dependence of the photocurrent quenching on the target concentration. This work not only provided a unique method for EPI generation among the PEC nanosystems but also offered a versatile and general protocol for future PEC bioanalysis development.

Determining the transport mechanism of an enzyme-catalytic complex metabolic network based on biological robustness.

PubMed

Wang, Lei

2013-04-01

Understanding the transport mechanism of 1,3-propanediol (1,3-PD) is of critical importance to do further research on gene regulation. Due to the lack of intracellular information, on the basis of enzyme-catalytic system, using biological robustness as performance index, we present a system identification model to infer the most possible transport mechanism of 1,3-PD, in which the performance index consists of the relative error of the extracellular substance concentrations and biological robustness of the intracellular substance concentrations. We will not use a Boolean framework but prefer a model description based on ordinary differential equations. Among other advantages, this also facilitates the robustness analysis, which is the main goal of this paper. An algorithm is constructed to seek the solution of the identification model. Numerical results show that the most possible transport way is active transport coupled with passive diffusion.

Auto-Tandem Catalysis in Ionic Liquids: Synthesis of 2-Oxazolidinones by Palladium-Catalyzed Oxidative Carbonylation of Propargylic Amines in EmimEtSO₄.

PubMed

Mancuso, Raffaella; Maner, Asif; Ziccarelli, Ida; Pomelli, Christian; Chiappe, Cinzia; Della Ca', Nicola; Veltri, Lucia; Gabriele, Bartolo

2016-07-08

A convenient carbonylative approach to 2-oxazolidinone derivatives carried out using an ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate, EmimEtSO₄) as the solvent is presented. It is based on the sequential concatenation of two catalytic cycles, both catalyzed by the same metal species (auto-tandem catalysis): the first cycle corresponds to the oxidative monoaminocarbonylation of the triple bond of propargylic amines to give the corresponding 2-ynamide intermediates, while the second one involves the cyclocarbonylation of the latter to yield 2-(2-oxooxazolidin-5-ylidene)-acetamides. Reactions are carried out using a simple catalytic system consisting of PdI₂ in conjunction with an excess of KI, and the catalyst/solvent system could be recycled several times without appreciable loss of activity after extraction of the organic product with Et₂O.

Structural insight into the substrate- and dioxygen-binding manner in the catalytic cycle of rieske nonheme iron oxygenase system, carbazole 1,9a-dioxygenase.

PubMed

Ashikawa, Yuji; Fujimoto, Zui; Usami, Yusuke; Inoue, Kengo; Noguchi, Haruko; Yamane, Hisakazu; Nojiri, Hideaki

2012-06-24

Dihydroxylation of tandemly linked aromatic carbons in a cis-configuration, catalyzed by multicomponent oxygenase systems known as Rieske nonheme iron oxygenase systems (ROs), often constitute the initial step of aerobic degradation pathways for various aromatic compounds. Because such RO reactions inherently govern whether downstream degradation processes occur, novel oxygenation mechanisms involving oxygenase components of ROs (RO-Os) is of great interest. Despite substantial progress in structural and physicochemical analyses, no consensus exists on the chemical steps in the catalytic cycles of ROs. Thus, determining whether conformational changes at the active site of RO-O occur by substrate and/or oxygen binding is important. Carbazole 1,9a-dioxygenase (CARDO), a RO member consists of catalytic terminal oxygenase (CARDO-O), ferredoxin (CARDO-F), and ferredoxin reductase. We have succeeded in determining the crystal structures of oxidized CARDO-O, oxidized CARDO-F, and both oxidized and reduced forms of the CARDO-O: CARDO-F binary complex. In the present study, we determined the crystal structures of the reduced carbazole (CAR)-bound, dioxygen-bound, and both CAR- and dioxygen-bound CARDO-O: CARDO-F binary complex structures at 1.95, 1.85, and 2.00 Å resolution. These structures revealed the conformational changes that occur in the catalytic cycle. Structural comparison between complex structures in each step of the catalytic mechanism provides several implications, such as the order of substrate and dioxygen bindings, the iron-dioxygen species likely being Fe(III)-(hydro)peroxo, and the creation of room for dioxygen binding and the promotion of dioxygen binding in desirable fashion by preceding substrate binding. The RO catalytic mechanism is proposed as follows: When the Rieske cluster is reduced, substrate binding induces several conformational changes (e.g., movements of the nonheme iron and the ligand residue) that create room for oxygen binding. Dioxygen bound in a side-on fashion onto nonheme iron is activated by reduction to the peroxo state [Fe(III)-(hydro)peroxo]. This state may react directly with the bound substrate, or O-O bond cleavage may occur to generate Fe(V)-oxo-hydroxo species prior to the reaction. After producing a cis-dihydrodiol, the product is released by reducing the nonheme iron. This proposed scheme describes the catalytic cycle of ROs and provides important information for a better understanding of the mechanism.

Novel Applications of the Methyltrioxorhenium/Hydrogen Peroxide Catalytic System

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

Stankovic, Sasa

Methylrhenium trioxide (MTO), CH 3Re0 3, was first prepared in 1979. An improved synthetic route to MTO was devised from dirhenium heptoxide and tetramethyltin in the presence of hexafluoro glutaric anhydride was reported by Herrmann in 1992. During the course of research on this dissertation we uncovered other reactions where the presence or absence of pyridine can, in some cases dramatically, affect the reaction outcome. This dissertation consists of four chapters. The first two chapters deal with the ,oxidation of water sensitive olefinic compounds with the hydrogen perox’ide/MTO system. Chapters 111 and IV focus on the oxidation of hydrazones withmore » the same catalytic system. Chapter I has been published in The Journal of Organic Chemistry and Chapter III in Chemical Communications. Chapters II and IV have been submitted for publication in The Journal of Organic Chemistry. Each section is selfcontained with its own equations, tables, figures and references. All of the work in this dissertation was performed by this author.« less

Evaluation of Catalytic and Thermal Cracking in a JP-8 Fueled Pulsed Detonation Engine (Postprint)

DTIC Science & Technology

2007-09-01

this research. Each 0.91-m-long heat exchanger was fabricated with a 50.8-mm-dia, inconel - 625 , Schedule-10 inner tube and a 63.5-mm-dia, inconel -600...detonation tube had an inconel heat exchanger (described later). The PDE cycle consisted of three equally timed phases--fill, fire, and purge, as shown in...prevent phase change. The fuel was pressure fed to the inlet of the fuel heating system (FHS). The FHS consisted of two inconel heat exchangers, a

Clean catalytic combustor program

NASA Technical Reports Server (NTRS)

Ekstedt, E. E.; Lyon, T. F.; Sabla, P. E.; Dodds, W. J.

1983-01-01

A combustor program was conducted to evolve and to identify the technology needed for, and to establish the credibility of, using combustors with catalytic reactors in modern high-pressure-ratio aircraft turbine engines. Two selected catalytic combustor concepts were designed, fabricated, and evaluated. The combustors were sized for use in the NASA/General Electric Energy Efficient Engine (E3). One of the combustor designs was a basic parallel-staged double-annular combustor. The second design was also a parallel-staged combustor but employed reverse flow cannular catalytic reactors. Subcomponent tests of fuel injection systems and of catalytic reactors for use in the combustion system were also conducted. Very low-level pollutant emissions and excellent combustor performance were achieved. However, it was obvious from these tests that extensive development of fuel/air preparation systems and considerable advancement in the steady-state operating temperature capability of catalytic reactor materials will be required prior to the consideration of catalytic combustion systems for use in high-pressure-ratio aircraft turbine engines.

Magnetic cobaltic nanoparticle-anchored carbon nanocomposite derived from cobalt-dipicolinic acid coordination polymer: An enhanced catalyst for environmental oxidative and reductive reactions.

PubMed

Wu, Chang-Hsun; Lin, Jyun-Ting; Lin, Kun-Yi Andrew

2018-05-01

Direct carbonization of cobalt complexes represents as a convenient approach to prepare magnetic carbon/cobalt nanocomposites (MCCNs) as heterogeneous environmental catalysts. However, most of MCCNs derived from consist of sheet-like carbon matrices with very sparse cobaltic nanoparticles (NPs), making them exhibit relatively low catalytic activities, porosity and magnetism. In this study, dipicolinic acid (DPA) is selected to prepare a 3-dimensional cobalt coordination polymer (CoDPA). MCCN derived from CoDPA can consist of a porous carbon matrix embedded with highly-dense Co 0 and Co 3 O 4 NPs. This magnetic Co 0 /Co 3 O 4 NP-anchored carbon composite (MCNC) appears as a promising heterogeneous catalyst for oxidative and reductive environmental catalytic reactions. As peroxymonosulfate (PMS) activation is selected as a model catalytic oxidative reaction, MCNC exhibits a much higher catalytic activity than Co 3 O 4 , a benchmark catalyst for PMS activation. The reductive catalytic activity of MCNC is demonstrated through 4-nitrophenol (4-NP) reduction in the presence of NaBH 4 . MCNC could rapidly react with NaBH 4 to generate H 2 for hydrogenation of 4-NP to 4-aminophenol (4-AP). In comparison with other precious metallic catalysts, MCNC also shows a relatively high catalytic activity. These results indicate that MCNC is a conveniently prepared and highly effective and stable carbon-supported cobaltic heterogeneous catalyst for versatile environmental catalytic applications. Copyright © 2018 Elsevier Inc. All rights reserved.

Process of producing liquid hydrocarbon fuels from biomass

DOEpatents

Kuester, J.L.

1987-07-07

A continuous thermochemical indirect liquefaction process is described to convert various biomass materials into diesel-type transportation fuels which fuels are compatible with current engine designs and distribution systems comprising feeding said biomass into a circulating solid fluidized bed gasification system to produce a synthesis gas containing olefins, hydrogen and carbon monoxide and thereafter introducing the synthesis gas into a catalytic liquefaction system to convert the synthesis gas into liquid hydrocarbon fuel consisting essentially of C[sub 7]-C[sub 17] paraffinic hydrocarbons having cetane indices of 50+. 1 fig.

Generation of a stable supramolecular hydrogen evolving photocatalyst by alteration of the catalytic center.

PubMed

Mengele, Alexander K; Kaufhold, Simon; Streb, Carsten; Rau, Sven

2016-04-21

A new dyad consisting of a Ru(II) chromophore, a tetrapyridophenazine bridging ligand and a Rh(Cp*)Cl catalytic center, [Ru(tbbpy)2(tpphz)Rh(Cp*)Cl]Cl(PF6)2, acts as durable photocatalyst for hydrogen production from water. Catalytic activity is observed for more than 650 hours. Electrochemical investigations reveal that up to two electrons can be transferred to the catalytic center by a thermodynamically favorable intramolecular process, which has so far not been reported for similar tpphz based supramolecular photocatalysts. Additionally, mercury poisoning tests indicate that the new dyad works as a homogeneous photocatalyst.

Solution structure of the catalytic domain of RICH protein from goldfish.

PubMed

Kozlov, Guennadi; Denisov, Alexey Y; Pomerantseva, Ekaterina; Gravel, Michel; Braun, Peter E; Gehring, Kalle

2007-03-01

Regeneration-induced CNPase homolog (RICH) is an axonal growth-associated protein, which is induced in teleost fish upon optical nerve injury. RICH consists of a highly acidic N-terminal domain, a catalytic domain with 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) activity and a C-terminal isoprenylation site. In vitro RICH and mammalian brain CNPase specifically catalyze the hydrolysis of 2',3'-cyclic nucleotides to produce 2'-nucleotides, but the physiologically relevant in vivo substrate remains unknown. Here, we report the NMR structure of the catalytic domain of goldfish RICH and describe its binding to CNPase inhibitors. The structure consists of a twisted nine-stranded antiparallel beta-sheet surrounded by alpha-helices on both sides. Despite significant local differences mostly arising from a seven-residue insert in the RICH sequence, the active site region is highly similar to that of human CNPase. Likewise, refinement of the catalytic domain of rat CNPase using residual dipolar couplings gave improved agreement with the published crystal structure. NMR titrations of RICH with inhibitors point to a similar catalytic mechanism for RICH and CNPase. The results suggest a functional importance for the evolutionarily conserved phosphodiesterase activity and hint of a link with pre-tRNA splicing.

When ruthenia met titania: Achieving extraordinary catalytic activity at low temperature by nanostructuring of oxides

DOE PAGES

Graciani, J.; Stacchiola, D.; Yang, F.; ...

2015-09-09

Nanostructured RuO x/TiO 2(110) catalysts have a remarkable catalytic activity for CO oxidation at temperatures in the range of 350–375 K. Furthermore, the RuO 2(110) surface has no activity. The state-of-the-art DFT calculations indicate that the main reasons for such an impressive improvement in the catalytic activity are: (i) a decrease of the diffusion barrier of adsorbed O atoms by around 40%, from 1.07 eV in RuO 2(110) to 0.66 eV in RuO x/TiO 2(110), which explains the shift of the activity to lower temperatures and (ii) a lowering of the barrier by 20% for the association of adsorbed COmore » and O species to give CO 2 (the main barrier for the CO oxidation reaction) passing from around 0.7 eV in RuO 2(110) to 0.55 eV in RuO x/TiO 2(110). We show that the catalytic properties of ruthenia are strongly modified when supported as nanostructures on titania, attaining higher activity at temperatures 100 K lower than that needed for pure ruthenia. As in other systems consisting of ceria nanostructures supported on titania, nanostructured ruthenia shows strongly modified properties compared to the pure oxide, consolidating the fact that the nanostructuring of oxides is a main way to attain higher catalytic activity at lower temperatures.« less

Different Device Architectures for Bulk-Heterojunction Solar Cells

NASA Astrophysics Data System (ADS)

Adam, Getachew; Munkhbat, Battulga; Denk, Patrick; Ulbricht, Christoph; Hrelescu, Calin; Scharber, Markus

2016-08-01

Titania is the most widely studied photocatalyst. In it’s mixed-phase configuration (anatase-rutile form) -as manifested in the commercially available P25 Degussa material- titania was previously found to exhibit the best photocatalytic properties reported for the pure system. A great deal of published research by various workers in the field have not fully explained the underlying mechanism for the observed behavior of mixed-phase titania photocatalysts. One of the prevalent hypothesis in the literature that is tested in this work involves the presence of small, active clusters of interwoven anatase and rutile crystallites or “catalytic “hot-spots””. Therefore, non-woven nanofibrous mats of titania were produced and upon calcination the mats consisted of nanostructured fibers with different anatase-rutile ratios. By assessing the photocatalytic and photoelectrochemical properties of these samples the optimized photocatalyst was determined. This consisted of TiO2 nanostructures annealed at 500˚C with an anatase /rutile content of 90/10. Since the performance of this material exceeded that of P25 complete structural characterization was employed to understand the catalytic mechanism involved. It was determined that the dominant factors controlling the photocatalytic behavior of the titania system are the relative particle size of the different phases of titania and the growth of rutile laths on anatase grains which allow for rapid electron transfer between the two phases. This explains how to optimize the response of the pure system.

Optimized nanostructured TiO2 photocatalysts

NASA Astrophysics Data System (ADS)

Topcu, Selda; Jodhani, Gagan; Gouma, Pelagia

2016-07-01

Titania is the most widely studied photocatalyst. In it’s mixed-phase configuration (anatase-rutile form) -as manifested in the commercially available P25 Degussa material- titania was previously found to exhibit the best photocatalytic properties reported for the pure system. A great deal of published research by various workers in the field have not fully explained the underlying mechanism for the observed behavior of mixed-phase titania photocatalysts. One of the prevalent hypothesis in the literature that is tested in this work involves the presence of small, active clusters of interwoven anatase and rutile crystallites or “catalytic “hot-spots””. Therefore, non-woven nanofibrous mats of titania were produced and upon calcination the mats consisted of nanostructured fibers with different anatase-rutile ratios. By assessing the photocatalytic and photoelectrochemical properties of these samples the optimized photocatalyst was determined. This consisted of TiO2 nanostructures annealed at 500˚C with an anatase /rutile content of 90/10. Since the performance of this material exceeded that of P25 complete structural characterization was employed to understand the catalytic mechanism involved. It was determined that the dominant factors controlling the photocatalytic behavior of the titania system are the relative particle size of the different phases of titania and the growth of rutile laths on anatase grains which allow for rapid electron transfer between the two phases. This explains how to optimize the response of the pure system.

Evaluation of a hybrid ion exchange-catalyst treatment technology for nitrate removal from drinking water.

PubMed

Bergquist, Allison M; Choe, Jong Kwon; Strathmann, Timothy J; Werth, Charles J

2016-06-01

Ion exchange (IX) is the most common approach to treating nitrate-contaminated drinking water sources, but the cost of salt to make regeneration brine, as well as the cost and environmental burden of waste brine disposal, are major disadvantages. A hybrid ion exchange-catalyst treatment system, in which waste brine is catalytically treated for reuse, shows promise for reducing costs and environmental burdens of the conventional IX system. An IX model with separate treatment and regeneration cycles was developed, and ion selectivity coefficients for each cycle were separately calibrated by fitting experimental data. Of note, selectivity coefficients for the regeneration cycle required fitting the second treatment cycle after incomplete resin regeneration. The calibrated and validated model was used to simulate many cycles of treatment and regeneration using the hybrid system. Simulated waste brines and a real brine obtained from a California utility were also evaluated for catalytic nitrate treatment in a packed-bed, flow-through column with 0.5 wt%Pd-0.05 wt%In/activated carbon support (PdIn/AC). Consistent nitrate removal and no apparent catalyst deactivation were observed over 23 d (synthetic brine) and 45 d (real waste brine) of continuous-flow treatment. Ion exchange and catalyst results were used to evaluate treatment of 1 billion gallons of nitrate-contaminated source water at a 0.5 MGD water treatment plant. Switching from a conventional IX system with a two bed volume regeneration to a hybrid system with the same regeneration length and sequencing batch catalytic reactor treatment would save 76% in salt cost. The results suggest the hybrid system has the potential to address the disadvantages of a conventional IX treatment systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

MERCURY OXIDATION PROMOTED BY A SELECTIVE CATALYTIC REDUCTION CATALYST UNDER SIMULATED POWDER RIVER BASIN COAL COMBUSTION CONDITIONS

EPA Science Inventory

A bench-scale reactor consisting of a natural gas burner and an electrically heated reactor housing a selective catalytic reduction (SCR) catalyst was constructed for studying elemental mercury oxidation under SCR conditions. A low sulfur Power River Basin (PRB) coal combustion ...

A photochemical strategy for lignin degradation at room temperature.

PubMed

Nguyen, John D; Matsuura, Bryan S; Stephenson, Corey R J

2014-01-29

The development of a room-temperature lignin degradation strategy consisting of a chemoselective benzylic oxidation with a recyclable oxidant ([4-AcNH-TEMPO]BF4) and a catalytic reductive C-O bond cleavage utilizing the photocatalyst [Ir(ppy)2(dtbbpy)]PF6 is described. This system was tested on relevant lignin model substrates containing β-O-4 linkages to generate fragmentation products in good to excellent yields.

Overexpression of PP2A-C5 that encodes the catalytic subunit 5 of protein phosphatase 2A in Arabidopsis confers better root and shoot development under salt conditions

USDA-ARS?s Scientific Manuscript database

Protein phosphatase 2A (PP2A) is an enzyme consisting of three subunits: a scaffolding A subunit, a regulatory B subunit and a catalytic C subunit. PP2As were shown to play diverse roles in eukaryotes. In this study, the function of the Arabidopsis PP2A-C5 gene that encodes the catalytic subunit 5 o...

Systems including catalysts in porous zeolite materials within a reactor for use in synthesizing hydrocarbons

DOEpatents

Rolllins, Harry W [Idaho Falls, ID; Petkovic, Lucia M [Idaho Falls, ID; Ginosar, Daniel M [Idaho Falls, ID

2012-07-24

Catalytic structures include a catalytic material disposed within a zeolite material. The catalytic material may be capable of catalyzing a formation of methanol from carbon monoxide and/or carbon dioxide, and the zeolite material may be capable of catalyzing a formation of hydrocarbon molecules from methanol. The catalytic material may include copper and zinc oxide. The zeolite material may include a first plurality of pores substantially defined by a crystal structure of the zeolite material and a second plurality of pores dispersed throughout the zeolite material. Systems for synthesizing hydrocarbon molecules also include catalytic structures. Methods for synthesizing hydrocarbon molecules include contacting hydrogen and at least one of carbon monoxide and carbon dioxide with such catalytic structures. Catalytic structures are fabricated by forming a zeolite material at least partially around a template structure, removing the template structure, and introducing a catalytic material into the zeolite material.

A modular, energy-based approach to the development of nickel containing molecular electrocatalysts for hydrogen production and oxidation.

PubMed

Shaw, Wendy J; Helm, Monte L; DuBois, Daniel L

2013-01-01

This review discusses the development of molecular electrocatalysts for H2 production and oxidation based on nickel. A modular approach is used in which the structure of the catalyst is divided into first, second, and outer coordination spheres. The first coordination sphere consists of the ligands bound directly to the metal center, and this coordination sphere can be used to control such factors as the presence or absence of vacant coordination sites, redox potentials, hydride donor abilities and other important thermodynamic parameters. The second coordination sphere includes functional groups such as pendent acids or bases that can interact with bound substrates such as H2 molecules and hydride ligands, but that do not form strong bonds with the metal center. These functional groups can play diverse roles such as assisting the heterolytic cleavage of H2, controlling intra- and intermolecular proton transfer reactions, and providing a physical pathway for coupling proton and electron transfer reactions. By controlling both the hydride donor ability of the catalysts using the first coordination sphere and the proton donor abilities of the functional groups in the second coordination sphere, catalysts can be designed that are biased toward H2 production, oxidation, or bidirectional (catalyzing both H2 oxidation and production). The outer coordination sphere is defined as that portion of the catalytic system that is beyond the second coordination sphere. This coordination sphere can assist in the delivery of protons and electrons to and from the catalytically active site, thereby adding another important avenue for controlling catalytic activity. Many features of these simple catalytic systems are good models for enzymes, and these simple systems provide insights into enzyme function and reactivity that may be difficult to probe in enzymes. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems. Copyright © 2013 Elsevier B.V. All rights reserved.

A measurement system for the atmospheric trace gases CH4 and CO

NASA Technical Reports Server (NTRS)

Condon, E. P.

1977-01-01

A system for measuring ambient clean air levels of the atmospheric trace gases methane and carbon monoxide is described. The analytical method consists of a gas chromatographic technique that incorporates sample preconcentration with catalytic conversion of CO to CH4 and subsequent flame ionization detection of these gases. The system has sufficient sensitivity and repeatability to make the precise measurements required to establish concentration profiles for CO and CH4 in the planetary boundary layer. A discussion of the bottle sampling program being conducted to obtain the samples for the concentration profiles is also presented.

Nickel(0)-Catalyzed Inert C-O Bond Functionalization: Organo Rare-Earth Metal Complex as the Coupling Partner.

PubMed

Yan, Xiangqian; Yang, Fanzhi; Cai, Guilong; Meng, Qingwei; Li, Xiaofang

2018-02-02

An organo rare-earth metal complex has been employed as a highly efficient nucleophile in Ni(0)-catalyzed C-O bond functionalization. The optimized catalytic system which consists of Ni(cod) 2 , PCy 3 , and t-BuONa could smoothly convert 1 equiv of naphthyl ethers to alkylated naphthalene analogues with 0.4 equiv of Ln(CH 2 SiMe 3 ) 3 (THF) 2 , delivering good to excellent yields. The reaction system could also activate the ArCH 2 -O bond with mild base.

Efficient Domino Hydroformylation/Benzoin Condensation: Highly Selective Synthesis of α-Hydroxy Ketones.

PubMed

Dong, Kaiwu; Sang, Rui; Soule, Jean-Francois; Bruneau, Christian; Franke, Robert; Jackstell, Ralf; Beller, Matthias

2015-12-07

An improved domino hydroformylation/benzoin condensation to give α-hydroxy ketones has been developed. Easily available olefins are smoothly converted into the corresponding α-hydroxy ketones in high yields with excellent regioselectivities. Key to success is the use of a specific catalytic system consisting of a rhodium/phosphine complex and the CO2 adduct of an N-heterocyclic carbene. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly efficient catalytic systems based on Pd-coated microbeads

NASA Astrophysics Data System (ADS)

Lim, Jin Hyun; Cho, Ahyoung; Lee, Seung Hwan; Park, Bumkyo; Kang, Dong Woo; Koo, Chong Min; Yu, Taekyung; Park, Bum Jun

2018-01-01

The efficiency of two prototype catalysis systems using palladium (Pd)-coated microparticles was investigated with regard to the recovery and recyclability of the catalytic particles. One such system was the interface-adsorption method, in which polymer particles coated with Pd nanoparticles strongly and irreversibly attach to the oil-water interface. Due to the irreversible adsorption of the catalytic particles to the interface, particle loss was completely prevented while mixing the aqueous solution and while collecting the products. The other system was based on the magnetic field-associated particle recovery method. The use of polymeric microparticles containing Pd nanoparticles and magnetite nanoparticles accelerated the sedimentation of the particles in the aqueous phase by applying a strong magnetic field, consequently suppressing drainage of the particles from the reactor along the product stream. Upon multiple runs of the catalytic reactions, it was found that conversion does not change significantly, demonstrating the excellent recyclability and performance efficiency in the catalytic processes.

Low and medium heating value coal gas catalytic combustor characterization

NASA Technical Reports Server (NTRS)

Schwab, J. A.

1982-01-01

Catalytic combustion with both low and medium heating value coal gases obtained from an operating gasifier was demonstrated. A practical operating range for efficient operation was determined, and also to identify potential problem areas were identified for consideration during stationary gas turbine engine design. The test rig consists of fuel injectors, a fuel-air premixing section, a catalytic reactor with thermocouple instrumentation and a single point, water cooled sample probe. The test rig included inlet and outlet transition pieces and was designed for installation into an existing test loop.

Analysis of in vitro evolution reveals the underlying distribution of catalytic activity among random sequences.

PubMed

Pressman, Abe; Moretti, Janina E; Campbell, Gregory W; Müller, Ulrich F; Chen, Irene A

2017-08-21

The emergence of catalytic RNA is believed to have been a key event during the origin of life. Understanding how catalytic activity is distributed across random sequences is fundamental to estimating the probability that catalytic sequences would emerge. Here, we analyze the in vitro evolution of triphosphorylating ribozymes and translate their fitnesses into absolute estimates of catalytic activity for hundreds of ribozyme families. The analysis efficiently identified highly active ribozymes and estimated catalytic activity with good accuracy. The evolutionary dynamics follow Fisher's Fundamental Theorem of Natural Selection and a corollary, permitting retrospective inference of the distribution of fitness and activity in the random sequence pool for the first time. The frequency distribution of rate constants appears to be log-normal, with a surprisingly steep dropoff at higher activity, consistent with a mechanism for the emergence of activity as the product of many independent contributions. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

Crystal Structure of the Catalytic Domain of a Serine Threonine Protein Phosphatase

NASA Technical Reports Server (NTRS)

Swinglel, Mark; Honkanel, Richard; Ciszak, Ewa

2003-01-01

Reversible phosphorylation of serine and threonine residues is a well-recognized mechanism in eukaryotic cells for the regulation of cell-cycle progression, cell growth and metabolism. Human serine/threonine phosphatases can be placed into two major families, PPP and PPM. To date the structure on one PPP family member (PPl) has been determined. Here we present the structure of a 323-residue catalytic domain of a second phosphatase belonging to the PPP family of enzyme. catalytic domain of the enzyme has been determined to 1.60Angstrom resolution and refined to R=17.5 and Rfree = 20.8%. The catalytic domain possesses a unique fold consisting of a largely monolithic structure, divisible into closely-associated helical and sheet regions. The catalytic site contains two manganese ions that are involved in substrate binding and catalysis. The enzyme crystallizes as a dimer that completely buries catalytic surfaces of both monomers, Also, the structure shows evidence of some flexibility around the active site cleft that may be related to substrate specificity of this enzyme.

Stopped-in-loop flow analysis system for successive determination of trace vanadium and iron in drinking water using their catalytic reactions.

PubMed

Ayala Quezada, Alejandro; Ohara, Keisuke; Ratanawimarnwong, Nuanlaor; Nacapricha, Duangjai; Murakami, Hiroya; Teshima, Norio; Sakai, Tadao

2015-11-01

An automated stopped-in-loop flow analysis (SILFA) system is proposed for the successive catalytic determination of vanadium and iron. The determination of vanadium was based on the p-anisidine oxidation by potassium bromate in the presence of Tiron as an activator to form a reddish dye, which has an absorption maximum at 510 nm. The selectivity of the vanadium determination was greatly improved by adding diphosphate as a masking agent of iron. For the iron determination, an iron-catalyzed oxidative reaction of p-anisidine by hydrogen peroxide with 1,10-phenanthroline as an activator to produce a reddish dye (510 nm) was employed. The SILFA system consisted of two peristaltic pumps, two six-port injection valves, a four-port selection valve, a heater device, a spectrophotometric detector and a data acquisition device. One six-port injection valve was used for the isolation of a mixed solution of standard/sample and reagent to promote each catalytic reaction, and another six-port injection valve was used for switching the reagent for vanadium or iron to achieve selective determination of each analyte. The above mentioned four-port selection valve was used to select standard solutions or sample. These three valves and the two peristaltic pumps were controlled by a built-in programmable logic controller in a touchscreen controller. The obtained results showed that the proposed SILFA monitoring system constituted an effective approach for the selective determination of vanadium and iron. The limits of detection, 0.052 and 0.55 µg L(-1), were obtained for vanadium and iron, respectively. The proposed system was successfully applied to drinking water samples without any preconcentration procedures. Copyright © 2015 Elsevier B.V. All rights reserved.

A study on the indirect urea dosing method in the Selective Catalytic Reduction system

NASA Astrophysics Data System (ADS)

Brzeżański, M.; Sala, R.

2016-09-01

This article presents the results of studies on concept solution of dosing urea in a gas phase in a selective catalytic reduction system. The idea of the concept was to heat-up and evaporate the water urea solution before introducing it into the exhaust gas stream. The aim was to enhance the processes of urea converting into ammonia, what is the target reductant for nitrogen oxides treatment. The study was conducted on a medium-duty Euro 5 diesel engine with exhaust line consisting of DOC catalyst, DPF filter and an SCR system with a changeable setup allowing to dose the urea in liquid phase (regular solution) and to dose it in a gas phase (concept solution). The main criteria was to assess the effect of physical state of urea dosed on the NOx conversion ratio in the SCR catalyst. In order to compare both urea dosing methods a special test procedure was developed which consisted of six test steps covering a wide temperature range of exhaust gas generated at steady state engine operation condition. Tests were conducted for different urea dosing quantities defined by the a equivalence ratio. Based on the obtained results, a remarkable improvement in NOx reduction was found for gas urea application in comparison to the standard liquid urea dosing. Measured results indicate a high potential to increase an efficiency of the SCR catalyst by using a gas phase urea and provide the basis for further scientific research on this type of concept.

[Study of hydrogen bonds in the "catalytic triad" of trypsin by NMR spectra at 1H, 13C, and 15N nuclei].

PubMed

Golubeb, N S; Gindin, V A; Ligaĭ, S S; Smirnov, S N

1994-05-01

The 1H and 13C NMR of trypsin stabilized by chemical modification with a hydrophilic polymer have been obtained in a wide range of pH (1.0-11.0). The spectral features referred to some nuclei of the "catalytic triad" have been identified using different NMR techniques as well as chemical modification with selective reagents. It was found that the monoprotonation of this system results in a quasi-symmetrical hydrogen bond formed between the basic groups which provided explanation for the discrepancies between the experimental findings obtained by different authors concerning the protonation site in this catalytic system. Simulation of the catalytic triad by a 15N-labelled low molecular model suggests that an increase in the OH-group acidity is unaccompanied by a discrete double proton transfer; however, a smooth shift of the bridging protons from one basic atom to another occurs with quasi-symmetrical hydrogen bonds formed in intermediate cases. On the basis of experimental data a new concept has been proposed for the mechanism of acid-base catalysis performed by pains of weak basic groups, such as His-Im and Asp(Glu)-COO- (pKa = 3-7) which are not capable of proton abstraction from alcoholic or water OH-groups (pKa > 13). The catalysis may consist in changing the charge densities on the reacting groups due to strong H-bonding and, on the other hand, in facilitating the free movement of a proton in the field of several basic atoms when going along the reaction coordinate. The energy of very strong hydrogen bonds thus formed diminishes the activation energy of the reaction.

The Thiamin Pyrophosphate-Motif

NASA Technical Reports Server (NTRS)

Dominiak, P.; Ciszak, E.

2003-01-01

Using databases the authors have identified a common thiamin pyrophosphate (TPP)-motif in the family of functionally diverse TPP-dependent enzymes. This common motif consists of multimeric organization of subunits and two catalytic centers. Each catalytic center (PP:PYR) is formed at the interface of the PP-domain binding the magnesium ion, pyrophosphate and amhopyrimidine ring of TPP, and the PYR-domain binding the aminopyrimidine ring of that cofactor. A pair of these catalytic centers constitutes the catalytic core (PP:PYR)(sub 2) within these enzymes. Analysis of the structural elements of this catalytic core reveals novel definition of the common amino acid sequences, which are GXPhiX(sub 4)(G)PhiXXGQ and GDGX(sub 25-30)NN in the PP-domain, and the EX(sub 4)(G)PhiXXGPhi in the PYR-domain, where Phi corresponds to a hydrophobic amino acid. This TPP-motif provides a novel tool for annotation of TPP-dependent enzymes useful in advancing functional proteomics.

Spontaneous emergence of cataclysmic networks in spatially extended systems

NASA Astrophysics Data System (ADS)

Manrubia, Susanna C.; Poyatos, Juan F.; Pérez-Mercader, Juan

2002-11-01

A system of interacting chemical species able to catalyse each others' production is studied. We consider a two-dimensional surface where single molecules attach, diffuse, catalytically interact, and decay. The population of species molecules and the network of interactions among them are dynamical entities. After a short transient time, robust catalytic cycles emerge and a "stationary" state of high diversity and large population numbers settles down. Population dynamics and physical space select among possible graphs of catalytic interactions. The organization of the system is robust: parasitic invaders are short-lived, their populations are kept at low levels, and are unable to sweep away the emerging catalytic cycles.

Mechanistic Studies on the Copper-Catalyzed N-Arylation of Amides

PubMed Central

Strieter, Eric R.; Bhayana, Brijesh; Buchwald, Stephen L.

2009-01-01

The copper-catalyzed N-arylation of amides, i.e., the Goldberg reaction, is an efficient method for the construction of products relevant to both industry and academic settings. Herein, we present mechanistic details concerning the catalytic and stoichiometric N-arylation of amides. In the context of the catalytic reaction, our findings reveal the importance of chelating diamine ligands in controlling the concentration of the active catalytic species. The consistency between the catalytic and stoichiometric results suggest that the activation of aryl halides occurs through a 1,2-diamine-ligated copper(I) amidate complex. Kinetic studies on the stoichiometric N-arylation of aryl iodides using 1,2-diamine ligated Cu(I) amidates also provide insights into the mechanism of aryl halide activation. PMID:19072233

The Design, Synthesis, and Characterization of Open Sites on Metal Clusters

NASA Astrophysics Data System (ADS)

Nigra, Michael Mark

Coordinatively unsaturated corner and edge atoms have been hypothesized to have the highest activity of sites responsible for many catalytic reactions on a metal surface. Recent studies have validated this hypothesis in varied reaction systems. However, quantification of different types of coordinatively unsaturated sites, and elucidation of their individual catalytic rates has remained a largely unresolved challenge when understanding catalysis on metal surfaces. Yet such structure-function knowledge would be invaluable to the design of more active and selective metal-surface catalysts in the future. I investigated the catalytic contributions of undercoordinated sites such as corner and edge atoms are investigated in a model reaction system using organic ligands bound to the gold nanoparticle surface. The catalyst consisted of 4 nm gold nanoparticles on a metal oxide support, using resazurin to resorufin as a model reaction system. My results demonstrate that in this system, corner atom sites are the most undercoordinated sites, and are over an order of magnitude more active when compared to undercoordinated edge atom sites, while terrace sites remain catalytically inactive for the reduction reaction of resazurin to resorufin. Catalytic activity has been also demonstrated for calixarene-bound gold nanoparticles using the reduction of 4-nitrophenol. With the 4-nitrophenol reduction reaction, a comparative study was undertaken to compare calixarene phosphine and calixarene thiol bound 4 nm gold particles. The results of the study suggested that a leached site was responsible for catalysis and not sites on the original gold nanoparticles. Future experiments with calixarene bound gold clusters could investigate ligand effects in reactions where the active site is not a leached or aggregated gold species, possibly in oxidation reactions, where electron-rich gold is hypothesized to be a good catalyst. The results that emphasize the enhanced catalytic activity of undercoordinated sites led me to synthesize small gold clusters consisting of a high fraction of coordinatively unsaturated open sites. This was enabled through an approach that utilized bulky calix[4]arene ligands that are bound to a gold core. Since the size of the calix[4]arene ligand is commensurate with the size of the gold cluster core, the calix[4]arene ligand does not pack closely together on the gold cluster surface. This in turn results in areas of accessible gold atom sites between ligands. Additionally, these calix[4]arene ligands prevent cluster aggregation and electronically tune the gold core in a manner conceptually similar to enzymes affecting reactivity through organic side-chains acting as ligands. I quantified the number of open sites that result from this packing problem on the gold cluster surface, using fluorescence probe chemisorption experiments. The results of these chemisorption measurements support the mechanical model of accessibility whereby accessibility is not dependent on the identity of the functional group, whether it be calixarene phosphines or N-heterocyclic carbenes, bound to the gold surface, but rather to the relative radii of curvature of bound ligands and the gold cluster core. Additional materials characterization was completed with transmission electron microscopy in both bright-field imaging of zeolites, in MCM-22 and delaminated ITQ-2 and UCB-1 materials, and in dark field imaging of glucan coatings on oxide particles. These materials could prove to be interesting materials as to use as supports for the calixarene-bound metal clusters described above or for other metal clusters.

Evolution of catalytic function

NASA Technical Reports Server (NTRS)

Joyce, G. F.

1993-01-01

An RNA-based evolution system was constructed in the laboratory and used to develop RNA enzymes with novel catalytic function. By controlling the nature of the catalytic task that the molecules must perform in order to survive, it is possible to direct the evolving population toward the expression of some desired catalytic behavior. More recently, this system has been coupled to an in vitro translation procedure, raising the possibility of evolving protein enzymes in the laboratory to produce novel proteins with desired catalytic properties. The aim of this line of research is to reduce darwinian evolution, the fundamental process of biology, to a laboratory procedure that can be made to operate in the service of organic synthesis.

Bipolar electrochemical mechanism for the propulsion of catalytic nanomotors in hydrogen peroxide solutions.

PubMed

Wang, Yang; Hernandez, Rose M; Bartlett, David J; Bingham, Julia M; Kline, Timothy R; Sen, Ayusman; Mallouk, Thomas E

2006-12-05

Bimetallic nanorods are propelled in aqueous solutions by the catalytic decomposition of hydrogen peroxide to oxygen and water. Several mechanisms (interfacial tension gradients, bubble recoil, viscous Brownian ratchet, self-electrophoresis) have been proposed for the transduction of chemical to mechanical energy in this system. From Tafel plots of anodic and cathodic hydrogen peroxide reactions at various metal (Au, Pt, Rh, Ni, Ru, and Pd) ultramicroelectrodes, we determine the potential at which the anodic and cathodic reaction rates are equal for each metal. These measurements allow one to predict the direction of motion of all possible bimetallic combinations according to the bipolar electrochemical (or self-electrophoretic) mechanism. These predictions are consistent with the observed direction of motion in all cases studied, providing strong support for the mechanism. We also find that segmented nanorods with one Au end and one poly(pyrrole) end containing catalase, an enzyme that decomposes hydrogen peroxide nonelectrochemically, perform the overall catalytic reaction at a rate similar to that of nanorods containing Au and Pt segments. However, in this case there is no observed axial movement, again supporting the bipolar electrochemical propulsion mechanism for bimetallic nanorods.

Orion EFT-1 Catalytic Tile Experiment Overview and Flight Measurements

NASA Technical Reports Server (NTRS)

Salazar, Giovanni; Amar, Adam; Hyatt, Andrew; Rezin, Marc D.

2016-01-01

This paper describes the design and results of a surface catalysis flight experiment flown on the Orion Multipurpose Crew Vehicle during Exploration Flight Test 1 (EFT1). Similar to previous Space Shuttle catalytic tile experiments, the present test consisted of a highly catalytic coating applied to an instrumented TPS tile. However, the present catalytic tile experiment contained significantly more instrumentation in order to better resolve the heating overshoot caused by the change in surface catalytic efficiency at the interface between two distinct materials. In addition to collecting data with unprecedented spatial resolution of the "overshoot" phenomenon, the experiment was also designed to prove if such a catalytic overshoot would be seen in turbulent flow in high enthalpy regimes. A detailed discussion of the results obtained during EFT1 is presented, as well as the challenges associated with data interpretation of this experiment. Results of material testing carried out in support of this flight experiment are also shown. Finally, an inverse heat conduction technique is employed to reconstruct the flight environments at locations upstream and along the catalytic coating. The data and analysis presented in this work will greatly contribute to our understanding of the catalytic "overshoot" phenomenon, and have a significant impact on the design of future spacecraft.

I.C. Engine emission reduction by copper oxide catalytic converter

NASA Astrophysics Data System (ADS)

Venkatesan, S. P.; Shubham Uday, Desai; Karan Hemant, Borana; Rajarshi Kushwanth Goud, Kagita; Lakshmana Kumar, G.; Pavan Kumar, K.

2017-05-01

The toxic gases emitted from diesel engines are more than petrol engines. Predicting the use of diesel engines, even more in future, this system is developed and can be used to minimize the harmful gases. Toxic gases include NOX, CO, HC and Smoke which are harmful to the atmosphere as well as to the human beings. The main aim of this work is to fabricate system, where the level of intensity of toxic gases is controlled through chemical reaction to more agreeable level. This system acts itself as an exhaust system; hence there is no needs to fit separate the silencer. The whole assembly is fitted in the exhaust pipe from engine. In this work, catalytic converter with copper oxide as a catalyst, by replacing noble catalysts such as platinum, palladium and rhodium is fabricated and fitted in the engine exhaust. With and without catalytic converter, the experimentations are carried out at different loads such as 0%, 25%, 50%, 75%, and 100% of maximum rated load. From the experimental results it is found that the maximum reduction is 32%, 61% and 21% for HC, NOx and CO respectively at 100% of maximum rated load when compared to that of without catalytic converter. This catalytic converter system is cash effective and more economical than the existing catalytic converter.

Use of Water-Fuel Mixture in Diesel Engines at Fishing Vessels

NASA Astrophysics Data System (ADS)

Klyus, Oleg; Bezyukov, O.

2017-06-01

The paper presents the laboratory test results determining physical parameters of fuel mixture made up of petroleum diesel oil, rapeseed oil methyl esters (up to 20%) and water (up to 2.5%). The obtained parameters prove that adding bio-components (rapeseed oil methyl esters) and water to fuel does not result in deterioration of their physical and chemical properties and are comparable to base fuel parameters, namely petroleum diesel oil. The mixture was a subject of bench testing with the use of a self-ignition engine by means of pre-catalytic fuel treatment. The treatment process consisted in fuel - catalytically active material direct contact on the atomizer body. At the comparable operational parameters for the engine, the obtained exhaust gases opacity was lower up to 60% due to the preliminary fuel mixture treatment in relation to the factory-made fuel injection system using petroleum diesel oil.

Bubble driven quasioscillatory translational motion of catalytic micromotors.

PubMed

Manjare, Manoj; Yang, Bo; Zhao, Y-P

2012-09-21

A new quasioscillatory translational motion has been observed for big Janus catalytic micromotors with a fast CCD camera. Such motional behavior is found to coincide with both the bubble growth and burst processes resulting from the catalytic reaction, and the competition of the two processes generates a net forward motion. Detailed physical models have been proposed to describe the above processes. It is suggested that the bubble growth process imposes a growth force moving the micromotor forward, while the burst process induces an instantaneous local pressure depression pulling the micromotor backward. The theoretic predictions are consistent with the experimental data.

Bubble Driven Quasioscillatory Translational Motion of Catalytic Micromotors

NASA Astrophysics Data System (ADS)

Manjare, Manoj; Yang, Bo; Zhao, Y.-P.

2012-09-01

A new quasioscillatory translational motion has been observed for big Janus catalytic micromotors with a fast CCD camera. Such motional behavior is found to coincide with both the bubble growth and burst processes resulting from the catalytic reaction, and the competition of the two processes generates a net forward motion. Detailed physical models have been proposed to describe the above processes. It is suggested that the bubble growth process imposes a growth force moving the micromotor forward, while the burst process induces an instantaneous local pressure depression pulling the micromotor backward. The theoretic predictions are consistent with the experimental data.

Dimension and bridging ligand effects on Mo-mediated catalytic transformation of dinitrogen to ammonia: Chain-like extended models of Nishibayashi’s catalyst

DOE PAGES

Sheng, Xiao -Lan; Batista, Enrique Ricardo; Duan, Yi -Xiang; ...

2016-11-01

Previous studies suggested that in Nishibayashi’s homogenous catalytic systems based on molybdenum (Mo) complexes, the bimetallic structure facilitated dinitrogen to ammonia conversion in comparison to the corresponding monometallic complexes, likely due to the through-bond interactions between the two Mo centers. However, more detailed model systems are necessary to support this bimetallic hypothesis, and to elucidate the multi-metallic effects on the catalytic mechanism. In this work, we computationally examined the effects of dimension as well as the types of bridging ligands on the catalytic activities of molybdenum-dinitrogen complexes by using a set of extended model systems based on Nishibayashi’s bimetallic structure.more » The polynuclear chains containing four ([Mo] 4) or more Mo centers were found to drastically enhance the catalytic performance by comparing with both the monometallic and bimetallic complexes. Carbide ([:C≡C:] 2–) was found to be a more effective bridging ligand than N 2 in terms of electronic charges dispersion between metal centers thereby facilitating reactions in the catalytic cycle. Furthermore, the mechanistic modelling suggests that in principle, more efficient catalytic system for N 2 to NH 3 transformation might be obtained by extending the polynuclear chain to a proper size in combination with an effective bridging ligand for charge dispersion.« less

Dimension and bridging ligand effects on Mo-mediated catalytic transformation of dinitrogen to ammonia: Chain-like extended models of Nishibayashi’s catalyst

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

Sheng, Xiao -Lan; Batista, Enrique Ricardo; Duan, Yi -Xiang

Previous studies suggested that in Nishibayashi’s homogenous catalytic systems based on molybdenum (Mo) complexes, the bimetallic structure facilitated dinitrogen to ammonia conversion in comparison to the corresponding monometallic complexes, likely due to the through-bond interactions between the two Mo centers. However, more detailed model systems are necessary to support this bimetallic hypothesis, and to elucidate the multi-metallic effects on the catalytic mechanism. In this work, we computationally examined the effects of dimension as well as the types of bridging ligands on the catalytic activities of molybdenum-dinitrogen complexes by using a set of extended model systems based on Nishibayashi’s bimetallic structure.more » The polynuclear chains containing four ([Mo] 4) or more Mo centers were found to drastically enhance the catalytic performance by comparing with both the monometallic and bimetallic complexes. Carbide ([:C≡C:] 2–) was found to be a more effective bridging ligand than N 2 in terms of electronic charges dispersion between metal centers thereby facilitating reactions in the catalytic cycle. Furthermore, the mechanistic modelling suggests that in principle, more efficient catalytic system for N 2 to NH 3 transformation might be obtained by extending the polynuclear chain to a proper size in combination with an effective bridging ligand for charge dispersion.« less

Development of a condenser for the dual catalyst water recovery system

NASA Technical Reports Server (NTRS)

Budinikas, P.; Rasouli, F.; Rabadi, N.

1983-01-01

Conceptual evaporation/condensation systems suitable for integration with the catalytic water recovery method were evaluated. The primary requirements for each concept were its capability to operate under zero-gravity conditions, condense recovered water from a vapor-noncondensable gas mixture, and integrate with the catalytic system. Specific energy requirements were estimated for concepts meeting the primary requirements, and the concept most suitable for integration with the catalytic system was proposed. A three-man rate condenser capable of integration with the proposed system, condensing water vapor in presence of noncondensables and transferring the heat of condensation to feed urine was designed, fabricated, and tested. It was treated with steam/air mixtures at atmospheric and elevated pressures and integrated with an actual catalytic water recovery system. The condenser has a condensation efficiency exceeding 90% and heat transfer rate of approximately 85% of theoretical value at coolant temperature ranging from 7 to 80 deg C.

Structure, signaling mechanism and regulation of the natriuretic peptide receptor guanylate cyclase.

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

Misono, K. S.; Philo, J. S.; Arakawa, T.

2011-06-01

Atrial natriuretic peptide (ANP) and the homologous B-type natriuretic peptide are cardiac hormones that dilate blood vessels and stimulate natriuresis and diuresis, thereby lowering blood pressure and blood volume. ANP and B-type natriuretic peptide counterbalance the actions of the renin-angiotensin-aldosterone and neurohormonal systems, and play a central role in cardiovascular regulation. These activities are mediated by natriuretic peptide receptor-A (NPRA), a single transmembrane segment, guanylyl cyclase (GC)-linked receptor that occurs as a homodimer. Here, we present an overview of the structure, possible chloride-mediated regulation and signaling mechanism of NPRA and other receptor GCs. Earlier, we determined the crystal structures ofmore » the NPRA extracellular domain with and without bound ANP. Their structural comparison has revealed a novel ANP-induced rotation mechanism occurring in the juxtamembrane region that apparently triggers transmembrane signal transduction. More recently, the crystal structures of the dimerized catalytic domain of green algae GC Cyg12 and that of cyanobacterium GC Cya2 have been reported. These structures closely resemble that of the adenylyl cyclase catalytic domain, consisting of a C1 and C2 subdomain heterodimer. Adenylyl cyclase is activated by binding of G{sub s}{alpha} to C2 and the ensuing 7{sup o} rotation of C1 around an axis parallel to the central cleft, thereby inducing the heterodimer to adopt a catalytically active conformation. We speculate that, in NPRA, the ANP-induced rotation of the juxtamembrane domains, transmitted across the transmembrane helices, may induce a similar rotation in each of the dimerized GC catalytic domains, leading to the stimulation of the GC catalytic activity.« less

Four-Component Catalytic Machinery: Reversible Three-State Control of Organocatalysis by Walking Back and Forth on a Track.

PubMed

Mittal, Nikita; Özer, Merve S; Schmittel, Michael

2018-04-02

A three-component supramolecular walker system is presented where a two-footed ligand (biped) walks back and forth on a tetrahedral 3D track upon the addition and removal of copper(I) ions, respectively. The addition of N-methylpyrrolidine as a catalyst to the walker system generates a four-component catalytic machinery, which acts as a three-state switchable catalytic ensemble in the presence of substrates for a conjugate addition. The copper(I)-ion-initiated walking process of the biped ligand on the track regulates the catalytic activity in three steps: ON versus int ON (intermediate ON) versus OFF. To establish the operation of the four-component catalytic machinery in a mixture of all constituents, forward and backward cycles were performed in situ illustrating that both the walking process and catalytic action are fully reversible and reproducible.

Root Cause Assessment of Pressure Drop Rise of a Packed Bed of Lithium Hydroxide in the International Space Station Trace Contaminant Control System

NASA Technical Reports Server (NTRS)

Aguilera, Tatiana; Perry, Jay L.

2009-01-01

The trace contaminant control system (TCCS) located in the International Space Station s (ISS) U.S. laboratory module employs physical adsorption, thermal catalytic oxidation, and chemical adsorption to remove trace chemical contamination produced by equipment offgassing and anthropogenic sources from the cabin atmosphere. The chemical adsorption stage, consisting of a packed bed of granular lithium hydroxide (LiOH), is located after the thermal catalytic oxidation stage and is designed to remove acid gas byproducts that may be formed in the upstream oxidation stage. While in service on board the ISS, the LiOH bed exhibited a change in flow resistance that leading to flow control difficulties in the TCCS. Post flight evaluation revealed LiOH granule size attrition among other changes. An experimental program was employed to investigate mechanisms hypothesized to contribute to the change in the packed bed s flow resistance. Background on the problem is summarized, including a discussion of likely mechanisms. The experimental program is described, results are presented, and implications for the future are discussed.

Gel-based morphological design of zirconium metal-organic frameworks.

PubMed

Bueken, Bart; Van Velthoven, Niels; Willhammar, Tom; Stassin, Timothée; Stassen, Ivo; Keen, David A; Baron, Gino V; Denayer, Joeri F M; Ameloot, Rob; Bals, Sara; De Vos, Dirk; Bennett, Thomas D

2017-05-01

The ability of metal-organic frameworks (MOFs) to gelate under specific synthetic conditions opens up new opportunities in the preparation and shaping of hierarchically porous MOF monoliths, which could be directly implemented for catalytic and adsorptive applications. In this work, we present the first examples of xero- or aerogel monoliths consisting solely of nanoparticles of several prototypical Zr 4+ -based MOFs: UiO-66-X (X = H, NH 2 , NO 2 , (OH) 2 ), UiO-67, MOF-801, MOF-808 and NU-1000. High reactant and water concentrations during synthesis were observed to induce the formation of gels, which were converted to monolithic materials by drying in air or supercritical CO 2 . Electron microscopy, combined with N 2 physisorption experiments, was used to show that irregular nanoparticle packing leads to pure MOF monoliths with hierarchical pore systems, featuring both intraparticle micropores and interparticle mesopores. Finally, UiO-66 gels were shaped into monolithic spheres of 600 μm diameter using an oil-drop method, creating promising candidates for packed-bed catalytic or adsorptive applications, where hierarchical pore systems can greatly mitigate mass transfer limitations.

Identification and Characterization of an Alternatively Spliced Isoform of the Human Protein Phosphatase 2Aα Catalytic Subunit*

PubMed Central

Migueleti, Deivid L. S.; Smetana, Juliana H. C.; Nunes, Hugo F.; Kobarg, Jörg; Zanchin, Nilson I. T.

2012-01-01

PP2A is the main serine/threonine-specific phosphatase in animal cells. The active phosphatase has been described as a holoenzyme consisting of a catalytic, a scaffolding, and a variable regulatory subunit, all encoded by multiple genes, allowing for the assembly of more than 70 different holoenzymes. The catalytic subunit can also interact with α4, TIPRL (TIP41, TOR signaling pathway regulator-like), the methyl-transferase LCMT-1, and the methyl-esterase PME-1. Here, we report that the gene encoding the catalytic subunit PP2Acα can generate two mRNA types, the standard mRNA and a shorter isoform, lacking exon 5, which we termed PP2Acα2. Higher levels of the PP2Acα2 mRNA, equivalent to the level of the longer PP2Acα mRNA, were detected in peripheral blood mononuclear cells that were left to rest for 24 h. After this time, the peripheral blood mononuclear cells are still viable and the PP2Acα2 mRNA decreases soon after they are transferred to culture medium, showing that generation of the shorter isoform depends on the incubation conditions. FLAG-tagged PP2Acα2 expressed in HEK293 is catalytically inactive. It displays a specific interaction profile with enhanced binding to the α4 regulatory subunit, but no binding to the scaffolding subunit and PME-1. Consistently, α4 out-competes PME-1 and LCMT-1 for binding to both PP2Acα isoforms in pulldown assays. Together with molecular modeling studies, this suggests that all three regulators share a common binding surface on the catalytic subunit. Our findings add important new insights into the complex mechanisms of PP2A regulation. PMID:22167190

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

Dagle, Robert A.; Lizarazo Adarme, Jair A.; Lebarbier, Vanessa MC

A composite Pd/ZnO/Al2O3-HZSM-5 (Si/Al=40) catalytic system was evaluated for the synthesis of gasoline-range hydrocarbons directly from synthesis gas. Bifunctional catalyst comprising PdZn metal and acid sites present the required catalytically active sites necessary for the methanol synthesis, methanol dehydration, and methanol-to-gasoline reactions. This system provides a unique catalytic pathway for the production of liquid hydrocarbons directly from syngas. However, selectivity control is difficult and poses many challenges. The composite catalytic system was evaluated under various process conditions. Investigated were the effects of temperature (310-375oC), pressure (300-1000 psig), time-on-stream (50 hrs), and gas-hour space velocity (740-2970 hr-1), using a H2/CO molarmore » syngas ratio of 2.0. By operating at the lower end of the temperature range investigated, liquid hydrocarbon formation was favored, as was decreased amounts of undesirable light hydrocarbons. However, lower operating temperatures also facilitated undesirable CO2 formation via the water-gas shift reaction. Higher operating pressures slightly favored liquid synthesis. Operating at relatively low pressures (e.g. 300 psig) was made possible, whereas for methanol synthesis alone higher pressure are usually required to achieve similar conversion levels (e.g. 1000 psig). Thermodynamic constraints on methanol synthesis are eased by pushing the equilibrium through hydrocarbon formation. Catalytic performance was also evaluated by altering Pd and Zn composition of the Pd/ZnO/Al2O3 catalyst. Of the catalysts and conditions tested, selectivity toward liquid hydrocarbon was highest when using a 5% Pd metal loading and Pd/Zn molar ratio of 0.25 and mixed with HZMS-5, operating at 310oC and 300 psig, CO conversion was 43 % and selectivity (carbon weight basis) to hydrocarbons was 49 wt. %. Of the hydrocarbon fraction, 44wt. % was in the C5-C12 liquid product range and consisted primarily of aromatic polymethylbenzenes. However, as syngas conversion increases with increasing temperature, selectivity to liquid product diminished. This is attributed, in large part, to increased saturation of the olefinic intermediates over PdZn metal sites. Under all the conditions and catalysts evaluated in this study, generating liquid product in high yield was challenging (<10 wt. % C5+ yield).« less

Ozonation of clofibric acid catalyzed by titanium dioxide.

PubMed

Rosal, Roberto; Gonzalo, María S; Rodríguez, Antonio; García-Calvo, Eloy

2009-09-30

The removal of clofibric acid from aqueous solution has been investigated in catalytic and non-catalytic semicontinuous ozonation runs. Kinetic data were analyzed using second order expressions for the reaction between organics and ozone or hydroxyl radicals. Catalytic runs used a commercial titanium dioxide catalyst consisting of fumed colloidal particles. The kinetic constant of the non-catalytic ozonation of clofibric acid at pH 3 was 8.16 x 10(-3)+/-3.4 x 10(-4)L mmol(-1)s(-1). The extent of mineralization during non-catalytic runs ranged from 50% at pH 7 to 20% at pH 3 in a reaction that essentially took place during the first 10-20 min. The catalyst increased the total extent of mineralization, its effect being more important during the first part of the reaction. The pseudo-homogeneous catalytic rate constant was 2.17 x 10(-2) L mmol(-1)s(-1) at pH 3 and 6.80 x 10(-1)L mmol(-1)s(-1) at pH 5, with up to a threefold increase with respect to non-catalytic constants using catalyst load of 1g/L. A set of stopped-flow experiments were designed to elucidate the role of catalyst, whose effect was probably due to the adsorption of organics on catalytic sites rather than to the promotion of ozone decomposition.

A sinter-resistant catalytic system fabricated by maneuvering the selectivity of SiO2 deposition onto the TiO2 surface versus the Pt nanoparticle surface.

PubMed

Lu, Ping; Campbell, Charles T; Xia, Younan

2013-10-09

A triphasic catalytic system (Pt/TiO2-SiO2) with an "islands in the sea" configuration was fabricated by controlling the selectivity of SiO2 deposition onto the surface of TiO2 versus the surface of Pt nanoparticles. The Pt surface was exposed, while the nanoparticles were supported on TiO2 and isolated from each other by SiO2 to achieve both significantly improved sinter resistance up to 700 °C and outstanding activity after high-temperature calcination. This work not only demonstrates the feasibility of using a new triphasic system with uncovered catalyst to maximize the thermal stability and catalytic activity but also offers a general approach to the synthesis of high-performance catalytic systems with tunable compositions.

Uniformity index measurement technology using thermocouples to improve performance in urea-selective catalytic reduction systems

NASA Astrophysics Data System (ADS)

Park, Sangki; Oh, Jungmo

2018-05-01

The current commonly used nitrogen oxides (NOx) emission reduction techniques employ hydrocarbons (HCs), urea solutions, and exhaust gas emissions as the reductants. Two of the primary denitrification NOx (DeNOx) catalyst systems are the HC-lean NOx trap (HC-LNT) catalyst and urea-selective catalytic reduction (urea-SCR) catalyst. The secondary injection method depends on the type of injector, injection pressure, atomization, and spraying technique. In addition, the catalyst reaction efficiency is directly affected by the distribution of injectors; hence, the uniformity index (UI) of the reductant is very important and is the basis for system optimization. The UI of the reductant is an indicator of the NOx conversion efficiency (NCE), and good UI values can reduce the need for a catalyst. Therefore, improving the UI can reduce the cost of producing a catalytic converter, which are expensive due to the high prices of the precious metals contained therein. Accordingly, measurement of the UI is an important process in the development of catalytic systems. Two of the commonly used methods for measuring the reductant UI are (i) measuring the exhaust emissions at many points located upstream/downstream of the catalytic converter and (ii) acquisition of a reductant distribution image on a section of the exhaust pipe upstream of the catalytic converter. The purpose of this study is to develop a system and measurement algorithms to measure the exothermic response distribution in the exhaust gas as the reductant passes through the catalytic converter of the SCR catalyst system using a set of thermocouples downstream of the SCR catalyst. The system is used to measure the reductant UI, which is applied in real-time to the actual SCR system, and the results are compared for various types of mixtures for various engine operating conditions and mixer types in terms of NCE.

40 CFR 1039.125 - What maintenance instructions must I give to buyers?

Code of Federal Regulations, 2011 CFR

2011-07-01

... maintaining and using the engine, including the emission-control system. The maintenance instructions also...,000 hours: Fuel injectors, turbochargers, catalytic converters, electronic control units, EGR systems..., catalytic converters, electronic control units, EGR systems (including related components, but excluding...

40 CFR 1039.125 - What maintenance instructions must I give to buyers?

Code of Federal Regulations, 2012 CFR

2012-07-01

... maintaining and using the engine, including the emission-control system. The maintenance instructions also...,000 hours: Fuel injectors, turbochargers, catalytic converters, electronic control units, EGR systems..., catalytic converters, electronic control units, EGR systems (including related components, but excluding...

40 CFR 1039.125 - What maintenance instructions must I give to buyers?

Code of Federal Regulations, 2013 CFR

2013-07-01

... maintaining and using the engine, including the emission-control system. The maintenance instructions also...,000 hours: Fuel injectors, turbochargers, catalytic converters, electronic control units, EGR systems..., catalytic converters, electronic control units, EGR systems (including related components, but excluding...

40 CFR 1039.125 - What maintenance instructions must I give to buyers?

Code of Federal Regulations, 2014 CFR

2014-07-01

... maintaining and using the engine, including the emission-control system. The maintenance instructions also...,000 hours: Fuel injectors, turbochargers, catalytic converters, electronic control units, EGR systems..., catalytic converters, electronic control units, EGR systems (including related components, but excluding...

The Thiamin Pyrophosphate-Motif

NASA Technical Reports Server (NTRS)

Dominiak, Paulina M.; Ciszak, Ewa M.

2003-01-01

Using databases the authors have identified a common thiamin pyrophosphate (TPP)-motif in the family of functionally diverse TPP-dependent enzymes. This common motif consists of multimeric organization of subunits, two catalytic centers, common amino acid sequence, and specific contacts to provide a flip-flop, or alternate site, mechanism of action. Each catalytic center [PP:PYR] is formed at the interface of the PP-domain binding the magnesium ion, pyrophosphate and aminopyrimidine ring of TPP, and the PYR-domain binding the aminopyrimidine ring of that cofactor. A pair of these catalytic centers constitutes the catalytic core [PP:PYR]* within these enzymes. Analysis of the structural elements of this catalytic core reveals novel definition of the common amino acid sequences, which are GX@&(G)@XXGQ, and GDGX25-30 within the PP- domain, and the E&(G)@XXG@ within the PYR-domain, where Q, corresponds to a hydrophobic amino acid. This TPP-motif provides a novel tool for annotation of TPP-dependent enzymes useful in advancing functional proteomics.

Mutational analysis of polynucleotide phosphorylase from Escherichia coli.

PubMed

Jarrige, Anne; Bréchemier-Baey, Dominique; Mathy, Nathalie; Duché, Ophélie; Portier, Claude

2002-08-16

Polynucleotide phosphorylase (PNPase), a homotrimeric exoribonuclease present in bacteria, is involved in mRNA degradation. In Escherichia coli, expression of this enzyme is autocontrolled at the translational level. We introduced about 30 mutations in the pnp gene by site-directed mutagenesis, most of them in phylogenetically conserved residues, and determined their effects on the three catalytic activities of PNPase, phosphorolysis, polymerisation and phosphate exchange, as well as on the efficiency of translational repression. The data are presented and discussed in the light of the crystallographic structure of PNPase from Streptomyces antibioticus. The results show that both PNPase activity and the presence of the KH and S1 RNA-binding domains are required for autocontrol. Deletions of these RNA-binding domains do not abolish any of the three catalytic activities, indicating that they are contained in a domain independent of the catalytic centre. Moreover, the catalytic centre was located around the tungsten-binding site identified by crystallography. Some mutations affect the three catalytic activities differently, an observation consistent with the presence of different subsites.

Appendices to the model description document for a computer program for the emulation/simulation of a space station environmental control and life support system

NASA Technical Reports Server (NTRS)

Yanosy, James L.

1988-01-01

A Model Description Document for the Emulation Simulation Computer Model was already published. The model consisted of a detailed model (emulation) of a SAWD CO2 removal subsystem which operated with much less detailed (simulation) models of a cabin, crew, and condensing and sensible heat exchangers. The purpose was to explore the utility of such an emulation simulation combination in the design, development, and test of a piece of ARS hardware, SAWD. Extensions to this original effort are presented. The first extension is an update of the model to reflect changes in the SAWD control logic which resulted from test. Also, slight changes were also made to the SAWD model to permit restarting and to improve the iteration technique. The second extension is the development of simulation models for more pieces of air and water processing equipment. Models are presented for: EDC, Molecular Sieve, Bosch, Sabatier, a new condensing heat exchanger, SPE, SFWES, Catalytic Oxidizer, and multifiltration. The third extension is to create two system simulations using these models. The first system presented consists of one air and one water processing system. The second consists of a potential air revitalization system.

Cu/Mn bimetallic catalysis enables carbonylative Suzuki-Miyaura coupling with unactivated alkyl electrophiles.

PubMed

Pye, Dominic R; Cheng, Li-Jie; Mankad, Neal P

2017-07-01

A bimetallic system consisting of Cu-carbene and Mn-carbonyl co-catalysts was employed for carbonylative C-C coupling of arylboronic esters with alkyl halides, allowing for the convergent synthesis of ketones. The system operates under mild conditions and exhibits complementary reactivity to Pd catalysis. The method is compatible with a wide range of arylboronic ester nucleophiles and proceeds smoothly for both primary and secondary alkyl iodide electrophiles. Preliminary mechanistic experiments corroborate a hypothetical catalytic mechanism consisting of co-dependent cycles wherein the Cu-carbene co-catalyst engages in transmetallation to generate an organocopper nucleophile, while the Mn-carbonyl co-catalyst activates the alkyl halide electrophile by single-electron transfer and then undergoes reversible carbonylation to generate an acylmanganese electrophile. The two cycles then intersect with a heterobimetallic, product-releasing C-C coupling step.

Catalytic Chemistry of Hydrocarbon Conversion Reactions on Metallic Single Crystals

NASA Astrophysics Data System (ADS)

Tysoe, Wilfred T.

The ability to be able to follow the chemistry of adsorbates on model catalyst surfaces has, in principle, allowed us to peer inside the “black box” of a catalytic reaction and understand the pathway. Such a strategy is most simply implemented for well-ordered single crystal model catalysts for which the catalytic reaction proceeds in ultrahigh vacuum. Thus, in order to be a good model for the supported catalyst, the single crystal should catalyze the reactions with kinetics identical to those for the supported system. This chapter focuses on catalytic systems that fulfill these criteria, namely alkene and alkyne hydrogenation and acetylene cyclotrimerization on Pd(111). The surface chemistry and geometries of the reactants in ultrahigh vacuum are explored in detail allowing fundamental insights into the catalytic reaction pathways to be obtained.

Unique behaviour of dinitrogen-bridged dimolybdenum complexes bearing pincer ligand towards catalytic formation of ammonia.

PubMed

Tanaka, Hiromasa; Arashiba, Kazuya; Kuriyama, Shogo; Sasada, Akira; Nakajima, Kazunari; Yoshizawa, Kazunari; Nishibayashi, Yoshiaki

2014-04-28

It is vital to design effective nitrogen fixation systems that operate under mild conditions, and to this end we recently reported an example of the catalytic formation of ammonia using a dinitrogen-bridged dimolybdenum complex bearing a pincer ligand, where up to twenty three equivalents of ammonia were produced based on the catalyst. Here we study the origin of the catalytic behaviour of the dinitrogen-bridged dimolybdenum complex bearing the pincer ligand with density functional theory calculations, based on stoichiometric and catalytic formation of ammonia from molecular dinitrogen under ambient conditions. Comparison of di- and mono-molybdenum systems shows that the dinitrogen-bridged dimolybdenum core structure plays a critical role in the protonation of the coordinated molecular dinitrogen in the catalytic cycle.

Dynamics of ultrathin V-oxide layers on Rh(111) in catalytic oxidation of ammonia and CO.

PubMed

von Boehn, B; Preiss, A; Imbihl, R

2016-07-20

Catalytic oxidation of ammonia and CO has been studied in the 10(-4) mbar range using a catalyst prepared by depositing ultra-thin vanadium oxide layers on Rh(111) (θV ≈ 0.2 MLE). Using photoemission electron microscopy (PEEM) as a spatially resolving method, we observe that upon heating in an atmosphere of NH3 and O2 the spatial homogeneity of the VOx layer is removed at 800 K and a pattern consisting of macroscopic stripes develops; at elevated temperatures this pattern transforms into a pattern of circular VOx islands. Under reaction conditions the neighboring VOx islands become attracted by each other and coalesce. Similar processes of pattern formation and island coalescence are observed in catalytic CO oxidation. Reoxidation of the reduced VOx catalyst proceeds via surface diffusion of oxygen adsorbed onto Rh(111). A pattern consisting of macroscopic circular VOx islands can also be obtained by heating a Rh(111)/VOx catalyst in pure O2.

Methods of using structures including catalytic materials disposed within porous zeolite materials to synthesize hydrocarbons

DOEpatents

Rollins, Harry W [Idaho Falls, ID; Petkovic, Lucia M [Idaho Falls, ID; Ginosar, Daniel M [Idaho Falls, ID

2011-02-01

Catalytic structures include a catalytic material disposed within a zeolite material. The catalytic material may be capable of catalyzing a formation of methanol from carbon monoxide and/or carbon dioxide, and the zeolite material may be capable of catalyzing a formation of hydrocarbon molecules from methanol. The catalytic material may include copper and zinc oxide. The zeolite material may include a first plurality of pores substantially defined by a crystal structure of the zeolite material and a second plurality of pores dispersed throughout the zeolite material. Systems for synthesizing hydrocarbon molecules also include catalytic structures. Methods for synthesizing hydrocarbon molecules include contacting hydrogen and at least one of carbon monoxide and carbon dioxide with such catalytic structures. Catalytic structures are fabricated by forming a zeolite material at least partially around a template structure, removing the template structure, and introducing a catalytic material into the zeolite material.

Crystal Structure of a Histidine Kinase Sensor Domain with Similarity to Periplasmic Binding Proteins

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

Cheung, J.; Le-Khac, M; Hendrickson, W

2009-01-01

Histidine kinase receptors are elements of the two-component signal transduction systems commonly found in bacteria and lower eukaryotes, where they are crucial for environmental adaption through the coupling of extracellular changes to intracellular responses. The typical two-component system consists of a membrane-spanning histidine kinase sensor and a cytoplasmic response regulator. In the calssic system, extracellular signals such as small molecule ligands and ions are detected by the periplasmic sensor domain of the histidine kinase receptor, which modulates the catalytic activity of the cytoplasmic histidine kinase domain and promotes ATP-dependent autophosphorylation of a conserved histidine residue. G. sulfurreducens genomic DNA wasmore » used.« less

Specific Inhibition of Herpes Simplex Virus DNA Polymerase by Helical Peptides Corresponding to the Subunit Interface

NASA Astrophysics Data System (ADS)

Digard, Paul; Williams, Kevin P.; Hensley, Preston; Brooks, Ian S.; Dahl, Charles E.; Coen, Donald M.

1995-02-01

The herpes simplex virus DNA polymerase consists of two subunits-a catalytic subunit and an accessory subunit, UL42, that increases processivity. Mutations affecting the extreme C terminus of the catalytic subunit specifically disrupt subunit interactions and ablate virus replication, suggesting that new antiviral drugs could be rationally designed to interfere with polymerase heterodimerization. To aid design, we performed circular dichroism (CD) spectroscopy and analytical ultracentrifugation studies, which revealed that a 36-residue peptide corresponding to the C terminus of the catalytic subunit folds into a monomeric structure with partial α-helical character. CD studies of shorter peptides were consistent with a model where two separate regions of α-helix interact to form a hairpin-like structure. The 36-residue peptide and a shorter peptide corresponding to the C-terminal 18 residues blocked UL42-dependent long-chain DNA synthesis at concentrations that had no effect on synthesis by the catalytic subunit alone or by calf thymus DNA polymerase δ and its processivity factor. These peptides, therefore, represent a class of specific inhibitors of herpes simplex virus DNA polymerase that act by blocking accessory-subunit-dependent synthesis. These peptides or their structures may form the basis for the synthesis of clinically effective drugs.

Catalytic Reactor for Inerting of Aircraft Fuel Tanks

DTIC Science & Technology

1974-06-01

Aluminum Panels After Triphase Corrosion Test 79 35 Inerting System Flows in Various Flight Modes 82 36 High Flow Reactor Parametric Data 84 37 System...AD/A-000 939 CATALYTIC REACTOR FOR INERTING OF AIRCRAFT FUEL TANKS George H. McDonald, et al AiResearch Manufacturing Company Prepared for: Air Force...190th Street 2b. GROUP Torrance, California .. REPORT TITLE CATALYTIC REACTOR FOR INERTING OF AIRCRAFT FUEL TANKS . OESCRIP TIVE NOTEs (Thpe of refpoft

Glycine and diglycine as possible catalytic factors in the prebiotic evolution of peptides.

PubMed

Plankensteiner, Kristof; Righi, Alessandro; Rode, Bernd M

2002-06-01

Mutual catalytic effects within the Salt-Induced Peptide Formation (SIPF) Reaction might be one little puzzle piece in the complicated process of the formation of complex peptidic systems and their chemical evolution on the prebiotic earth. The catalytic effects of glycine and diglycine on the formation of dipeptides from mixed amino acid systems in the SIPF Reaction was investigated for systems with leucine, proline, valine and aspartic acid and showed to result in a significant increase of the yield of the majority of the produced dipeptides. The results of the experiments strongly confirm previous theories on the catalytic mechanism and show the ability of the SIPF Reaction to produce a very diverse set of peptide products with relevance to the formation of a biosphere.

Glycine and Diglycine as Possible Catalytic Factors in the Prebiotic Evolution of Peptides

NASA Astrophysics Data System (ADS)

Plankensteiner, Kristof; Righi, Alessandro; Rode, Bernd M.

2002-06-01

Mutual catalytic effects within the Salt-Induced Peptide Formation (SIPF) Reaction might be one little puzzle piece in the complicated process of the formation of complex peptidic systems and their chemical evolution on the prebiotic earth. The catalytic effects of glycine and diglycine on the formation of dipeptides from mixed amino acid systems in the SIPF Reaction was investigated for systems with leucine, proline, valine and aspartic acid and showed to result in a significant increase of the yield of the majority of the produced dipeptides. The results of the experiments strongly confirm previous theories on the catalytic mechanism and show the ability of the SIPF Reaction to produce a very diverse set of peptide products with relevance to the formation of a biosphere.

Caterpillar, Inc. — Converter GP-Catalytic Technology (CGP) system

EPA Pesticide Factsheets

This EPA memo approves Caterpillar Inc. request for Caterpillar Converter GP-Catalytic Technology (CGP) system for certain wheeled hydraulic excavators in reducing emissions and will be posted on the National Clean Diesel Verified Technologies List.

Complex Wall Boundary Conditions for Modeling Combustion in Catalytic Channels

NASA Astrophysics Data System (ADS)

Zhu, Huayang; Jackson, Gregory

2000-11-01

Monolith catalytic reactors for exothermic oxidation are being used in automobile exhaust clean-up and ultra-low emissions combustion systems. The reactors present a unique coupling between mass, heat, and momentum transport in a channel flow configuration. The use of porous catalytic coatings along the channel wall presents a complex boundary condition when modeled with the two-dimensional channel flow. This current work presents a 2-D transient model for predicting the performance of catalytic combustion systems for methane oxidation on Pd catalysts. The model solves the 2-D compressible transport equations for momentum, species, and energy, which are solved with a porous washcoat model for the wall boundary conditions. A time-splitting algorithm is used to separate the stiff chemical reactions from the convective/diffusive equations for the channel flow. A detailed surface chemistry mechanism is incorporated for the catalytic wall model and is used to predict transient ignition and steady-state conversion of CH4-air flows in the catalytic reactor.

Effect of inlet cone pipe angle in catalytic converter

NASA Astrophysics Data System (ADS)

Amira Zainal, Nurul; Farhain Azmi, Ezzatul; Arifin Samad, Mohd

2018-03-01

The catalytic converter shows significant consequence to improve the performance of the vehicle start from it launched into production. Nowadays, the geometric design of the catalytic converter has become critical to avoid the behavior of backpressure in the exhaust system. The backpressure essentially reduced the performance of vehicles and increased the fuel consumption gradually. Consequently, this study aims to design various models of catalytic converter and optimize the volume of fluid flow inside the catalytic converter by changing the inlet cone pipe angles. Three different geometry angles of the inlet cone pipe of the catalytic converter were assessed. The model is simulated in Solidworks software to determine the optimum geometric design of the catalytic converter. The result showed that by decreasing the divergence angle of inlet cone pipe will upsurge the performance of the catalytic converter.

Reversible active site sulfoxygenation can explain the oxygen tolerance of a NAD+-reducing [NiFe] hydrogenase and its unusual infrared spectroscopic properties.

PubMed

Horch, Marius; Lauterbach, Lars; Mroginski, Maria Andrea; Hildebrandt, Peter; Lenz, Oliver; Zebger, Ingo

2015-02-25

Oxygen-tolerant [NiFe] hydrogenases are metalloenzymes that represent valuable model systems for sustainable H2 oxidation and production. The soluble NAD(+)-reducing [NiFe] hydrogenase (SH) from Ralstonia eutropha couples the reversible cleavage of H2 with the reduction of NAD(+) and displays a unique O2 tolerance. Here we performed IR spectroscopic investigations on purified SH in various redox states in combination with density functional theory to provide structural insights into the catalytic [NiFe] center. These studies revealed a standard-like coordination of the active site with diatomic CO and cyanide ligands. The long-lasting discrepancy between spectroscopic data obtained in vitro and in vivo could be solved on the basis of reversible cysteine oxygenation in the fully oxidized state of the [NiFe] site. The data are consistent with a model in which the SH detoxifies O2 catalytically by means of an NADH-dependent (per)oxidase reaction involving the intermediary formation of stable cysteine sulfenates. The occurrence of two catalytic activities, hydrogen conversion and oxygen reduction, at the same cofactor may inspire the design of novel biomimetic catalysts performing H2-conversion even in the presence of O2.

Development and Progress in Enabling the Photocatalyst Ti02 Visible-Light-Active

NASA Technical Reports Server (NTRS)

Levine, Lanfang H.; Coutts, Janelle L.; Clausen, Christian A.

2011-01-01

Photocatalytic oxidation (PCO) of organic contaminants is a promising air and water quality management approach which offers energy and cost savings compared to thermal catalytic oxidation (TCO). The most widely used photocatalyst, anatase TiO2, has a wide band gap (3.2 eV) and is activated by UV photons. Since solar radiation consists of less than 4% UV, but contains 45% visible light, catalysts capable of utilizing these visible photons need to be developed to make peo approaches more efficient, economical, and safe. Researchers have attempted various approaches to enable TiO2 to be visible-light-active with varied degrees of success'. Strategies attempted thus far fall into three categories based on their electrochemical' mechanisms: 1) narrowing the band gap of TiO2 by implantation of transition metal elements or nonmetal elements such as N, S, and C, 2) modifying electron-transfer processes during PCO by adsorbing sensitizing dyes, and 3) employing light-induced interfacial electron transfer in the heteronanojunction systems consisting of narrow band gap semiconductors represented by metal sulfides and TiO2. There are diverse technical approaches to implement each of these strategies. This paper presents a review of these approaches and results of the photocatalytic activity and photonic efficiency of the end .products under visible light. Although resulting visible-light-active (VLA) photocatalysts show promise, there is often no comparison with unmodified TiO2 under UV. In a limited number of studies where such comparison was provided, the UV-induced catalytic activity of bare TiO2 is much greater than the visible-light-induced catalytic activity of the VLA catalyst. Furthermore, VLA-catalysts have much lower quantum efficiency compared to the approx.50% quantum efficiency of UV-catalysts. This stresses the need for continuing research in this area.

An Evaluation of the Vapor Phase Catalytic Ammonia Removal Process for Use in a Mars Transit Vehicle

NASA Technical Reports Server (NTRS)

Flynn, Michael; Borchers, Bruce

1998-01-01

An experimental program has been developed to evaluate the potential of the Vapor Phase Catalytic Ammonia Reduction (VPCAR) technology for use as a Mars Transit Vehicle water purification system. Design modifications which will be required to ensure proper operation of the VPCAR system in reduced gravity are also evaluated. The VPCAR system is an integrated wastewater treatment technology that combines a distillation process with high temperature catalytic oxidation. The distillation portion of the system utilizes a vapor compression distillation process to provide an energy efficient phase change separation. This portion of the system removes any inorganic salts and large molecular weight, organic contaminates, i.e., non-volatile, from the product water stream and concentrates these contaminates into a byproduct stream. To oxidize the volatile organic compounds and ammonia, a vapor phase, high temperature catalytic oxidizer is used. This catalytic system converts these compounds along with the aqueous product into CO2, H2O, and N2O. A secondary catalytic bed can then be used to reduce the N2O to nitrogen and oxygen (although not evaluated in this study). This paper describes the design specification of the VPCAR process, the relative benefits of its utilization in a Mars Transit Vehicle, and the design modification which will be required to ensure its proper operation in reduced gravity. In addition, the results of an experimental evaluation of the processors is presented. This evaluation presents the processors performance based upon product water purity, water recovery rates, and power.

Case Study of the Innovation Process Characterizing the Development of the Three-Way Catalytic Converter System

DOT National Transportation Integrated Search

1979-11-01

This report traces the development of the three-way catalytic converter system from its origins in automaker and chemical firm research in the 1950s, to present plans preparing the system to be the auto exhaust emission control device most widely use...

An Experimental Investigation into NO sub X Control of a Gas Turbine Combustor and Augmentor Tube Incorporating a Catalytic Reduction System

DTIC Science & Technology

1990-03-01

An initial experimental investigation was conducted to examine the feasibility of NOx emission control using catalytic reduction techniques in the ...current configuration impractical. Recommendations for alternative configurations are presented. The results of the investigation have proven that further study is warranted....used as a gas generator and catalytic reduction system. Four data runs were made. Three runs were completed without the catalyst installed

A general method for the catalytic nazarov cyclization of heteroaromatic compounds.

PubMed

Malona, John A; Colbourne, Jessica M; Frontier, Alison J

2006-11-23

A general, catalytic method for efficient Nazarov cyclization of systems containing heteroaromatic components has been developed. Scandium triflate was identified as the most reactive promoter, and it was found that addition of lithium perchlorate was necessary for synthetically useful catalytic cyclizations. The method was used to synthesize a range of cyclopentanone-fused heteroaromatic systems in 36-97% yield, and the reactivity trends observed demonstrate the impact of polarization on cyclization efficiency. [reaction: see text].

Method to produce catalytically active nanocomposite coatings

DOEpatents

Erdemir, Ali; Eryilmaz, Osman Levent; Urgen, Mustafa; Kazmanli, Kursat

2016-02-09

A nanocomposite coating and method of making and using the coating. The nanocomposite coating is disposed on a base material, such as a metal or ceramic; and the nanocomposite consists essentially of a matrix of an alloy selected from the group of Cu, Ni, Pd, Pt and Re which are catalytically active for cracking of carbon bonds in oils and greases and a grain structure selected from the group of borides, carbides and nitrides.

The eukaryotic RNA exosome: same scaffold but variable catalytic subunits.

PubMed

Lykke-Andersen, Søren; Tomecki, Rafal; Jensen, Torben Heick; Dziembowski, Andrzej

2011-01-01

The RNA exosome is a versatile ribonucleolytic protein complex that participates in a multitude of cellular RNA processing and degradation events. It consists of an invariable nine-subunit core that associates with a variety of enzymatically active subunits and co-factors. These contribute to or even provide the catalytic activity and substrate specificity of the complex. The S. cerevisiae exosome has been intensively studied since its discovery in 1997 and thus serves as the archetype of eukaryotic exosomes. Notably, its catalytic potential, derived exclusively from associated subunits, differs between the nuclear and cytoplasmic versions of the complex. The same holds true for other eukaryotes, however, recent discoveries from various laboratories including our own have revealed that there are variations on this theme. Here, we review the latest findings concerning catalytic subunits of eukaryotic exosomes, and we discuss the apparent need for differential composition and subcellular distribution of exosome variants.

Boosting hot electron flux and catalytic activity at metal-oxide interfaces of PtCo bimetallic nanoparticles.

PubMed

Lee, Hyosun; Lim, Juhyung; Lee, Changhwan; Back, Seoin; An, Kwangjin; Shin, Jae Won; Ryoo, Ryong; Jung, Yousung; Park, Jeong Young

2018-06-08

Despite numerous studies, the origin of the enhanced catalytic performance of bimetallic nanoparticles (NPs) remains elusive because of the ever-changing surface structures, compositions, and oxidation states of NPs under reaction conditions. An effective strategy for obtaining critical clues for the phenomenon is real-time quantitative detection of hot electrons induced by a chemical reaction on the catalysts. Here, we investigate hot electrons excited on PtCo bimetallic NPs during H 2 oxidation by measuring the chemicurrent on a catalytic nanodiode while changing the Pt composition of the NPs. We reveal that the presence of a CoO/Pt interface enables efficient transport of electrons and higher catalytic activity for PtCo NPs. These results are consistent with theoretical calculations suggesting that lower activation energy and higher exothermicity are required for the reaction at the CoO/Pt interface.

Catalytic wet oxidation: mathematical modeling of multicompound destruction.

PubMed

Yang, J; Hand, D W; Hokanson, D R; Crittenden, J C; Oman, E J

2003-01-01

A mathematical model of a three-phase catalytic reactor, CatReac, was developed for analysis and optimization of a catalytic oxidation reactor that is used in the International Space Station potable water processor. The packed-bed catalytic reactor, known as the volatile reactor assembly (VRA), is operated as a three-phase reactor and contains a proprietary catalyst, a pure-oxygen gas phase, and the contaminated water. The contaminated water being fed to the VRA primarily consists of acetic acid, acetone, ethanol, 1-propanol, 2-propanol, and propionic acid ranging in concentration from 1 to 10 mg/L. The Langmuir-Hinshelwood Hougen-Watson (L-H) (Hougen, 1943) expression was used to describe the surface reaction rate for these compounds. Single and multicompound short-column experiments were used to determine the L-H rate parameters and calibrate the model. The model was able to predict steady-state multicomponent effluent profiles for short and full-scale reactor experiments.

PARAMETRIC EVALUATION OF VOC/HAP (VOLATILE ORGANIC COMPOUNDS-HAZARDOUS/TOXIC AIR POLLUTANTS) DESTRUCTION VIA CATALYTIC INCINERATION

EPA Science Inventory

The report describes the use of a pilot-scale catalytic incineration unit/solvent generation system to investigate the effectiveness of catalytic incineration as a way to destroy volatile organic compounds (VOCs) and hazardous/toxic air pollutants (HAPs). Objectives of the study ...

Structures of the Peptidoglycan N-Acetylglucosamine Deacetylase Bc1974 and Its Complexes with Zinc Metalloenzyme Inhibitors.

PubMed

Giastas, Petros; Andreou, Athena; Papakyriakou, Athanasios; Koutsioulis, Dimitris; Balomenou, Stavroula; Tzartos, Socrates J; Bouriotis, Vassilis; Eliopoulos, Elias E

2018-02-06

The cell wall peptidoglycan is recognized as a primary target of the innate immune system, and usually its disintegration results in bacterial lysis. Bacillus cereus, a close relative of the highly virulent Bacillus anthracis, contains 10 polysaccharide deacetylases. Among these, the peptidoglycan N-acetylglucosamine deacetylase Bc1974 is the highest homologue to the Bacillus anthracis Ba1977 that is required for full virulence and is involved in resistance to the host's lysozyme. These metalloenzymes belong to the carbohydrate esterase family 4 (CE4) and are attractive targets for the development of new anti-infective agents. Herein we report the first X-ray crystal structures of the NodB domain of Bc1974, the conserved catalytic core of CE4s, in the unliganded form and in complex with four known metalloenzyme inhibitors and two amino acid hydroxamates that target the active site metal. These structures revealed the presence of two conformational states of a catalytic loop known as motif-4 (MT4), which were not observed previously for peptidoglycan deacetylases, but were recently shown in the structure of a Vibrio clolerae chitin deacetylase. By employing molecular docking of a substrate model, we describe a catalytic mechanism that probably involves initial binding of the substrate in a receptive, more open state of MT4 and optimal catalytic activity in the closed state of MT4, consistent with the previous observations. The ligand-bound structures presented here, in addition to the five Bc1974 inhibitors identified, provide a valuable basis for the design of antibacterial agents that target the peptidoglycan deacetylase Ba1977.

Chiral Symmetry Breaking in Peptide Systems During Formation of Life on Earth.

PubMed

Konstantinov, Konstantin K; Konstantinova, Alisa F

2018-03-01

Chiral symmetry breaking in complex chemical systems with a large number of amino acids and a large number of similar reactions was considered. It was shown that effective averaging over similar reaction channels may result in very weak effective enantioselectivity of forward reactions, which does not allow most of the known models to result in chiral symmetry breaking during formation of life on Earth. Models with simple and catalytic synthesis of a single amino acid, formation of peptides up to length five, and sedimentation of insoluble pair of substances were considered. It was shown that depending on the model and the values of the parameters, chiral symmetry breaking may occur in up to about 10% out of all possible unique insoluble pair combinations even in the absence of any catalytic synthesis and that minimum total number of amino acids in the pair is 5. If weak enantioselective forward catalytic synthesis of amino acids is present, then the number of possible variants, in which chiral symmetry breaking may occur, increases substantially. It was shown that that the most interesting catalysts have zero or one amino acid of "incorrect" chirality. If the parameters of the model are adjusted in such a way to result in an increase of concentration of longer peptides, then catalysts with two amino acids of incorrect chirality start to appear at peptides of length five. Models of chiral symmetry breaking in the presence of epimerization were considered for peptides up to length three. It was shown that the range of parameters in which chiral symmetry breaking could occur significantly shrinks in comparison to previously considered models with peptides up to length two. An experiment of chiral symmetry breaking was proposed. The experiment consists of a three-step cycle: reversible catalytic synthesis of amino acids, reversible synthesis of peptides, and irreversible sedimentation of insoluble substances.

Chiral Symmetry Breaking in Peptide Systems During Formation of Life on Earth

NASA Astrophysics Data System (ADS)

Konstantinov, Konstantin K.; Konstantinova, Alisa F.

2018-03-01

Chiral symmetry breaking in complex chemical systems with a large number of amino acids and a large number of similar reactions was considered. It was shown that effective averaging over similar reaction channels may result in very weak effective enantioselectivity of forward reactions, which does not allow most of the known models to result in chiral symmetry breaking during formation of life on Earth. Models with simple and catalytic synthesis of a single amino acid, formation of peptides up to length five, and sedimentation of insoluble pair of substances were considered. It was shown that depending on the model and the values of the parameters, chiral symmetry breaking may occur in up to about 10% out of all possible unique insoluble pair combinations even in the absence of any catalytic synthesis and that minimum total number of amino acids in the pair is 5. If weak enantioselective forward catalytic synthesis of amino acids is present, then the number of possible variants, in which chiral symmetry breaking may occur, increases substantially. It was shown that that the most interesting catalysts have zero or one amino acid of "incorrect" chirality. If the parameters of the model are adjusted in such a way to result in an increase of concentration of longer peptides, then catalysts with two amino acids of incorrect chirality start to appear at peptides of length five. Models of chiral symmetry breaking in the presence of epimerization were considered for peptides up to length three. It was shown that the range of parameters in which chiral symmetry breaking could occur significantly shrinks in comparison to previously considered models with peptides up to length two. An experiment of chiral symmetry breaking was proposed. The experiment consists of a three-step cycle: reversible catalytic synthesis of amino acids, reversible synthesis of peptides, and irreversible sedimentation of insoluble substances.

Method of fabricating a catalytic structure

DOEpatents

Rollins, Harry W [Idaho Falls, ID; Petkovic, Lucia M [Idaho Falls, ID; Ginosar, Daniel M [Idaho Falls, ID

2009-09-22

A precursor to a catalytic structure comprising zinc oxide and copper oxide. The zinc oxide has a sheet-like morphology or a spherical morphology and the copper oxide comprises particles of copper oxide. The copper oxide is reduced to copper, producing the catalytic structure. The catalytic structure is fabricated by a hydrothermal process. A reaction mixture comprising a zinc salt, a copper salt, a hydroxyl ion source, and a structure-directing agent is formed. The reaction mixture is heated under confined volume conditions to produce the precursor. The copper oxide in the precursor is reduced to copper. A method of hydrogenating a carbon oxide using the catalytic structure is also disclosed, as is a system that includes the catalytic structure.

Systems analysis of electricity production from coal using fuel cells

NASA Technical Reports Server (NTRS)

Fleming, D. K.

1983-01-01

Gasifiers, heat transfer, gas stability, quench, water-gas shift reaction, reforming-methanation, other catalytic reactions, compressors and expanders, acid-gas removal, the fuel cell, and catalytic combustors are described. System pressure drops, efficiency of rotating power equipment, heat exchangers, chemical reactions, steam systems, and the fuel cell subsystems are discussed.

Removal of ethylene from air stream by adsorption and plasma-catalytic oxidation using silver-based bimetallic catalysts supported on zeolite.

PubMed

Trinh, Quang Hung; Lee, Sang Baek; Mok, Young Sun

2015-03-21

Dynamic adsorption of ethylene on 13X zeolite-supported Ag and Ag-M(x)O(y) (M: Co, Cu, Mn, and Fe), and plasma-catalytic oxidation of the adsorbed ethylene were investigated. The experimental results showed that the incorporation of Ag into zeolite afforded a marked enhancement in the adsorptivity for ethylene. The addition of transition metal oxides was found to have a positive influence on the ethylene adsorption, except Fe(x)O(y). The presence of the additional metal oxides, however, appeared to somewhat interrupt the diffusion of ozone into the zeolite micro-pores, leading to a decrease in the plasma-catalytic oxidation efficiency of the ethylene adsorbed there. Among the second additional metal oxides, Fe(x)O(y) was able to reduce the emission of ozone during the plasma-catalytic oxidation stage while keeping a high effectiveness for the oxidative removal of the adsorbed ethylene. The periodical treatment consisting of adsorption followed by plasma-catalytic oxidation may be a promising energy-efficient ethylene abatement method. Copyright © 2014 Elsevier B.V. All rights reserved.

A Janus cobalt-based catalytic material for electro-splitting of water

NASA Astrophysics Data System (ADS)

Cobo, Saioa; Heidkamp, Jonathan; Jacques, Pierre-André; Fize, Jennifer; Fourmond, Vincent; Guetaz, Laure; Jousselme, Bruno; Ivanova, Valentina; Dau, Holger; Palacin, Serge; Fontecave, Marc; Artero, Vincent

2012-09-01

The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable and efficient systems for the conversion and storage of renewable energy sources. The production of hydrogen through water splitting seems a promising and appealing solution. We found that a robust nanoparticulate electrocatalytic material, H2-CoCat, can be electrochemically prepared from cobalt salts in a phosphate buffer. This material consists of metallic cobalt coated with a cobalt-oxo/hydroxo-phosphate layer in contact with the electrolyte and mediates H2 evolution from neutral aqueous buffer at modest overpotentials. Remarkably, it can be converted on anodic equilibration into the previously described amorphous cobalt oxide film (O2-CoCat or CoPi) catalysing O2 evolution. The switch between the two catalytic forms is fully reversible and corresponds to a local interconversion between two morphologies and compositions at the surface of the electrode. After deposition, the noble-metal-free coating thus functions as a robust, bifunctional and switchable catalyst.

Hybrid lean premixing catalytic combustion system for gas turbines

DOEpatents

Critchley, Ian L.

2003-12-09

A system and method of combusting a hydrocarbon fuel is disclosed. The system combines the accuracy and controllability of an air staging system with the ultra-low emissions achieved by catalytic combustion systems without the need for a pre-heater. The result is a system and method that is mechanically simple and offers ultra-low emissions over a wide range of power levels, fuel properties and ambient operating conditions.

Method of preparing and utilizing a catalyst system for an oxidation process on a gaseous hydrocarbon stream

DOEpatents

Berry, David A; Shekhawat, Dushyant; Smith, Mark; Haynes, Daniel

2013-07-16

The disclosure relates to a method of utilizing a catalyst system for an oxidation process on a gaseous hydrocarbon stream with a mitigation of carbon accumulation. The system is comprised of a catalytically active phase deposited onto an oxygen conducting phase, with or without supplemental support. The catalytically active phase has a specified crystal structure where at least one catalytically active metal is a cation within the crystal structure and coordinated with oxygen atoms within the crystal structure. The catalyst system employs an optimum coverage ratio for a given set of oxidation conditions, based on a specified hydrocarbon conversion and a carbon deposition limit. Specific embodiments of the catalyst system are disclosed.

Second-Order Biomimicry: In Situ Oxidative Self-Processing Converts Copper(I)/Diamine Precursor into a Highly Active Aerobic Oxidation Catalyst.

PubMed

McCann, Scott D; Lumb, Jean-Philip; Arndtsen, Bruce A; Stahl, Shannon S

2017-04-26

A homogeneous Cu-based catalyst system consisting of [Cu(MeCN) 4 ]PF 6 , N , N '-di- tert -butylethylenediamine (DBED), and p -( N , N -dimethylamino)pyridine (DMAP) mediates efficient aerobic oxidation of alcohols. Mechanistic study of this reaction shows that the catalyst undergoes an in situ oxidative self-processing step, resulting in conversion of DBED into a nitroxyl that serves as an efficient cocatalyst for aerobic alcohol oxidation. Insights into this behavior are gained from kinetic studies, which reveal an induction period at the beginning of the reaction that correlates with the oxidative self-processing step, EPR spectroscopic analysis of the catalytic reaction mixture, which shows the buildup of the organic nitroxyl species during steady state turnover, and independent synthesis of oxygenated DBED derivatives, which are shown to serve as effective cocatalysts and eliminate the induction period in the reaction. The overall mechanism bears considerable resemblance to enzymatic reactivity. Most notable is the "oxygenase"-type self-processing step that mirrors generation of catalytic cofactors in enzymes via post-translational modification of amino acid side chains. This higher-order function within a synthetic catalyst system presents new opportunities for the discovery and development of biomimetic catalysts.

Catalytic Destruction of a Surrogate Organic Hazardous Air Pollutant as a Potential Co-benefit for Coal-fired Selective Catalyst Reduction Systems

EPA Science Inventory

Catalytic destruction of benzene (C6H6), a surrogate for organic hazardous air pollutants (HAPs) produced from coal combustion, was investigated using a commercial selective catalytic reduction (SCR) catalyst for evaluating the potential co-benefit of the SCR technology for reduc...

Characterization of nicotinamidases: steady state kinetic parameters, classwide inhibition by nicotinaldehydes, and catalytic mechanism.

PubMed

French, Jarrod B; Cen, Yana; Vrablik, Tracy L; Xu, Ping; Allen, Eleanor; Hanna-Rose, Wendy; Sauve, Anthony A

2010-12-14

Nicotinamidases are metabolic enzymes that hydrolyze nicotinamide to nicotinic acid. These enzymes are widely distributed across biology, with examples found encoded in the genomes of Mycobacteria, Archaea, Eubacteria, Protozoa, yeast, and invertebrates, but there are none found in mammals. Although recent structural work has improved our understanding of these enzymes, their catalytic mechanism is still not well understood. Recent data show that nicotinamidases are required for the growth and virulence of several pathogenic microbes. The enzymes of Saccharomyces cerevisiae, Drosophila melanogaster, and Caenorhabditis elegans regulate life span in their respective organisms, consistent with proposed roles in the regulation of NAD(+) metabolism and organismal aging. In this work, the steady state kinetic parameters of nicotinamidase enzymes from C. elegans, Sa. cerevisiae, Streptococcus pneumoniae (a pathogen responsible for human pneumonia), Borrelia burgdorferi (the pathogen that causes Lyme disease), and Plasmodium falciparum (responsible for most human malaria) are reported. Nicotinamidases are generally efficient catalysts with steady state k(cat) values typically exceeding 1 s(-1). The K(m) values for nicotinamide are low and in the range of 2 -110 μM. Nicotinaldehyde was determined to be a potent competitive inhibitor of these enzymes, binding in the low micromolar to low nanomolar range for all nicotinamidases tested. A variety of nicotinaldehyde derivatives were synthesized and evaluated as inhibitors in kinetic assays. Inhibitions are consistent with reaction of the universally conserved catalytic Cys on each enzyme with the aldehyde carbonyl carbon to form a thiohemiacetal complex that is stabilized by a conserved oxyanion hole. The S. pneumoniae nicotinamidase can catalyze exchange of (18)O into the carboxy oxygens of nicotinic acid with H(2)(18)O. The collected data, along with kinetic analysis of several mutants, allowed us to propose a catalytic mechanism that explains nicotinamidase and nicotinic acid (18)O exchange chemistry for the S. pneumoniae enzyme involving key catalytic residues, a catalytic transition metal ion, and the intermediacy of a thioester intermediate.

Development of a high-temperature durable catalyst for use in catalytic combustors for advanced automotive gas turbine engines

NASA Astrophysics Data System (ADS)

Tong, H.; Snow, G. C.; Chu, E. K.; Chang, R. L. S.; Angwin, M. J.; Pessagno, S. L.

1981-09-01

Durable catalytic reactors for advanced gas turbine engines were developed. Objectives were: to evaluate furnace aging as a cost effective catalytic reactor screening test, measure reactor degradation as a function of furnace aging, demonstrate 1,000 hours of combustion durability, and define a catalytic reactor system with a high probability of successful integration into an automotive gas turbine engine. Fourteen different catalytic reactor concepts were evaluated, leading to the selection of one for a durability combustion test with diesel fuel for combustion conditions. Eight additional catalytic reactors were evaluated and one of these was successfully combustion tested on propane fuel. This durability reactor used graded cell honeycombs and a combination of noble metal and metal oxide catalysts. The reactor was catalytically active and structurally sound at the end of the durability test.

Development of a high-temperature durable catalyst for use in catalytic combustors for advanced automotive gas turbine engines

NASA Technical Reports Server (NTRS)

Tong, H.; Snow, G. C.; Chu, E. K.; Chang, R. L. S.; Angwin, M. J.; Pessagno, S. L.

1981-01-01

Durable catalytic reactors for advanced gas turbine engines were developed. Objectives were: to evaluate furnace aging as a cost effective catalytic reactor screening test, measure reactor degradation as a function of furnace aging, demonstrate 1,000 hours of combustion durability, and define a catalytic reactor system with a high probability of successful integration into an automotive gas turbine engine. Fourteen different catalytic reactor concepts were evaluated, leading to the selection of one for a durability combustion test with diesel fuel for combustion conditions. Eight additional catalytic reactors were evaluated and one of these was successfully combustion tested on propane fuel. This durability reactor used graded cell honeycombs and a combination of noble metal and metal oxide catalysts. The reactor was catalytically active and structurally sound at the end of the durability test.

Structure and catalytic regulatory function of ubiquitin specific protease 11 N-terminal and ubiquitin-like domains.

PubMed

Harper, Stephen; Gratton, Hayley E; Cornaciu, Irina; Oberer, Monika; Scott, David J; Emsley, Jonas; Dreveny, Ingrid

2014-05-13

The ubiquitin specific protease 11 (USP11) is implicated in DNA repair, viral RNA replication, and TGFβ signaling. We report the first characterization of the USP11 domain architecture and its role in regulating the enzymatic activity. USP11 consists of an N-terminal "domain present in USPs" (DUSP) and "ubiquitin-like" (UBL) domain, together referred to as DU domains, and the catalytic domain harboring a second UBL domain. Crystal structures of the DU domains show a tandem arrangement with a shortened β-hairpin at the two-domain interface and altered surface characteristics compared to the homologues USP4 and USP15. A conserved VEVY motif is a signature feature at the two-domain interface that shapes a potential protein interaction site. Small angle X-ray scattering and gel filtration experiments are consistent with the USP11DU domains and full-length USP11 being monomeric. Unexpectedly, we reveal, through kinetic assays of a series of deletion mutants, that the catalytic activity of USP11 is not regulated through intramolecular autoinhibition or activation by the N-terminal DU or UBL domains. Moreover, ubiquitin chain cleavage assays with all eight linkages reveal a preference for Lys(63)-, Lys(6)-, Lys(33)-, and Lys(11)-linked chains over Lys(27)-, Lys(29)-, and Lys(48)-linked and linear chains consistent with USP11's function in DNA repair pathways that is mediated by the protease domain. Our data support a model whereby USP11 domains outside the catalytic core domain serve as protein interaction or trafficking modules rather than a direct regulatory function of the proteolytic activity. This highlights the diversity of USPs in substrate recognition and regulation of ubiquitin deconjugation.

Oxidative Dehydrogenation on Nanocarbon: Insights into the Reaction Mechanism and Kinetics via in Situ Experimental Methods.

PubMed

Qi, Wei; Yan, Pengqiang; Su, Dang Sheng

2018-03-20

Sustainable and environmentally benign catalytic processes are vital for the future to supply the world population with clean energy and industrial products. The replacement of conventional metal or metal oxide catalysts with earth abundant and renewable nonmetallic materials has attracted considerable research interests in the field of catalysis and material science. The stable and efficient catalytic performance of nanocarbon materials was discovered at the end of last century, and these materials are considered as potential alternatives for conventional metal-based catalysts. With its rapid development in the past 20 years, the research field of carbon catalysis has been experiencing a smooth transition from the discovery of novel nanocarbon materials or related new reaction systems to the atomistic-level mechanistic understanding on the catalytic process and the subsequent rational design of the practical catalytic reaction systems. In this Account, we summarize the recent progress in the kinetic and mechanistic studies on nanocarbon catalyzed alkane oxidative dehydrogenation (ODH) reactions. The paper attempts to extract general concepts and basic regularities for carbon catalytic process directing us on the way for rational design of novel efficient metal-free catalysts. The nature of the active sites for ODH reactions has been revealed through microcalorimetric analysis, ambient pressure X-ray photoelectron spectroscopy (XPS) measurement, and in situ chemical titration strategies. The detailed kinetic analysis and in situ catalyst structure characterization suggests that carbon catalyzed ODH reactions involve the redox cycles of the ketonic carbonyl-hydroxyl pairs, and the key physicochemical parameters (activation energy, reaction order, and rate/equilibrium constants, etc.) of the carbon catalytic systems are proposed and compared with conventional transition metal oxide catalysts. The proposal of the intrinsic catalytic activity (TOF) provides the possibility for the fair comparisons of different nanocarbon catalysts and the consequent structure-function relation regularity. Surface modification and heteroatom doping are proved as the most effective strategies to adjust the catalytic property (activity and product selectivity etc.) of the nanocarbon catalysts. Nanocarbon is actually a proper candidate platform helping us to understand the classical catalytic reaction mechanism better, since there is no lattice oxygen and all the catalytic process happens on nanocarbon surface. This Account also exhibits the importance of the in situ structural characterizations for heterogeneous nanocarbon catalysis. The research strategy and methods proposed for carbon catalysts may also shed light on other complicated catalytic systems or fields concerning the applications of nonmetallic materials, such as energy storage and environment protection etc.

Catalytic conversion of corncob and corncob pretreatment hydrolysate to furfural in a biphasic system with addition of sodium chloride.

PubMed

Qing, Qing; Guo, Qi; Zhou, Linlin; Wan, Yilun; Xu, Youqing; Ji, Huilong; Gao, Xiaohang; Zhang, Yue

2017-02-01

Catalytic conversion of corncob pretreatment hydrolysate and raw corncob into furfural in a modified biphasic system by SO 4 2- /SnO 2 - MMT solid catalyst has been developed. The influence of the organic solvent type, organic to water phase ratio, sodium chloride concentration, reaction temperature and time on the furfural production were comparatively evaluated. The results showed that furfural yields of 81.7% and 66.1% were achieved at 190°C for 15mins and 190°C for 20mins, respectively, for corncob pretreatment hydrolysate and raw corncob by this solid catalyst. The solid catalyst used in this study exhibited good stability and high efficiency applied in the modified biphasic system in addition to excellent recyclability. The proposed catalytic system displayed high performance for catalytic conversion of lignocellulosic biomass into important platform chemicals and has great potential in industrial application. Copyright © 2016 Elsevier Ltd. All rights reserved.

Simultaneous probing of bulk liquid phase and catalytic gas-liquid-solid interface under working conditions using attenuated total reflection infrared spectroscopy

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

Meemken, Fabian; Müller, Philipp; Hungerbühler, Konrad

Design and performance of a reactor set-up for attenuated total reflection infrared (ATR-IR) spectroscopy suitable for simultaneous reaction monitoring of bulk liquid and catalytic solid-liquid-gas interfaces under working conditions are presented. As advancement of in situ spectroscopy an operando methodology for gas-liquid-solid reaction monitoring was developed that simultaneously combines catalytic activity and molecular level detection at the catalytically active site of the same sample. Semi-batch reactor conditions are achieved with the analytical set-up by implementing the ATR-IR flow-through cell in a recycle reactor system and integrating a specifically designed gas feeding system coupled with a bubble trap. By the usemore » of only one spectrometer the design of the new ATR-IR reactor cell allows for simultaneous detection of the bulk liquid and the catalytic interface during the working reaction. Holding two internal reflection elements (IRE) the sample compartments of the horizontally movable cell are consecutively flushed with reaction solution and pneumatically actuated, rapid switching of the cell (<1 s) enables to quasi simultaneously follow the heterogeneously catalysed reaction at the catalytic interface on a catalyst-coated IRE and in the bulk liquid on a blank IRE. For a complex heterogeneous reaction, the asymmetric hydrogenation of 2,2,2-trifluoroacetophenone on chirally modified Pt catalyst the elucidation of catalytic activity/enantioselectivity coupled with simultaneous monitoring of the catalytic solid-liquid-gas interface is shown. Both catalytic activity and enantioselectivity are strongly dependent on the experimental conditions. The opportunity to gain improved understanding by coupling measurements of catalytic performance and spectroscopic detection is presented. In addition, the applicability of modulation excitation spectroscopy and phase-sensitive detection are demonstrated.« less

Exhaust gas purification system for lean burn engine

DOEpatents

Haines, Leland Milburn

2002-02-19

An exhaust gas purification system for a lean burn engine includes a thermal mass unit and a NO.sub.x conversion catalyst unit downstream of the thermal mass unit. The NO.sub.x conversion catalyst unit includes at least one catalyst section. Each catalyst section includes a catalytic layer for converting NO.sub.x coupled to a heat exchanger. The heat exchanger portion of the catalyst section acts to maintain the catalytic layer substantially at a desired temperature and cools the exhaust gas flowing from the catalytic layer into the next catalytic section in the series. In a further aspect of the invention, the exhaust gas purification system includes a dual length exhaust pipe upstream of the NO.sub.x conversion catalyst unit. The dual length exhaust pipe includes a second heat exchanger which functions to maintain the temperature of the exhaust gas flowing into the thermal mass downstream near a desired average temperature.

Comparison of the kinetic parameters of the truncated catalytic subunit and holoenzyme of human DNA polymerase ε

PubMed Central

Zahurancik, Walter J.; Baranovskiy, Andrey G.; Tahirov, Tahir H.; Suo, Zucai

2015-01-01

Numerous genetic studies have provided compelling evidence to establish DNA polymerase ε (Polε) as the primary DNA polymerase responsible for leading strand synthesis during eukaryotic nuclear genome replication. Polε is a heterotetramer consisting of a large catalytic subunit that contains the conserved polymerase core domain as well as a 3′ → 5′ exonuclease domain common to many replicative polymerases. In addition, Polε possesses three small subunits that lack a known catalytic activity but associate with components involved in a variety of DNA replication and maintenance processes. Previous enzymatic characterization of the Polε heterotetramer from budding yeast suggested that the small subunits slightly enhance DNA synthesis by Polε in vitro. However, similar studies of the human Polε heterote-tramer (hPolε) have been limited by the difficulty of obtaining hPolε in quantities suitable for thorough investigation of its catalytic activity. Utilization of a baculovirus expression system for overexpression and purification of hPolε from insect host cells has allowed for isolation of greater amounts of active hPolε, thus enabling a more detailed kinetic comparison between hPolε and an active N-terminal fragment of the hPolε catalytic subunit (p261N), which is readily overexpressed in Escherichia coli. Here, we report the first pre-steady-state studies of fully-assembled hPolε. We observe that the small subunits increase DNA binding by hPolε relative to p261N, but do not increase processivity during DNA synthesis on a single-stranded M13 template. Interestingly, the 3′ → 5′ exonuclease activity of hPolε is reduced relative to p261N on matched and mismatched DNA substrates, indicating that the presence of the small subunits may regulate the proofreading activity of hPolε and sway hPolε toward DNA synthesis rather than proofreading. PMID:25684708

Predicting CYP2C19 Catalytic Parameters for Enantioselective Oxidations Using Artificial Neural Networks and a Chirality Code

PubMed Central

Hartman, Jessica H.; Cothren, Steven D.; Park, Sun-Ha; Yun, Chul-Ho; Darsey, Jerry A.; Miller, Grover P.

2013-01-01

Cytochromes P450 (CYP for isoforms) play a central role in biological processes especially metabolism of chiral molecules; thus, development of computational methods to predict parameters for chiral reactions is important for advancing this field. In this study, we identified the most optimal artificial neural networks using conformation-independent chirality codes to predict CYP2C19 catalytic parameters for enantioselective reactions. Optimization of the neural networks required identifying the most suitable representation of structure among a diverse array of training substrates, normalizing distribution of the corresponding catalytic parameters (kcat, Km, and kcat/Km), and determining the best topology for networks to make predictions. Among different structural descriptors, the use of partial atomic charges according to the CHelpG scheme and inclusion of hydrogens yielded the most optimal artificial neural networks. Their training also required resolution of poorly distributed output catalytic parameters using a Box-Cox transformation. End point leave-one-out cross correlations of the best neural networks revealed that predictions for individual catalytic parameters (kcat and Km) were more consistent with experimental values than those for catalytic efficiency (kcat/Km). Lastly, neural networks predicted correctly enantioselectivity and comparable catalytic parameters measured in this study for previously uncharacterized CYP2C19 substrates, R- and S-propranolol. Taken together, these seminal computational studies for CYP2C19 are the first to predict all catalytic parameters for enantioselective reactions using artificial neural networks and thus provide a foundation for expanding the prediction of cytochrome P450 reactions to chiral drugs, pollutants, and other biologically active compounds. PMID:23673224

Selective catalytic reduction system and process for control of NO.sub.x emissions in a sulfur-containing gas stream

DOEpatents

Sobolevskiy, Anatoly

2015-08-11

An exhaust gas treatment process, apparatus, and system for reducing the concentration of NOx, CO and hydrocarbons in a gas stream, such as an exhaust stream (29), via selective catalytic reduction with ammonia is provided. The process, apparatus and system include a catalytic bed (32) having a reducing only catalyst portion (34) and a downstream reducing-plus-oxidizing portion (36). Each portion (34, 36) includes an amount of tungsten. The reducing-plus-oxidizing catalyst portion (36) advantageously includes a greater amount of tungsten than the reducing catalyst portion (36) to markedly limit ammonia salt formation.

Method and apparatus for thermal management of vehicle exhaust systems

DOEpatents

Benson, David K.; Potter, Thomas F.

1995-01-01

A catalytic converter is surrounded by variable conductance insulation for maintaining the operating temperature of the catalytic converter at an optimum level, for inhibiting heat loss when raising catalytic converter temperature to light-off temperature, for storing excess heat to maintain or accelerate reaching light-off temperature, and for conducting excess heat away from the catalytic converter after reaching light-off temperature. The variable conductance insulation includes vacuum gas control and metal-to-metal thermal shunt mechanisms. Radial and axial shielding inhibits radiation and convection heat loss. Thermal storage media includes phase change material, and heat exchanger chambers and fluids carry heat to and from the catalytic converter.

Packed-bed catalytic cracking of oak derived pyrolytic vapors

USDA-ARS?s Scientific Manuscript database

Catalytic upgrading of pyrolysis vapors derived from oak was carried out using a fixed-bed catalytic column at 425 deg C. The vapors were drawn by splitting a fraction from the full stream of vapors produced at 500 deg C in a 5 kg/hr bench-scale fast pyrolysis reactor system downstream the cyclone s...

A Bioinspired Catalytic Aerobic Oxidative C–H Functionalization of Primary Aliphatic Amines: Synthesis of 1,2-Disubstituted Benzimidazoles

PubMed Central

Nguyen, Khac Minh Huy; Largeron, Martine

2015-01-01

Aerobic oxidative C–H functionalization of primary aliphatic amines has been accomplished with a biomimetic cooperative catalytic system to furnish 1,2-disubstituted benzimidazoles that play an important role as drug discovery targets. This one-pot atom-economical multistep process, which proceeds under mild conditions, with ambient air and equimolar amounts of each coupling partner, constitutes a convenient environmentally friendly strategy to functionalize non-activated aliphatic amines that remain challenging substrates for non-enzymatic catalytic aerobic systems. PMID:26206475

Installation for the catalytic afterburning of exhaust gases in the exhaust gas system of an internal combustion engine

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

Lange, K.

1974-12-06

An installation is described for the catalytic afterburning of exhaust gases in an internal combustion engine. The system includes a line by-passing the installation for the catalytic afterburning, in which is arranged a throttle valve actuated in dependence on the temperature of the installation. The throttle valve also can be actuated independently of the temperature of the installation, but in dependence of the oil pressure which continues to exist for a short period of time after turning off the engine.

A comparative evaluation on the emission characteristics of ceramic and metallic catalytic converter in internal combustion engine

NASA Astrophysics Data System (ADS)

Leman, A. M.; Jajuli, Afiqah; Rahman, Fakhrurrazi; Feriyanto, Dafit; Zakaria, Supaat

2017-09-01

Enforcement of a stricter regulation on exhaust emission by many countries has led to utilization of catalytic converter to reduce the harmful pollutant emission. Ceramic and metallic catalytic converters are the most common type of catalytic converter used. The purpose of this study is to evaluate the performance of the ceramic and metallic catalytic converter on its conversion efficiency using experimental measurement. Both catalysts were placed on a modified exhaust system equipped with a Mitshubishi 4G93 single cylinder petrol engine that was tested on an eddy current dynamometer under steady state conditions for several engine speeds. The experimental results show that the metallic catalytic converter reduced a higher percentage of CO up to 98.6% reduction emissions while ceramic catalytic converter had a better reduction efficiency of HC up to 85.4% and 87.2% reduction of NOx.

Switchable Hydrolase Based on Reversible Formation of Supramolecular Catalytic Site Using a Self-Assembling Peptide.

PubMed

Zhang, Chunqiu; Shafi, Ramim; Lampel, Ayala; MacPherson, Douglas; Pappas, Charalampos G; Narang, Vishal; Wang, Tong; Maldarelli, Charles; Ulijn, Rein V

2017-11-13

The reversible regulation of catalytic activity is a feature found in natural enzymes which is not commonly observed in artificial catalytic systems. Here, we fabricate an artificial hydrolase with pH-switchable activity, achieved by introducing a catalytic histidine residue at the terminus of a pH-responsive peptide. The peptide exhibits a conformational transition from random coil to β-sheet by changing the pH from acidic to alkaline. The β-sheet self-assembles to form long fibrils with the hydrophobic edge and histidine residues extending in an ordered array as the catalytic microenvironment, which shows significant esterase activity. Catalytic activity can be reversible switched by pH-induced assembly/disassembly of the fibrils into random coils. At higher concentrations, the peptide forms a hydrogel which is also catalytically active and maintains its reversible (de-)activation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Method and apparatus for monitoring a hydrocarbon-selective catalytic reduction device

DOEpatents

Schmieg, Steven J; Viola, Michael B; Cheng, Shi-Wai S; Mulawa, Patricia A; Hilden, David L; Sloane, Thompson M; Lee, Jong H

2014-05-06

A method for monitoring a hydrocarbon-selective catalytic reactor device of an exhaust aftertreatment system of an internal combustion engine operating lean of stoichiometry includes injecting a reductant into an exhaust gas feedstream upstream of the hydrocarbon-selective catalytic reactor device at a predetermined mass flowrate of the reductant, and determining a space velocity associated with a predetermined forward portion of the hydrocarbon-selective catalytic reactor device. When the space velocity exceeds a predetermined threshold space velocity, a temperature differential across the predetermined forward portion of the hydrocarbon-selective catalytic reactor device is determined, and a threshold temperature as a function of the space velocity and the mass flowrate of the reductant is determined. If the temperature differential across the predetermined forward portion of the hydrocarbon-selective catalytic reactor device is below the threshold temperature, operation of the engine is controlled to regenerate the hydrocarbon-selective catalytic reactor device.

40 CFR 63.1567 - What are my requirements for inorganic HAP emissions from catalytic reforming units?

Code of Federal Regulations, 2013 CFR

2013-07-01

... different reactors in the catalytic reforming unit are regenerated in separate regeneration systems, then these emission limitations apply to each separate regeneration system. These emission limitations apply... catalyst rejuvenation operations during coke burn-off and catalyst regeneration. You can choose from the...

40 CFR 63.1567 - What are my requirements for inorganic HAP emissions from catalytic reforming units?

Code of Federal Regulations, 2012 CFR

2012-07-01

... different reactors in the catalytic reforming unit are regenerated in separate regeneration systems, then these emission limitations apply to each separate regeneration system. These emission limitations apply... catalyst rejuvenation operations during coke burn-off and catalyst regeneration. You can choose from the...

40 CFR 63.1567 - What are my requirements for inorganic HAP emissions from catalytic reforming units?

Code of Federal Regulations, 2014 CFR

2014-07-01

... different reactors in the catalytic reforming unit are regenerated in separate regeneration systems, then these emission limitations apply to each separate regeneration system. These emission limitations apply... catalyst rejuvenation operations during coke burn-off and catalyst regeneration. You can choose from the...

INDUSTRIAL BOILER RETROFIT FOR NOX CONTROL: COMBINED SELECTIVE NONCATALYTIC REDUCTION AND SELECTIVE CATALYTIC REDUCTION

EPA Science Inventory

The paper describes retrofitting and testing a 590 kW (2 MBtu/hr), oil-fired, three-pass, fire-tube package boiler with a combined selective noncatalytic reduction (SNCR) and selective catalytic reduction (SCR) system. The system demonstrated 85% nitrogen oxides (NOx) reduction w...

Porous media for catalytic renewable energy conversion

NASA Astrophysics Data System (ADS)

Hotz, Nico

2012-05-01

A novel flow-based method is presented to place catalytic nanoparticles into a reactor by sol-gelation of a porous ceramic consisting of copper-based nanoparticles, silica sand, ceramic binder, and a gelation agent. This method allows for the placement of a liquid precursor containing the catalyst into the final reactor geometry without the need of impregnating or coating of a substrate with the catalytic material. The so generated foam-like porous ceramic shows properties highly appropriate for use as catalytic reactor material, e.g., reasonable pressure drop due to its porosity, high thermal and catalytic stability, and excellent catalytic behavior. The catalytic activity of micro-reactors containing this foam-like ceramic is tested in terms of their ability to convert alcoholic biofuel (e.g. methanol) to a hydrogen-rich gas mixture with low concentrations of carbon monoxide (up to 75% hydrogen content and less than 0.2% CO, for the case of methanol). This gas mixture is subsequently used in a low-temperature fuel cell, converting the hydrogen directly to electricity. A low concentration of CO is crucial to avoid poisoning of the fuel cell catalyst. Since conventional Polymer Electrolyte Membrane (PEM) fuel cells require CO concentrations far below 100 ppm and since most methods to reduce the mole fraction of CO (such as Preferential Oxidation or PROX) have CO conversions of up to 99%, the alcohol fuel reformer has to achieve initial CO mole fractions significantly below 1%. The catalyst and the porous ceramic reactor of the present study can successfully fulfill this requirement.

Dimerization Interface of 3-Hydroxyacyl-CoA Dehydrogenase Tunes the Formation of Its Catalytic Intermediate

PubMed Central

Jin, Ying-Hua; Fan, Jun; Sun, Fei

2014-01-01

3-hydroxyacyl-CoA dehydrogenase (HAD, EC 1.1.1.35) is a homodimeric enzyme localized in the mitochondrial matrix, which catalyzes the third step in fatty acid β-oxidation. The crystal structures of human HAD and subsequent complexes with cofactor/substrate enabled better understanding of HAD catalytic mechanism. However, numerous human diseases were found related to mutations at HAD dimerization interface that is away from the catalytic pocket. The role of HAD dimerization in its catalytic activity needs to be elucidated. Here, we solved the crystal structure of Caenorhabditis elegans HAD (cHAD) that is highly conserved to human HAD. Even though the cHAD mutants (R204A, Y209A and R204A/Y209A) with attenuated interactions on the dimerization interface still maintain a dimerization form, their enzymatic activities significantly decrease compared to that of the wild type. Such reduced activities are in consistency with the reduced ratios of the catalytic intermediate formation. Further molecular dynamics simulations results reveal that the alteration of the dimerization interface will increase the fluctuation of a distal region (a.a. 60–80) that plays an important role in the substrate binding. The increased fluctuation decreases the stability of the catalytic intermediate formation, and therefore the enzymatic activity is attenuated. Our study reveals the molecular mechanism about the essential role of the HAD dimerization interface in its catalytic activity via allosteric effects. PMID:24763278

Fluorescent aptasensor for detection of four tetracycline veterinary drugs in milk based on catalytic hairpin assembly reaction and displacement of G-quadruplex.

PubMed

Zhou, Chen; Zou, Haimin; Sun, Chengjun; Ren, Dongxia; Xiong, Wei; Li, Yongxin

2018-05-01

Based on a novel signal amplification strategy by catalytic hairpin assembly and displacement of G-quadruplex DNA, an enzyme-free, non-label fluorescent aptasensing approach was established for sensitive detection of four tetracycline veterinary drugs in milk. The network consisted of a pair of partially complementary DNA hairpins (HP1 and HP2). The DNA aptamer of four tetracycline veterinary drugs was located at the sticky end of the HP1. The ring region of HP1 rich in G and C could form a stable G-quadruplex structure, which could emit specific fluorescence signal after binding with the fluorescent dye and N-methylmesoporphyrin IX (NMM). When presented in the system, the target analytes would be repeatedly used to trigger a recycling procedure between the hairpins, generating numerous HP1-HP2 duplex complexes and displacing G-quadruplex DNA. Thus, the sensitive detection of target analytes was achieved in a wide linear range (0-1000 μg/L) with the detection limit of 4.6 μg/L. Moreover, this proposed method showed high discrimination efficiency towards target analytes against other common mismatched veterinary drugs, and could be successfully applied to the analysis of milk samples. Graphical abstract Schematic of target analyte detection based on catalytic hairpin assembly reaction and displacement of G-quadruplex.

TEMPO functionalized C60 fullerene deposited on gold surface for catalytic oxidation of selected alcohols

NASA Astrophysics Data System (ADS)

Piotrowski, Piotr; Pawłowska, Joanna; Sadło, Jarosław Grzegorz; Bilewicz, Renata; Kaim, Andrzej

2017-05-01

C60TEMPO10 catalytic system linked to a microspherical gold support through a covalent S-Au bond was developed. The C60TEMPO10@Au composite catalyst had a particle size of 0.5-0.8 μm and was covered with the fullerenes derivative of 2.3 nm diameter bearing ten nitroxyl groups; the organic film showed up to 50 nm thickness. The catalytic composite allowed for the oxidation under mild conditions of various primary and secondary alcohols to the corresponding aldehyde and ketone analogues with efficiencies as high as 79-98%, thus giving values typical for homogeneous catalysis, while retaining at the same time all the advantages of heterogeneous catalysis, e.g., easy separation by filtration from the reaction mixture. The catalytic activity of the resulting system was studied by means of high pressure liquid chromatography. A redox mechanism was proposed for the process. In the catalytic cycle of the oxidation process, the TEMPO moiety was continuously regenerated in situ with an applied primary oxidant, for example, O2/Fe3+ system. The new intermediate composite components and the final catalyst were characterized by various spectroscopic methods and thermogravimetry.

Carbon Dioxide Reduction Systems

NASA Technical Reports Server (NTRS)

Burghardt, Stanley I.; Chandler, Horace W.; Taylor, T. I.; Walden, George

1961-01-01

The Methoxy system for regenerating oxygen from carbon dioxide was studied. Experiments indicate that the reaction between carbon dioxide and hydrogen can be carried out with ease in an efficient manner and with excellent heat conservation. A small reactor capable of handling the C02 expired by three men has been built and operated. The decomposition of methane by therma1,arc and catalytic processes was studied. Both the arc and catalytic processes gave encouraging results with over 90 percent of the methane being decomposed to carbon and hydrogen in some of the catalytic processes. Control of the carbon deposition in both the catalytic and arc processes is of great importance to prevent catalyst deactivation and short circuiting of electrical equipment. Sensitive analytical techniques have been developed for all of the components present in the reactor effluent streams.

Design and Experimentation with Sandwich Microstructure for Catalytic Combustion-Type Gas Sensors

PubMed Central

Gu, Jun-Tao; Zhang, Yong-De; Jiang, Jin-Gang

2014-01-01

The traditional handmade catalytic combustion gas sensor has some problems such as a pairing difficulty, poor consistency, high power consumption, and not being interchangeable. To address these issues, integrated double catalytic combustion of alcohol gas sensor was designed and manufactured using silicon micro-electro-mechanical systems (MEMS) technology. The temperature field of the sensor is analyzed using the ANSYS finite element analysis method. In this work, the silicon oxide-PECVD-oxidation technique is used to manufacture a SiO2-Si3N2-SiO2 microstructure carrier with a sandwich structure, while wet etching silicon is used to form a beam structure to reduce the heat consumption. Thin-film technology is adopted to manufacture the platinum-film sensitive resistance. Nano Al2O3-ZrO-ThO is coated to format the sensor carrier, and the sensitive unit is dipped in a Pt-Pd catalyst solution to form the catalytic sensitive bridge arm. Meanwhile the uncoated catalyst carrier is considered as the reference unit, realizing an integrated chip based on a micro double bridge and forming sensors. The lines of the Pt thin-film resistance have been observed with an electronic microscope. The compensation of the sensitive material carriers and compensation materials have been analyzed using an energy spectrum. The results show that the alcohol sensor can detect a volume fraction between 0 and 4,500 × 10−6 and has good linear output characteristic. The temperature ranges from −20 to +40 °C. The humidity ranges from 30% to 85% RH. The zero output of the sensor is less than ±2.0% FS. The power consumption is ≤0.2 W, and both the response and recovery time are approximately 20 s. PMID:24625742

Fluidized bed catalytic pyrolysis of eucalyptus over hzsm-5: effect of acid density and gallium modification on catalyst deactivation

USDA-ARS?s Scientific Manuscript database

Catalytic fast pyrolysis of eucalyptus wood was performed on a continuous laboratory scale fluidized bed fast pyrolysis system. Catalytic activity was monitored from use of fresh catalyst up to a cumulative biomass to catalyst ratio (B/C) of 4/1 over extruded pellets of three different ZSM-5 catalys...

Catalytic Oxidation of Hydroquinone in Aqueous Solution over Bimetallic PdCo Catalyst Supported on Carbon: Effect of Interferents and Electrochemical Measurement.

PubMed

Ye, Weichun; Shi, Xuezhao; Zhang, Yane; Hong, Chenghui; Wang, Chunming; Budzianowski, Wojciech M; Xue, Desheng

2016-02-10

Palladium-cobalt alloy nanoparticles were synthesized and dispersed on carbon black support, aiming to have a less expensive catalyst. Catalytic behaviors of PdCo/C catalyst for the oxidation of hydroquinone (HQ) with H2O2 in aqueous solution were evaluated using high-performance liquid chromatography (HPLC). The results revealed that PdCo/C catalyst had better catalytic activity than an equal amount of commercial Pd/C and Co/C catalysts because of the d-band hybridization between Pd and Co. The effects of pH value, solvent, and various interferents including inorganic and organic compounds on the efficiency of HQ oxidation were further investigated. Furthermore, on the basis of mixed potential theory, comprehensive electrochemical measurements such as the open-circuit potential-time (OCP-t) technique and Tafel plot were efficient to assess the catalytic activity of the catalyst, and the results obtained were consistent with those of HPLC measurements. The efficient HQ oxidation was closely associated with the catalytic activity of PdCo nanoparticles because they accelerated the electron-transfer process and facilitated the generation of OH radicals.

Transition metal catalysis in the generation of petroleum and natural gas. Final report

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

Mango, F.D.

1997-01-21

This project originated on the premise that natural gas could be formed catalytically in the earth rather than thermally as commonly believed. The intention was to test this hypothetical view and to explore generally the role of sedimentary metals in the generation of light hydrocarbons (C1 - C9). We showed the metalliferous source rocks are indeed catalytic in the generation of natural gas. Various metal compounds in the pure state show the same levels of catalytic activity as sedimentary rocks and the products are identical. Nickel is particularly active among the early transition metals and is projected to remain catalyticallymore » robust at all stages of catagenesis. Nickel oxide promotes the formation of n-alkanes in addition to natural gas (NG), demonstrating the full scope of the hypothetical catalytic process: The composition of catalytic gas duplicates the entire range of natural gas, from so-called wet gas to dry gas (60 to 95+ wt % methane), while gas generated thermally is consistently depleted in methane (10 to 60 wt % methane). These results support the view that metal catalysis is a major pathway through which natural gas is formed in the earth.« less

Transition metal catalysis in the generation of petroleum and natural gas. Final report, September 1, 1992--October 31, 1995

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

Mango, F.D.

1997-01-21

This project originated on the premise that natural gas could be formed catalytically in the earth rather than thermally as commonly believed. The intention was to test this hypothetical view and to explore generally the role of sedimentary metals in the generation of light hydrocarbons (C1 - C9). We showed the metalliferous source rocks are indeed catalytic in the generation of natural gas. Various metal compounds in the pure state show the same levels of catalytic activity as sedimentary rocks and the products are identical. Nickel is particularly active among the early transition metals and is projected to remain catalyticallymore » robust at all stages of catagenesis. Nickel oxide promotes the formation of n-alkanes in addition to natural gas (NG), demonstrating the full scope of the hypothetical catalytic process. The composition of catalytic gas duplicates the entire range of natural gas, from so-called wet gas to dry gas (60 to 95+ wt % methane), while gas generated thermally is consistently depleted in methane (10 to 60 wt % methane). These results support the view that metal catalysis is a major pathway through which natural gas is formed in the earth.« less

Design, integration and preliminary results of the IXV Catalysis experiment

NASA Astrophysics Data System (ADS)

Viladegut, Alan; Panerai, F.; Chazot, O.; Pichon, T.; Bertrand, P.; Verdy, C.; Coddet, C.

2017-06-01

The CATalytic Experiment (CATE) is an in-flight demonstration of catalysis effects at the surface of thermal protection materials. A high-catalytic coating was applied over the baseline ceramic material on the windward side of the intermediate experimental vehicle (IXV). The temperature jump due to different catalytic activities was detected during re-entry through measurements made with near-surface thermocouples on the windward side of the vehicle. The experiment aimed at contributing to the development and validation of gas/surface interaction models for re-entry applications. The present paper summarizes the design of CATE and its integration on the windward side of the IXV. Results of a qualification campaign at the Plasmatron facility of the von Karman Institute for Fluid Dynamics are presented. They provided an experimental evidence of the temperature jump at the low-to-high catalytic interface of the heat shield under aerothermal conditions relevant to the actual IXV flight. These tests also gave confidence so that the high-catalytic patch would not endanger the integrity of the vehicle and the safety of the mission. A preliminary assessment of flight data from the thermocouple measurements shows consistency with results of the qualification tests.

Recent progress in asymmetric bifunctional catalysis using multimetallic systems.

PubMed

Shibasaki, Masakatsu; Kanai, Motomu; Matsunaga, Shigeki; Kumagai, Naoya

2009-08-18

The concept of bifunctional catalysis, wherein both partners of a bimolecular reaction are simultaneously activated, is very powerful for designing efficient asymmetric catalysts. Catalytic asymmetric processes are indispensable for producing enantiomerically enriched compounds in modern organic synthesis, providing more economical and environmentally benign results than methods requiring stoichiometric amounts of chiral reagents. Extensive efforts in this field have produced many asymmetric catalysts, and now a number of reactions can be rendered asymmetric. We have focused on the development of asymmetric catalysts that exhibit high activity, selectivity, and broad substrate generality under mild reaction conditions. Asymmetric catalysts based on the concept of bifunctional catalysis have emerged as a particularly effective class, enabling simultaneous activation of multiple reaction components. Compared with conventional catalysts, bifunctional catalysts generally exhibit enhanced catalytic activity and higher levels of stereodifferentiation under milder reaction conditions, attracting much attention as next-generation catalysts for prospective practical applications. In this Account, we describe recent advances in enantioselective catalysis with bifunctional catalysts. Since our identification of heterobimetallic rare earth-alkali metal-BINOL (REMB) complexes, we have developed various types of bifunctional multimetallic catalysts. The REMB catalytic system is effective for catalytic asymmetric Corey-Chaykovsky epoxidation and cyclopropanation. A dinucleating Schiff base has emerged as a suitable multidentate ligand for bimetallic catalysts, promoting catalytic syn-selective nitro-Mannich, anti-selective nitroaldol, and Mannich-type reactions. The sugar-based ligand GluCAPO provides a suitable platform for polymetallic catalysts; structural elucidation revealed that their higher order polymetallic structures are a determining factor for their function in the catalytic asymmetric Strecker reaction. Rational design identified a related ligand, FujiCAPO, which exhibits superior performance in catalytic asymmetric conjugate addition of cyanide to enones and a catalytic asymmetric Diels-Alder-type reaction. The combination of an amide-based ligand with a rare earth metal constitutes a unique catalytic system: the ligand-metal association is in equilibrium because of structural flexibility. These catalytic systems are effective for asymmetric amination of highly coordinative substrate as well as for Mannich-type reaction of alpha-cyanoketones, in which hydrogen bonding cooperatively contributes to substrate activation and stereodifferentiation. Most of the reactions described here generate stereogenic tetrasubstituted carbons or quaternary carbons, noteworthy accomplishments even with modern synthetic methods. Several reactions have been incorporated into the asymmetric synthesis of therapeutics (or their candidate molecules) such as Tamiflu, AS-3201 (ranirestat), GRL-06579A, and ritodrine, illustrating the usefulness of bifunctional asymmetric catalysis.

Method and apparatus for thermal management of vehicle exhaust systems

DOEpatents

Benson, D.K.; Potter, T.F.

1995-12-26

A catalytic converter is surrounded by variable conductance insulation for maintaining the operating temperature of the catalytic converter at an optimum level, for inhibiting heat loss when raising catalytic converter temperature to light-off temperature, for storing excess heat to maintain or accelerate reaching light-off temperature, and for conducting excess heat away from the catalytic converter after reaching light-off temperature. The variable conductance insulation includes vacuum gas control and metal-to-metal thermal shunt mechanisms. Radial and axial shielding inhibits radiation and convection heat loss. Thermal storage media includes phase change material, and heat exchanger chambers and fluids carry heat to and from the catalytic converter. 7 figs.

40 CFR 63.1567 - What are my requirements for inorganic HAP emissions from catalytic reforming units?

Code of Federal Regulations, 2011 CFR

2011-07-01

... reactors in the catalytic reforming unit are regenerated in separate regeneration systems, then these emission limitations apply to each separate regeneration system. These emission limitations apply to... rejuvenation operations during coke burn-off and catalyst regeneration. You can choose from the two options in...

Surface Catalytic Efficiency of Advanced Carbon Carbon Candidate Thermal Protection Materials for SSTO Vehicles

NASA Technical Reports Server (NTRS)

Stewart, David A.

1996-01-01

The catalytic efficiency (atom recombination coefficients) for advanced ceramic thermal protection systems was calculated using arc-jet data. Coefficients for both oxygen and nitrogen atom recombination on the surfaces of these systems were obtained to temperatures of 1650 K. Optical and chemical stability of the candidate systems to the high energy hypersonic flow was also demonstrated during these tests.

The crystal structure of pectate lyase peli from soft rot pathogen Erwinia chrysanthemi in complex with its substrate.

PubMed

Creze, Christophe; Castang, Sandra; Derivery, Emmanuel; Haser, Richard; Hugouvieux-Cotte-Pattat, Nicole; Shevchik, Vladimir E; Gouet, Patrice

2008-06-27

The crystallographic structure of the family 3 polysaccharide lyase (PL-3) PelI from Erwinia chrysanthemi has been solved to 1.45 A resolution. It consists of an N-terminal domain harboring a fibronectin type III fold linked to a catalytic domain displaying a parallel beta-helix topology. The N-terminal domain is located away from the active site and is not involved in the catalytic process. After secretion in planta, the two domains are separated by E. chrysanthemi proteases. This event turns on the hypersensitive response of the host. The structure of the single catalytic domain determined to 2.1 A resolution shows that the domain separation unveils a "Velcro"-like motif of asparagines, which might be recognized by a plant receptor. The structure of PelI in complex with its substrate, a tetragalacturonate, has been solved to 2.3 A resolution. The sugar binds from subsites -2 to +2 in one monomer of the asymmetric unit, although it lies on subsites -1 to +3 in the other. These two "Michaelis complexes" have never been observed simultaneously before and are consistent with the dual mode of bond cleavage in this substrate. The bound sugar adopts a mixed 2(1) and 3(1) helical conformation similar to that reported in inactive mutants from families PL-1 and PL-10. However, our study suggests that the catalytic base in PelI is not a conventional arginine but a lysine as proposed in family PL-9.

Diesel engine catalytic combustor system. [aircraft engines

NASA Technical Reports Server (NTRS)

Ream, L. W. (Inventor)

1984-01-01

A low compression turbocharged diesel engine is provided in which the turbocharger can be operated independently of the engine to power auxiliary equipment. Fuel and air are burned in a catalytic combustor to drive the turbine wheel of turbine section which is initially caused to rotate by starter motor. By opening a flapper value, compressed air from the blower section is directed to catalytic combustor when it is heated and expanded, serving to drive the turbine wheel and also to heat the catalytic element. To start, engine valve is closed, combustion is terminated in catalytic combustor, and the valve is then opened to utilize air from the blower for the air driven motor. When the engine starts, the constituents in its exhaust gas react in the catalytic element and the heat generated provides additional energy for the turbine section.

BLIMPK/Streamline Surface Catalytic Heating Predictions on the Space Shuttle Orbiter

NASA Technical Reports Server (NTRS)

Marichalar, Jeremiah J.; Rochelle, William C.; Kirk, Benjamin S.; Campbell, Charles H.

2006-01-01

This paper describes the results of an analysis of localized catalytic heating effects to the U.S. Space Shuttle Orbiter Thermal Protection System (TPS). The analysis applies to the High-temperature Reusable Surface Insulation (HRSI) on the lower fuselage and wing acreage, as well as the critical Reinforced Carbon-Carbon on the nose cap, chin panel and the wing leading edge. The object of the analysis was to use a modified two-layer approach to predict the catalytic heating effects on the Orbiter windward HRSI tile acreage, nose cap, and wing leading edge assuming localized highly catalytic or fully catalytic surfaces. The method incorporated the Boundary Layer Integral Matrix Procedure Kinetic (BLIMPK) code with streamline inputs from viscous Navier-Stokes solutions to produce heating rates for localized fully catalytic and highly catalytic surfaces as well as for nominal partially catalytic surfaces (either Reinforced Carbon-Carbon or Reaction Cured Glass) with temperature-dependent recombination coefficients. The highly catalytic heating results showed very good correlation with Orbiter Experiments STS-2, -3, and -5 centerline and STS-5 wing flight data for the HRSI tiles. Recommended catalytic heating factors were generated for use in future Shuttle missions in the event of quick-time analysis of damaged or repaired TPS areas during atmospheric reentry. The catalytic factors are presented along the streamlines as well as a function of stagnation enthalpy so they can be used for arbitrary trajectories.

Catalytic conversion of methane to methanol using Cu-zeolites.

PubMed

Alayon, Evalyn Mae C; Nachtegaal, Maarten; Ranocchiari, Marco; van Bokhoven, Jeroen A

2012-01-01

The conversion of methane to value-added liquid chemicals is a promising answer to the imminent demand for fuels and chemical synthesis materials in the advent of a dwindling petroleum supply. Current technology requires high energy input for the synthesis gas production, and is characterized by low overall selectivity, which calls for alternative reaction routes. The limitation to achieve high selectivity is the high C-H bond strength of methane. High-temperature reaction systems favor gas-phase radical reactions and total oxidation. This suggests that the catalysts for methane activation should be active at low temperatures. The enzymatic-inspired metal-exchanged zeolite systems apparently fulfill this need, however, methanol yield is low and a catalytic process cannot yet be established. Homogeneous and heterogeneous catalytic systems have been described which stabilize the intermediate formed after the first C-H activation. The understanding of the reaction mechanism and the determination of the active metal sites are important for formulating strategies for the upgrade of methane conversion catalytic technologies.

Dynamics of catalytic tubular microjet engines: Dependence on geometry and chemical environment

NASA Astrophysics Data System (ADS)

LiJ. X. L.; G. S. H. Contributed Equally To This Work., Jinxing; Huang, Gaoshan; Ye, Mengmeng; Li, Menglin; Liu, Ran; Mei, Yongfeng

2011-12-01

Strain-engineered tubular microjet engines with various geometric dimensions hold interesting autonomous motions in an aqueous fuel solution when propelled by catalytic decomposition of hydrogen peroxide to oxygen and water. The catalytically-generated oxygen bubbles expelled from microtubular cavities propel the microjet step by step in discrete increments. We focus on the dynamics of our tubular microjets in one step and build up a body deformation model to elucidate the interaction between tubular microjets and the bubbles they produce. The average microjet velocity is calculated analytically based on our model and the obtained results demonstrate that the velocity of the microjet increases linearly with the concentration of hydrogen peroxide. The geometric dimensions of the microjet, such as length and radius, also influence its dynamic characteristics significantly. A close consistency between experimental and calculated results is achieved despite a small deviation due to the existence of an approximation in the model. The results presented in this work improve our understanding regarding catalytic motions of tubular microjets and demonstrate the controllability of the microjet which may have potential applications in drug delivery and biology.Strain-engineered tubular microjet engines with various geometric dimensions hold interesting autonomous motions in an aqueous fuel solution when propelled by catalytic decomposition of hydrogen peroxide to oxygen and water. The catalytically-generated oxygen bubbles expelled from microtubular cavities propel the microjet step by step in discrete increments. We focus on the dynamics of our tubular microjets in one step and build up a body deformation model to elucidate the interaction between tubular microjets and the bubbles they produce. The average microjet velocity is calculated analytically based on our model and the obtained results demonstrate that the velocity of the microjet increases linearly with the concentration of hydrogen peroxide. The geometric dimensions of the microjet, such as length and radius, also influence its dynamic characteristics significantly. A close consistency between experimental and calculated results is achieved despite a small deviation due to the existence of an approximation in the model. The results presented in this work improve our understanding regarding catalytic motions of tubular microjets and demonstrate the controllability of the microjet which may have potential applications in drug delivery and biology. Electronic supplementary information (ESI) available: I. Video of the catalytic motion of a typical microjet moving in a linear way. II. Detailed numerical analyses: Reynolds number calculation, displacement of the microjet and the bubble after separation, and example of experimental velocity calculation. See DOI: 10.1039/c1nr10840a

Catalytic reactor for automobile

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

Vroman, W.R.

1977-05-03

A catalytic reactor of oval cross section consists of a generally cylindrical catalytic substrate clamped between paired housing shells and spaced from them by a mesh support that extends around the oval periphery of the substrate and slightly overlaps the latter's axially opposite end to provide locating projections. The support and housing are preferably interlocked by one or more pairs of inwardly opening channels of the housing having portions of the mesh support confined inside, each pair being spaced axially by a rib of the housing projecting into the mesh support. The housing has axially endwise converging cam portions adjacentmore » and axially endwise of the opposite ends of the substrate to engage the locating projections and center the assembled substrate and mesh support within the housing during manufacture of the reactor.« less

Hydrogen production from bio-fuels using precious metal catalysts

NASA Astrophysics Data System (ADS)

Pasel, Joachim; Wohlrab, Sebastian; Rotov, Mikhail; Löhken, Katrin; Peters, Ralf; Stolten, Detlef

2017-11-01

Fuel cell systems with integrated autothermal reforming unit require active and robust catalysts for H2 production. Thus, an experimental screening of catalysts for autothermal reforming of commercial biodiesel fuel was performed. Catalysts consisted of a monolithic cordierite substrate, an oxide support (γ-Al2O3) and Pt, Ru, Ni, PtRh and PtRu as active phase. Experiments were run by widely varying the O2/C and H2O/C molar ratios at different gas hourly space velocities. Fresh and aged catalysts were characterized by temperature programmed methods and thermogravimetry to find correlations with catalytic activity and stability.

Green technology for conversion of renewable hydrocarbon based on plasma-catalytic approach

NASA Astrophysics Data System (ADS)

Fedirchyk, Igor; Nedybaliuk, Oleg; Chernyak, Valeriy; Demchina, Valentina

2016-09-01

The ability to convert renewable biomass into fuels and chemicals is one of the most important steps on our path to green technology and sustainable development. However, the complex composition of biomass poses a major problem for established conversion technologies. The high temperature of thermochemical biomass conversion often leads to the appearance of undesirable byproducts and waste. The catalytic conversion has reduced yield and feedstock range. Plasma-catalytic reforming technology opens a new path for biomass conversion by replacing feedstock-specific catalysts with free radicals generated in the plasma. We studied the plasma-catalytic conversion of several renewable hydrocarbons using the air plasma created by rotating gliding discharge. We found that plasma-catalytic hydrocarbon conversion can be conducted at significantly lower temperatures (500 K) than during the thermochemical ( 1000 K) and catalytic (800 K) conversion. By using gas chromatography, we determined conversion products and found that conversion efficiency of plasma-catalytic conversion reaches over 85%. We used obtained data to determine the energy yield of hydrogen in case of plasma-catalytic reforming of ethanol and compared it with other plasma-based hydrogen-generating systems.

Water recovery by catalytic treatment of urine vapor

NASA Technical Reports Server (NTRS)

Budininkas, P.; Quattrone, P. D.; Leban, M. I.

1980-01-01

The objective of this investigation was to demonstrate the feasibility of water recovery on a man-rated scale by the catalytic processing of untreated urine vapor. For this purpose, two catalytic systems, one capable of processing an air stream containing low urine vapor concentrations and another to process streams with high urine vapor concentrations, were designed, constructed, and tested to establish the quality of the recovered water.

Development of Vapor-Phase Catalytic Ammonia Removal System

NASA Technical Reports Server (NTRS)

Flynn, Michael; Fisher, John; Kiss, Mark; Borchers, Bruce; Tleimat, Badawi; Tleimat, Maher; Quinn, Gregory; Fort, James; Nalette, Tim; Baker, Gale;

A model for the evaluation of systemic risk in stock markets

NASA Astrophysics Data System (ADS)

Caetano, Marco Antonio Leonel; Yoneyama, Takashi

2011-06-01

Systemic risk refers to the possibility of a collapse of an entire financial system or market, differing from the risk associated with any particular individual or a group pertaining to the system, which may include banks, government, brokers, and creditors. After the 2008 financial crisis, a significant amount of effort has been directed to the study of systemic risk and its consequences around the world. Although it is very difficult to predict when people begin to lose confidence in a financial system, it is possible to model the relationships among the stock markets of different countries and perform a Monte Carlo-type analysis to study the contagion effect. Because some larger and stronger markets influence smaller ones, a model inspired by a catalytic chemical model is proposed. In chemical reactions, reagents with higher concentrations tend to favor their conversion to products. In order to modulate the conversion process, catalyzers may be used. In this work, a mathematical modeling is proposed with bases on the catalytic chemical reaction model. More specifically, the Hang Seng and Dow Jones indices are assumed to dominate Ibovespa (the Brazilian Stock Market index), such that the indices of strong markets are taken as being analogous to the concentrations of the reagents and the indices of smaller markets as concentrations of products. The role of the catalyst is to model the degree of influence of one index on another. The actual data used to fit the model parameter consisted of the Hang Seng index, Dow Jones index, and Ibovespa, since 1993. “What if” analyses were carried out considering some intervention policies.

Enhanced DNA Sensing via Catalytic Aggregation of Gold Nanoparticles

PubMed Central

Huttanus, Herbert M.; Graugnard, Elton; Yurke, Bernard; Knowlton, William B.; Kuang, Wan; Hughes, William L.; Lee, Jeunghoon

2014-01-01

A catalytic colorimetric detection scheme that incorporates a DNA-based hybridization chain reaction into gold nanoparticles was designed and tested. While direct aggregation forms an inter-particle linkage from only ones target DNA strand, the catalytic aggregation forms multiple linkages from a single target DNA strand. Gold nanoparticles were functionalized with thiol-modified DNA strands capable of undergoing hybridization chain reactions. The changes in their absorption spectra were measured at different times and target concentrations and compared against direct aggregation. Catalytic aggregation showed a multifold increase in sensitivity at low target concentrations when compared to direct aggregation. Gel electrophoresis was performed to compare DNA hybridization reactions in catalytic and direct aggregation schemes, and the product formation was confirmed in the catalytic aggregation scheme at low levels of target concentrations. The catalytic aggregation scheme also showed high target specificity. This application of a DNA reaction network to gold nanoparticle-based colorimetric detection enables highly-sensitive, field-deployable, colorimetric readout systems capable of detecting a variety of biomolecules. PMID:23891867

Selective catalytic reduction system and process using a pre-sulfated zirconia binder

DOEpatents

Sobolevskiy, Anatoly; Rossin, Joseph A.

2010-06-29

A selective catalytic reduction (SCR) process with a palladium catalyst for reducing NOx in a gas, using hydrogen as a reducing agent is provided. The process comprises contacting the gas stream with a catalyst system, the catalyst system comprising (ZrO.sub.2)SO.sub.4, palladium, and a pre-sulfated zirconia binder. The inclusion of a pre-sulfated zirconia binder substantially increases the durability of a Pd-based SCR catalyst system. A system for implementing the disclosed process is further provided.

Identification of a catalytic iron-hydride at the H-cluster of [FeFe]-hydrogenase

DOE PAGES

Mulder, David W.; Guo, Yisong; Ratzloff, Michael W.; ...

2016-12-14

Hydrogenases couple electrochemical potential to the reversible chemical transformation of H 2 and protons, yet the reaction mechanism and composition of intermediates are not fully understood. In this Communication we describe the biophysical properties of a hydride-bound state (H hyd) of the [FeFe]-hydrogenase from Chlamydomonas reinhardtii. The catalytic H-cluster of [FeFe]-hydrogenase consists of a [4Fe-4S] subcluster ([4Fe-4S] H) linked by a cysteine thiol to an azadithiolate-bridged 2Fe subcluster ([2Fe] H) with CO and CN- ligands. Mossbauer analysis and density functional theory (DFT) calculations show that H hyd consists of a reduced [4Fe-4S] H + coupled to a diferrous [2Fe] Hmore » with a terminally bound Fe-hydride. The existence of the Fe-hydride in Hhyd was demonstrated by an unusually low Mossbauer isomer shift of the distal Fe of the [2Fe] H subcluster. As a result, a DFT model of H hyd shows that the Fe-hydride is part of a H-bonding network with the nearby bridging azadithiolate to facilitate fast proton exchange and catalytic turnover.« less

Vacuum distillation: vapor filtered-catalytic oxidation water reclamation system utilizing radioisotopes

NASA Technical Reports Server (NTRS)

Honegger, R. J.; Remus, G. A.; Kurg, E. K.

1971-01-01

The development of a functional model water reclamation system is discussed. The system produces potable water by distillation from the urine and respiration-perspiration condensate at the normal rate generated by four men. Basic processes employed are vacuum distillation, vapor filtration, vapor phase catalytic oxidation, and condensation. The system is designed to use four 75-watt isotope heaters for distillation thermal input, and one 45-watt isotope for the catalytic oxidation unit. The system is capable of collecting and storing urine, and provides for stabilizing the urine by chemical pretreatment. The functional model system is designed for operation in a weightless condition with liquid-vapor phase separators for the evaporator still, and centrifugal separators for urine collection and vapor condensation. The system provides for storing and dispensing reclaimed potable water. The system operates in a batch mode for 40 days, with urine residues accumulating in the evaporator. The evaporator still and residue are removed to storage and replaced with a fresh still for the next 40-day period.

Appendices to the user's manual for a computer program for the emulation/simulation of a space station environmental control and life support system

NASA Technical Reports Server (NTRS)

Yanosy, James L.

1988-01-01

A user's Manual for the Emulation Simulation Computer Model was published previously. The model consisted of a detailed model (emulation) of a SAWD CO2 removal subsystem which operated with much less detailed (simulation) models of a cabin, crew, and condensing and sensible heat exchangers. The purpose was to explore the utility of such an emulation/simulation combination in the design, development, and test of a piece of ARS hardware - SAWD. Extensions to this original effort are presented. The first extension is an update of the model to reflect changes in the SAWD control logic which resulted from the test. In addition, slight changes were also made to the SAWD model to permit restarting and to improve the iteration technique. The second extension is the development of simulation models for more pieces of air and water processing equipment. Models are presented for: EDC, Molecular Sieve, Bosch, Sabatier, a new condensing heat exchanger, SPE, SFWES, Catalytic Oxidizer, and multifiltration. The third extension is to create two system simulations using these models. The first system presented consists of one air and one water processing system, the second a potential Space Station air revitalization system.

Magnetic α-Fe2O3/MCM-41 nanocomposites: preparation, characterization, and catalytic activity for methylene blue degradation.

PubMed

Ursachi, Irina; Stancu, Alexandru; Vasile, Aurelia

2012-07-01

Catalysts based on nanosized magnetic iron oxide stabilized inside the pore system of ordered mesoporous silica MCM-41 have been prepared. The obtained materials were characterized by powder X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and N(2) adsorption-desorption isotherm. XRD analysis showed that the obtained materials consist from the pure hematite crystalline phase (α-Fe(2)O(3)) dispersed within ordered mesoporous silica MCM-41. Magnetic measurements show that the obtained nanocomposites exhibit at room temperature weak ferromagnetic behavior with slender hysteresis. The catalytic activity of the magnetic α-Fe(2)O(3)/MCM-41 nanocomposites was evaluated by the degradation of methylene blue (MB) aqueous solution. For this purpose, an ultrasound-assisted Fenton-like process was used. The effect of solution pH on degradation of MB was investigated. The results indicated that US-H(2)O(2)-α-Fe(2)O(3)/MCM-41 nanocomposite system is effective for the degradation of MB, suggesting its great potential in removal of dyes from wastewater. It was found that the degradation rate of MB increases with decrease in the pH value of the solution. Copyright © 2012 Elsevier Inc. All rights reserved.

Gel-based morphological design of zirconium metal–organic frameworks† †Electronic supplementary information (ESI) available: Optical microscopy, PDF TGA, Hg intrusion, nanoindentation, gels of various Zr-MOFs, oil-drop process. See DOI: 10.1039/c6sc05602d Click here for additional data file.

PubMed Central

Bueken, Bart; Van Velthoven, Niels; Willhammar, Tom; Stassin, Timothée; Stassen, Ivo; Keen, David A.; Baron, Gino V.; Denayer, Joeri F. M.; Ameloot, Rob; Bals, Sara

2017-01-01

The ability of metal–organic frameworks (MOFs) to gelate under specific synthetic conditions opens up new opportunities in the preparation and shaping of hierarchically porous MOF monoliths, which could be directly implemented for catalytic and adsorptive applications. In this work, we present the first examples of xero- or aerogel monoliths consisting solely of nanoparticles of several prototypical Zr4+-based MOFs: UiO-66-X (X = H, NH2, NO2, (OH)2), UiO-67, MOF-801, MOF-808 and NU-1000. High reactant and water concentrations during synthesis were observed to induce the formation of gels, which were converted to monolithic materials by drying in air or supercritical CO2. Electron microscopy, combined with N2 physisorption experiments, was used to show that irregular nanoparticle packing leads to pure MOF monoliths with hierarchical pore systems, featuring both intraparticle micropores and interparticle mesopores. Finally, UiO-66 gels were shaped into monolithic spheres of 600 μm diameter using an oil-drop method, creating promising candidates for packed-bed catalytic or adsorptive applications, where hierarchical pore systems can greatly mitigate mass transfer limitations. PMID:28553536

Second-Order Biomimicry: In Situ Oxidative Self-Processing Converts Copper(I)/Diamine Precursor into a Highly Active Aerobic Oxidation Catalyst

PubMed Central

2017-01-01

A homogeneous Cu-based catalyst system consisting of [Cu(MeCN)4]PF6, N,N′-di-tert-butylethylenediamine (DBED), and p-(N,N-dimethylamino)pyridine (DMAP) mediates efficient aerobic oxidation of alcohols. Mechanistic study of this reaction shows that the catalyst undergoes an in situ oxidative self-processing step, resulting in conversion of DBED into a nitroxyl that serves as an efficient cocatalyst for aerobic alcohol oxidation. Insights into this behavior are gained from kinetic studies, which reveal an induction period at the beginning of the reaction that correlates with the oxidative self-processing step, EPR spectroscopic analysis of the catalytic reaction mixture, which shows the buildup of the organic nitroxyl species during steady state turnover, and independent synthesis of oxygenated DBED derivatives, which are shown to serve as effective cocatalysts and eliminate the induction period in the reaction. The overall mechanism bears considerable resemblance to enzymatic reactivity. Most notable is the “oxygenase”-type self-processing step that mirrors generation of catalytic cofactors in enzymes via post-translational modification of amino acid side chains. This higher-order function within a synthetic catalyst system presents new opportunities for the discovery and development of biomimetic catalysts. PMID:28470049

Catalytic wet-oxidation of human wastes produced in space: the effects of temperature elevation.

PubMed

Takeda, N; Takahashi, Y

1992-01-01

The filtrate of non-catalytical wet-oxidation sewage sludge was wet-oxidized again at 290 degrees C and 300 degrees C with a Ru-Rh catalyst. At each temperature, repeated batch tests were carried out. Both oxidation and denitrification efficiency of organic matter in the raw material were studied. In the 16 times batch tests at 300 degrees C, high and stable oxidation occurred. 98.0% of organic carbon in the raw material was oxidized and 98.3% of organic nitrogen was denitrified. At 290 degrees C, though high and stable denitrification occurred, oxidation did not occur highly and stably. A catalytic wet-oxidation system studied at 300 degrees C will be useful as a waste management system for a human life support system, where almost all food is resupplied from the earth. This system can prevent organic waste accumulation in the life support system.

Mussel-Inspired Polydopamine Functionalized Plasmonic Nanocomposites for Single-Particle Catalysis.

PubMed

Wang, Jun-Gang; Hua, Xin; Li, Meng; Long, Yi-Tao

2017-01-25

Polydopamine functionalized plasmonic nanocomposites with well-distributed catalytically active small gold nanoislands around large gold core were fabricated without using any chemical reductant or surfactant. The optical properties, surface molecular structures, and ensemble catalytic activity of the gold nanocomposites were investigated by time-of-flight secondary ion mass spectrometry and UV-vis spectroscopy, respectively. Moreover, the considerable catalytic activity of the nanocomposites toward 4-nitrophenol reduction was real time monitored by dark-field spectroscopy techniques at the single-nanoparticle level avoiding averaging effects in bulk systems. According to the obtained plasmonic signals from individual nanocomposites, the electron charging and discharging rates for these nanocomposites during the catalytic process were calculated. Our results offer new insights into the design and synthesis of plasmonic nanocomposites for future catalytic applications as well as a further mechanistic understanding of the electron transfer during the catalytic process at the single-nanoparticle level.

Catalytic ignition of hydrogen/oxygen

NASA Technical Reports Server (NTRS)

Green, James M.; Zurawski, Robert L.

1988-01-01

An experimental program was conducted to evaluate the catalytic ignition of gaseous hydrogen and oxygen. Shell 405 granular catalyst and a unique monolithic sponge catalyst were tested. Mixture ratio, mass flow rate, propellant inlet temperature, and back pressure were varied parametrically in testing to determine the operational limits of a catalytic igniter. The test results showed that the gaseous hydrogen/oxygen propellant combination can be ignited catalytically using Shell 405 catalyst over a wide range of mixture ratios, mass flow rates, and propellant injection temperatures. These operating conditions must be optimized to ensure reliable ignition for an extended period of time. The results of the experimental program and the established operational limits for a catalytic igniter using both the granular and monolithic catalysts are presented. The capabilities of a facility constructed to conduct the igniter testing and the advantages of a catalytic igniter over other ignition systems for gaseous hydrogen and oxygen are also discussed.

A comprehensive study of catalytic, morphological and electronic properties of ligand-protected gold nanoclusters using XPS, STM, XAFS, and TPD techniques

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

Wu, Qiyuan; Cen, Jiajie; Zhao, Yue

Ultra-small gold nanoclusters were synthesized via a ligand exchange method and deposited onto different TiO2 supports to study their properties. STM imaging revealed that the as-synthesized gold nanoclusters had 2-D morphology consisting of monolayers of gold atoms. In conclusion, subsequent XPS, XAFS, and CO oxidation TPD results indicated that heat treatments of gold clusters at different temperatures significantly altered their electronic and catalytic properties due to ligand deprotection and cluster agglomeration.

Catalytic membranes for fuel cells

DOEpatents

Liu, Di-Jia [Naperville, IL; Yang, Junbing [Bolingbrook, IL; Wang, Xiaoping [Naperville, IL

2011-04-19

A fuel cell of the present invention comprises a cathode and an anode, one or both of the anode and the cathode including a catalyst comprising a bundle of longitudinally aligned graphitic carbon nanotubes including a catalytically active transition metal incorporated longitudinally and atomically distributed throughout the graphitic carbon walls of said nanotubes. The nanotubes also include nitrogen atoms and/or ions chemically bonded to the graphitic carbon and to the transition metal. Preferably, the transition metal comprises at least one metal selected from the group consisting of Fe, Co, Ni, Mn, and Cr.

FAST TRACK COMMUNICATION: Novel mechanism for nanoscale catalysis

NASA Astrophysics Data System (ADS)

Msezane, Alfred Z.; Felfli, Zineb; Sokolovski, Dmitri

2010-10-01

The interplay between Regge resonances and Ramsauer-Townsend minima in the electron elastic total cross sections for Au and Pd atoms along with their large electron affinities is proposed as the fundamental atomic mechanism responsible for the observed exceptional catalytic properties of Au nanoparticles and to explain why the combination Au-Pd possesses an even higher catalytic activity than Au or Pd separately when catalyzing H2O2, consistent with recent experiments. The investigation uses the recent complex angular momentum description of electron scattering from neutral atoms and the proposed mechanism in general.

A comprehensive study of catalytic, morphological and electronic properties of ligand-protected gold nanoclusters using XPS, STM, XAFS, and TPD techniques

DOE PAGES

Wu, Qiyuan; Cen, Jiajie; Zhao, Yue; ...

2017-12-08

Ultra-small gold nanoclusters were synthesized via a ligand exchange method and deposited onto different TiO2 supports to study their properties. STM imaging revealed that the as-synthesized gold nanoclusters had 2-D morphology consisting of monolayers of gold atoms. In conclusion, subsequent XPS, XAFS, and CO oxidation TPD results indicated that heat treatments of gold clusters at different temperatures significantly altered their electronic and catalytic properties due to ligand deprotection and cluster agglomeration.

Speculation on quantum mechanics and the operation of life giving catalysts.

PubMed

Haydon, Nathan; McGlynn, Shawn E; Robus, Olin

2011-02-01

The origin of life necessitated the formation of catalytic functionalities in order to realize a number of those capable of supporting reactions that led to the proliferation of biologically accessible molecules and the formation of a proto-metabolic network. Here, the discussion of the significance of quantum behavior on biological systems is extended from recent hypotheses exploring brain function and DNA mutation to include origins of life considerations in light of the concept of quantum decoherence and the transition from the quantum to the classical. Current understandings of quantum systems indicate that in the context of catalysis, substrate-catalyst interaction may be considered as a quantum measurement problem. Exploration of catalytic functionality necessary for life's emergence may have been accommodated by quantum searches within metal sulfide compartments, where catalyst and substrate wave function interaction may allow for quantum based searches of catalytic phase space. Considering the degree of entanglement experienced by catalytic and non catalytic outcomes of superimposed states, quantum contributions are postulated to have played an important role in the operation of efficient catalysts that would provide for the kinetic basis for the emergence of life.

Kinetics and mechanism of olefin catalytic hydroalumination by organoaluminum compounds

NASA Astrophysics Data System (ADS)

Koledina, K. F.; Gubaidullin, I. M.

2016-05-01

The complex reaction mechanism of α-olefin catalytic hydroalumination by alkylalanes is investigated via mathematical modeling that involves plotting the kinetic models for the individual reactions that make up a complex system and a separate study of their principles. Kinetic parameters of olefin catalytic hydroalumination are estimated. Activation energies of the possible steps of the schemes of complex reaction mechanisms are compared and possible reaction pathways are determined.

Direct Catalytic Anti-Markovnikov Hydroetherification of Alkenols

PubMed Central

Hamilton, David S.; Nicewicz, David A.

2012-01-01

A direct intramolecular anti-Markovnikov hydroetherification reaction of alkenols is described. By employing catalytic quantities of commercially-available 9-mesityl-10-methylacridinium perchlorate and 2-phenylmalononitrile as a redox-cycling source of a hydrogen atom, we report the anti-Markovnikov hydroetherification of alkenes with complete regioselectivity. In addition, we present results demonstrating that this novel catalytic system can be applied to the anti-Markovnikov hydrolactonization of alkenoic acids. PMID:23113557

Apparatus for the investigation of high-temperature, high-pressure gas-phase heterogeneous catalytic and photo-catalytic materials.

PubMed

Alvino, Jason F; Bennett, Trystan; Kler, Rantej; Hudson, Rohan J; Aupoil, Julien; Nann, Thomas; Golovko, Vladimir B; Andersson, Gunther G; Metha, Gregory F

2017-05-01

A high-temperature, high-pressure, pulsed-gas sampling and detection system has been developed for testing new catalytic and photocatalytic materials for the production of solar fuels. The reactor is fitted with a sapphire window to allow the irradiation of photocatalytic samples from a lamp or solar simulator light source. The reactor has a volume of only 3.80 ml allowing for the investigation of very small quantities of a catalytic material, down to 1 mg. The stainless steel construction allows the cell to be heated to 350 °C and can withstand pressures up to 27 bar, limited only by the sapphire window. High-pressure sampling is made possible by a computer controlled pulsed valve that delivers precise gas flow, enabling catalytic reactions to be monitored across a wide range of pressures. A residual gas analyser mass spectrometer forms a part of the detection system, which is able to provide a rapid, real-time analysis of the gas composition within the photocatalytic reaction chamber. This apparatus is ideal for investigating a number of industrially relevant reactions including photocatalytic water splitting and CO 2 reduction. Initial catalytic results using Pt-doped and Ru nanoparticle-doped TiO 2 as benchmark experiments are presented.

Cu/Mn bimetallic catalysis enables carbonylative Suzuki–Miyaura coupling with unactivated alkyl electrophiles† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc01170a Click here for additional data file.

PubMed Central

Pye, Dominic R.; Cheng, Li-Jie

2017-01-01

A bimetallic system consisting of Cu-carbene and Mn-carbonyl co-catalysts was employed for carbonylative C–C coupling of arylboronic esters with alkyl halides, allowing for the convergent synthesis of ketones. The system operates under mild conditions and exhibits complementary reactivity to Pd catalysis. The method is compatible with a wide range of arylboronic ester nucleophiles and proceeds smoothly for both primary and secondary alkyl iodide electrophiles. Preliminary mechanistic experiments corroborate a hypothetical catalytic mechanism consisting of co-dependent cycles wherein the Cu-carbene co-catalyst engages in transmetallation to generate an organocopper nucleophile, while the Mn-carbonyl co-catalyst activates the alkyl halide electrophile by single-electron transfer and then undergoes reversible carbonylation to generate an acylmanganese electrophile. The two cycles then intersect with a heterobimetallic, product-releasing C–C coupling step. PMID:28966784

A Markovian engine for a biological energy transducer: the catalytic wheel.

PubMed

Tsong, Tian Yow; Chang, Cheng-Hung

2007-04-01

The molecular machines in biological cells are made of proteins, DNAs and other classes of molecules. The structures of these molecules are characteristically "soft", highly flexible, and yet their interactions with other molecules or ions are specific and selective. This chapter discusses a prevalent form, the catalytic wheel, or the energy transducer of cells, examines its mechanism of action, and extracts from it a set of simple but general rules for understanding the energetics of the biomolecular devices. These rules should also benefit design of manmade nanometer scale machines such as rotary motors or track-guided linear transporters. We will focus on an electric work that, by matching system dynamics and then enhancing the conformational fluctuation of one or several driver proteins, converts stochastic input of energy into rotation or locomotion of a receptor protein. The spatial (or barrier) and temporal symmetry breakings required for selected driver/receptor combinations are examined. This electric ratchet consists of a core engine that follows the Markovian dynamic, alleviates difficulties encountered in rigid mechanical model, and tailors to the soft-matter characteristics of the biomolecules.

Turning goals into results: the power of catalytic mechanisms.

PubMed

Collins, J

1999-01-01

Most executives have a big, hairy, audacious goal. They write vision statements, formalize procedures, and develop complicated incentive programs--all in pursuit of that goal. In other words, with the best of intentions, they install layers of stultifying bureaucracy. But it doesn't have to be that way. In this article, Jim Collins introduces the catalytic mechanism, a simple yet powerful managerial tool that helps translate lofty aspirations into concrete reality. Catalytic mechanisms are the crucial link between objectives and performance; they are a galvanizing, nonbureaucratic means to turn one into the other. What's the difference between catalytic mechanisms and most traditional managerial controls? Catalytic mechanisms share five characteristics. First, they produce desired results in unpredictable ways. Second, they distribute power for the benefit of the overall system, often to the discomfort of those who traditionally hold power. Third, catalytic mechanisms have teeth. Fourth, they eject "viruses"--those people who don't share the company's core values. Finally, they produce an ongoing effect. Catalytic mechanisms are just as effective for reaching individual goals as they are for corporate ones. To illustrate how catalytic mechanisms work, the author draws on examples of individuals and organizations that have relied on such mechanisms to achieve their goals. The same catalytic mechanism that works in one organization, however, will not necessarily work in another. Catalytic mechanisms must be tailored to specific goals and situations. To help readers get started, the author offers some general principles that support the process of building catalytic mechanisms effectively.

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 °C. Part 9: reference procedure for the measurement of catalytic concentration of alkaline phosphatase International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Scientific Division, Committee on Reference Systems of Enzymes (C-RSE) (1)).

PubMed

Schumann, Gerhard; Klauke, Rainer; Canalias, Francesca; Bossert-Reuther, Steffen; Franck, Paul F H; Gella, F-Javier; Jørgensen, Poul J; Kang, Dongchon; Lessinger, Jean-Marc; Panteghini, Mauro; Ceriotti, Ferruccio

2011-09-01

Abstract This paper is the ninth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 °C and the certification of reference preparations. Other parts deal with: Part 1. The concept of reference procedures for the measurement of catalytic activity concentrations of enzymes; Part 2. Reference procedure for the measurement of catalytic concentration of creatine kinase; Part 3. Reference procedure for the measurement of catalytic concentration of lactate dehydrogenase; Part 4. Reference procedure for the measurement of catalytic concentration of alanine aminotransferase; Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase; Part 6. Reference procedure for the measurement of catalytic concentration of γ-glutamyltransferase; Part 7. Certification of four reference materials for the determination of enzymatic activity of γ-glutamyltransferase, lactate dehydrogenase, alanine aminotransferase and creatine kinase at 37 °C; Part 8. Reference procedure for the measurement of catalytic concentration of α-amylase. The procedure described here is derived from the previously described 30 °C IFCC reference method. Differences are tabulated and commented on in Appendix 1.

Removal of disinfection by-products from contaminated water using a synthetic goethite catalyst via catalytic ozonation and a biofiltration system.

PubMed

Wang, Yu-Hsiang; Chen, Kuan-Chung

2014-09-10

The effects of synthetic goethite (α-FeOOH) used as the catalyst in catalytic ozonation for the degradation of disinfection by-product (DBP) precursors are investigated. A biofiltration column applied following the catalytic ozonation process is used to evaluate the efficiency of removing DBP precursors via biotreatment. Ozone can rapidly react with aromatic compounds and oxidize organic compounds, resulting in a decrease in the fluorescence intensity of dissolved organic matter (DOM). In addition, catalytic ozonation can break down large organic molecules, which causes a blue shift in the emission-excitation matrix spectra. Water treated with catalytic ozonation is composed of low-molecular structures, including soluble microbial products (SMPs) and other aromatic proteins (APs). The DOM in SMPs and APs is removed by subsequent biofiltration. Catalytic ozonation has a higher removal efficiency for dissolved organic carbon and higher ultraviolet absorbance at 254 nm compared to those of ozonation without a catalyst. The use of catalytic ozonation and subsequent biofiltration leads to a lower DBP formation potential during chlorination compared to that obtained using ozonation and catalytic ozonation alone. Regarding DBP species during chlorination, the bromine incorporation factor (BIF) of trihalomethanes and haloacetic acids increases with increasing catalyst dosage in catalytic ozonation. Moreover, the highest BIF is obtained for catalytic ozonation and subsequent biofiltration.

Removal of Disinfection By-Products from Contaminated Water Using a Synthetic Goethite Catalyst via Catalytic Ozonation and a Biofiltration System·

PubMed Central

Wang, Yu-Hsiang; Chen, Kuan-Chung

2014-01-01

The effects of synthetic goethite (α-FeOOH) used as the catalyst in catalytic ozonation for the degradation of disinfection by-product (DBP) precursors are investigated. A biofiltration column applied following the catalytic ozonation process is used to evaluate the efficiency of removing DBP precursors via biotreatment. Ozone can rapidly react with aromatic compounds and oxidize organic compounds, resulting in a decrease in the fluorescence intensity of dissolved organic matter (DOM). In addition, catalytic ozonation can break down large organic molecules, which causes a blue shift in the emission-excitation matrix spectra. Water treated with catalytic ozonation is composed of low-molecular structures, including soluble microbial products (SMPs) and other aromatic proteins (APs). The DOM in SMPs and APs is removed by subsequent biofiltration. Catalytic ozonation has a higher removal efficiency for dissolved organic carbon and higher ultraviolet absorbance at 254 nm compared to those of ozonation without a catalyst. The use of catalytic ozonation and subsequent biofiltration leads to a lower DBP formation potential during chlorination compared to that obtained using ozonation and catalytic ozonation alone. Regarding DBP species during chlorination, the bromine incorporation factor (BIF) of trihalomethanes and haloacetic acids increases with increasing catalyst dosage in catalytic ozonation. Moreover, the highest BIF is obtained for catalytic ozonation and subsequent biofiltration. PMID:25211774

HOMOGENEOUS CATALYTIC OXIDATION OF HYDROCARBONS IN ALTERNATIVE SOLVENTS

EPA Science Inventory

Homogeneous Catalytic Oxidations of Hydrocarbons in Alternative Solvent Systems

Michael A. Gonzalez* and Thomas M. Becker, Sustainable Technology Division, Office of Research and Development; United States Environmental Protection Agency, 26 West Martin Luther King Drive, ...

CATALYTIC OXIDATION OF GROUNDWATER STRIPPING EMISSIONS

EPA Science Inventory

The paper reviews the applicability of catalytic oxidation to control ground-water air stripping gaseous effluents, with special attention to system designs and case histories. The variety of contaminants and catalyst poisons encountered in stripping operations are also reviewed....

Dynamic Disorder in Quasi-Equilibrium Enzymatic Systems

PubMed Central

Chaudhury, Srabanti; Igoshin, Oleg A.

2010-01-01

Conformations and catalytic rates of enzymes fluctuate over a wide range of timescales. Despite these fluctuations, there exist some limiting cases in which the enzymatic catalytic rate follows the macroscopic rate equation such as the Michaelis-Menten law. In this paper we investigate the applicability of macroscopic rate laws for fluctuating enzyme systems in which catalytic transitions are slower than ligand binding-dissociation reactions. In this quasi-equilibrium limit, for an arbitrary reaction scheme we show that the catalytic rate has the same dependence on ligand concentrations as obtained from mass-action kinetics even in the presence of slow conformational fluctuations. These results indicate that the timescale of conformational dynamics – no matter how slow – will not affect the enzymatic rate in quasi-equilibrium limit. Our numerical results for two enzyme-catalyzed reaction schemes involving multiple substrates and inhibitors further support our general theory. PMID:20808776

A virus-based biocatalyst

NASA Astrophysics Data System (ADS)

Carette, Noëlle; Engelkamp, Hans; Akpa, Eric; Pierre, Sebastien J.; Cameron, Neil R.; Christianen, Peter C. M.; Maan, Jan C.; Thies, Jens C.; Weberskirch, Ralf; Rowan, Alan E.; Nolte, Roeland J. M.; Michon, Thierry; van Hest, Jan C. M.

2007-04-01

Virus particles are probably the most precisely defined nanometre-sized objects that can be formed by protein self-assembly. Although their natural function is the storage and transport of genetic material, they have more recently been applied as scaffolds for mineralization and as containers for the encapsulation of inorganic compounds. The reproductive power of viruses has been used to develop versatile analytical methods, such as phage display, for the selection and identification of (bio)active compounds. To date, the combined use of self-assembly and reproduction has not been used for the construction of catalytic systems. Here we describe a self-assembled system based on a plant virus that has its coat protein genetically modified to provide it with a lipase enzyme. Using single-object and bulk catalytic studies, we prove that the virus-anchored lipase molecules are catalytically active. This anchored biocatalyst, unlike man-made supported catalysts, has the capability to reproduce itself in vivo, generating many independent catalytically active copies.

Palladium Nanoparticle-Loaded Cellulose Paper: A Highly Efficient, Robust, and Recyclable Self-Assembled Composite Catalytic System.

PubMed

Zheng, Guangchao; Kaefer, Katharina; Mourdikoudis, Stefanos; Polavarapu, Lakshminarayana; Vaz, Belén; Cartmell, Samantha E; Bouleghlimat, Azzedine; Buurma, Niklaas J; Yate, Luis; de Lera, Ángel R; Liz-Marzán, Luis M; Pastoriza-Santos, Isabel; Pérez-Juste, Jorge

2015-01-15

We present a novel strategy based on the immobilization of palladium nanoparticles (Pd NPs) on filter paper for development of a catalytic system with high efficiency and recyclability. Oleylamine-capped Pd nanoparticles, dispersed in an organic solvent, strongly adsorb on cellulose filter paper, which shows a great ability to wick fluids due to its microfiber structure. Strong van der Waals forces and hydrophobic interactions between the particles and the substrate lead to nanoparticle immobilization, with no desorption upon further immersion in any solvent. The prepared Pd NP-loaded paper substrates were tested for several model reactions such as the oxidative homocoupling of arylboronic acids, the Suzuki cross-coupling reaction, and nitro-to-amine reduction, and they display efficient catalytic activity and excellent recyclability and reusability. This approach of using NP-loaded paper substrates as reusable catalysts is expected to open doors for new types of catalytic support for practical applications.

Crystal structure of a catalytically active, non-toxic endopeptidase derivative of Clostridium botulinum toxin A.

PubMed

Masuyer, Geoffrey; Thiyagarajan, Nethaji; James, Peter L; Marks, Philip M H; Chaddock, John A; Acharya, K Ravi

2009-03-27

Botulinum neurotoxins (BoNTs) modulate cholinergic nerve terminals to result in neurotransmitter blockade. BoNTs consists of catalytic (LC), translocation (Hn) and cell-binding domains (Hc). The binding function of the Hc domain is essential for BoNTs to bind the neuronal cell membrane, therefore, removal of the Hc domain results in a product that retains the endopeptidase activity of the LC but is non-toxic. Thus, a molecule consisting of LC and Hn domains of BoNTs, termed LHn, is a suitable molecule for engineering novel therapeutics. The structure of LHA at 2.6 A reported here provides an understanding of the structural implications and challenges of engineering therapeutic molecules that combine functional properties of LHn of BoNTs with specific ligand partners to target different cell types.

Design and fabrication of miniaturized PEM fuel cell combined microreactor with self-regulated hydrogen mechanism

NASA Astrophysics Data System (ADS)

Balakrishnan, A.; Frei, M.; Kerzenmacher, S.; Reinecke, H.; Mueller, C.

2015-12-01

In this work we present the design and fabrication of the miniaturized PEM fuel cell combined microreactor system with hydrogen regulation mechanism and testing of prototype microreactor. The system consists of two components (i) fuel cell component and (ii) microreactor component. The fuel cell component represents the miniaturized PEM fuel cell system (combination of screen printed fuel cell assembly and an on-board hydrogen storage medium). Hydrogen production based on catalytic hydrolysis of chemical hydride takes place in the microreactor component. The self-regulated hydrogen mechanism based on the gaseous hydrogen produced from the catalytic hydrolysis of sodium borohydride (NaBH4) gets accumulated as bubbles at the vicinity of the hydrophobic coated hydrogen exhaust holes. When the built up hydrogen bubbles pressure exceeds the burst pressure at the hydrogen exhaust holes the bubble collapses. This collapse causes a surge of fresh NaBH4 solution onto the catalyst surface leading to the removal of the reaction by-products formed at the active sites of the catalyst. The catalyst used in the system is platinum deposited on a base substrate. Nickel foam, carbon porous medium (CPM) and ceramic plate were selected as candidates for base substrate for developing a robust catalyst surface. For the first time the platinum layer fabricated by pulsed electrodeposition and dealloying (EPDD) technique is used for hydrolysis of NaBH4. The major advantages of such platinum catalyst layers are its high surface area and their mechanical stability. Prototype microreactor system with self-regulated hydrogen mechanism is demonstrated.

[Synthesis of vitamin K2 by isopentenyl transferase NovA in Pichia pastoris Gpn12].

PubMed

Wu, Xihua; Li, Zhemin; Liu, Hui; Wang, Peng; Wang, Li; Fang, Xue; Sun, Xiaowen; Ni, Wenfeng; Yang, Qiang; Zheng, Zhiming; Zhao, Genhai

2018-01-25

The effect of methanol addition on the heterologous expression of isoprenyl transferase NovQ was studied in Pichia pastoris Gpn12, with menadione and isopentenol as precursors to catalyze vitamin K2 (MK-3) synthesis. The expression of NovQ increased by 36% when 2% methanol was added every 24 h. The influence of initial pH, temperature, methanol addition, precursors (menadione, isopentenol) addition, catalytic time and cetyltrimethyl-ammonium bromide (CTAB) addition were explored in the P. pastoris whole-cell catalytic synthesis process of MK-3 in shaking flask. Three significant factors were then studied by response surface method. The optimal catalytic conditions obtained were as follows: catalytic temperature 31.56 ℃, menadione 295.54 mg/L, catalytic time 15.87 h. Consistent with the response surface prediction results, the optimized yield of MK-3 reached 98.47 mg/L in shaking flask, 35% higher than that of the control group. On this basis, the production in a 30-L fermenter reached 189.67 mg/L when the cell catalyst of 220 g/L (dry weight) was used to catalyze the synthesis for 24 h. This method laid the foundation for the large-scale production of MK-3 by P. pastoris Gpn12.

Bio-inspired nanocatalysts for the oxygen reduction reaction.

PubMed

Grumelli, Doris; Wurster, Benjamin; Stepanow, Sebastian; Kern, Klaus

2013-01-01

Electrochemical conversions at fuel cell electrodes are complex processes. In particular, the oxygen reduction reaction has substantial overpotential limiting the electrical power output efficiency. Effective and inexpensive catalytic interfaces are therefore essential for increased performance. Taking inspiration from enzymes, earth-abundant metal centres embedded in organic environments present remarkable catalytic active sites. Here we show that these enzyme-inspired centres can be effectively mimicked in two-dimensional metal-organic coordination networks self-assembled on electrode surfaces. Networks consisting of trimesic acid and bis-pyridyl-bispyrimidine coordinating to single iron and manganese atoms on Au(111) effectively catalyse the oxygen reduction and reveal distinctive catalytic activity in alkaline media. These results demonstrate the potential of surface-engineered metal-organic networks for electrocatalytic conversions. Specifically designed coordination complexes at surfaces inspired by enzyme cofactors represent a new class of nanocatalysts with promising applications in electrocatalysis.

Development of a sorber trace contaminant control system including pre- and post-sorbers for a catalytic oxidizer

NASA Technical Reports Server (NTRS)

Olcott, T. M.

1972-01-01

A general methodology was developed for spacecraft contaminant control system design. Elements considered for contaminant control were catalytic oxidation with isotope or electrical heat and pre- and post-sorbers, charcoal with regeneration and non-regeneration, and reactive constituents. A technique is described for sizing a charcoal bed for a multiple contaminant load.

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 12 2010-07-01 2010-07-01 true Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

40 CFR Table 10 to Subpart Uuu of... - Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 12 2011-07-01 2009-07-01 true Continuous Monitoring Systems for Organic HAP Emissions From Catalytic Cracking Units 10 Table 10 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE...

Crystal structure of metagenomic β-xylosidase/ α-l-arabinofuranosidase activated by calcium.

PubMed

Matsuzawa, Tomohiko; Kaneko, Satoshi; Kishine, Naomi; Fujimoto, Zui; Yaoi, Katsuro

2017-09-01

The crystal structure of metagenomic β-xylosidase/α-l-arabinofuranosidase CoXyl43, activated by calcium ions, was determined in its apo and complexed forms with xylotriose or l-arabinose in the presence and absence of calcium. The presence of calcium ions dramatically increases the kcat of CoXyl43 for p-nitrophenyl β-d-xylopyranoside and reduces the Michaelis constant for p-nitrophenyl α-l-arabinofuranoside. CoXyl43 consists of a single catalytic domain comprised of a five-bladed β-propeller. In the presence of calcium, a single calcium ion was observed at the centre of this catalytic domain, behind the catalytic pocket. In the absence of calcium, the calcium ion was replaced with one sodium ion and one water molecule, and the positions of these cations were shifted by 1.3 Å. The histidine-319 side chain, which coordinates to the 2-hydroxyl oxygen atom of the bound xylose molecule in the catalytic pocket, also coordinates to the calcium ion, but not to the sodium ion. The calcium-dependent increase in activity appears to be caused by the structural change in the catalytic pocket induced by the tightly bound calcium ion and coordinating water molecules, and by the protonation state of glutamic acid-268, the catalytic acid of the enzyme. Our findings further elucidate the complex relationship between metal ions and glycosidases. © The Authors 2017. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Functional characterization of the non-catalytic ectodomains of the nucleotide pyrophosphatase/phosphodiesterase NPP1.

PubMed Central

Gijsbers, Rik; Ceulemans, Hugo; Bollen, Mathieu

2003-01-01

The ubiquitous nucleotide pyrophosphatases/phosphodiesterases NPP1-3 consist of a short intracellular N-terminal domain, a single transmembrane domain and a large extracellular part, comprising two somatomedin-B-like domains, a catalytic domain and a poorly defined C-terminal domain. We show here that the C-terminal domain of NPP1-3 is structurally related to a family of DNA/RNA non-specific endonucleases. However, none of the residues that are essential for catalysis by the endonucleases are conserved in NPP1-NPP3, suggesting that the nuclease-like domain of NPP1-3 does not represent a second catalytic domain. Truncation analysis revealed that the nuclease-like domain of NPP1 is required for protein stability, for the targeting of NPP1 to the plasma membrane and for the expression of catalytic activity. We also demonstrate that 16 conserved cysteines in the somatomedin-B-like domains of NPP1, in concert with two flanking cysteines, mediate the dimerization of NPP1. The K173Q polymorphism of NPP1, which maps to the second somatomedin-B-like domain and has been associated with the aetiology of insulin resistance, did not affect the dimerization or catalytic activity of NPP1, and did not endow NPP1 with an affinity for the insulin receptor. Our data suggest that the non-catalytic ectodomains contribute to the subunit structure, stability and function of NPP1-3. PMID:12533192

Demonstration of catalytic combustion with residual fuel

NASA Technical Reports Server (NTRS)

Dodds, W. J.; Ekstedt, E. E.

1981-01-01

An experimental program was conducted to demonstrate catalytic combustion of a residual fuel oil. Three catalytic reactors, including a baseline configuration and two backup configurations based on baseline test results, were operated on No. 6 fuel oil. All reactors were multielement configurations consisting of ceramic honeycomb catalyzed with palladium on stabilized alumina. Stable operation on residual oil was demonstrated with the baseline configuration at a reactor inlet temperature of about 825 K (1025 F). At low inlet temperature, operation was precluded by apparent plugging of the catalytic reactor with residual oil. Reduced plugging tendency was demonstrated in the backup reactors by increasing the size of the catalyst channels at the reactor inlet, but plugging still occurred at inlet temperature below 725 K (845 F). Operation at the original design inlet temperature of 589 K (600 F) could not be demonstrated. Combustion efficiency above 99.5% was obtained with less than 5% reactor pressure drop. Thermally formed NO sub x levels were very low (less than 0.5 g NO2/kg fuel) but nearly 100% conversion of fuel-bound nitrogen to NO sub x was observed.

Optical manipulation and catalytic activity enhanced by surface plasmon effect

NASA Astrophysics Data System (ADS)

Zou, Ningmu; Min, Jiang; Jiao, Wenxiang; Wang, Guanghui

2017-02-01

For optical manipulation, a nano-optical conveyor belt consisting of an array of gold plasmonic non-concentric nano-rings (PNNRs) is demonstrated for the realization of trapping and unidirectional transportation of nanoparticles by polarization rotation of excitation beam. These hot spots of an asymmetric plasmonic nanostructure are polarization dependent, therefore, one can use the incident polarization state to manipulate the trapped targets. Trapped particles could be transferred between adjacent PNNRs in a given direction just by rotating the polarization of incident beam due to unbalanced potential. The angular dependent distribution of electric field around PNNR has been solved using the three- dimensional finite-difference time-domain (FDTD) technique. For optical enhanced catalytic activity, the spectral properties of dimers of Au nanorod-Au nanorod nanostructures under the excitation of 532nm photons have been investigated. With a super-resolution catalytic mapping technique, we identified the existence of "hot spot" in terms of catalytic reactivity at the gap region within the twined plasmonic nanostructure. Also, FDTD calculation has revealed an intrinsic correlation between hot electron transfer.

Liquid-phase pulsed laser ablation synthesis of graphitized carbon-encapsulated palladium core-shell nanospheres for catalytic reduction of nitrobenzene to aniline

NASA Astrophysics Data System (ADS)

Kim, Yu-jin; Ma, Rory; Reddy, D. Amaranatha; Kim, Tae Kyu

2015-12-01

Graphitized carbon-encapsulated palladium (Pd) core-shell nanospheres were produced via pulsed laser ablation of a solid Pd foil target submerged in acetonitrile. The microstructural features and optical properties of these nanospheres were characterized via high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy. Microstructural analysis indicated that the core-shell nanostructures consisted of single-crystalline cubic metallic Pd spheres that serve as the core material, over which graphitized carbon was anchored as a heterogeneous shell. The absorbance spectrum of the synthesized nanostructures exhibited a broad (absorption) band at ∼264 nm; this band corresponded to the typical inter-band transition of a metallic system and resulted possibly from the absorbance of the ionic Pd2+. The catalytic properties of the Pd and Pd@C core-shell nanostructures were investigated using the reduction of nitrobenzene to aniline by an excess amount of NaBH4 in an aqueous solution at room temperature, as a model reaction. Owing to the graphitized carbon-layered structure and the high specific surface area, the resulting Pd@C nanostructures exhibited higher conversion efficiencies than their bare Pd counterparts. In fact, the layered structure provided access to the surface of the Pd nanostructures for the hydrogenation reaction, owing to the synergistic effect between graphitized carbon and the nanostructures. Their unique structure and excellent catalytic performance render Pd@C core-shell nanostructures highly promising candidates for catalysis applications.

Model systems: how chemical biologists study RNA

PubMed Central

Rios, Andro C.; Tor, Yitzhak

2009-01-01

Ribonucleic acids are structurally and functionally sophisticated biomolecules and the use of models, frequently truncated or modified sequences representing functional domains of the natural systems, is essential to their exploration. Functional non-coding RNAs such as miRNAs, riboswitches, and, in particular, ribozymes, have changed the view of RNA’s role in biology and its catalytic potential. The well-known truncated hammerhead model has recently been refined and new data provide a clearer molecular picture of the elements responsible for its catalytic power. A model for the spliceosome, a massive and highly intricate ribonucleoprotein, is also emerging, although its true utility is yet to be cemented. Such catalytic model systems could also serve as “chemo-paleontological” tools, further refining the RNA world hypothesis and its relevance to the origin and evolution of life. PMID:19879179

N-Tosylhydrazone directed annulation via C-H/N-N bond activation in Ru(ii)/PEG-400 as homogeneous recyclable catalytic system: a green synthesis of isoquinolines.

PubMed

Deshmukh, Dewal S; Bhanage, Bhalchandra M

2018-06-21

A green and sustainable methodology for the synthesis of isoquinolines using Ru(ii)/PEG-400 as a homogeneous recyclable catalytic system has been demonstrated. N-Tosylhydrazone, a rarely explored directing group, has been successfully employed for an annulation type of reaction with alkynes via C-H/N-N activation. A short reaction time with a simple extraction procedure, a wide substrate scope with high yields of products, easily prepared substrates, biodegradable solvent, and scalability up to the gram level enhance the efficiency and sustainability of the proposed protocol. Further, the expensive ruthenium-based homogeneous catalytic system could be reused up to a fourth consecutive cycle without any loss in its activity.

Woodstove Emission Sampling Methods Comparability Analysis and In-situ Evaluation of New Technology Woodstoves.

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

Simons, Carl A.

1988-06-01

One major objective of this study was to compare several woodstove particulate emission sampling methods under laboratory and in-situ conditions. The laboratory work compared the EPA Method 5H, EPA Method 5G, and OMNI Automated Woodstove Emission Sampler (AWES)/Data LOG'r particulate emission sampling systems. A second major objective of the study was to evaluate the performance of two integral catalytic, two low emission non-catalytic, and two conventional technology woodstoves under in-situ conditions with AWES/Data LOG'r system. The AWES/Data LOG'r and EPA Method 5G sampling systems were also compared in an in-situ test on one of the integral catalytic woodstove models. 7more » figs., 12 tabs.« less

Template-Mediated Ni(II) Dispersion in Mesoporous SiO2 for Preparation of Highly Dispersed Ni Catalysts: Influence of Template Type.

PubMed

Ning, Xin; Lu, Yiyuan; Fu, Heyun; Wan, Haiqin; Xu, Zhaoyi; Zheng, Shourong

2017-06-07

Supported Ni catalysts on three mesoporous SiO 2 supports (i.e., SBA-15, MCM-41, and HMS) were prepared using a solid-state reaction between Ni(NO 3 ) 2 and organic template-occluded mesoporous SiO 2 . For comparison, supported Ni catalysts on mesoporous SiO 2 synthesized by the conventional impregnation method were also included. The catalysts were characterized by scanning electron microscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, N 2 adsorption, X-ray photoelectron spectroscopy, H 2 temperature-programmed reduction, transmission electron microscopy, and transmission electron microscopy-energy-dispersive X-ray. The catalytic properties of the catalysts were evaluated using gas-phase catalytic hydrodechlorination of 1,2-dichloroethane. The results showed that upon grinding Ni(NO 3 ) 2 with template-occluded mesoporous SiO 2 , strong coordination between Ni 2+ and dodecylamine was identified in the Ni(NO 3 ) 2 -HMS system. Additionally, the results of H 2 temperature-programmed reduction revealed that NiO in calcined NiO/HMS was reduced at higher temperature than those in calcined NiO/SBA-15 and NiO/MCM-41, reflecting the presence of a strong interaction between NiO and mesoporous SiO 2 in NiO/HMS. Consistently, the average particle sizes of metallic Ni were found to be 2.7, 3.4, and 9.6 nm in H 2 -reduced Ni/HMS, Ni/SBA-15, and Ni/MCM-41, respectively, indicative of a much higher Ni dispersion in Ni/HMS. For the catalytic hydrodechlorination of 1,2-dichloroethane, Ni/MCM-41 synthesized by the solid-state reaction method exhibited a catalytic activity similar to that prepared by the impregnation method, while higher catalytic activities were observed on Ni/HMS and Ni/SBA-15 than on their counterparts prepared by the impregnation method. Furthermore, a higher conversion was identified on Ni/HMS than on Ni/SBA-15 and Ni/MCM-41, highlighting the importance of template type for the preparation of highly dispersed metal catalysts on mesoporous SiO 2 .

Electron microscopy study of gold nanoparticles deposited on transition metal oxides.

PubMed

Akita, Tomoki; Kohyama, Masanori; Haruta, Masatake

2013-08-20

Many researchers have investigated the catalytic performance of gold nanoparticles (GNPs) supported on metal oxides for various catalytic reactions of industrial importance. These studies have consistently shown that the catalytic activity and selectivity depend on the size of GNPs, the kind of metal oxide supports, and the gold/metal oxide interface structure. Although researchers have proposed several structural models for the catalytically active sites and have identified the specific electronic structures of GNPs induced by the quantum effect, recent experimental and theoretical studies indicate that the perimeter around GNPs in contact with the metal oxide supports acts as an active site in many reactions. Thus, it is of immense importance to investigate the detailed structures of the perimeters and the contact interfaces of gold/metal oxide systems by using electron microscopy at an atomic scale. This Account describes our investigation, at the atomic scale using electron microscopy, of GNPs deposited on metal oxides. In particular, high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) are valuable tools to observe local atomic structures, as has been successfully demonstrated for various nanoparticles, surfaces, and material interfaces. TEM can be applied to real powder catalysts as received without making special specimens, in contrast to what is typically necessary to observe bulk materials. For precise structure analyses at an atomic scale, model catalysts prepared by using well-defined single-crystalline substrates are also adopted for TEM observations. Moreover, aberration-corrected TEM, which has high spatial resolution under 0.1 nm, is a promising tool to observe the interface structure between GNPs and metal oxide supports including oxygen atoms at the interfaces. The oxygen atoms in particular play an important role in the behavior of gold/metal oxide interfaces, because they may participate in catalytic reaction steps. Detailed information about the interfacial structures between GNPs and metal oxides provides valuable structure models for theoretical calculations which can elucidate the local electronic structure effective for activating a reactant molecule. Based on our observations with HRTEM and HAADF-STEM, we report the detailed structure of gold/metal oxide interfaces.

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

NONE

Toshiba Display Services, a television picture-tube manufacturer in Horseheads, NY, recently was able to meet stringent state regulations to reduce emissions from two of its film applications lines by installing a regenerative catalytic oxidation system. Toshiba officials initially evaluated several technologies to control volatile organic compounds. After deciding that oxidation was the best technology for its facility, the company invited a number of suppliers to submit proposals. Because all of the oxidation technologies considered by Toshiba had the capability to achieve the destruction and removal efficiency requirement, the company combined the second and third decision elements and conducted an in-depthmore » comparison of the initial capital and ongoing operating costs for each proposal. Officials narrowed the field to two systems--the lowest-cost regenerative thermal oxidation system on the market and a regenerative catalytic oxidation system. The company selected St. Louis, Mo.-based Monsanto Enviro-Chem Systems Inc., to install its DynaCycle{reg_sign} regenerative catalytic oxidation system, marking the first Dyna-Cycle installation in a US television picture-tube facility.« less

Thermogravimetric kinetic modelling of in-situ catalytic pyrolytic conversion of rice husk to bioenergy using rice hull ash catalyst.

PubMed

Loy, Adrian Chun Minh; Gan, Darren Kin Wai; Yusup, Suzana; Chin, Bridgid Lai Fui; Lam, Man Kee; Shahbaz, Muhammad; Unrean, Pornkamol; Acda, Menandro N; Rianawati, Elisabeth

2018-08-01

The thermal degradation behaviour and kinetic parameter of non-catalytic and catalytic pyrolysis of rice husk (RH) using rice hull ash (RHA) as catalyst were investigated using thermogravimetric analysis at four different heating rates of 10, 20, 50 and 100 K/min. Four different iso conversional kinetic models such as Kissinger, Friedman, Kissinger-Akahira-Sunose (KAS) and Ozawa-Flynn-Wall (OFW) were applied in this study to calculate the activation energy (E A ) and pre-exponential value (A) of the system. The E A of non-catalytic and catalytic pyrolysis was found to be in the range of 152-190 kJ/mol and 146-153 kJ/mol, respectively. The results showed that the catalytic pyrolysis of RH had resulted in a lower E A as compared to non-catalytic pyrolysis of RH and other biomass in literature. Furthermore, the high Gibb's free energy obtained in RH implied that it has the potential to serve as a source of bioenergy production. Copyright © 2018 Elsevier Ltd. All rights reserved.

Geometric tuning of self-propulsion for Janus catalytic particles

NASA Astrophysics Data System (ADS)

Michelin, Sébastien; Lauga, Eric

2017-02-01

Catalytic swimmers have attracted much attention as alternatives to biological systems for examining collective microscopic dynamics and the response to physico-chemical signals. Yet, understanding and predicting even the most fundamental characteristics of their individual propulsion still raises important challenges. While chemical asymmetry is widely recognized as the cornerstone of catalytic propulsion, different experimental studies have reported that particles with identical chemical properties may propel in opposite directions. Here, we show that, beyond its chemical properties, the detailed shape of a catalytic swimmer plays an essential role in determining its direction of motion, demonstrating the compatibility of the classical theoretical framework with experimental observations.

Geometric tuning of self-propulsion for Janus catalytic particles

PubMed Central

Michelin, Sébastien; Lauga, Eric

2017-01-01

Catalytic swimmers have attracted much attention as alternatives to biological systems for examining collective microscopic dynamics and the response to physico-chemical signals. Yet, understanding and predicting even the most fundamental characteristics of their individual propulsion still raises important challenges. While chemical asymmetry is widely recognized as the cornerstone of catalytic propulsion, different experimental studies have reported that particles with identical chemical properties may propel in opposite directions. Here, we show that, beyond its chemical properties, the detailed shape of a catalytic swimmer plays an essential role in determining its direction of motion, demonstrating the compatibility of the classical theoretical framework with experimental observations. PMID:28205563

Geometric tuning of self-propulsion for Janus catalytic particles.

PubMed

Michelin, Sébastien; Lauga, Eric

2017-02-13

Catalytic swimmers have attracted much attention as alternatives to biological systems for examining collective microscopic dynamics and the response to physico-chemical signals. Yet, understanding and predicting even the most fundamental characteristics of their individual propulsion still raises important challenges. While chemical asymmetry is widely recognized as the cornerstone of catalytic propulsion, different experimental studies have reported that particles with identical chemical properties may propel in opposite directions. Here, we show that, beyond its chemical properties, the detailed shape of a catalytic swimmer plays an essential role in determining its direction of motion, demonstrating the compatibility of the classical theoretical framework with experimental observations.

Method to monitor HC-SCR catalyst NOx reduction performance for lean exhaust applications

DOEpatents

Viola, Michael B [Macomb Township, MI; Schmieg, Steven J [Troy, MI; Sloane, Thompson M [Oxford, MI; Hilden, David L [Shelby Township, MI; Mulawa, Patricia A [Clinton Township, MI; Lee, Jong H [Rochester Hills, MI; Cheng, Shi-Wai S [Troy, MI

2012-05-29

A method for initiating a regeneration mode in selective catalytic reduction device utilizing hydrocarbons as a reductant includes monitoring a temperature within the aftertreatment system, monitoring a fuel dosing rate to the selective catalytic reduction device, monitoring an initial conversion efficiency, selecting a determined equation to estimate changes in a conversion efficiency of the selective catalytic reduction device based upon the monitored temperature and the monitored fuel dosing rate, estimating changes in the conversion efficiency based upon the determined equation and the initial conversion efficiency, and initiating a regeneration mode for the selective catalytic reduction device based upon the estimated changes in conversion efficiency.

Charge Transfer and Catalysis at the Metal Support Interface

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

Baker, Lawrence Robert

Kinetic, electronic, and spectroscopic characterization of model Pt–support systems are used to demonstrate the relationship between charge transfer and catalytic activity and selectivity. The results show that charge flow controls the activity and selectivity of supported metal catalysts. This dissertation builds on extensive existing knowledge of metal–support interactions in heterogeneous catalysis. The results show the prominent role of charge transfer at catalytic interfaces to determine catalytic activity and selectivity. Further, this research demonstrates the possibility of selectively driving catalytic chemistry by controlling charge flow and presents solid-state devices and doped supports as novel methods for obtaining electronic control over catalyticmore » reaction kinetics.« less

Integrated nonthermal treatment system study

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

Biagi, C.; Bahar, D.; Teheranian, B.

1997-01-01

This report presents the results of a study of nonthermal treatment technologies. The study consisted of a systematic assessment of five nonthermal treatment alternatives. The treatment alternatives consist of widely varying technologies for safely destroying the hazardous organic components, reducing the volume, and preparing for final disposal of the contact-handled mixed low-level waste (MLLW) currently stored in the US Department of Energy complex. The alternatives considered were innovative nonthermal treatments for organic liquids and sludges, process residue, soil and debris. Vacuum desorption or various washing approaches are considered for treatment of soil, residue and debris. Organic destruction methods include mediatedmore » electrochemical oxidation, catalytic wet oxidation, and acid digestion. Other methods studied included stabilization technologies and mercury separation of treatment residues. This study is a companion to the integrated thermal treatment study which examined 19 alternatives for thermal treatment of MLLW waste. The quantities and physical and chemical compositions of the input waste are based on the inventory database developed by the US Department of Energy. The Integrated Nonthermal Treatment Systems (INTS) systems were evaluated using the same waste input (2,927 pounds per hour) as the Integrated Thermal Treatment Systems (ITTS). 48 refs., 68 figs., 37 tabs.« less

SELECTIVE CATALYTIC REDUCTION MERCURY FIELD SAMPLING PROJECT

EPA Science Inventory

The report details an investigation on the effect of selective catalytic reduction (SCR), selective noncatalytic reduction (SNCR), and flue gas conditioning on the speciation and removal of mercury at power plants. If SCR and/or SNCR systems enhance mercury conversion/capture, t...

Flexibility Matters: Cooperative Active Sites in Covalent Organic Framework and Threaded Ionic Polymer.

PubMed

Sun, Qi; Aguila, Briana; Perman, Jason; Nguyen, Nicholas; Ma, Shengqian

2016-12-07

The combination of two or more reactive centers working in concert on a substrate to facilitate the reaction is now considered state of the art in catalysis, yet there still remains a tremendous challenge. Few heterogeneous systems of this sort have been exploited, as the active sites spatially separated within the rigid framework are usually difficult to cooperate. It is now shown that this roadblock can be surpassed. The underlying principle of the strategy presented here is the integration of catalytic components with excellent flexibility and porous heterogeneous catalysts, as demonstrated by the placement of linear ionic polymers in close proximity to surface Lewis acid active sites anchored on the walls of a covalent organic framework (COF). Using the cycloaddition of the epoxides and CO 2 as a model reaction, dramatic activity improvements have been achieved for the composite catalysts in relation to the individual catalytic component. Furthermore, they also clearly outperform the benchmark catalytic systems formed by the combination of the molecular organocatalysts and heterogeneous Lewis acid catalysts, while affording additional recyclability. The extraordinary flexibility and enriched concentration of the catalytically active moieties on linear polymers facilitate the concerted catalysis, thus leading to superior catalytic performance. This work therefore uncovers an entirely new strategy for designing bifunctional catalysts with double-activation behavior and opens a new avenue in the design of multicapable systems that mimic biocatalysis.

40 CFR Table 24 to Subpart Uuu of... - Continuous Monitoring Systems for Inorganic HAP Emissions From Catalytic Reforming Units

Code of Federal Regulations, 2010 CFR

2010-07-01

... Inorganic HAP Emissions From Catalytic Reforming Units As stated in § 63.1567(b)(1), you shall meet each requirement in the following table that applies to you. If you use this type of control device for your vent . . . You shall install and operate this type of continuous monitoring system . . . 1. Wet scrubber...

40 CFR Table 3 to Subpart Uuu of... - Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 13 2014-07-01 2014-07-01 false Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units 3 Table 3 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 3 Table 3 to Subpart UUU of Part 63—Continous Monitoring...

40 CFR Table 3 to Subpart Uuu of... - Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 13 2013-07-01 2012-07-01 true Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units 3 Table 3 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 3 Table 3 to Subpart UUU of Part 63—Continous Monitoring...

40 CFR Table 3 to Subpart Uuu of... - Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 13 2012-07-01 2012-07-01 false Continous Monitoring Systems for Metal HAP Emissions From Catalytic Cracking Units 3 Table 3 to Subpart UUU of Part 63 Protection of... Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 3 Table 3 to Subpart UUU of Part 63—Continous Monitoring...

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

PubMed Central

Moreno-Marrodan, Carmen; Liguori, Francesca

2017-01-01

The catalytic partial hydrogenation of substituted alkynes to alkenes is a process of high importance in the manufacture of several market chemicals. The present paper shortly reviews the heterogeneous catalytic systems engineered for this reaction under continuous flow and in the liquid phase. The main contributions appeared in the literature from 1997 up to August 2016 are discussed in terms of reactor design. A comparison with batch and industrial processes is provided whenever possible. PMID:28503209

Base-Controlled Completely Selective Linear or Branched Rhodium(I)-Catalyzed C-H ortho-Alkylation of Azines without Preactivation.

PubMed

Tran, Gaël; Hesp, Kevin D; Mascitti, Vincent; Ellman, Jonathan A

2017-05-15

A [Rh I ]/bisphosphine/base catalytic system for the ortho-selective C-H alkylation of azines by acrylates and acrylamides is reported. This catalytic system features an unprecedented complete linear or branched selectivity that is solely dependent on the catalytic base that is used. Complete branched selectivity is even achieved for ethyl methacrylate, which enables the introduction of a quaternary carbon center. Excellent functional group compatibility is demonstrated for both linear and branched alkylations. The operational simplicity and broad scope of this transformation allow for rapid access to functionalized azines of direct pharmaceutical and agrochemical relevance. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Catalytic Reforming of Oxygenates: State of the Art and Future Prospects.

PubMed

Li, Di; Li, Xinyu; Gong, Jinlong

2016-10-12

This Review describes recent advances in the design, synthesis, reactivity, selectivity, structural, and electronic properties of the catalysts for reforming of a variety of oxygenates (e.g., from simple monoalcohols to higher polyols, then to sugars, phenols, and finally complicated mixtures like bio-oil). A comprehensive exploration of the structure-activity relationship in catalytic reforming of oxygenates is carried out, assisted by state-of-the-art characterization techniques and computational tools. Critical emphasis has been given on the mechanisms of these heterogeneous-catalyzed reactions and especially on the nature of the active catalytic sites and reaction pathways. Similarities and differences (reaction mechanisms, design and synthesis of catalysts, as well as catalytic systems) in the reforming process of these oxygenates will also be discussed. A critical overview is then provided regarding the challenges and opportunities for research in this area with a focus on the roles that systems of heterogeneous catalysis, reaction engineering, and materials science can play in the near future. This Review aims to present insights into the intrinsic mechanism involved in catalytic reforming and provides guidance to the development of novel catalysts and processes for the efficient utilization of oxygenates for energy and environmental purposes.

Advanced treatment of biologically pretreated coal chemical industry wastewater using the catalytic ozonation process combined with a gas-liquid-solid internal circulating fluidized bed reactor.

PubMed

Li, Zhipeng; Liu, Feng; You, Hong; Ding, Yi; Yao, Jie; Jin, Chao

2018-04-01

This paper investigated the performance of the combined system of catalytic ozonation and the gas-liquid-solid internal circulating fluidized bed reactor for the advanced treatment of biologically pretreated coal chemical industry wastewater (CCIW). The results indicated that with ozonation alone for 60min, the removal efficiency of chemical oxygen demand (COD) could reach 34%. The introduction of activated carbon, pumice, γ-Al 2 O 3 carriers improved the removal performance of COD, and the removal efficiency was increased by 8.6%, 4.2%, 2%, respectively. Supported with Mn, the catalytic performance of activated carbon and γ-Al 2 O 3 were improved significantly with COD removal efficiencies of 46.5% and 41.3%, respectively; however, the promotion effect of pumice supported with Mn was insignificant. Activated carbon supported with Mn had the best catalytic performance. The catalytic ozonation combined system of MnO X /activated carbon could keep ozone concentration at a lower level in the liquid phase, and promote the transfer of ozone from the gas phase to the liquid phase to improve ozonation efficiency.

Detailed kinetics and regulation of mammalian 2-oxoglutarate dehydrogenase

PubMed Central

2011-01-01

Background Mitochondrial 2-oxoglutarate (α-ketoglutarate) dehydrogenase complex (OGDHC), a key regulatory point of tricarboxylic acid (TCA) cycle, plays vital roles in multiple pathways of energy metabolism and biosynthesis. The catalytic mechanism and allosteric regulation of this large enzyme complex are not fully understood. Here computer simulation is used to test possible catalytic mechanisms and mechanisms of allosteric regulation of the enzyme by nucleotides (ATP, ADP), pH, and metal ion cofactors (Ca2+ and Mg2+). Results A model was developed based on an ordered ter-ter enzyme kinetic mechanism combined with con-formational changes that involve rotation of one lipoic acid between three catalytic sites inside the enzyme complex. The model was parameterized using a large number of kinetic data sets on the activity of OGDHC, and validated by comparison of model predictions to independent data. Conclusions The developed model suggests a hybrid rapid-equilibrium ping-pong random mechanism for the kinetics of OGDHC, consistent with previously reported mechanisms, and accurately describes the experimentally observed regulatory effects of cofactors on the OGDHC activity. This analysis provides a single consistent theoretical explanation for a number of apparently contradictory results on the roles of phosphorylation potential, NAD (H) oxidation-reduction state ratio, as well as the regulatory effects of metal ions on ODGHC function. PMID:21943256

Interface problems between material recycling systems and plants

NASA Astrophysics Data System (ADS)

Nitta, Keiji; Oguchi, Mitsuo; Otsubo, Koji

A most important problem to creating a CELSS system to be used in space, for example, for a Lunar Base or Manned Mars mission, seems to be how to design and operate the various material recycling system to be used on the missions. Recent studies of a Lunar Base habitat have identified examples of CELSS configurations to be used for the Plant Cultivation Module. Material recycling subsystems to be installed in the Plant Cultivation Modules are proposed to consist of various sub-systems, such as dehumidifier, oxygen separation systems, catalytic wet oxidation systems, nitrogen adjusting systems, including tanks, and so on. The required performances of such various material recycling subsystems are determined based on precise metabolic data of derived from the various species of plants to be selected and investigated. The plant metabolic data, except that for wheat and potato, has not been fully collected at the present time. Therefore, much additional plant cultivation data is required to determine the performances of each material recycling subsystems introduced in Plant Cultivation Modules.

Catalytic Metal Free Production of Large Cage Structure Carbon Particles: A Candidate for Hydrogen Storage

NASA Technical Reports Server (NTRS)

Kimura, Yuki; Nuth, Joseph A., III; Ferguson, Frank T.

2005-01-01

We will demonstrate that carbon particles consisting of large cages can be produced without catalytic metal. The carbon particles were produced in CO gas as well as by introduction of 5% methane gas into the CO gas. The gas-produced carbon particles were able to absorb approximately 16.2 wt% of hydrogen. This value is 2.5 times higher than the 6.5 wt% goal for the vehicular hydrogen storage proposed by the Department of Energy in the USA. Therefore, we believe that this carbon particle is an excellent candidate for hydrogen storage for fuel cells.

Polyvinylpyrrolidone adsorption effects on the morphologies of synthesized platinum particles and its catalytic activity

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

Ooi, Mahayatun Dayana Johan; Aziz, Azlan Abdul; Nanobiotechnology Research and Innovation

Flower-like Platinum micro-structures were synthesized from different concentration of the PVP using solvothermal method. At 5.0×10{sup −3} mmol of PVP, well-defined flower-like pattern consists of triangular petals radiating from the centre were produced whereas larger flower network developed at higher PVP concentration. High degree of crystallinity was obtained upon each increment of PVP. The well defined flower like pattern synthesized using 5.0×10{sup −3} mmol PVP exhibit the highest catalytic activity and stability towards electro-oxidation of formic acid.

Determination of a Kinetic Rate Expression for the Oxidation of Chloroform Over a 2% Platinum/Alpha-Alumina Catalyst

DTIC Science & Technology

1992-04-01

1 :--.. - .-C1 r 1,-r ... r - nlns r’,rt n wa~r ’te r .sn data source,. q ath.tad m.,,tA1fMnq the ddta flCa,,dr d 0 . 11 EC~m, .n’ . - r, In .7- ,m...effluent and are potential catalytic inhibitors . Rate expression 5 accounts for only the inhibition due the adsorption of the reaction product(s). Rate...tempcraturc being required to achieve a similar chloroform conversion. These results indicate that HCI is a strong catalytic inhibitor and is consistent with

Model predictive control of a lean-burn gasoline engine coupled with a passive selective catalytic reduction system

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

Chen, Pingen; Lin, Qinghua; Prikhodko, Vitaly Y.

Lean-burn gasoline engines have demonstrated 10–20% engine efficiency gain over stoichiometric engines and are widely considered as a promising technology for meeting the 54.5 miles-per-gallon (mpg) Corporate Average Fuel Economy standard by 2025. Nevertheless, NOx emissions control for lean-burn gasoline for meeting the stringent EPA Tier 3 emission standards has been one of the main challenges towards the commercialization of highly-efficient lean-burn gasoline engines in the United States. Passive selective catalytic reduction (SCR) systems, which consist of a three-way catalyst and SCR, have demonstrated great potentials of effectively reducing NOx emissions for lean gasoline engines but may cause significant fuelmore » penalty due to ammonia generation via rich engine combustion. The purpose of this study is to develop a model-predictive control (MPC) scheme for a lean-burn gasoline engine coupled with a passive SCR system to minimize the fuel penalty associated with passive SCR operation while satisfying stringent NOx and NH3 emissions requirements. Simulation results demonstrate that the MPC-based control can reduce the fuel penalty by 47.7% in a simulated US06 cycle and 32.0% in a simulated UDDS cycle, compared to the baseline control, while achieving over 96% deNOx efficiency and less than 15 ppm tailpipe ammonia slip. The proposed MPC control can potentially enable high engine efficiency gain for highly-efficient lean-burn gasoline engine while meeting the stringent EPA Tier 3 emission standards.« less

Automated stopped-in-dual-loop flow analysis system for catalytic determination of vanadium in drinking water.

PubMed

Teshima, Norio; Kuno, Masami; Ueda, Minoru; Ueda, Hisashi; Ohno, Shinsuke; Sakai, Tadao

2009-07-15

An automated stopped-in-dual-loop flow analysis (SIDL-FA) system is proposed for the determination of vanadium in drinking water. The chemistry is based on the vanadium-catalyzed oxidation reaction of p-anisidine by bromate in the presence of Tiron as an activator to produce a dye (lambda(max)=510 nm). A SIDL-FA system basically consists of a selection valve, three pumps (one is for delivering of standard/sample, and others are for reagents), two six-way injection valves, a spectrophotometric detector and a data acquisition device. A 100-microL coiled loop around a heated device is fitted onto each six-way injection valve. A well-mixed solution containing reagents and standard/sample is loaded into the first loop on a six-way valve, and then the same solution is loaded into the second loop on another six-way valve. The solutions are isolated by switching these two six-way valves, so that the catalytic reaction can be promoted. The net waste can be zero in this stage, because all pumps are turned off. Then each resulting solution is dispensed to the detector with suitable time lag. A touchscreen controller is developed to automatically carry out the original SIDL-FA protocol. The proposed SIDL-FA method allows vanadium to be quantified in the range of 0.1-2 microg L(-1) and is applied to the determination of vanadium in drinking water samples.

Synthesis of nickel entities: From highly stable zerovalent nanoclusters to nanowires. Growth control and catalytic behavior.

PubMed

Peinetti, Ana S; Mizrahi, Martín; Requejo, Félix G; Buceta, David; López-Quintela, M Arturo; González, Graciela A; Battaglini, Fernando

2018-04-15

Non-noble metal nanoclusters synthesis is receiving increased attention due to their unique catalytic properties and lower cost. Herein, the synthesis of ligand-free Ni nanoclusters with an average diameter of 0.7 nm corresponding to a structure of 13 atoms is presented; they exhibit a zero-valence state and a high stability toward oxidation and thermal treatment. The nanoclusters formation method consists in the electroreduction of nickel ions inside an ordered mesoporous alumina; also, by increasing the current density, other structures can be obtained reaching to nanowires of 10 nm diameter. A seed-mediated mechanism is proposed to explain the growth to nanowires inside these mesoporous cavities. The size dependence on the catalytic behavior of these entities is illustrated by studying the reduction of methylene blue where the nanoclusters show an outstanding performance. Copyright © 2018 Elsevier Inc. All rights reserved.

Ab initio study on the dynamics of furfural at the liquid-solid interfaces

NASA Astrophysics Data System (ADS)

Dang, Hongli; Xue, Wenhua; Shields, Darwin; Liu, Yingdi; Jentoft, Friederike; Resasco, Daniel; Wang, Sanwu

2013-03-01

Catalytic biomass conversion sometimes occurs at the liquid-solid interfaces. We report ab initio molecular dynamics simulations at finite temperatures for the catalytic reactions involving furfural at the water-Pd and water-Cu interfaces. We found that, during the dynamic process, the furan ring of furfural prefers to be parallel to the Pd surface and the aldehyde group tends to be away from the Pd surface. On the other hand, at the water-Cu(111) interface, furfural prefers to be tilted to the Cu surface while the aldehyde group is bonded to the surface. In both cases, interaction of liquid water and furfural is identified. The difference of dynamic process of furfural at the two interfaces suggests different catalytic reaction mechanisms for the conversion of furfural, consistent with the experimental investigations. Supported by DOE (DE-SC0004600). Simulations and calculations were performed on XSED's and NERSC's supercomputers

Evolution of a designed retro-aldolase leads to complete active site remodeling

PubMed Central

Giger, Lars; Caner, Sami; Obexer, Richard; Kast, Peter; Baker, David; Ban, Nenad; Hilvert, Donald

2013-01-01

Evolutionary advances are often fueled by unanticipated innovation. Directed evolution of a computationally designed enzyme suggests that dramatic molecular changes can also drive the optimization of primitive protein active sites. The specific activity of an artificial retro-aldolase was boosted >4,400 fold by random mutagenesis and screening, affording catalytic efficiencies approaching those of natural enzymes. However, structural and mechanistic studies reveal that the engineered catalytic apparatus, consisting of a reactive lysine and an ordered water molecule, was unexpectedly abandoned in favor of a new lysine residue in a substrate binding pocket created during the optimization process. Structures of the initial in silico design, a mechanistically promiscuous intermediate, and one of the most evolved variants highlight the importance of loop mobility and supporting functional groups in the emergence of the new catalytic center. Such internal competition between alternative reactive sites may have characterized the early evolution of many natural enzymes. PMID:23748672

Comparing the Caputo, Caputo-Fabrizio and Atangana-Baleanu derivative with fractional order: Fractional cubic isothermal auto-catalytic chemical system

NASA Astrophysics Data System (ADS)

Saad, K. M.

2018-03-01

In this work we extend the standard model for a cubic isothermal auto-catalytic chemical system (CIACS) to a new model of a fractional cubic isothermal auto-catalytic chemical system (FCIACS) based on Caputo (C), Caputo-Fabrizio (CF) and Atangana-Baleanu in the Liouville-Caputo sense (ABC) fractional time derivatives, respectively. We present approximate solutions for these extended models using the q -homotopy analysis transform method ( q -HATM). We solve the FCIACS with the C derivative and compare our results with those obtained using the CF and ABC derivatives. The ranges of convergence of the solutions are found and the optimal values of h , the auxiliary parameter, are derived. Finally, these solutions are compared with numerical solutions of the various models obtained using finite differences and excellent agreement is found.

The Metabolic Core and Catalytic Switches Are Fundamental Elements in the Self-Regulation of the Systemic Metabolic Structure of Cells

PubMed Central

De la Fuente, Ildefonso M.; Cortes, Jesus M.; Perez-Pinilla, Martin B.; Ruiz-Rodriguez, Vicente; Veguillas, Juan

2011-01-01

Background Experimental observations and numerical studies with dissipative metabolic networks have shown that cellular enzymatic activity self-organizes spontaneously leading to the emergence of a metabolic core formed by a set of enzymatic reactions which are always active under all environmental conditions, while the rest of catalytic processes are only intermittently active. The reactions of the metabolic core are essential for biomass formation and to assure optimal metabolic performance. The on-off catalytic reactions and the metabolic core are essential elements of a Systemic Metabolic Structure which seems to be a key feature common to all cellular organisms. Methodology/Principal Findings In order to investigate the functional importance of the metabolic core we have studied different catalytic patterns of a dissipative metabolic network under different external conditions. The emerging biochemical data have been analysed using information-based dynamic tools, such as Pearson's correlation and Transfer Entropy (which measures effective functionality). Our results show that a functional structure of effective connectivity emerges which is dynamical and characterized by significant variations of bio-molecular information flows. Conclusions/Significance We have quantified essential aspects of the metabolic core functionality. The always active enzymatic reactions form a hub –with a high degree of effective connectivity- exhibiting a wide range of functional information values being able to act either as a source or as a sink of bio-molecular causal interactions. Likewise, we have found that the metabolic core is an essential part of an emergent functional structure characterized by catalytic modules and metabolic switches which allow critical transitions in enzymatic activity. Both, the metabolic core and the catalytic switches in which also intermittently-active enzymes are involved seem to be fundamental elements in the self-regulation of the Systemic Metabolic Structure. PMID:22125607

Solid State Energy Conversion Energy Alliance (SECA)

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

Hennessy, Daniel; Sibisan, Rodica; Rasmussen, Mike

2011-09-12

The overall objective is to develop a Solid Oxide Fuel Cell (SOFC) stack that can be economically produced in high volumes and mass customized for different applications in transportation, stationary power generation, and military market sectors. In Phase I, work will be conducted on system design and integration, stack development, and development of reformers for natural gas and gasoline. Specifically, Delphi-Battelle will fabricate and test a 5 kW stationary power generation system consisting of a SOFC stack, a steam reformer for natural gas, and balance-of-plant (BOP) components, having an expected efficiency of ≥ 35 percent (AC/LHV). In Phase II andmore » Phase III, the emphasis will be to improve the SOFC stack, reduce start-up time, improve thermal cyclability, demonstrate operation on diesel fuel, and substantially reduce materials and manufacturing cost by integrating several functions into one component and thus reducing the number of components in the system. In Phase II, Delphi-Battelle will fabricate and demonstrate two SOFC systems: an improved stationary power generation system consisting of an improved SOFC stack with integrated reformation of natural gas, and the BOP components, with an expected efficiency of ≥ 40 percent (AC/LHV), and a mobile 5 kW system for heavy-duty trucks and military power applications consisting of an SOFC stack, reformer utilizing anode tailgate recycle for diesel fuel, and BOP components, with an expected efficiency of ≥ 30 percent (DC/LHV). Finally, in Phase III, Delphi-Battelle will fabricate and test a 5 kW Auxiliary Power Unit (APU) for mass-market automotive application consisting of an optimized SOFC stack, an optimized catalytic partial oxidation (CPO) reformer for gasoline, and BOP components, having an expected efficiency of ≥ 30 percent (DC/LHV) and a factory cost of ≤ $400/kW.« less

Solid State Energy Conversion Energy Alliance (SECA)

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

Hennessy, Daniel; Sibisan, Rodica; Rasmussen, Mike

2011-09-12

The overall objective is to develop a solid oxide fuel cell (SOFC) stack that can be economically produced in high volumes and mass customized for different applications in transportation, stationary power generation, and military market sectors. In Phase I, work will be conducted on system design and integration, stack development, and development of reformers for natural gas and gasoline. Specifically, Delphi-Battelle will fabricate and test a 5 kW stationary power generation system consisting of a SOFC stack, a steam reformer for natural gas, and balance-of-plant (BOP) components, having an expected efficiency of 35 percent (AC/LHV). In Phase II and Phasemore » III, the emphasis will be to improve the SOFC stack, reduce start-up time, improve thermal cyclability, demonstrate operation on diesel fuel, and substantially reduce materials and manufacturing cost by integrating several functions into one component and thus reducing the number of components in the system. In Phase II, Delphi-Battelle will fabricate and demonstrate two SOFC systems: an improved stationary power generation system consisting of an improved SOFC stack with integrated reformation of natural gas, and the BOP components, with an expected efficiency of ≥40 percent (AC/LHV), and a mobile 5 kW system for heavy-duty trucks and military power applications consisting of an SOFC stack, reformer utilizing anode tailgate recycle for diesel fuel, and BOP components, with an expected efficiency of ≥30 percent (DC/LHV). Finally, in Phase III, Delphi-Battelle will fabricate and test a 5 kW Auxiliary Power Unit (APU) for mass-market automotive application consisting of an optimized SOFC stack, an optimized catalytic partial oxidation (CPO) reformer for gasoline, and BOP components, having an expected efficiency of 30 percent (DC/LHV) and a factory cost of ≤$400/kW.« less

Study of the dynamics of the MoO2-Mo2C system for catalytic partial oxidation reactions

NASA Astrophysics Data System (ADS)

Cuba Torres, Christian Martin

On a global scale, the energy demand is largely supplied by the combustion of non-renewable fossil fuels. However, their rapid depletion coupled with environmental and sustainability concerns are the main drivers to seek for alternative energetic strategies. To this end, the sustainable generation of hydrogen from renewable resources such as biodiesel would represent an attractive alternative solution to fossil fuels. Furthermore, hydrogen's lower environmental impact and greater independence from foreign control make it a strong contender for solving this global problem. Among a wide variety of methods for hydrogen production, the catalytic partial oxidation offers numerous advantages for compact and mobile fuel processing systems. For this reaction, the present work explores the versatility of the Mo--O--C catalytic system under different synthesis methods and reforming conditions using methyl oleate as a surrogate biodiesel. MoO2 exhibits good catalytic activity and exhibits high coke-resistance even under reforming conditions where long-chain oxygenated compounds are prone to form coke. Moreover, the lattice oxygen present in MoO2 promotes the Mars-Van Krevelen mechanism. Also, it is introduced a novel beta-Mo2C synthesis by the in-situ formation method that does not utilize external H2 inputs. Herein, the MoO 2/Mo2C system maintains high catalytic activity for partial oxidation while the lattice oxygen serves as a carbon buffer for preventing coke formation. This unique feature allows for longer operation reforming times despite slightly lower catalytic activity compared to the catalysts prepared by the traditional temperature-programmed reaction method. Moreover, it is demonstrated by a pulse reaction technique that during the phase transformation of MoO2 to beta-Mo2C, the formation of Mo metal as an intermediate is not responsible for the sintering of the material wrongly assumed by the temperature-programmed method.

Ruthenium on rutile catalyst, catalytic system, and method for aqueous phase hydrogenations

DOEpatents

Elliot, Douglas C.; Werpy, Todd A.; Wang, Yong; Frye, Jr., John G.

2001-01-01

An essentially nickel- and rhenium-free catalyst is described comprising ruthenium on a titania support where the titania is greater than 75% rutile. A catalytic system containing a nickel-free catalyst comprising ruthenium on a titania support where the titania is greater than 75% rutile, and a method using this catalyst in the hydrogenation of an organic compound in the aqueous phase is also described.

Catalytic dehydration of ethanol using transition metal oxide catalysts.

PubMed

Zaki, T

2005-04-15

The aim of this work is to study catalytic ethanol dehydration using different prepared catalysts, which include Fe(2)O(3), Mn(2)O(3), and calcined physical mixtures of both ferric and manganese oxides with alumina and/or silica gel. The physicochemical properties of these catalysts were investigated via X-ray powder diffraction (XRD), acidity measurement, and nitrogen adsorption-desorption at -196 degrees C. The catalytic activities of such catalysts were tested through conversion of ethanol at 200-500 degrees C using a catalytic flow system operated under atmospheric pressure. The results obtained indicated that the dehydration reaction on the catalyst relies on surface acidity, whereas the ethylene production selectivity depends on the catalyst chemical constituents.

A hybrid biocatalyst consisting of silver nanoparticle and naphthalenethiol self-assembled monolayer prepared for anchoring glucose oxidase and its use for an enzymatic biofuel cell

NASA Astrophysics Data System (ADS)

Christwardana, Marcelinus; Kim, Do-Heyoung; Chung, Yongjin; Kwon, Yongchai

2018-01-01

A novel hybrid biocatalyst is synthesized by the enzyme composite consisting of silver nanoparticle (AgNP), naphthalene-thiol based couplers (Naph-SH) and glucose oxidase (GOx), which is then bonded with the supporter consisting of polyethyleneimine (PEI) and carbon nanotube (CNT) (CNT/PEI/AgNPs/Naph-SH/GOx) to facilitate glucose oxidation reaction (GOR). Here, the AgNPs play a role in obstructing denaturation of the GOx molecules from the supporter because of Ag-thiol bond, while the PEIs have the AgNPs keep their states without getting ionized by hydrogen peroxide produced during anodic reaction. The Naph-SHs also prevent ionization of the AgNP by forming self-assembled monolayer on their surface. Such roles of each component enable the catalyst to form (i) hydrophobic interaction between the GOx molecules and supporter and (ii) π-conjugated electron pathway between the GOx molecules and AgNP, promoting electron transfer. Catalytic nature of the catalyst is characterized by measuring catalytic activity and performance of enzymatic biofuel cell (EBC) using the catalyst. Regarding the catalytic activity, the catalyst leads to high electron transfer rate constant (9.6 ± 0.4 s-1), low Michaelis-Menten constant (0.51 ± 0.04 mM), and low charge transfer resistance (7.3 Ω cm2) and high amount of immobilized GOx (54.6%), while regarding the EBC performance, high maximum power density (1.46 ± 0.07 mW cm-2) with superior long-term stability result are observed.

Catalytic and Thermal 1,2-Rearrangement of (α-Mercaptobenzyl)trimethylsilane

NASA Astrophysics Data System (ADS)

Zhang, Jie; Cui, Mengzhong; Feng, Shengyu; Sun, Xiaomin; Feng, Dacheng

2009-09-01

The mechanisms of catalytic and thermal 1,2-rearrangement of (α-mercaptobenzyl)trimethylsilane were studied by using density functional theory (DFT) at the MP2/6-31+G(d,p)//B3LYP/6-31G(d) levels. The results show that (α-mercaptobenzyl)trimethylsilane rearranges to (benzylthio)trimethylsilane through a trimethylsilyl group migration from C to S atom via a transition state of pentacoordinate Si atom with or without radical initiators. The low reaction activation energy (15.1 kcal/mol) is responsible for the fast rearrangement in the presence of radical initiators. Both radical and nonradical thermal rearrangement mechanisms were suggested, and the radical mechanism dominates through its self-catalyzing. These results are consistent with the experiment results. The activation energy (ΔHact = 15.1 kcal/mol) for the rate-determining step within the self-catalytic cycle is low enough to make (trimethylsilylbenzyl)thiyl radical be a reasonable catalyst for the thermal rearrangement. The catalytic and thermal 1,2-rearrangement mechanisms of (α-mercaptobenzyl)trimethylsilane, especially the self-catalytic radical mechanism, were revealed for the first time. The comparison of the rearrangement mechanisms between (α-mercaptobenzyl)trimethylsilane and silylmethanethiol discloses the factors in determining the reaction mechanism of such kinds of mercaptoalkyl-functionalized organosilanes. The phenyl group is found to be favorable for the radical rearrangement, thus making (α-mercaptobenzyl)trimethylsilane instable.

A new group of glycoside hydrolase family 13 α-amylases with an aberrant catalytic triad

PubMed Central

Sarian, Fean D.; Janeček, Štefan; Pijning, Tjaard; Ihsanawati; Nurachman, Zeily; Radjasa, Ocky K.; Dijkhuizen, Lubbert; Natalia, Dessy; van der Maarel, Marc J. E. C.

2017-01-01

α-Amylases are glycoside hydrolase enzymes that act on the α(1→4) glycosidic linkages in glycogen, starch, and related α-glucans, and are ubiquitously present in Nature. Most α-amylases have been classified in glycoside hydrolase family 13 with a typical (β/α)8-barrel containing two aspartic acid and one glutamic acid residue that play an essential role in catalysis. An atypical α-amylase (BmaN1) with only two of the three invariant catalytic residues present was isolated from Bacillus megaterium strain NL3, a bacterial isolate from a sea anemone of Kakaban landlocked marine lake, Derawan Island, Indonesia. In BmaN1 the third residue, the aspartic acid that acts as the transition state stabilizer, was replaced by a histidine. Three-dimensional structure modeling of the BmaN1 amino acid sequence confirmed the aberrant catalytic triad. Glucose and maltose were found as products of the action of the novel α-amylase on soluble starch, demonstrating that it is active in spite of the peculiar catalytic triad. This novel BmaN1 α-amylase is part of a group of α-amylases that all have this atypical catalytic triad, consisting of aspartic acid, glutamic acid and histidine. Phylogenetic analysis showed that this group of α-amylases comprises a new subfamily of the glycoside hydrolase family 13. PMID:28287181

Catalytic oxidation of o-aminophenols and aromatic amines by mushroom tyrosinase.

PubMed

Muñoz-Muñoz, Jose Luis; Garcia-Molina, Francisco; Garcia-Ruiz, Pedro Antonio; Varon, Ramon; Tudela, Jose; Rodriguez-Lopez, Jose N; Garcia-Canovas, Francisco

2011-12-01

The kinetics of tyrosinase acting on o-aminophenols and aromatic amines as substrates was studied. The catalytic constants of aromatic monoamines and o-diamines were both low, these results are consistent with our previous mechanism in which the slow step is the transfer of a proton by a hydroxyl to the peroxide in oxy-tyrosinase (Fenoll et al., Biochem. J. 380 (2004) 643-650). In the case of o-aminophenols, the hydroxyl group indirectly cooperates in the transfer of the proton and consequently the catalytic constants in the action of tyrosinase on these compounds are higher. In the case of aromatic monoamines, the Michaelis constants are of the same order of magnitude than for monophenols, which suggests that the monophenols bind better (higher binding constant) to the enzyme to facilitate the π-π interactions between the aromatic ring and a possible histidine of the active site. In the case of aromatic o-diamines, both the catalytic and Michaelis constants are low, the values of the catalytic constants being lower than those of the corresponding o-diphenols. The values of the Michaelis constants of the aromatic o-diamines are slightly lower than those of their corresponding o-diphenols, confirming that the aromatic o-diamines bind less well (lower binding constant) to the enzyme. Copyright © 2011 Elsevier B.V. All rights reserved.

Predominant nonproductive substrate binding by fungal cellobiohydrolase I and implications for activity improvement.

PubMed

Rabinovich, Mikhail L; Melnik, Maria S; Herner, Mikhail L; Voznyi, Yakov V; Vasilchenko, Lilia G

2018-05-21

Enzymatic conversion of the most abundant renewable source of organic compounds, cellulose to fermentable sugars is attractive for production of green fuels and chemicals. The major component of industrial enzyme systems, cellobiohydrolase I from Hypocrea jecorina (Trichoderma reesei) (HjCel7A) processively splits disaccharide units from the reducing ends of tightly packed cellulose chains. HjCel7A consists of a catalytic domain (CD) and a carbohydrate-binding module (CBM) separated by a linker peptide. A tunnel-shaped substrate-binding site in the CD includes 9 subsites for β-D-glucose units, 7 of which (-7 to -1) precede the catalytic center. Low catalytic activity of Cel7A is the bottleneck and the primary target for improvement. Here it is shown for the first time that, in spite of much lower apparent k cat of HjCel7A at the hydrolysis of β-1,4-glucosidic linkages in the fluorogenic cellotetra- and -pentaose compared to the structurally related endoglucanase I (HjCel7B), the specificity constants (catalytic efficiency) k cat /K m for both enzymes are almost equal in these reactions. The observed activity difference appears from strong nonproductive substrate binding by HjCel7A, particularly significant for MU-β-cellotetraose (MUG 4 ). Interaction of substrates with the subsites -6 and -5 proximal to the non-conserved Gln101 residue in HjCel7A decreases K m,ap by >1500 times. HjCel7A can be nonproductively bound onto cellulose surface with K d ∼2-9 nM via CBM and CD that captures 6 terminal glucose units of cellulose chain. Decomposition of this nonproductive complex can determine the rate of cellulose conversion. MUG 4 is a promising substrate to select active cellobiohydrolase I variants with reduced nonproductive substrate binding. This article is protected by copyright. All rights reserved.

Molecular cloning and developmental expression of the catalytic and 65-kDa regulatory subunits of protein phosphatase 2A in Drosophila.

PubMed Central

Mayer-Jaekel, R E; Baumgartner, S; Bilbe, G; Ohkura, H; Glover, D M; Hemmings, B A

1992-01-01

cDNA clones encoding the catalytic subunit and the 65-kDa regulatory subunit of protein phosphatase 2A (PR65) from Drosophila melanogaster have been isolated by homology screening with the corresponding human cDNAs. The Drosophila clones were used to analyze the spatial and temporal expression of the transcripts encoding these two proteins. The Drosophila PR65 cDNA clones contained an open reading frame of 1773 nucleotides encoding a protein of 65.5 kDa. The predicted amino acid sequence showed 75 and 71% identity to the human PR65 alpha and beta isoforms, respectively. As previously reported for the mammalian PR65 isoforms, Drosophila PR65 is composed of 15 imperfect repeating units of approximately 39 amino acids. The residues contributing to this repeat structure show also the highest sequence conservation between species, indicating a functional importance for these repeats. The gene encoding Drosophila PR65 was located at 29B1,2 on the second chromosome. A major transcript of 2.8 kilobase (kb) encoding the PR65 subunit and two transcripts of 1.6 and 2.5 kb encoding the catalytic subunit could be detected throughout Drosophila development. All of these mRNAs were most abundant during early embryogenesis and were expressed at lower levels in larvae and adult flies. In situ hybridization of different developmental stages showed a colocalization of the PR65 and catalytic subunit transcripts. The mRNA expression is high in the nurse cells and oocytes, consistent with a high equally distributed expression in early embryos. In later embryonal development, the expression remains high in the nervous system and the gonads but the overall transcript levels decrease. In third instar larvae, high levels of mRNA could be observed in brain, imaginal discs, and in salivary glands. These results indicate that protein phosphatase 2A transcript levels change during development in a tissue and in a time-specific manner. Images PMID:1320961

Multifunctional Au-Fe3O4@MOF core-shell nanocomposite catalysts with controllable reactivity and magnetic recyclability

NASA Astrophysics Data System (ADS)

Ke, Fei; Wang, Luhuan; Zhu, Junfa

2014-12-01

The recovery and reuse of expensive catalysts are important in both heterogeneous and homogeneous catalysis due to economic and environmental reasons. This work reports a novel multifunctional magnetic core-shell gold catalyst which can be easily prepared and shows remarkable catalytic properties in the reduction of 4-nitrophenol. The novel Au-Fe3O4@metal-organic framework (MOF) catalyst consists of a superparamagnetic Au-Fe3O4 core and a porous MOF shell with controllable thickness. Small Au nanoparticles (NPs) of 3-5 nm are mainly sandwiched between the Fe3O4 core and the porous MOF shell. Catalytic studies show that the core-shell structured Au-Fe3O4@MOF catalyst has a much higher catalytic activity than other reported Au-based catalysts toward the reduction of 4-nitrophenol. Moreover, this catalyst can be easily recycled due to the presence of the superparamagnetic core. Therefore, compared to conventional catalysts used in the reduction of 4-nitrophenol, this porous MOF-based magnetic catalyst is green, cheap and promising for industrial applications.The recovery and reuse of expensive catalysts are important in both heterogeneous and homogeneous catalysis due to economic and environmental reasons. This work reports a novel multifunctional magnetic core-shell gold catalyst which can be easily prepared and shows remarkable catalytic properties in the reduction of 4-nitrophenol. The novel Au-Fe3O4@metal-organic framework (MOF) catalyst consists of a superparamagnetic Au-Fe3O4 core and a porous MOF shell with controllable thickness. Small Au nanoparticles (NPs) of 3-5 nm are mainly sandwiched between the Fe3O4 core and the porous MOF shell. Catalytic studies show that the core-shell structured Au-Fe3O4@MOF catalyst has a much higher catalytic activity than other reported Au-based catalysts toward the reduction of 4-nitrophenol. Moreover, this catalyst can be easily recycled due to the presence of the superparamagnetic core. Therefore, compared to conventional catalysts used in the reduction of 4-nitrophenol, this porous MOF-based magnetic catalyst is green, cheap and promising for industrial applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05421k

A Palladium Iodide-Catalyzed Oxidative Aminocarbonylation-Heterocyclization Approach to Functionalized Benzimidazoimidazoles.

PubMed

Veltri, Lucia; Giofrè, Salvatore V; Devo, Perry; Romeo, Roberto; Dobbs, Adrian P; Gabriele, Bartolo

2018-02-02

A novel carbonylative approach to the synthesis of functionalized 1H-benzo[d]imidazo[1,2-a]imidazoles is presented. The method consists of the oxidative aminocarbonylation of N-substituted-1-(prop-2-yn-1-yl)-1H-benzo[d]imidazol-2-amines, carried out in the presence of secondary nucleophilic amines, to give the corresponding alkynylamide intermediates, followed by in situ conjugated addition and double-bond isomerization, to give 2-(1-alkyl-1H-benzo[d]imidazo[1,2-a]imidazol-2-yl)acetamides. Products were obtained in good to excellent yields (64-96%) and high turnover numbers (192-288 mol of product per mol of catalyst) under relatively mild conditions (100 °C under 20 atm of a 4:1 mixture of CO-air), using a simple catalytic system, consisting of PdI 2 (0.33 mol %) in conjunction with KI (0.33 equiv).

Peroxiredoxins in plants and cyanobacteria.

PubMed

Dietz, Karl-Josef

2011-08-15

Peroxiredoxins (Prx) are central elements of the antioxidant defense system and the dithiol-disulfide redox regulatory network of the plant and cyanobacterial cell. They employ a thiol-based catalytic mechanism to reduce H2O2, alkylhydroperoxide, and peroxinitrite. In plants and cyanobacteria, there exist 2-CysPrx, 1-CysPrx, PrxQ, and type II Prx. Higher plants typically contain at least one plastid 2-CysPrx, one nucleo-cytoplasmic 1-CysPrx, one chloroplast PrxQ, and one each of cytosolic, mitochondrial, and plastidic type II Prx. Cyanobacteria express variable sets of three or more Prxs. The catalytic cycle consists of three steps: (i) peroxidative reduction, (ii) resolving step, and (iii) regeneration using diverse electron donors such as thioredoxins, glutaredoxins, cyclophilins, glutathione, and ascorbic acid. Prx proteins undergo major conformational changes in dependence of their redox state. Thus, they not only modulate cellular reactive oxygen species- and reactive nitrogen species-dependent signaling, but depending on the Prx type they sense the redox state, transmit redox information to binding partners, and function as chaperone. They serve in context of photosynthesis and respiration, but also in metabolism and development of all tissues, for example, in nodules as well as during seed and fruit development. The article surveys the current literature and attempts a mostly comprehensive coverage of present day knowledge and concepts on Prx mechanism, regulation, and function and thus on the whole Prx systems in plants.

Conversion of wood residues to diesel fuel

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

Kuester, J.L.

1981-01-01

The basic approach is indirect liquefaction, i.e., thermal gasification followed by catalytic liquefaction. The indirect approach results in separation of the oxygen in the biomass feedstock, i.e., oxygenated compounds do not appear in the liquid hydrocarbon fuel product. The general conversion scheme is shown. The process is capable of accepting a wide variety of feedstocks. Potential products include medium quality gas, normal propanol, paraffinic fuel and/or high octane gasoline. A flow diagram of the continuous laboratory unit is shown. A fluidized bed pyrolysis system is used for gasification. Capacity is about 10 lbs/h of feedstock. The pyrolyzer can be fluidizedmore » with recycle pyrolysis gas, steam or recycle liquefaction system off gas or some combination thereof. Tars are removed in a wet scrubber. Unseparated pyrolysis gases are utilized as feed to a modified Fischer-Tropsch reactor. The liquid condensate from the reactor consists of a normal propanol-water phase and a paraffinic hydrocarbon phase. The reactor can be operated to optimize for either product. If a high octane gasoline is desired, the paraffinic fuel is passed through a conventional catalytic reformer. The normal propanol could be used as a fuel extender if blended with the hydrocarbon fuel products. Off gases from the downstream reactors are of high quality due to the accumulation of low molecular weight paraffins.« less

DEMONSTRATION OF POTENTIAL FOR SELECTIVE CATALYTIC REDUCTION AND DIESEL PARTICULATE FILTERS

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

McGILL,R; KHAIR, M; SHARP, C

2003-08-24

This project addresses the potential for Selective Catalytic Reduction (SCR) devices (using urea as reductant) together with Diesel Particulate Filters (DPF) and low-pressure loop exhaust gas recirculation (EGR) to achieve future stringent emissions standards for heavy-duty engines powering Class 8 vehicles. Two emission control systems consisting of the three technologies (EGR, SCR, and DPF) were calibrated on a Caterpillar C-12 heavy-duty diesel engine. Results of these calibrations showed good promise in meeting the 2010 heavy-duty emission standards as set forth by the Environmental Protection Agency (EPA). These two emission control systems were developed to evaluate a series of fuels thatmore » have similar formulations except for their sulfur content. Additionally, one fuel, code-named BP15, was also evaluated. This fuel was prepared by processing straight-run distillate stocks through a commercial, single stage hydrotreater employing high activity catalyst at maximum severity. An additional goal of this program is to provide data for an on-going EPA technology review that evaluates progress toward meeting 2007/2010 emission standards. These emissions levels were to be achieved not only on the transient test cycles but in other modes of operation such as the steady-state Euro-III style emission test known as the OICA (Organisation Internationale des Compagnies d'Automobiles) or the ESC (European Stationary Cycle). Additionally, hydrocarbon and carbon monoxide emissions standards are to be met.« less

Heterobimetallic transition metal/rare earth metal bifunctional catalysis: a Cu/Sm/Schiff base complex for syn-selective catalytic asymmetric nitro-Mannich reaction.

PubMed

Handa, Shinya; Gnanadesikan, Vijay; Matsunaga, Shigeki; Shibasaki, Masakatsu

2010-04-07

The full details of a catalytic asymmetric syn-selective nitro-Mannich reaction promoted by heterobimetallic Cu/Sm/dinucleating Schiff base complexes are described, demonstrating the effectiveness of the heterobimetallic transition metal/rare earth metal bifunctional catalysis. The first-generation system prepared from Cu(OAc)(2)/Sm(O-iPr)(3)/Schiff base 1a = 1:1:1 with an achiral phenol additive was partially successful for achieving the syn-selective catalytic asymmetric nitro-Mannich reaction. The substrate scope and limitations of the first-generation system remained problematic. After mechanistic studies on the catalyst prepared from Sm(O-iPr)(3), we reoptimized the catalyst preparation method, and a catalyst derived from Sm(5)O(O-iPr)(13) showed broader substrate generality as well as higher reactivity and stereoselectivity compared to Sm(O-iPr)(3). The optimal system with Sm(5)O(O-iPr)(13) was applicable to various aromatic, heteroaromatic, and isomerizable aliphatic N-Boc imines, giving products in 66-99% ee and syn/anti = >20:1-13:1. Catalytic asymmetric synthesis of nemonapride is also demonstrated using the catalyst derived from Sm(5)O(O-iPr)(13).

Active biopolymers in green non-conventional media: a sustainable tool for developing clean chemical processes.

PubMed

Lozano, Pedro; Bernal, Juana M; Nieto, Susana; Gomez, Celia; Garcia-Verdugo, Eduardo; Luis, Santiago V

2015-12-21

The greenness of chemical processes turns around two main axes: the selectivity of catalytic transformations, and the separation of pure products. The transfer of the exquisite catalytic efficiency shown by enzymes in nature to chemical processes is an important challenge. By using appropriate reaction systems, the combination of biopolymers with supercritical carbon dioxide (scCO2) and ionic liquids (ILs) resulted in synergetic and outstanding platforms for developing (multi)catalytic green chemical processes, even under flow conditions. The stabilization of biocatalysts, together with the design of straightforward approaches for separation of pure products including the full recovery and reuse of enzymes/ILs systems, are essential elements for developing clean chemical processes. By understanding structure-function relationships of biopolymers in ILs, as well as for ILs themselves (e.g. sponge-like ionic liquids, SLILs; supported ionic liquids-like phases, SILLPs, etc.), several integral green chemical processes of (bio)catalytic transformation and pure product separation are pointed out (e.g. the biocatalytic production of biodiesel in SLILs, etc.). Other developments based on DNA/ILs systems, as pathfinder studies for further technological applications in the near future, are also considered.

Efficient Decarbonylation of Furfural to Furan Catalyzed by Zirconia-Supported Palladium Clusters with Low Atomicity.

PubMed

Ishida, Tamao; Kume, Kurumi; Kinjo, Kota; Honma, Tetsuo; Nakada, Kengo; Ohashi, Hironori; Yokoyama, Takushi; Hamasaki, Akiyuki; Murayama, Haruno; Izawa, Yusuke; Utsunomiya, Masaru; Tokunaga, Makoto

2016-12-20

Decarbonylation of furfural to furan was efficiently catalyzed by ZrO 2 -supported Pd clusters in the liquid phase under a N 2 atmosphere without additives. Although Pd/C and Pd/Al 2 O 3 have frequently been used for decarbonylation, Pd/ZrO 2 exhibited superior catalytic performance compared with these conventional catalysts. Transmission electron microscopy and X-ray absorption fine structure measurements revealed that the size of the Pd particles decreased with an increase in the specific surface area of ZrO 2 . ZrO 2 with a high surface area immobilized Pd as clusters consisting of several (three to five) Pd atoms, whereas Pd aggregated to form nanoparticles on other supports such as carbon and Al 2 O 3 despite their high surface areas. The catalytic activity of Pd/ZrO 2 was enhanced with a decrease in particle size, and the smallest Pd/ZrO 2 was the most active catalyst for decarbonylation. When CeO 2 was used as the support, a decrease in Pd particle size with an increase in surface area was also observed. Single Pd atoms were deposited on CeO 2 with a high surface area, with a strong interaction through the formation of a Pd-O-Ce bond, which led to a lower catalytic activity than that of Pd/ZrO 2 . This result suggests that zero-valent small Pd clusters consisting of more than one Pd atom are the active species for the decarbonylation reaction. Recycling tests proved that Pd/ZrO 2 maintained its catalytic activity until its sixth use. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The decomposition of mixed oxide Ag2Cu2O3: Structural features and the catalytic properties in CO and C2H4 oxidation

NASA Astrophysics Data System (ADS)

Svintsitskiy, Dmitry A.; Kardash, Tatyana Yu.; Slavinskaya, Elena M.; Stonkus, Olga A.; Koscheev, Sergei V.; Boronin, Andrei I.

2018-01-01

The mixed silver-copper oxide Ag2Cu2O3 with a paramelaconite crystal structure is a promising material for catalytic applications. The as-prepared sample of Ag2Cu2O3 consisted of brick-like particles extended along the [001] direction. A combination of physicochemical techniques such as TEM, XPS and XRD was applied to investigate the structural features of this mixed silver-copper oxide. The thermal stability of Ag2Cu2O3 was investigated using in situ XRD under different reaction conditions, including a catalytic CO + O2 mixture. The first step of Ag2Cu2O3 decomposition was accompanied by the appearance of ensembles consisting of silver nanoparticles with sizes of 5-15 nm. Silver nanoparticles were strongly oriented to each other and to the surface of the initial Ag2Cu2O3 bricks. Based on the XRD data, it was shown that the release of silver occurred along the a and b axes of the paramelaconite structure. Partial decomposition of Ag2Cu2O3 accompanied by the formation of silver nanoparticles was observed during prolonged air storage under ambient conditions. The high reactivity is discussed as a reason for spontaneous decomposition during Ag2Cu2O3 storage. The full decomposition of the mixed oxide into metallic silver and copper (II) oxide took place at temperatures higher than 300 °C regardless of the nature of the reaction medium (helium, air, CO + O2). Catalytic properties of partially and fully decomposed samples of mixed silver-copper oxide were measured in low-temperature CO oxidation and C2H4 epoxidation reactions.

Catalytic recombination of nitrogen and oxygen on high-temperature reusable surface insulation

NASA Technical Reports Server (NTRS)

Scott, C. D.

1980-01-01

The energy transfer catalytic recombination coefficient for nitrogen and oxygen recombination on the surface coating of high-temperature reusable surface insulation (HRSI) is inferred from stagnation point heat flux measurements in a high-temperature dissociated arc jet flow. The resulting catalytic recombination coefficients are correlated with an Arrhenius model for convenience, and these expressions may be used to account for catalytic recombination effects in predictions of the heat flux on the HRSI thermal protection system of the Space Shuttle Orbiter during reentry flight. Analysis of stagnation point pressure and total heat balance enthalpy measurements indicates that the arc heater reservoir conditions are not in chemical equilibrium. This is contrary to what is usually assumed for arc jet analysis and indicates the need for suitable diagnostics and analyses, especially when dealing with chemical reaction phenomena such as catalytic recombination heat transfer effects.

Oxygen transport membrane system and method for transferring heat to catalytic/process reactors

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

Kelly, Sean M.; Kromer, Brian R.; Litwin, Michael M.

A method and apparatus for producing heat used in a synthesis gas production process is provided. The disclosed method and apparatus include a plurality of tubular oxygen transport membrane elements adapted to separate oxygen from an oxygen containing stream contacting the retentate side of the membrane elements. The permeated oxygen is combusted with a hydrogen containing synthesis gas stream contacting the permeate side of the tubular oxygen transport membrane elements thereby generating a reaction product stream and radiant heat. The present method and apparatus also includes at least one catalytic reactor containing a catalyst to promote the steam reforming reactionmore » wherein the catalytic reactor is surrounded by the plurality of tubular oxygen transport membrane elements. The view factor between the catalytic reactor and the plurality of tubular oxygen transport membrane elements radiating heat to the catalytic reactor is greater than or equal to 0.5« less

Oxygen transport membrane system and method for transferring heat to catalytic/process reactors

DOEpatents

Kelly, Sean M; Kromer, Brian R; Litwin, Michael M; Rosen, Lee J; Christie, Gervase Maxwell; Wilson, Jamie R; Kosowski, Lawrence W; Robinson, Charles

2014-01-07

A method and apparatus for producing heat used in a synthesis gas production is provided. The disclosed method and apparatus include a plurality of tubular oxygen transport membrane elements adapted to separate oxygen from an oxygen containing stream contacting the retentate side of the membrane elements. The permeated oxygen is combusted with a hydrogen containing synthesis gas stream contacting the permeate side of the tubular oxygen transport membrane elements thereby generating a reaction product stream and radiant heat. The present method and apparatus also includes at least one catalytic reactor containing a catalyst to promote the stream reforming reaction wherein the catalytic reactor is surrounded by the plurality of tubular oxygen transport membrane elements. The view factor between the catalytic reactor and the plurality of tubular oxygen transport membrane elements radiating heat to the catalytic reactor is greater than or equal to 0.5.

Long-range electrostatics-induced two-proton transfer captured by neutron crystallography in an enzyme catalytic site

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

Gerlits, Oksana; Wymore, Troy; Das, Amit

Neutron crystallography was used to directly locate two protons before and after a pH-induced two-proton transfer between catalytic aspartic acid residues and the hydroxy group of the bound clinical drug darunavir, located in the catalytic site of enzyme HIV-1 protease. The two-proton transfer is triggered by electrostatic effects arising from protonation state changes of surface residues far from the active site. The mechanism and pH effect are supported by quantum mechanics/molecular mechanics (QM/MM) calculations. The low-pH proton configuration in the catalytic site is deemed critical for the catalytic action of this enzyme and may apply more generally to other asparticmore » proteases. Neutrons therefore represent a superb probe to obtain structural details for proton transfer reactions in biological systems at a truly atomic level.« less

Long-range electrostatics-induced two-proton transfer captured by neutron crystallography in an enzyme catalytic site

DOE PAGES

Gerlits, Oksana; Wymore, Troy; Das, Amit; ...

2016-03-09

Neutron crystallography was used to directly locate two protons before and after a pH-induced two-proton transfer between catalytic aspartic acid residues and the hydroxy group of the bound clinical drug darunavir, located in the catalytic site of enzyme HIV-1 protease. The two-proton transfer is triggered by electrostatic effects arising from protonation state changes of surface residues far from the active site. The mechanism and pH effect are supported by quantum mechanics/molecular mechanics (QM/MM) calculations. The low-pH proton configuration in the catalytic site is deemed critical for the catalytic action of this enzyme and may apply more generally to other asparticmore » proteases. Neutrons therefore represent a superb probe to obtain structural details for proton transfer reactions in biological systems at a truly atomic level.« less

Long-Range Electrostatics-Induced Two-Proton Transfer Captured by Neutron Crystallography in an Enzyme Catalytic Site.

PubMed

Gerlits, Oksana; Wymore, Troy; Das, Amit; Shen, Chen-Hsiang; Parks, Jerry M; Smith, Jeremy C; Weiss, Kevin L; Keen, David A; Blakeley, Matthew P; Louis, John M; Langan, Paul; Weber, Irene T; Kovalevsky, Andrey

2016-04-11

Neutron crystallography was used to directly locate two protons before and after a pH-induced two-proton transfer between catalytic aspartic acid residues and the hydroxy group of the bound clinical drug darunavir, located in the catalytic site of enzyme HIV-1 protease. The two-proton transfer is triggered by electrostatic effects arising from protonation state changes of surface residues far from the active site. The mechanism and pH effect are supported by quantum mechanics/molecular mechanics (QM/MM) calculations. The low-pH proton configuration in the catalytic site is deemed critical for the catalytic action of this enzyme and may apply more generally to other aspartic proteases. Neutrons therefore represent a superb probe to obtain structural details for proton transfer reactions in biological systems at a truly atomic level. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A conceptual design of catalytic gasification fuel cell hybrid power plant with oxygen transfer membrane

NASA Astrophysics Data System (ADS)

Shi, Wangying; Han, Minfang

2017-09-01

A hybrid power generation system integrating catalytic gasification, solid oxide fuel cell (SOFC), oxygen transfer membrane (OTM) and gas turbine (GT) is established and system energy analysis is performed. In this work, the catalytic gasifier uses steam, recycled anode off-gas and pure oxygen from OTM system to gasify coal, and heated by hot cathode off-gas at the same time. A zero-dimension SOFC model is applied and verified by fitting experimental data. Thermodynamic analysis is performed to investigate the integrated system performance, and system sensitivities on anode off-gas back flow ratio, SOFC fuel utilization, temperature and pressure are discussed. Main conclusions are as follows: (1) System overall electricity efficiency reaches 60.7%(HHV) while the gasifier operates at 700 °C and SOFC at 850 °C with system pressure at 3.04 bar; (2) oxygen enriched combustion simplify the carbon-dioxide capture process, which derives CO2 of 99.2% purity, but results in a penalty of 6.7% on system electricity efficiency; (3) with SOFC fuel utilization or temperature increasing, the power output of SOFC increases while GT power output decreases, and increasing system pressure can improve both the performance of SOFC and GT.

Fluorine-doped carbon nanotubes as an efficient metal-free catalyst for destruction of organic pollutants in catalytic ozonation.

PubMed

Wang, Jing; Chen, Shuo; Quan, Xie; Yu, Hongtao

2018-01-01

Metal-free carbon materials have been presented to be potential alternatives to metal-based catalysts for heterogeneous catalytic ozonation, yet the catalytic performance still needs to be enhanced. Doping carbon with non-metallic heteroatoms (e.g., N, B, and F) could alter the electronic structure and electrochemical properties of original carbon materials, has been considered to be an effective method for improving the catalytic activity of carbon materials. Herein, fluorine-doped carbon nanotubes (F-CNTs) were synthesized via a facile method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The as-synthesized F-CNTs exhibited notably enhanced catalytic activity towards catalytic ozonation for the degradation of organic pollutants. The oxalic acid removal efficiency of optimized F-CNTs was approximately two times as much as that of pristine CNTs, and even exceeded those of four conventional metal-based catalysts (ZnO, Al 2 O 3 , Fe 2 O 3 , and MnO 2 ). The XPS and Raman studies confirmed that the covalent CF bonds were formed at the sp 3 C sites instead of sp 2 C sites on CNTs, not only resulting in high positive charge density of C atoms adjacent to F atoms, but remaining the delocalized π-system with intact carbon structure of F-CNTs, which then favored the conversion of ozone molecules (O 3 ) into reactive oxygen species (ROS) and contributed to the high oxalic acid removal efficiency. Furthermore, electron spin resonance (ESR) studies revealed that superoxide radicals (O 2 - ) and singlet oxygen ( 1 O 2 ) might be the dominant ROS that responsible for the degradation of oxalic acid in these catalytic systems. Copyright © 2017 Elsevier Ltd. All rights reserved.

Catalytic intermolecular carbon electrophile induced semipinacol rearrangement.

PubMed

Zhang, Qing-Wei; Zhang, Xiao-Bo; Li, Bao-Sheng; Xiang, Kai; Zhang, Fu-Min; Wang, Shao-Hua; Tu, Yong-Qiang

2013-02-25

A catalytic intermolecular carbon electrophile induced semipinacol rearrangement was realized and the asymmetric version was also preliminarily accomplished with 92% and 82% ee. The complex tricyclic system architecture with four continuous stereogenic centers could be achieved from simple starting materials in a single step under mild conditions.

Catalytic Hydrogenation of Organic Compounds without H2 Supply: An Electrochemical System

ERIC Educational Resources Information Center

Navarro, Daniela Maria do Amaral Ferraz; Navarro, Marcelo

2004-01-01

An experiment developed for an undergraduate organic chemistry laboratory course that can be used to introduce the catalytic hydrogenation reaction, catalysis electrochemical principles and gas chromatography is presented. The organic compounds hydrogenated by the electrocatalytic hydrogenation (ECH) process were styrene, benzaldehyde and…

The Crystal Structures of the Open and Catalytically Competent Closed Conformation of Escherichia coli Glycogen Synthase

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

Sheng, Fang; Jia, Xiaofei; Yep, Alejandra

2009-07-06

Escherichia coli glycogen synthase (EcGS, EC 2.4.1.21) is a retaining glycosyltransferase (GT) that transfers glucose from adenosine diphosphate glucose to a glucan chain acceptor with retention of configuration at the anomeric carbon. EcGS belongs to the GT-B structural superfamily. Here we report several EcGS x-ray structures that together shed considerable light on the structure and function of these enzymes. The structure of the wild-type enzyme bound to ADP and glucose revealed a 15.2 degrees overall domain-domain closure and provided for the first time the structure of the catalytically active, closed conformation of a glycogen synthase. The main chain carbonyl groupmore » of His-161, Arg-300, and Lys-305 are suggested by the structure to act as critical catalytic residues in the transglycosylation. Glu-377, previously thought to be catalytic is found on the alpha-face of the glucose and plays an electrostatic role in the active site and as a glucose ring locator. This is also consistent with the structure of the EcGS(E377A)-ADP-HEPPSO complex where the glucose moiety is either absent or disordered in the active site« less

Catalytic cracking of model compounds of bio-oil over HZSM-5 and the catalyst deactivation.

PubMed

Chen, Guanyi; Zhang, Ruixue; Ma, Wenchao; Liu, Bin; Li, Xiangping; Yan, Beibei; Cheng, Zhanjun; Wang, Tiejun

2018-08-01

The catalytic cracking upgrading reactions over HZSM-5 of different model compounds of bio-oil have been studied with a self-designed fluid catalytic cracking (FCC) equipment. Typical bio-oil model compounds, such as acetic acid, guaiacol, n-heptane, acetol and ethyl acetate, were chosen to study the products distribution, reaction pathway and deactivation of catalysts. The results showed: C 6 -C 8 aromatic hydrocarbons, C 2 -C 4 olefins, C 1 -C 5 alkanes, CO and CO 2 were the main products, and the selectivity of olefins was: ethylene>propylene>butylene. Catalyst characterization methods, such as FI-IR, TG-TPO and Raman, were used to study the deactivation mechanism of catalysts. According to the catalyst characterization results, a catalyst deactivation mechanism was proposed as follows: Firstly, the precursor which consisted of a large number of long chain saturated aliphatic hydrocarbons and a small amount CC of aromatics formed on the catalyst surface. Then the active sites of catalysts had been covered, the coke type changed from thermal coke to catalytic coke and gradually blocked the channels of the molecular sieve, which accelerated the deactivation of catalyst. Copyright © 2018 Elsevier B.V. All rights reserved.

Structural Analysis of a Family 81 Glycoside Hydrolase Implicates Its Recognition of β-1,3-Glucan Quaternary Structure.

PubMed

Pluvinage, Benjamin; Fillo, Alexander; Massel, Patricia; Boraston, Alisdair B

2017-09-05

Family 81 glycoside hydrolases (GHs), which are known to cleave β-1,3-glucans, are found in archaea, bacteria, eukaryotes, and viruses. Here we examine the structural and functional features of the GH81 catalytic module, BhGH81, from the Bacillus halodurans protein BH0236 to probe the molecular basis of β-1,3-glucan recognition and cleavage. BhGH81 displayed activity on laminarin, curdlan, and pachyman, but not scleroglucan; the enzyme also cleaved β-1,3-glucooligosaccharides as small as β-1,3-glucotriose. The crystal structures of BhGH81 in complex with various β-1,3-glucooligosaccharides revealed distorted sugars in the -1 catalytic subsite and an arrangement consistent with an inverting catalytic mechanism having a proposed conformational itinerary of 2 S 0 → 2,5 B ‡ → 5 S 1 . Notably, the architecture of the catalytic site, location of an adjacent ancillary β-1,3-glucan binding site, and the surface properties of the enzyme indicate the likely ability to recognize the double and/or triple-helical quaternary structures adopted by β-1,3-glucans. Copyright © 2017 Elsevier Ltd. All rights reserved.

Asymmetric intermolecular cobalt-catalyzed Pauson-Khand reaction using a P-stereogenic bis-phosphane.

PubMed

Orgué, Sílvia; León, Thierry; Riera, Antoni; Verdaguer, Xavier

2015-01-16

The asymmetric intermolecular and catalytic Pauson-Khand reaction has remained an elusive goal since Khand and Pauson discovered this transformation. Using a novel family of P-stereogenic phosphanes, we developed the first catalytic system with useful levels of enantioselection for the reaction of norbornadiene and trimethylsilylacetylene. The results demonstrate that Co-bisphosphane systems are sufficiently reactive and that they lead to high selectivity in the intermolecular process.

Decoupled ARX and RBF Neural Network Modeling Using PCA and GA Optimization for Nonlinear Distributed Parameter Systems.

PubMed

Zhang, Ridong; Tao, Jili; Lu, Renquan; Jin, Qibing

2018-02-01

Modeling of distributed parameter systems is difficult because of their nonlinearity and infinite-dimensional characteristics. Based on principal component analysis (PCA), a hybrid modeling strategy that consists of a decoupled linear autoregressive exogenous (ARX) model and a nonlinear radial basis function (RBF) neural network model are proposed. The spatial-temporal output is first divided into a few dominant spatial basis functions and finite-dimensional temporal series by PCA. Then, a decoupled ARX model is designed to model the linear dynamics of the dominant modes of the time series. The nonlinear residual part is subsequently parameterized by RBFs, where genetic algorithm is utilized to optimize their hidden layer structure and the parameters. Finally, the nonlinear spatial-temporal dynamic system is obtained after the time/space reconstruction. Simulation results of a catalytic rod and a heat conduction equation demonstrate the effectiveness of the proposed strategy compared to several other methods.

Magnetic diatomite(Kieselguhr)/Fe2O3/TiO2 composite as an efficient photo-Fenton system for dye degradation

NASA Astrophysics Data System (ADS)

Barbosa, Isaltino A.; Zanatta, Lucas D.; Espimpolo, Daniela M.; da Silva, Douglas L.; Nascimento, Leandro F.; Zanardi, Fabrício B.; de Sousa Filho, Paulo C.; Serra, Osvaldo A.; Iamamoto, Yassuko

2017-10-01

We explored the potential use of diatomite/Fe2O3/TiO2 composites as catalysts for heterogeneous photo-Fenton degradation of methylene blue under neutral pH. Such system consists in magnetic solids synthesized by co-precipitation with Fe2+/Fe3+ in the presence of diatomite, followed by impregnation of TiO2. The results showed that the optimal amount of the catalyst was 2.0 g L-1, since aggregation phenomena become significant above this concentration, which decreases the photodegradation activity. The catalyst is highly efficient in the degradation of methylene blue and shows an easy recovery by an external magnetic field. This allows for an effective catalyst reuse without significant loss of activity in catalytic cycles, which is a highly interesting prospect for recyclable dye degradation systems.

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

Camacho-Bunquin, Jeffrey; Shou, Heng; Aich, Payoli

An integrated atomic layer deposition-catalysis (I-ALD-CAT) tool was developed, combining an ALD manifold with a plug-flow reactor system for the synthesis of supported catalytic materials by ALD and immediate evaluation of catalyst reactivity using gas-phase probe reactions. The I-ALD-CAT system can deliver gaseous reagents comprised of 12 different metal ALD precursors, 4 oxidizing or reducing agents, and 4 catalytic reaction feeds to either of the two plug-flow reactors. The system can employ reactor pressures and temperatures in the range of 10-3–1 bar and 300–1000 K, respectively. The instrument is also equipped with a gas chromatograph and a mass spectrometer unitmore » for the detection and quantification of volatile species from ALD and catalytic reactions. In this report, we demonstrate the use of the I-ALD-CAT tool for the ALD of platinum active sites and Al2O3 overcoats, and evaluation of catalyst propylene hydrogenation activity.« less

Structure-guided systems-level engineering of oxidation-prone methionine residues in catalytic domain of an alkaline α-amylase from Alkalimonas amylolytica for significant improvement of both oxidative stability and catalytic efficiency.

PubMed

Yang, Haiquan; Liu, Long; Shin, Hyun-dong; Li, Jianghua; Du, Guocheng; Chen, Jian

2013-01-01

High oxidative stability and catalytic efficiency are required for the alkaline α-amylases to keep the enzymatic performance under the harsh conditions in detergent industries. In this work, we attempted to significantly improve both the oxidative stability and catalytic efficiency of an alkaline α-amylase from Alkalimonas amylolytica by engineering the five oxidation-prone methionine residues around the catalytic domain via a systematic approach. Specifically, based on the tertiary structure analysis, five methionines (Met 145, Met 214, Met 229, Met 247 and Met 317) were individually substituted with oxidation-resistant threonine, isoleucine and alaline, respectively. Among the created 15 mutants, 7 mutants M145A, M145I, M214A, M229A, M229T, M247T and M317I showed significantly enhanced oxidative stability or catalytic efficiency. In previous work, we found that the replacement of M247 with leucine could significantly improve the oxidative stability. Thus, these 8 positive mutants (M145A, M145I, M214A, M229A, M229T, M247T, M247L and M317I) were used to conduct the second round of combinational mutations. Among the constructed 85 mutants (25 two-point mutants, 36 three-point mutants, 16 four-point mutants and 8 five-point mutants), the mutant M145I-214A-229T-247T-317I showed a 5.4-fold increase in oxidative stability and a 3.0-fold increase in catalytic efficiency. Interestingly, the specific activity, alkaline stability and thermal stability of this mutant were also increased. The increase of salt bridge and hydrogen bonds around the catalytic domain contributed to the significantly improved catalytic efficiency and stability, as revealed by the three-dimensional structure model of wild-type alkaline α-amylase and its mutant M145I-214A-229T-247T-317I. With the significantly improved oxidative stability and catalytic efficiency, the mutant M145I-214A-229T-247T-317I has a great potential as a detergent additive, and this structure-guided systems engineering strategy may be useful for the protein engineering of the other microbial enzymes to fulfill industrial requirements.

Assessment of the Vapor Phase Catalytic Ammonia Removal (VPCAR) Technology at the MSFC ECLS Test Facility

NASA Technical Reports Server (NTRS)

Tomes, Kristin; Long, David; Carter, Layne; Flynn, Michael

2007-01-01

The Vapor Phase Catalytic Ammonia. Removal (VPCAR) technology has been previously discussed as a viable option for. the Exploration Water Recovery System. This technology integrates a phase change process with catalytic oxidation in the vapor phase to produce potable water from exploration mission wastewaters. A developmental prototype VPCAR was designed, built and tested under funding provided by a National Research. Announcement (NRA) project. The core technology, a Wiped Film Rotating Device (WFRD) was provided by Water Reuse Technologies under the NRA, whereas Hamilton Sundstrand Space Systems International performed the hardware integration and acceptance test. of the system. Personnel at the-Ames Research Center performed initial systems test of the VPCAR using ersatz solutions. To assess the viability of this hardware for Exploration. Life Support (ELS) applications, the hardware has been modified and tested at the MSFC ECLS Test facility. This paper summarizes the hardware modifications and test results and provides an assessment of this technology for the ELS application.

Automated X-ray quality control of catalytic converters

NASA Astrophysics Data System (ADS)

Shashishekhar, N.; Veselitza, D.

2017-02-01

Catalytic converters are devices attached to the exhaust system of automobile or other engines to eliminate or substantially reduce polluting emissions. They consist of coated substrates enclosed in a stainless steel housing. The substrate is typically made of ceramic honeycombs; however stainless steel foil honeycombs are also used. The coating is usually a slurry of alumina, silica, rare earth oxides and platinum group metals. The slurry also known as the wash coat is applied to the substrate in two doses, one on each end of the substrate; in some cases multiple layers of coating are applied. X-ray imaging is used to inspect the applied coating depth on a substrate to confirm compliance with quality requirements. Automated image analysis techniques are employed to measure the coating depth from the X-ray image. Coating depth is assessed by analysis of attenuation line profiles in the image. Edge detection algorithms with noise reduction and outlier rejection are used to calculate the coating depth at a specified point along an attenuation line profile. Quality control of the product is accomplished using several attenuation line profile regions for coating depth measurements, with individual pass or fail criteria specified for each region.

Surveying Rubisco Diversity and Temperature Response to Improve Crop Photosynthetic Efficiency.

PubMed

Orr, Douglas J; Alcântara, André; Kapralov, Maxim V; Andralojc, P John; Carmo-Silva, Elizabete; Parry, Martin A J

2016-10-01

The threat to global food security of stagnating yields and population growth makes increasing crop productivity a critical goal over the coming decades. One key target for improving crop productivity and yields is increasing the efficiency of photosynthesis. Central to photosynthesis is Rubisco, which is a critical but often rate-limiting component. Here, we present full Rubisco catalytic properties measured at three temperatures for 75 plants species representing both crops and undomesticated plants from diverse climates. Some newly characterized Rubiscos were naturally "better" compared to crop enzymes and have the potential to improve crop photosynthetic efficiency. The temperature response of the various catalytic parameters was largely consistent across the diverse range of species, though absolute values showed significant variation in Rubisco catalysis, even between closely related species. An analysis of residue differences among the species characterized identified a number of candidate amino acid substitutions that will aid in advancing engineering of improved Rubisco in crop systems. This study provides new insights on the range of Rubisco catalysis and temperature response present in nature, and provides new information to include in models from leaf to canopy and ecosystem scale. © 2016 American Society of Plant Biologists. All Rights Reserved.

Incorporation of catalytic dehydrogenation into Fischer-Tropsch synthesis to lower carbon dioxide emissions

DOEpatents

Huffman, Gerald P

2012-09-18

A method for producing liquid fuels includes the steps of gasifying a starting material selected from a group consisting of coal, biomass, carbon nanotubes and mixtures thereof to produce a syngas, subjecting that syngas to Fischer-Tropsch synthesis (FTS) to produce a hyrdrocarbon product stream, separating that hydrocarbon product stream into C1-C4 hydrocarbons and C5+ hydrocarbons to be used as liquid fuels and subjecting the C1-C4 hydrocarbons to catalytic dehydrogenation (CDH) to produce hydrogen and carbon nanotubes. The hydrogen produced by CDH is recycled to be mixed with the syngas incident to the FTS reactor in order to raise the hydrogen to carbon monoxide ratio of the syngas to values of 2 or higher, which is required to produce liquid hydrocarbon fuels. This is accomplished with little or no production of carbon dioxide, a greenhouse gas. The carbon is captured in the form of a potentially valuable by-product, multi-walled carbon nanotubes (MWNT), while huge emissions of carbon dioxide are avoided and very large quantities of water employed for the water-gas shift in traditional FTS systems are saved.

Nanoplasmonically Engineered Interfaces on Amorphous TiO2 for Highly Efficient Photocatalysis in Hydrogen Evolution.

PubMed

Liang, Huijun; Meng, Qiuxia; Wang, Xiaobing; Zhang, Hucheng; Wang, Jianji

2018-04-25

The nanoplasmonic metal-driven photocatalytic activity depends heavily on the spacing between metal nanoparticles (NPs) and semiconductors, and this work shows that ethylene glycol (EG) is an ideal candidate for interface spacer. Controlling the synthetic systems at pH 3, the composite of Ag NPs with EG-stabilized amorphous TiO 2 (Ag/TiO 2 -3) was synthesized by the facile light-induced reduction. It is verified that EG spacers can set up suitable geometric arrangement in the composite: the twin hydroxyls act as stabilizers to bind Ag NPs and TiO 2 together and the nonconductive alkyl chains consisting only of two CH 2 are able to separate the two building blocks completely and also provide the shortest channels for an efficient transfer of radiation energies to reach TiO 2 . Employed as photocatalysts in hydrogen evolution under visible light, amorphous TiO 2 hardly exhibits the catalytic activity due to high defect density, whereas Ag/TiO 2 -3 represents a remarkably high catalytic efficiency. The enhancement mechanism of the reaction rate is proposed by the analysis of the compositional, structural, and optical properties from a series of Ag/TiO 2 composites.

Catalytic ignition model in a monolithic reactor with in-depth reaction

NASA Technical Reports Server (NTRS)

Tien, Ta-Ching; Tien, James S.

1990-01-01

Two transient models have been developed to study the catalytic ignition in a monolithic catalytic reactor. The special feature in these models is the inclusion of thermal and species structures in the porous catalytic layer. There are many time scales involved in the catalytic ignition problem, and these two models are developed with different time scales. In the full transient model, the equations are non-dimensionalized by the shortest time scale (mass diffusion across the catalytic layer). It is therefore accurate but is computationally costly. In the energy-integral model, only the slowest process (solid heat-up) is taken as nonsteady. It is approximate but computationally efficient. In the computations performed, the catalyst is platinum and the reactants are rich mixtures of hydrogen and oxygen. One-step global chemical reaction rates are used for both gas-phase homogeneous reaction and catalytic heterogeneous reaction. The computed results reveal the transient ignition processes in detail, including the structure variation with time in the reactive catalytic layer. An ignition map using reactor length and catalyst loading is constructed. The comparison of computed results between the two transient models verifies the applicability of the energy-integral model when the time is greater than the second largest time scale of the system. It also suggests that a proper combined use of the two models can catch all the transient phenomena while minimizing the computational cost.

40 CFR 60.107 - Reporting and recordkeeping requirements.

Code of Federal Regulations, 2011 CFR

2011-07-01

... in the gases discharged to the atmosphere from any fluid catalytic cracking unit catalyst regenerator... concurrent with a startup, shutdown, or malfunction of the fluid catalytic cracking unit or control system... cracking unit catalyst regenerator for which the owner or operator seeks to comply with § 60.104(b)(1) is...

40 CFR 60.107 - Reporting and recordkeeping requirements.

Code of Federal Regulations, 2010 CFR

2010-07-01

... in the gases discharged to the atmosphere from any fluid catalytic cracking unit catalyst regenerator... concurrent with a startup, shutdown, or malfunction of the fluid catalytic cracking unit or control system... cracking unit catalyst regenerator for which the owner or operator seeks to comply with § 60.104(b)(1) is...

An Experimental Study of a Catalytic Combustor for an Expendable Turbojet Engine

DTIC Science & Technology

1978-03-01

automobiles have catalytic converters in their exhaust systems for oxidizing unburned hydrocarbons, carbon monoxide, etc., to produce a cleaner exhaust. A...1 ratio for automobiles . Other noble metals are sometimes used, in varying ratio and loading (amount of catalyst. per area) configerations (Ref 7). 2

Biobased methacrylic acid via selective catalytic decarboxylation of itaconic acid

USDA-ARS?s Scientific Manuscript database

We report a bio-based route to methacrylic acid via selective decarboxylation of itaconic acid utilizing catalytic ruthenium carbonyl propionate in an aqueous solvent system. High selectivity (>90%) was achieved at low catalyst loading (0.1 mol %) with high substrate concentration (5.5 M) at low tem...

Catalytic domains of the LAR and CD45 protein tyrosine phosphatases from Escherichia coli expression systems: Purification and characterization for specificity and mechanism

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

Cho, Hyeongjin; Ramer, S.E.; Itoh, Michiyasu

1992-01-14

The cytoplasmic domains of two human transmembrane protein tyrosine phosphatases (PTPases), LAR and CD45, have been expressed in Escherichia coli, purified to near-homogeneity, and compared for catalytic efficiency toward several phosphotyrosine-containing peptide substrates. A 615-residue LAR fragment (LAR-D1D2) containing both tandemly repeated PTPase domains shows almost identical specific activity and high catalytic efficiency as the 40-kDa single-domain LAR-D1 fragment, consistent with a single functional active site in the 70-kDa LAR-D1D2 enzyme. A 90-kDa fragment of the human leukocyte CD45 PTPase, containing two similar tandemly repeated PTPase domains, shows parallel specificity to LAR-D1 and LAR-D1D2 with a high k{sub cat}/K{sub M}more » value for a phosphotyrosyl undecapeptide. Sufficient purified LAR-D1 and LAR-D1D2 PTPases were available to demonstrate enzymatic exchange of {sup 18}O from {sup 18}O{sub 4} inorganic phosphate into H{sub 2} {sup 16}O at rates of {approximately}1 {times} 10{sup {minus}2} s{sup {minus}1}. The oxygen-18 exchange probably proceeds via a phosphoenzyme intermediate. Brief incubation of all three PTPase fragments with a ({sup 32}P)phosphotyrosyl peptide substrate prior to quench with SDS sample buffer and gel electrophoresis led to autoradiographic detection of {sup 32}P-labeled enzymes. Pulse/chase studies on the LAR {sup 32}P-enzyme showed turnover of the labeled phosphoryl group.« less

In Situ and ex Situ Catalytic Pyrolysis of Pine in a Bench-Scale Fluidized Bed Reactor System

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

Iisa, Kristiina; French, Richard J.; Orton, Kellene A.

In situ and ex situ catalytic pyrolysis were compared in a system with two 2-in. bubbling fluidized bed reactors. Pine was pyrolyzed in the system with a catalyst, HZSM-5 with a silica-to-alumina ratio of 30, placed either in the first (pyrolysis) reactor or the second (upgrading) reactor. Both the pyrolysis and upgrading temperatures were 500 degrees C, and the weight hourly space velocity was 1.1 h -1. Five catalytic cycles were completed in each experiment. The catalytic cycles were continued until oxygenates in the vapors became dominant. The catalyst was then oxidized, after which a new catalytic cycle was begun.more » The in situ configuration gave slightly higher oil yield but also higher oxygen content than the ex situ configuration, which indicates that the catalyst deactivated faster in the in situ configuration than the ex situ configuration. Analysis of the spent catalysts confirmed higher accumulation of metals in the in situ experiment. In all experiments, the organic oil mass yields varied between 14 and 17% and the carbon efficiencies between 20 and 25%. The organic oxygen concentrations in the oils were 16-18%, which represented a 45% reduction compared to corresponding noncatalytic pyrolysis oils prepared in the same fluidized bed reactor system. GC/MS analysis showed the oils to contain one- to four-ring aromatic hydrocarbons and a variety of oxygenates (phenols, furans, benzofurans, methoxyphenols, naphthalenols, indenols). Lastly, high fractions of oxygen were rejected as water, CO, and CO 2, which indicates the importance of dehydration, decarbonylation, and decarboxylation reactions. Light gases were the major sources of carbon losses, followed by char and coke.« less

In Situ and ex Situ Catalytic Pyrolysis of Pine in a Bench-Scale Fluidized Bed Reactor System

DOE PAGES

Iisa, Kristiina; French, Richard J.; Orton, Kellene A.; ...

2016-02-03

In situ and ex situ catalytic pyrolysis were compared in a system with two 2-in. bubbling fluidized bed reactors. Pine was pyrolyzed in the system with a catalyst, HZSM-5 with a silica-to-alumina ratio of 30, placed either in the first (pyrolysis) reactor or the second (upgrading) reactor. Both the pyrolysis and upgrading temperatures were 500 degrees C, and the weight hourly space velocity was 1.1 h -1. Five catalytic cycles were completed in each experiment. The catalytic cycles were continued until oxygenates in the vapors became dominant. The catalyst was then oxidized, after which a new catalytic cycle was begun.more » The in situ configuration gave slightly higher oil yield but also higher oxygen content than the ex situ configuration, which indicates that the catalyst deactivated faster in the in situ configuration than the ex situ configuration. Analysis of the spent catalysts confirmed higher accumulation of metals in the in situ experiment. In all experiments, the organic oil mass yields varied between 14 and 17% and the carbon efficiencies between 20 and 25%. The organic oxygen concentrations in the oils were 16-18%, which represented a 45% reduction compared to corresponding noncatalytic pyrolysis oils prepared in the same fluidized bed reactor system. GC/MS analysis showed the oils to contain one- to four-ring aromatic hydrocarbons and a variety of oxygenates (phenols, furans, benzofurans, methoxyphenols, naphthalenols, indenols). Lastly, high fractions of oxygen were rejected as water, CO, and CO 2, which indicates the importance of dehydration, decarbonylation, and decarboxylation reactions. Light gases were the major sources of carbon losses, followed by char and coke.« less

Method For Selective Catalytic Reduction Of Nitrogen Oxides

DOEpatents

Mowery-Evans, Deborah L.; Gardner, Timothy J.; McLaughlin, Linda I.

2005-02-15

A method for catalytically reducing nitrogen oxide compounds (NO.sub.x, defined as nitric oxide, NO, +nitrogen dioxide, NO.sub.2) in a gas by a material comprising a base metal consisting essentially of CuO and Mn, and oxides of Mn, on an activated metal hydrous metal oxide support, such as HMO:Si. A promoter, such as tungsten oxide or molybdenum oxide, can be added and has been shown to increase conversion efficiency. This method provides good conversion of NO.sub.x to N.sub.2, good selectivity, good durability, resistance to SO.sub.2 aging and low toxicity compared with methods utilizing vanadia-based catalysts.

Method for selective catalytic reduction of nitrogen oxides

DOEpatents

Mowery-Evans, Deborah L [Broomfield, CO; Gardner, Timothy J [Albuquerque, NM; McLaughlin, Linda I [Albuquerque, NM

2005-02-15

A method for catalytically reducing nitrogen oxide compounds (NO.sub.x, defined as nitric oxide, NO, +nitrogen dioxide, NO.sub.2) in a gas by a material comprising a base metal consisting essentially of CuO and Mn, and oxides of Mn, on an activated metal hydrous metal oxide support, such as HMO:Si. A promoter, such as tungsten oxide or molybdenum oxide, can be added and has been shown to increase conversion efficiency. This method provides good conversion of NO.sub.x to N.sub.2, good selectivity, good durability, resistance to SO.sub.2 aging and low toxicity compared with methods utilizing vanadia-based catalysts.

Rare isotope studies involving catalytic oxidation of CO over platinum-tin oxide

NASA Technical Reports Server (NTRS)

Upchurch, Billy T.; Wood, George M., Jr.; Hess, Robert V.; Hoyt, Ronald F.

1987-01-01

Results of studies utilizing normal and rare oxygen isotopes in the catalytic oxidation of carbon monoxide over a platinum-tin oxide catalyst substrate are presented. Chemisorption of labeled carbon monoxide on the catalyst followed by thermal desorption yielded a carbon dioxide product with an oxygen-18 composition consistent with the formation of a carbonate-like intermediate in the chemisorption process. The efficacy of a method developed for the oxygen-18 labeling of the platinum-tin oxide catalyst surface for use in closed cycle pulsed care isotope carbon dioxide lasers is demonstrated for the equivalent of 10 to the 6th power pulses at 10 pulses per second.

Bifunctional catalytic electrode

NASA Technical Reports Server (NTRS)

Cisar, Alan (Inventor); Murphy, Oliver J. (Inventor); Clarke, Eric (Inventor)

2005-01-01

The present invention relates to an oxygen electrode for a unitized regenerative hydrogen-oxygen fuel cell and the unitized regenerative fuel cell having the oxygen electrode. The oxygen electrode contains components electrocatalytically active for the evolution of oxygen from water and the reduction of oxygen to water, and has a structure that supports the flow of both water and gases between the catalytically active surface and a flow field or electrode chamber for bulk flow of the fluids. The electrode has an electrocatalyst layer and a diffusion backing layer interspersed with hydrophilic and hydrophobic regions. The diffusion backing layer consists of a metal core having gas diffusion structures bonded to the metal core.

Active and Recyclable Catalytic Synthesis of Indoles by Reductive Cyclization of 2-(2-Nitroaryl)acetonitriles in the Presence of Co-Rh Heterobimetallic Nanoparticles with Atmospheric Hydrogen under Mild Conditions.

PubMed

Choi, Isaac; Chung, Hyunho; Park, Jang Won; Chung, Young Keun

2016-11-04

A cobalt-rhodium heterobimetallic nanoparticle-catalyzed reductive cyclization of 2-(2-nitroaryl)acetonitriles to indoles has been achieved. The tandem reaction proceeds without any additives under the mild conditions (1 atm H 2 and 25 °C). This procedure could be scaled up to the gram scale. The catalytic system is significantly stable under these reaction conditions and could be reused more than ten times without loss of catalytic activity.

Structure-function relationships in Gan42B, an intracellular GH42 β-galactosidase from Geobacillus stearothermophilus.

PubMed

Solomon, Hodaya V; Tabachnikov, Orly; Lansky, Shifra; Salama, Rachel; Feinberg, Hadar; Shoham, Yuval; Shoham, Gil

2015-12-01

Geobacillus stearothermophilus T-6 is a Gram-positive thermophilic soil bacterium that contains a battery of degrading enzymes for the utilization of plant cell-wall polysaccharides, including xylan, arabinan and galactan. A 9.4 kb gene cluster has recently been characterized in G. stearothermophilus that encodes a number of galactan-utilization elements. A key enzyme of this degradation system is Gan42B, an intracellular GH42 β-galactosidase capable of hydrolyzing short β-1,4-galactosaccharides into galactose units, making it of high potential for various biotechnological applications. The Gan42B monomer is made up of 686 amino acids, and based on sequence homology it was suggested that Glu323 is the catalytic nucleophile and Glu159 is the catalytic acid/base. In the current study, the detailed three-dimensional structure of wild-type Gan42B (at 2.45 Å resolution) and its catalytic mutant E323A (at 2.50 Å resolution), as determined by X-ray crystallography, are reported. These structures demonstrate that the three-dimensional structure of the Gan42B monomer generally correlates with the overall fold observed for GH42 proteins, consisting of three main domains: an N-terminal TIM-barrel domain, a smaller mixed α/β domain, and the smallest all-β domain at the C-terminus. The two catalytic residues are located in the TIM-barrel domain in a pocket-like active site such that their carboxylic functional groups are about 5.3 Å from each other, consistent with a retaining mechanism. The crystal structure demonstrates that Gan42B is a homotrimer, resembling a flowerpot in general shape, in which each monomer interacts with the other two to form a cone-shaped tunnel cavity in the centre. The cavity is ∼35 Å at the wide opening and ∼5 Å at the small opening and ∼40 Å in length. The active sites are situated at the interfaces between the monomers, so that every two neighbouring monomers participate in the formation of each of the three active sites of the trimer. They are located near the small opening of the cone tunnel, all facing the centre of the cavity. The biological relevance of this trimeric structure is supported by independent results obtained from gel-permeation chromatography. These data and their comparison to the structural data of related GH42 enzymes are used for a more general discussion concerning structure-activity aspects in this GH family.

Get Beyond Limits: From Colloidal Tectonics Concept to the Engineering of Eco-friendly Catalytic Systems

NASA Astrophysics Data System (ADS)

Leclercq, Loïc

2018-05-01

The interactions between two or more molecules or colloidal particles can be used to obtain a variety of self-assembled systems called supramolecules or supracolloids. There is a clear, but neglected, convergence between these two fields. Indeed, the packing of molecules into colloidal or supracolloidal particles emerges as a smart solution to build an infinite variety of reversible systems with predictable properties. In this respect, the molecular building blocks are called “tectons” whereas “colloidal tectonics” describes the spontaneous formation of (supra)colloidal structures using tectonic subunits. As a consequence, a bottom-up edification is allowed from tectons into (supra)colloidal particles with higher degrees of organization. These (supra)colloidal systems can be very useful to obtain catalysts with tunable amphiphilic properties. In this perspective, an overview of colloidal tectonics concept is presented as well as its use for the design of new, smart and flexible catalytic systems. Finally, the advantages of these catalytic devices are discussed and the perspective of future developments is addressed especially in the context of “green chemistry”.

Get Beyond Limits: From Colloidal Tectonics Concept to the Engineering of Eco-Friendly Catalytic Systems

PubMed Central

Leclercq, Loïc

2018-01-01

The interactions between two or more molecules or colloidal particles can be used to obtain a variety of self-assembled systems called supramolecules or supracolloids. There is a clear, but neglected, convergence between these two fields. Indeed, the packing of molecules into colloidal or supracolloidal particles emerges as a smart solution to build an infinite variety of reversible systems with predictable properties. In this respect, the molecular building blocks are called “tectons” whereas “colloidal tectonics” describes the spontaneous formation of (supra)colloidal structures using tectonic subunits. As a consequence, a bottom-up edification is allowed from tectons into (supra)colloidal particles with higher degrees of organization (Graphical Abstract). These (supra)colloidal systems can be very useful to obtain catalysts with tunable amphiphilic properties. In this perspective, an overview of colloidal tectonics concept is presented as well as its use for the design of new, smart, and flexible catalytic systems. Finally, the advantages of these catalytic devices are discussed and the perspective of future developments is addressed especially in the context of “green chemistry.”

Combined hydrothermal liquefaction and catalytic hydrothermal gasification system and process for conversion of biomass feedstocks

DOEpatents

Elliott, Douglas C.; Neuenschwander, Gary G.; Hart, Todd R.

2017-09-12

A combined hydrothermal liquefaction (HTL) and catalytic hydrothermal gasification (CHG) system and process are described that convert various biomass-containing sources into separable bio-oils and aqueous effluents that contain residual organics. Bio-oils may be converted to useful bio-based fuels and other chemical feedstocks. Residual organics in HTL aqueous effluents may be gasified and converted into medium-BTU product gases and directly used for process heating or to provide energy.

Selective catalytic reduction system and process for treating NOx emissions using a palladium and rhodium or ruthenium catalyst

DOEpatents

Sobolevskiy, Anatoly [Orlando, FL; Rossin, Joseph A [Columbus, OH; Knapke, Michael J [Columbus, OH

2011-07-12

A process for the catalytic reduction of nitrogen oxides (NOx) in a gas stream (29) in the presence of H.sub.2 is provided. The process comprises contacting the gas stream with a catalyst system (38) comprising zirconia-silica washcoat particles (41), a pre-sulfated zirconia binder (44), and a catalyst combination (40) comprising palladium and at least one of rhodium, ruthenium, or a mixture of ruthenium and rhodium.

Metal and Metal Oxide Interactions and Their Catalytic Consequences for Oxygen Reduction Reaction

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

Jia, Qingying; Ghoshal, Shraboni; Li, Jingkun

2017-06-01

Many industrial catalysts are composed of metal particles supported on metal oxides (MMO). It is known that the catalytic activity of MMO materials is governed by metal and metal oxide interactions (MMOI), but how to optimize MMO systems via manipulation of MMOI remains unclear, due primarily to the ambiguous nature of MMOI. Herein, we develop a Pt/NbOx/C system with tunable structural and electronic properties via a modified arc plasma deposition method. We unravel the nature of MMOI by characterizing this system under reactive conditions utilizing combined electrochemical, microscopy, and in situ spectroscopy. We show that Pt interacts with the Nbmore » in unsaturated NbOx owing to the oxygen deficiency in the MMO interface, whereas Pt interacts with the O in nearly saturated NbOx, and further interacts with Nb when the oxygen atoms penetrate into the Pt cluster at elevated potentials. While the Pt–Nb interactions do not benefit the inherent activity of Pt toward oxygen reduction reaction (ORR), the Pt–O interactions improve the ORR activity by shortening the Pt–Pt bond distance. Pt donates electrons to NbOx in both Pt–Nb and Pt–O cases. The resultant electron efficiency stabilizes low-coordinated Pt sites, hereby stabilizing small Pt particles. This determines the two characteristic features of MMO systems: dispersion of small metal particles and high catalytic durability. These findings contribute to our understandings of MMO catalytic systems.« less

Anatomy of F1-ATPase powered rotation.

PubMed

Martin, James L; Ishmukhametov, Robert; Hornung, Tassilo; Ahmad, Zulfiqar; Frasch, Wayne D

2014-03-11

F1-ATPase, the catalytic complex of the ATP synthase, is a molecular motor that can consume ATP to drive rotation of the γ-subunit inside the ring of three αβ-subunit heterodimers in 120° power strokes. To elucidate the mechanism of ATPase-powered rotation, we determined the angular velocity as a function of rotational position from single-molecule data collected at 200,000 frames per second with unprecedented signal-to-noise. Power stroke rotation is more complex than previously understood. This paper reports the unexpected discovery that a series of angular accelerations and decelerations occur during the power stroke. The decreases in angular velocity that occurred with the lower-affinity substrate ITP, which could not be explained by an increase in substrate-binding dwells, provides direct evidence that rotation depends on substrate binding affinity. The presence of elevated ADP concentrations not only increased dwells at 35° from the catalytic dwell consistent with competitive product inhibition but also decreased the angular velocity from 85° to 120°, indicating that ADP can remain bound to the catalytic site where product release occurs for the duration of the power stroke. The angular velocity profile also supports a model in which rotation is powered by Van der Waals repulsive forces during the final 85° of rotation, consistent with a transition from F1 structures 2HLD1 and 1H8E (Protein Data Bank).

Anatomy of F1-ATPase powered rotation

PubMed Central

Martin, James L.; Ishmukhametov, Robert; Hornung, Tassilo; Ahmad, Zulfiqar; Frasch, Wayne D.

2014-01-01

F1-ATPase, the catalytic complex of the ATP synthase, is a molecular motor that can consume ATP to drive rotation of the γ-subunit inside the ring of three αβ-subunit heterodimers in 120° power strokes. To elucidate the mechanism of ATPase-powered rotation, we determined the angular velocity as a function of rotational position from single-molecule data collected at 200,000 frames per second with unprecedented signal-to-noise. Power stroke rotation is more complex than previously understood. This paper reports the unexpected discovery that a series of angular accelerations and decelerations occur during the power stroke. The decreases in angular velocity that occurred with the lower-affinity substrate ITP, which could not be explained by an increase in substrate-binding dwells, provides direct evidence that rotation depends on substrate binding affinity. The presence of elevated ADP concentrations not only increased dwells at 35° from the catalytic dwell consistent with competitive product inhibition but also decreased the angular velocity from 85° to 120°, indicating that ADP can remain bound to the catalytic site where product release occurs for the duration of the power stroke. The angular velocity profile also supports a model in which rotation is powered by Van der Waals repulsive forces during the final 85° of rotation, consistent with a transition from F1 structures 2HLD1 and 1H8E (Protein Data Bank). PMID:24567403

Deletion of a non-catalytic region increases the enzymatic activity of a β-agarase from Flammeovirga sp. MY04

NASA Astrophysics Data System (ADS)

Han, Wenjun; Gu, Jingyan; Liu, Huihui; Li, Fuchuan; Wu, Zhihong; Li, Yuezhong

2015-10-01

A Glycoside hydrolase (GH) typically contains one catalytic module and varied non-catalytic regions (NCRs). However, effects of the NCRs to the catalytic modules remain mostly unclear except the carbohydrate-binding modules (CBMs). AgaG4 is a GH16 endo- β-agarase of the agarolytic marine bacterium Flammeovirga sp. MY04. The enzyme consists of an extra sugar-binding peptide within the catalytic module, with no predictable CBMs but function-unknown sequences in the NCR, which is a new characteristic of agarase sequences. In this study, we deleted the NCR sequence, a 140-amino acid peptide at the C-terminus and expressed the truncated gene, agaG4-T140, in Escherichia coli. After purification and refolding, the truncated agarase rAgaG4-T140 retained the same catalytic temperature and pH value as rAgaG4. Using combined fluorescent labeling, HPLC and MS/MS techniques, we identified the end-products of agarose degradation by rAgaG4-T140 as neoagarotetraose and neoagarohexaose, with a final molar ratio of 1.53:1 and a conversion ratio of approximately 70%, which were similar to those of rAgaG4. However, the truncated agarase rAgaG4-T140 markedly decreased in protein solubility by 15 times and increased in enzymatic activities by 35 times. The oligosaccharide production of rAgaG4-T140 was approximately 25 times the weight of that produced by equimolar rAgaG4. This study provides some insights into the influences of NCR on the biochemical characteristics of agarase AgaG4 and implies some new strategies to improve the properties of a GH enzyme.

Differential catalytic promiscuity of the alkaline phosphatase superfamily bimetallo core reveals mechanistic features underlying enzyme evolution

DOE PAGES

Sunden, Fanny; AlSadhan, Ishraq; Lyubimov, Artem; ...

2017-10-25

Members of enzyme superfamilies specialize in different reactions but often exhibit catalytic promiscuity for one another's reactions, consistent with catalytic promiscuity as an important driver in the evolution of new enzymes. Wanting to understand how catalytic promiscuity and other factors may influence evolution across a superfamily, we turned to the well-studied alkaline phosphatase (AP) superfamily, comparing three of its members, two evolutionarily distinct phosphatases and a phosphodiesterase. Here, we mutated distinguishing active-site residues to generate enzymes that had a common Zn 2+ bimetallo core but little sequence similarity and different auxiliary domains. We then tested the catalytic capabilities of thesemore » pruned enzymes with a series of substrates. A substantial rate enhancement of ~1011-fold for both phosphate mono- and diester hydrolysis by each enzyme indicated that the Zn 2+ bimetallo core is an effective mono/di-esterase generalist and that the bimetallo cores were not evolutionarily tuned to prefer their cognate reactions. In contrast, our pruned enzymes were ineffective sulfatases, and this limited promiscuity may have provided a driving force for founding the distinct one-metal-ion branch that contains all known AP superfamily sulfatases. Finally, our pruned enzymes exhibited 10 7–10 8-fold phosphotriesterase rate enhancements, despite absence of such enzymes within the AP superfamily. We speculate that the superfamily active-site architecture involved in nucleophile positioning prevents accommodation of the additional triester substituent. Overall, we suggest that catalytic promiscuity, and the ease or difficulty of remodeling and building onto existing protein scaffolds, have greatly influenced the course of enzyme evolution. Uncovering principles and properties of enzyme function, promiscuity, and repurposing provides lessons for engineering new enzymes.« less

Differential catalytic promiscuity of the alkaline phosphatase superfamily bimetallo core reveals mechanistic features underlying enzyme evolution

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

Sunden, Fanny; AlSadhan, Ishraq; Lyubimov, Artem

Members of enzyme superfamilies specialize in different reactions but often exhibit catalytic promiscuity for one another's reactions, consistent with catalytic promiscuity as an important driver in the evolution of new enzymes. Wanting to understand how catalytic promiscuity and other factors may influence evolution across a superfamily, we turned to the well-studied alkaline phosphatase (AP) superfamily, comparing three of its members, two evolutionarily distinct phosphatases and a phosphodiesterase. Here, we mutated distinguishing active-site residues to generate enzymes that had a common Zn 2+ bimetallo core but little sequence similarity and different auxiliary domains. We then tested the catalytic capabilities of thesemore » pruned enzymes with a series of substrates. A substantial rate enhancement of ~1011-fold for both phosphate mono- and diester hydrolysis by each enzyme indicated that the Zn 2+ bimetallo core is an effective mono/di-esterase generalist and that the bimetallo cores were not evolutionarily tuned to prefer their cognate reactions. In contrast, our pruned enzymes were ineffective sulfatases, and this limited promiscuity may have provided a driving force for founding the distinct one-metal-ion branch that contains all known AP superfamily sulfatases. Finally, our pruned enzymes exhibited 10 7–10 8-fold phosphotriesterase rate enhancements, despite absence of such enzymes within the AP superfamily. We speculate that the superfamily active-site architecture involved in nucleophile positioning prevents accommodation of the additional triester substituent. Overall, we suggest that catalytic promiscuity, and the ease or difficulty of remodeling and building onto existing protein scaffolds, have greatly influenced the course of enzyme evolution. Uncovering principles and properties of enzyme function, promiscuity, and repurposing provides lessons for engineering new enzymes.« less

Structural Analysis of a Family 101 Glycoside Hydrolase in Complex with Carbohydrates Reveals Insights into Its Mechanism.

PubMed

Gregg, Katie J; Suits, Michael D L; Deng, Lehua; Vocadlo, David J; Boraston, Alisdair B

2015-10-16

O-Linked glycosylation is one of the most abundant post-translational modifications of proteins. Within the secretory pathway of higher eukaryotes, the core of these glycans is frequently an N-acetylgalactosamine residue that is α-linked to serine or threonine residues. Glycoside hydrolases in family 101 are presently the only known enzymes to be able to hydrolyze this glycosidic linkage. Here we determine the high-resolution structures of the catalytic domain comprising a fragment of GH101 from Streptococcus pneumoniae TIGR4, SpGH101, in the absence of carbohydrate, and in complex with reaction products, inhibitor, and substrate analogues. Upon substrate binding, a tryptophan lid (residues 724-WNW-726) closes on the substrate. The closing of this lid fully engages the substrate in the active site with Asp-764 positioned directly beneath C1 of the sugar residue bound within the -1 subsite, consistent with its proposed role as the catalytic nucleophile. In all of the bound forms of the enzyme, however, the proposed catalytic acid/base residue was found to be too distant from the glycosidic oxygen (>4.3 Å) to serve directly as a general catalytic acid/base residue and thereby facilitate cleavage of the glycosidic bond. These same complexes, however, revealed a structurally conserved water molecule positioned between the catalytic acid/base and the glycosidic oxygen. On the basis of these structural observations we propose a new variation of the retaining glycoside hydrolase mechanism wherein the intervening water molecule enables a Grotthuss proton shuttle between Glu-796 and the glycosidic oxygen, permitting this residue to serve as the general acid/base catalytic residue. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI

DOE PAGES

Ratzloff, Michael W.; Artz, Jacob H.; Mulder, David W.; ...

2018-05-23

The [FeFe]-hydrogenases ([FeFe] H 2ases) catalyze reversible H 2 activation at the H-cluster, which is composed of a [4Fe-4S] H subsite linked by a cysteine thiolate to a bridged, organometallic [2Fe-2S] ([2Fe] H) subsite. Profoundly different geometric models of the H-cluster redox states that orchestrate the electron/proton transfer steps of H 2 bond activation have been proposed. We have examined this question in the [FeFe] H 2ase I from Clostridium acetobutylicum (CaI) by Fourier-transform infrared (FTIR) spectroscopy with temperature annealing and H/D isotope exchange to identify the relevant redox states and define catalytic transitions. One-electron reduction of H ox ledmore » to formation of H redH + ([4Fe-4S] H 2+-Fe I-Fe I) and H red' ([4Fe-4S] H 1+-Fe II-Fe I), with both states characterized by low frequency μ-CO IR modes consistent with a fully bridged [2Fe] H. Similar μ-CO IR modes were also identified for H redH + of the [FeFe] H 2ase from Chlamydomonas reinhardtii (CrHydA1). The CaI proton-transfer variant C298S showed enrichment of an H/D isotope-sensitive μ-CO mode, a component of the hydride bound H-cluster IR signal, H hyd. Equilibrating CaI with increasing amounts of NaDT, and probed at cryogenic temperatures, showed H redH + was converted to H hyd. Over an increasing temperature range from 10 to 260 K catalytic turnover led to loss of Hhyd and appearance of H ox, consistent with enzymatic turnover and H 2 formation. The results show for CaI that the μ-CO of [2Fe] H remains bridging for all of the 'H red' states and that H redH + is on pathway to H hyd and H 2 evolution in the catalytic mechanism. Here, this provides a blueprint for designing small molecule catalytic analogs« less

CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI

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

Ratzloff, Michael W.; Artz, Jacob H.; Mulder, David W.

The [FeFe]-hydrogenases ([FeFe] H 2ases) catalyze reversible H 2 activation at the H-cluster, which is composed of a [4Fe-4S] H subsite linked by a cysteine thiolate to a bridged, organometallic [2Fe-2S] ([2Fe] H) subsite. Profoundly different geometric models of the H-cluster redox states that orchestrate the electron/proton transfer steps of H 2 bond activation have been proposed. We have examined this question in the [FeFe] H 2ase I from Clostridium acetobutylicum (CaI) by Fourier-transform infrared (FTIR) spectroscopy with temperature annealing and H/D isotope exchange to identify the relevant redox states and define catalytic transitions. One-electron reduction of H ox ledmore » to formation of H redH + ([4Fe-4S] H 2+-Fe I-Fe I) and H red' ([4Fe-4S] H 1+-Fe II-Fe I), with both states characterized by low frequency μ-CO IR modes consistent with a fully bridged [2Fe] H. Similar μ-CO IR modes were also identified for H redH + of the [FeFe] H 2ase from Chlamydomonas reinhardtii (CrHydA1). The CaI proton-transfer variant C298S showed enrichment of an H/D isotope-sensitive μ-CO mode, a component of the hydride bound H-cluster IR signal, H hyd. Equilibrating CaI with increasing amounts of NaDT, and probed at cryogenic temperatures, showed H redH + was converted to H hyd. Over an increasing temperature range from 10 to 260 K catalytic turnover led to loss of Hhyd and appearance of H ox, consistent with enzymatic turnover and H 2 formation. The results show for CaI that the μ-CO of [2Fe] H remains bridging for all of the 'H red' states and that H redH + is on pathway to H hyd and H 2 evolution in the catalytic mechanism. Here, this provides a blueprint for designing small molecule catalytic analogs« less

CO-Bridged H-Cluster Intermediates in the Catalytic Mechanism of [FeFe]-Hydrogenase CaI.

PubMed

Ratzloff, Michael W; Artz, Jacob H; Mulder, David W; Collins, Reuben T; Furtak, Thomas E; King, Paul W

2018-06-20

The [FeFe]-hydrogenases ([FeFe] H 2 ases) catalyze reversible H 2 activation at the H-cluster, which is composed of a [4Fe-4S] H subsite linked by a cysteine thiolate to a bridged, organometallic [2Fe-2S] ([2Fe] H ) subsite. Profoundly different geometric models of the H-cluster redox states that orchestrate the electron/proton transfer steps of H 2 bond activation have been proposed. We have examined this question in the [FeFe] H 2 ase I from Clostridium acetobutylicum (CaI) by Fourier-transform infrared (FTIR) spectroscopy with temperature annealing and H/D isotope exchange to identify the relevant redox states and define catalytic transitions. One-electron reduction of H ox led to formation of H red H + ([4Fe-4S] H 2+ -Fe I -Fe I ) and H red ' ([4Fe-4S] H 1+ -Fe II -Fe I ), with both states characterized by low frequency μ-CO IR modes consistent with a fully bridged [2Fe] H . Similar μ-CO IR modes were also identified for H red H + of the [FeFe] H 2 ase from Chlamydomonas reinhardtii (CrHydA1). The CaI proton-transfer variant C298S showed enrichment of an H/D isotope-sensitive μ-CO mode, a component of the hydride bound H-cluster IR signal, H hyd . Equilibrating CaI with increasing amounts of NaDT, and probed at cryogenic temperatures, showed H red H + was converted to H hyd . Over an increasing temperature range from 10 to 260 K catalytic turnover led to loss of H hyd and appearance of H ox , consistent with enzymatic turnover and H 2 formation. The results show for CaI that the μ-CO of [2Fe] H remains bridging for all of the "H red " states and that H red H + is on pathway to H hyd and H 2 evolution in the catalytic mechanism. These results provide a blueprint for designing small molecule catalytic analogs.

Scope and mechanism in palladium-catalyzed isomerizations of highly substituted allylic, homoallylic, and alkenyl alcohols.

PubMed

Larionov, Evgeny; Lin, Luqing; Guénée, Laure; Mazet, Clément

2014-12-03

Herein we report the palladium-catalyzed isomerization of highly substituted allylic alcohols and alkenyl alcohols by means of a single catalytic system. The operationally simple reaction protocol is applicable to a broad range of substrates and displays a wide functional group tolerance, and the products are usually isolated in high chemical yield. Experimental and computational mechanistic investigations provide complementary and converging evidence for a chain-walking process consisting of repeated migratory insertion/β-H elimination sequences. Interestingly, the catalyst does not dissociate from the substrate in the isomerization of allylic alcohols, whereas it disengages during the isomerization of alkenyl alcohols when additional substituents are present on the alkyl chain.

Eco-Friendly Magnetic Iron Oxide Pillared Montmorillonite for Advanced Catalytic Degradation of Dichlorophenol

EPA Science Inventory

Eco-friendly pillared montmorillonites, in which the pillars consist of iron oxide are expected to have interesting and unusual magnetic properties that are applicable for environmental decontamination. Completely “green” and effective composite was synthesized using mild reactio...

Structural and biochemical characterization of glycoside hydrolase family 79 β-glucuronidase from Acidobacterium capsulatum.

PubMed

Michikawa, Mari; Ichinose, Hitomi; Momma, Mitsuru; Biely, Peter; Jongkees, Seino; Yoshida, Makoto; Kotake, Toshihisa; Tsumuraya, Yoichi; Withers, Stephen G; Fujimoto, Zui; Kaneko, Satoshi

2012-04-20

We present the first structure of a glycoside hydrolase family 79 β-glucuronidase from Acidobacterium capsulatum, both as a product complex with β-D-glucuronic acid (GlcA) and as its trapped covalent 2-fluoroglucuronyl intermediate. This enzyme consists of a catalytic (β/α)(8)-barrel domain and a β-domain with irregular Greek key motifs that is of unknown function. The enzyme showed β-glucuronidase activity and trace levels of β-glucosidase and β-xylosidase activities. In conjunction with mutagenesis studies, these structures identify the catalytic residues as Glu(173) (acid base) and Glu(287) (nucleophile), consistent with the retaining mechanism demonstrated by (1)H NMR analysis. Glu(45), Tyr(243), Tyr(292)-Gly(294), and Tyr(334) form the catalytic pocket and provide substrate discrimination. Consistent with this, the Y292A mutation, which affects the interaction between the main chains of Gln(293) and Gly(294) and the GlcA carboxyl group, resulted in significant loss of β-glucuronidase activity while retaining the side activities at wild-type levels. Likewise, although the β-glucuronidase activity of the Y334F mutant is ~200-fold lower (k(cat)/K(m)) than that of the wild-type enzyme, the β-glucosidase activity is actually 3 times higher and the β-xylosidase activity is only 2.5-fold lower than the equivalent parameters for wild type, consistent with a role for Tyr(334) in recognition of the C6 position of GlcA. The involvement of Glu(45) in discriminating against binding of the O-methyl group at the C4 position of GlcA is revealed in the fact that the E45D mutant hydrolyzes PNP-β-GlcA approximately 300-fold slower (k(cat)/K(m)) than does the wild-type enzyme, whereas 4-O-methyl-GlcA-containing oligosaccharides are hydrolyzed only 7-fold slower.

Structural and Biochemical Characterization of Glycoside Hydrolase Family 79 β-Glucuronidase from Acidobacterium capsulatum

PubMed Central

Michikawa, Mari; Ichinose, Hitomi; Momma, Mitsuru; Biely, Peter; Jongkees, Seino; Yoshida, Makoto; Kotake, Toshihisa; Tsumuraya, Yoichi; Withers, Stephen G.; Fujimoto, Zui; Kaneko, Satoshi

2012-01-01

We present the first structure of a glycoside hydrolase family 79 β-glucuronidase from Acidobacterium capsulatum, both as a product complex with β-d-glucuronic acid (GlcA) and as its trapped covalent 2-fluoroglucuronyl intermediate. This enzyme consists of a catalytic (β/α)8-barrel domain and a β-domain with irregular Greek key motifs that is of unknown function. The enzyme showed β-glucuronidase activity and trace levels of β-glucosidase and β-xylosidase activities. In conjunction with mutagenesis studies, these structures identify the catalytic residues as Glu173 (acid base) and Glu287 (nucleophile), consistent with the retaining mechanism demonstrated by 1H NMR analysis. Glu45, Tyr243, Tyr292–Gly294, and Tyr334 form the catalytic pocket and provide substrate discrimination. Consistent with this, the Y292A mutation, which affects the interaction between the main chains of Gln293 and Gly294 and the GlcA carboxyl group, resulted in significant loss of β-glucuronidase activity while retaining the side activities at wild-type levels. Likewise, although the β-glucuronidase activity of the Y334F mutant is ∼200-fold lower (kcat/Km) than that of the wild-type enzyme, the β-glucosidase activity is actually 3 times higher and the β-xylosidase activity is only 2.5-fold lower than the equivalent parameters for wild type, consistent with a role for Tyr334 in recognition of the C6 position of GlcA. The involvement of Glu45 in discriminating against binding of the O-methyl group at the C4 position of GlcA is revealed in the fact that the E45D mutant hydrolyzes PNP-β-GlcA approximately 300-fold slower (kcat/Km) than does the wild-type enzyme, whereas 4-O-methyl-GlcA-containing oligosaccharides are hydrolyzed only 7-fold slower. PMID:22367201

SUSTAINABLE CATALYTIC TREATMENT OF WASTE ION EXCHANGE BRINES FOR REUSE DURING OXYANION TREATMENT IN DRINKING WATER

EPA Science Inventory

We expect the proposed work to result in the design of full-scale treatment systems for catalytic brine treatment that provides a more economical and sustainable option for removing mixtures of oxyanions from drinking water at small water treatment utilities. This will allo...

Adaptive Model Predictive Control of Diesel Engine Selective Catalytic Reduction (SCR) Systems

ERIC Educational Resources Information Center

McKinley, Thomas L.

2009-01-01

Selective catalytic reduction or SCR is coming into worldwide use for diesel engine emissions reduction for on- and off-highway vehicles. These applications are characterized by broad operating range as well as rapid and unpredictable changes in operating conditions. Significant nonlinearity, input and output constraints, and stringent performance…

Catalytic Converters Maintain Air Quality in Mines

NASA Technical Reports Server (NTRS)

2014-01-01

At Langley Research Center, engineers developed a tin-oxide based washcoat to prevent oxygen buildup in carbon dioxide lasers used to detect wind shears. Airflow Catalyst Systems Inc. of Rochester, New York, licensed the technology and then adapted the washcoat for use as a catalytic converter to treat the exhaust from diesel mining equipment.

Dynamic restructuring drives catalytic activity on nanoporous gold–silver alloy catalysts

DOE PAGES

Zugic, Branko; Wang, Lucun; Heine, Christian; ...

2016-12-19

Bimetallic, nanostructured materials hold promise for improving catalyst activity and selectivity, yet little is known about the dynamic compositional and structural changes that these systems undergo during pretreatment that leads to efficient catalyst function. Here we use ozone-activated silver–gold alloys in the form of nanoporous gold as a case study to demonstrate the dynamic behaviour of bimetallic systems during activation to produce a functioning catalyst. We show that it is these dynamic changes that give rise to the observed catalytic activity. Advanced in situ electron microscopy and X-ray photoelectron spectroscopy are used to demonstrate that major restructuring and compositional changesmore » occur along the path to catalytic function for selective alcohol oxidation. Transient kinetic measurements correlate the restructuring to three types of oxygen on the surface. The direct influence of changes in surface silver concentration and restructuring at the nanoscale on oxidation activity is demonstrated. Finally, our results demonstrate that characterization of these dynamic changes is necessary to unlock the full potential of bimetallic catalytic materials.« less

Preparation of Pd-Loaded Hierarchical FAU Membranes and Testing in Acetophenone Hydrogenation.

PubMed

Molinari, Raffaele; Lavorato, Cristina; Mastropietro, Teresa F; Argurio, Pietro; Drioli, Enrico; Poerio, Teresa

2016-03-22

Pd-loaded hierarchical FAU (Pd-FAU) membranes, containing an intrinsic secondary non-zeolitic (meso)porosity, were prepared and tested in the catalytic transfer hydrogenation of acetophenone (AP) to produce phenylethanol (PE), an industrially relevant product. The best operating conditions were preliminarily identified by testing different solvents and organic hydrogen donors in a batch hydrogenation process where micron-sized FAU seeds were employed as catalyst support. Water as solvent and formic acid as hydrogen source resulted to be the best choice in terms of conversion for the catalytic hydrogenation of AP, providing the basis for the design of a green and sustainable process. The best experimental conditions were selected and applied to the Pd-loaded FAU membrane finding enhanced catalytic performance such as a five-fold higher productivity than with the unsupported Pd-FAU crystals (11.0 vs. 2.2 mgproduct gcat(-1)·h(-1)). The catalytic performance of the membrane on the alumina support was also tested in a tangential flow system obtaining a productivity higher than that of the batch system (22.0 vs. 11.0 mgproduct gcat(-1)·h(-1)).

Dynamic restructuring drives catalytic activity on nanoporous gold–silver alloy catalysts

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

Zugic, Branko; Wang, Lucun; Heine, Christian

Bimetallic, nanostructured materials hold promise for improving catalyst activity and selectivity, yet little is known about the dynamic compositional and structural changes that these systems undergo during pretreatment that leads to efficient catalyst function. Here we use ozone-activated silver–gold alloys in the form of nanoporous gold as a case study to demonstrate the dynamic behaviour of bimetallic systems during activation to produce a functioning catalyst. We show that it is these dynamic changes that give rise to the observed catalytic activity. Advanced in situ electron microscopy and X-ray photoelectron spectroscopy are used to demonstrate that major restructuring and compositional changesmore » occur along the path to catalytic function for selective alcohol oxidation. Transient kinetic measurements correlate the restructuring to three types of oxygen on the surface. The direct influence of changes in surface silver concentration and restructuring at the nanoscale on oxidation activity is demonstrated. Finally, our results demonstrate that characterization of these dynamic changes is necessary to unlock the full potential of bimetallic catalytic materials.« less

A competing, dual mechanism for catalytic direct benzene hydroxylation from combined experimental-DFT studies† †Electronic supplementary information (ESI) available: For experimental catalytic details and mechanistic procedures, including GC and GC-MS traces, additional figures (Fig. S1–S25), computational data including Cartesian coordinates and energies of all stationary points reported in the text. See DOI: 10.1039/c7sc02898a

PubMed Central

Vilella, Laia; Conde, Ana

2017-01-01

A dual mechanism for direct benzene catalytic hydroxylation is described. Experimental studies and DFT calculations have provided a mechanistic explanation for the acid-free, TpxCu-catalyzed hydroxylation of benzene with hydrogen peroxide (Tpx = hydrotrispyrazolylborate ligand). In contrast with other catalytic systems that promote this transformation through Fenton-like pathways, this system operates through a copper-oxyl intermediate that may interact with the arene ring following two different, competitive routes: (a) electrophilic aromatic substitution, with the copper-oxyl species acting as the formal electrophile, and (b) the so-called rebound mechanism, in which the hydrogen is abstracted by the Cu–O moiety prior to the C–O bond formation. Both pathways contribute to the global transformation albeit to different extents, the electrophilic substitution route seeming to be largely favoured. PMID:29619184

Processing and synthesis of multi-metallic nano oxide ceramics via liquid-feed flame spray pyrolysis

NASA Astrophysics Data System (ADS)

Azurdia, Jose Antonio

The liquid-feed flame spray pyrolysis (LF-FSP) process aerosolizes metal-carboxylate precursors dissolved in alcohol with oxygen and combusts them at >1500°C. The products are quenched rapidly (˜10s msec) to < 400°C. By selecting the appropriate precursor mixtures, the compositions of the resulting oxide nanopowders can be tailored easily, which lends itself to combinatorial studies of systems facilitating material property optimization. The resulting nanopowders typically consist of single crystal particles with average particle sizes (APS) < 35 nm, specific surface areas (SSA) of 20-60 m2/g and spherical morphology. LF-FSP provides access to novel single phase nanopowders, known phases at compositions outside their published phase diagrams, intimate mixing at nanometer length scales in multi metallic oxide nanopowders, and control of stoichiometry to ppm levels. The materials produced may exhibit unusual properties including structural, catalytic, and photonic ones and lower sintering temperatures. Prior studies used LF-FSP to produce MgAl2O4 spinel for applications in transparent armor and IR radomes. In these studies, a stable spinel structure with a (MgO)0.1(Al2O3)0.9 composition well outside the known phase field was observed. The work reported here extends this observation to two other spinel systems: Al2O3-NiO, Al2O3-CoOx; followed by three series of transition metal binary oxides, NiO-CoO, NiO-MoO3, NiO-CuO. The impetus to study spinels derives both from the fact that a number of them are known transparent ceramics, but also others offer high SSAs coupled with unusual phases that suggest potentially novel catalytic materials. Because LF-FSP provides access to any composition, comprehensive studies of the entire tie-lines were conducted rather than just compositions of value for catalytic applications. Initial efforts established baseline properties for the nano aluminate spinels, then three binary transition metal oxide sets (Ni-Co, Ni-Mo and Ni-Cu) known for their catalytic properties. These materials then serve as baseline studies for ternary systems, such as Al:(Ni-Co)O, or Al(Ni-Cu)O likely to offer superior catalytic properties because of the relatively high SSA Al2O3. The final chapter returns to photonic materials, in the MgO-Y2O 3 system targeting transparent ceramics through select compositions along the tie-line. The work presented here builds on the MgAl2O 4 spinel material and continues to develop the processing techniques required to achieve transparent nano-grained ceramic materials. Thus the overall goal of this dissertation was to systematically produce novel nano-oxide materials and characterized their material properties. The first chapters focus on solid solutions at low Ni or Co amounts that form phase pure spinels outside the expected composition range, at 21-22 mol % NiO and CoO. Additionally, (NiO)0.22(Al2O3) 0.78 was found to be very stable, as it did not convert to alpha-Al 2O3 plus cubic-NiO on heating to 1200°C for 10 h. The last chapter is a preliminary step toward identifying optimal Y 2O3-MgO powders that can be transparent ceramics. Ball milling led to much higher adsorption of surface species. Preliminary sintering studies of the this system showed that vacuum has the largest effect on lowering the temperature of maximum shrinkage rate by ≤ 80°C.

Catalytic membrane reactor for water and wastewater treatment

NASA Astrophysics Data System (ADS)

Heng, Samuel

A double membrane reactor was fabricated and assessed for continuous treatment of water containing organic contaminants by ozonation. This innovative reactor consisted of a zeolite membrane prepared on the inner surface of a porous a-alumina support, which served as water selective extractor and active contactor, and a porous stainless membrane which was the ozone gas diffuser. The coupling of membrane separation and chemical oxidation was found to be highly beneficial to both processes. The total organic carbon (TOC) removal rate at the retentate was enhanced by up to 2.2 times, as compared to membrane ozonation. Simultaneously, clean water (< 2 mg C.L-1 ) was consistently produced on the permeate side, using a feed solution containing up to 1000 mg C.L-1, while the retentate was concentrated and treated. Most significantly, the addition of an adsorbing material, as a bed or a coated layer, onto the pores of the membrane support, was shown to further enhance TOC degradation, permeated TOC concentration, permeate flux, and moreover, ozone yield. The achievements of this project included: (1) The development of a novel low-temperature zeolite membrane activation method that generates consistently high quality membranes (i.e. high reproducibility and fewer defects). (2) The demonstration that gamma-alumina and gamma-alumina supported catalysts do not have significant activity and that the TOC removal enhancement usually observed during catalytic ozonation was due primarily to the contribution of adsorption and metal leaching. Thermogravimetric analysis (TGA) and elemental analysis (EA) of the spent catalyst showed that, during catalytic ozonation, oxygenated by-products of increased adsorbability were concentrated onto the gamma-alumina contactor, and were subsequently degraded. (3) The development of a method for coating high surface area gamma-alumina layers onto the grains of zeolite membrane support used as the active membrane contactor.

Synthesis and catalytic activity of electrospun NiO/NiCo2O4 nanotubes for CO and acetaldehyde oxidation

NASA Astrophysics Data System (ADS)

Kim, Il Hee; Lee, Hyerim; Yu, Areum; Jeong, Jae Hwan; Lee, Youngmi; Kim, Myung Hwa; Lee, Chongmok; Dok Kim, Young

2018-04-01

NiO/NiCo2O4 nanotubes with a diameter of approximately 100 nm are synthesized using Ni and Co precursors via electro-spinning and subsequent calcination processes. The tubular structure is confirmed via transmission electron microscopy imaging, whereas the structures and elemental compositions of the nanotubes are determined using x-ray diffraction, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. N2 adsorption isotherm data reveal that the surface of the nanotubes consists of micropores, thereby resulting in a significantly higher surface area (˜20 m2 g-1) than expected for a flat-surface structure (<15 m2 g-1). Herein, we present a study of the catalytic activity of our novel NiO/NiCo2O4 nanotubes for CO and acetaldehyde oxidation. The catalytic activity of NiO/NiCo2O4 is superior to Pt below 100 °C for CO oxidation. For acetaldehyde oxidation, the total oxidation activity of NiO/NiCo2O4 for acetaldehyde is comparable with that of Pt. Coexistence of many under-coordinated Co and Ni active sites in our structure is suggested be related to the high catalytic activity. It is suggested that our novel NiO/NiCo2O4 tubular structures with surface microporosity can be of interest for a variety of applications, including the catalytic oxidation of harmful gases.

Splitting of the O–O bond at the heme-copper catalytic site of respiratory oxidases

PubMed Central

Poiana, Federica; von Ballmoos, Christoph; Gonska, Nathalie; Blomberg, Margareta R. A.; Ädelroth, Pia; Brzezinski, Peter

2017-01-01

Heme-copper oxidases catalyze the four-electron reduction of O2 to H2O at a catalytic site that is composed of a heme group, a copper ion (CuB), and a tyrosine residue. Results from earlier experimental studies have shown that the O–O bond is cleaved simultaneously with electron transfer from a low-spin heme (heme a/b), forming a ferryl state (PR; Fe4+=O2−, CuB2+–OH−). We show that with the Thermus thermophilus ba3 oxidase, at low temperature (10°C, pH 7), electron transfer from the low-spin heme b to the catalytic site is faster by a factor of ~10 (τ ≅ 11 μs) than the formation of the PR ferryl (τ ≅110 μs), which indicates that O2 is reduced before the splitting of the O–O bond. Application of density functional theory indicates that the electron acceptor at the catalytic site is a high-energy peroxy state [Fe3+–O−–O−(H+)], which is formed before the PR ferryl. The rates of heme b oxidation and PR ferryl formation were more similar at pH 10, indicating that the formation of the high-energy peroxy state involves proton transfer within the catalytic site, consistent with theory. The combined experimental and theoretical data suggest a general mechanism for O2 reduction by heme-copper oxidases. PMID:28630929

Synthesis and catalytic activity of electrospun NiO/NiCo2O4 nanotubes for CO and acetaldehyde oxidation.

PubMed

Kim, Il Hee; Lee, Hyerim; Yu, Areum; Jeong, Jae Hwan; Lee, Youngmi; Kim, Myung Hwa; Lee, Chongmok; Kim, Young Dok

2018-04-27

NiO/NiCo 2 O 4 nanotubes with a diameter of approximately 100 nm are synthesized using Ni and Co precursors via electro-spinning and subsequent calcination processes. The tubular structure is confirmed via transmission electron microscopy imaging, whereas the structures and elemental compositions of the nanotubes are determined using x-ray diffraction, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. N 2 adsorption isotherm data reveal that the surface of the nanotubes consists of micropores, thereby resulting in a significantly higher surface area (∼20 m 2 g -1 ) than expected for a flat-surface structure (<15 m 2 g -1 ). Herein, we present a study of the catalytic activity of our novel NiO/NiCo 2 O 4 nanotubes for CO and acetaldehyde oxidation. The catalytic activity of NiO/NiCo 2 O 4 is superior to Pt below 100 °C for CO oxidation. For acetaldehyde oxidation, the total oxidation activity of NiO/NiCo 2 O 4 for acetaldehyde is comparable with that of Pt. Coexistence of many under-coordinated Co and Ni active sites in our structure is suggested be related to the high catalytic activity. It is suggested that our novel NiO/NiCo 2 O 4 tubular structures with surface microporosity can be of interest for a variety of applications, including the catalytic oxidation of harmful gases.

Propitious Dendritic Cu2O-Pt Nanostructured Anodes for Direct Formic Acid Fuel Cells.

PubMed

El-Nagar, Gumaa A; Mohammad, Ahmad M; El-Deab, Mohamed S; El-Anadouli, Bahgat E

2017-06-14

This study introduces a novel competent dendritic copper oxide-platinum nanocatalyst (nano-Cu 2 O-Pt) immobilized onto a glassy carbon (GC) substrate for formic acid (FA) electro-oxidation (FAO); the prime reaction in the anodic compartment of direct formic acid fuel cells (DFAFCs). Interestingly, the proposed catalyst exhibited an outstanding improvement for FAO compared to the traditional platinum nanoparticles (nano-Pt) modified GC (nano-Pt/GC) catalyst. This was evaluated from steering the reaction mechanism toward the desired direct route producing carbon dioxide (CO 2 ); consistently with mitigating the other undesired indirect pathway producing carbon monoxide (CO); the potential poison deteriorating the catalytic activity of typical Pt-based catalysts. Moreover, the developed catalyst showed a reasonable long-term catalytic stability along with a significant lowering in onset potential of direct FAO that ultimately reduces the polarization and amplifies the fuel cell's voltage. The observed catalytic enhancement was believed to originate bifunctionally; while nano-Pt represented the base for the FA adsorption, nanostructured copper oxide (nano-Cu 2 O) behaved as a catalytic mediator facilitating the charge transfer during FAO and providing the oxygen atmosphere inspiring the poison's (CO) oxidation at relatively lower potential. Surprisingly, moreover, nano-Cu 2 O induced a surface retrieval of nano-Pt active sites by capturing the poisoning CO via "a spillover mechanism" to renovate the Pt surface for the direct FAO. Finally, the catalytic tolerance of the developed catalyst toward halides' poisoning was discussed.

Mechanistic and kinetic study on the catalytic hydrolysis of COS in small clusters of sulfuric acid.

PubMed

Li, Kai; Song, Xin; Zhu, Tingting; Wang, Chi; Sun, Xin; Ning, Ping; Tang, Lihong

2018-01-01

The catalytic hydrolysis of carbonyl sulfide (COS) and the effect of small clusters of H 2 O and H 2 SO 4 have been studied by theoretical calculations. The addition of H 2 SO 4 could increase the enthalpy change (ΔH<0) and decrease relative energy of products (relative energy<0), resulting in hydrolysis reaction changed from an endothermic reaction to an exothermic reaction. Further, H 2 SO 4 decreases the energy barrier by 5.25 kcal/mol, and it enhances the catalytic hydrolysis through the hydrogen transfer effect. The (COS + H 2 SO 4 -H 2 O) reaction has the lowest energy barrier of 29.97 kcal/mol. Although an excess addition of H 2 O and H 2 SO 4 increases the energy barrier, decreases the catalytic hydrolysis, which is consistent with experimental observations. The order of the energy barriers for the three reactions from low to high are as follows: COS + H 2 SO 4 -H 2 O < COS + H 2 O + H 2 SO 4 -H 2 O < COS + H 2 O+(H 2 SO 4 ) 2 . Kinetic simulations show that the addition of H 2 SO 4 can increase the reaction rate constants. Consequently, adding an appropriate amount of sulfuric acid promotes the catalytic hydrolysis of COS both kinetically and thermodynamically. Copyright © 2017 Elsevier Ltd. All rights reserved.

Molecular system identification for enzyme directed evolution and design

NASA Astrophysics Data System (ADS)

Guan, Xiangying; Chakrabarti, Raj

2017-09-01

The rational design of chemical catalysts requires methods for the measurement of free energy differences in the catalytic mechanism for any given catalyst Hamiltonian. The scope of experimental learning algorithms that can be applied to catalyst design would also be expanded by the availability of such methods. Methods for catalyst characterization typically either estimate apparent kinetic parameters that do not necessarily correspond to free energy differences in the catalytic mechanism or measure individual free energy differences that are not sufficient for establishing the relationship between the potential energy surface and catalytic activity. Moreover, in order to enhance the duty cycle of catalyst design, statistically efficient methods for the estimation of the complete set of free energy differences relevant to the catalytic activity based on high-throughput measurements are preferred. In this paper, we present a theoretical and algorithmic system identification framework for the optimal estimation of free energy differences in solution phase catalysts, with a focus on one- and two-substrate enzymes. This framework, which can be automated using programmable logic, prescribes a choice of feasible experimental measurements and manipulated input variables that identify the complete set of free energy differences relevant to the catalytic activity and minimize the uncertainty in these free energy estimates for each successive Hamiltonian design. The framework also employs decision-theoretic logic to determine when model reduction can be applied to improve the duty cycle of high-throughput catalyst design. Automation of the algorithm using fluidic control systems is proposed, and applications of the framework to the problem of enzyme design are discussed.

An alternative synthetic approach for efficient catalytic conversion of syngas to ethanol.

PubMed

Yue, Hairong; Ma, Xinbin; Gong, Jinlong

2014-05-20

Ethanol is an attractive end product and a versatile feedstock because a widespread market exists for its commercial use as a fuel additive or a potential substitute for gasoline. Currently, ethanol is produced primarily by fermentation of biomass-derived sugars, particularly those containing six carbons, but coproducts 5-carbon sugars and lignin remain unusable. Another major process for commercial production of ethanol is hydration of ethylene over solid acidic catalysts, yet not sustainable considering the depletion of fossil fuels. Catalytic conversion of synthetic gas (CO + H2) could produce ethanol in large quantities. However, the direct catalytic conversion of synthetic gas to ethanol remains challenging, and no commercial process exists as of today although the research has been ongoing for the past 90 years, since such the process suffers from low yield and poor selectivity due to slow kinetics of the initial C-C bond formation and fast chain growth of the C2 intermediates. This Account describes recent developments in an alternative approach for the synthesis of ethanol via synthetic gas. This process is an integrated technology consisting of the coupling of CO with methanol to form dimethyl oxalate and the subsequent hydrogenation to yield ethanol. The byproduct of the second step (methanol) can be separated and used in circulation as the feedstock for the coupling step. The coupling reaction of carbon monoxide for producing dimethyl oxalate takes place under moderate reaction conditions with high selectivity (∼95%), which ideally leads to a self-closing, nonwaste, catalytic cycling process. This Account also summarizes the progress on the development of copper-based catalysts for the hydrogenation reaction with remarkable efficiencies and stability. The unique lamellar structure and the cooperative effect between surface Cu(0) and Cu(+) species are responsible for the activity of the catalyst with high yield of ethanol (∼91%). The understanding of nature of valence states of Cu could also guide the rational design of Cu-based catalysts for other similar reactions, particularly for hydrogenation catalytic systems. In addition, by regulating the reaction condition and the surface structure of the catalysts, the products in the hydrogenation steps, such as ethanol, methyl glycolate, and ethylene glycol, could be tuned efficiently. This synthetic approach enables a more sustainable ethanol, methyl glycolate, and ethylene glycol synthesis in industry and greatly reduces the dependence on petroleum resources and the emission of the greenhouse gas.

Transient and sustained elementary flux mode networks on a catalytic string-based chemical evolution model.

PubMed

Pereira, José A

2014-08-01

Theoretical models designed to test the metabolism-first hypothesis for prebiotic evolution have yield strong indications about the hypothesis validity but could sometimes use a more extensive identification between model objects and real objects towards a more meaningful interpretation of results. In an attempt to go in that direction, the string-based model SSE ("steady state evolution") was developed, where abstract molecules (strings) and catalytic interaction rules are based on some of the most important features of carbon compounds in biological chemistry. The system is open with a random inflow and outflow of strings but also with a permanent string food source. Although specific catalysis is a key aspect of the model, used to define reaction rules, the focus is on energetics rather than kinetics. Standard energy change tables were constructed and used with standard formation reactions to track energy flows through the interpretation of equilibrium constant values. Detection of metabolic networks on the reaction system was done with elementary flux mode (EFM) analysis. The combination of these model design and analysis options enabled obtaining metabolic and catalytic networks showing several central features of biological metabolism, some more clearly than in previous models: metabolic networks with stepwise synthesis, energy coupling, catalysts regulation, SN2 coupling, redox coupling, intermediate cycling, coupled inverse pathways (metabolic cycling), autocatalytic cycles and catalytic cascades. The results strongly suggest that the main biological metabolism features, including the genotype-phenotype interpretation, are caused by the principles of catalytic systems and are prior to modern genetic systems principles. It also gives further theoretical support to the thesis that the basic features of biologic metabolism are a consequence of the time evolution of a random catalyst search working on an open system with a permanent food source. The importance of the food source characteristics and evolutionary possibilities are discussed. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

A Finite-Rate-Catalytic Model For Hypersonic Flows Informed By Molecular Dynamics

NASA Astrophysics Data System (ADS)

Schwartzentruber, T. E.; Valentini, P.; Norman, P.; Sorensen, C.

2011-05-01

The implementation of a finite-rate catalytic (FRC) wall boundary condition within a general 3D unstructured CFD solver is described. A set of one-step gas-surface chemical equations and atomistic parameters that deter- mine the reaction rates must be prescribed as input to the model. The chemical rate equations are solved at each wall face in the CFD simulation and result in a net production of species at the wall. In order for a finite- rate gas-surface reaction model to be consistent at equilibrium, it is determined that not all forward and back- ward rates can be specified arbitrarily. Provided that the forward rates for each surface recombination are as- signed, the backward rates must be determined using equilibrium constants that are consistent with the gas- phase chemistry model and thermodynamics. Reactive molecular dynamics (MD) simulations are performed us- ing the ReaxFFSiO potential to investigate oxygen-silica interactions. β-quartz and amorphous SiO2 surfaces are accommodated to a high temperature gas via MD simulation and reach a steady-state surface coverage. In addition to stable surface reconstructions a number of active sites are observed on which recombination occurs. Single collision MD simulations are performed where gas-phase oxygen atoms interact with the most dominant active site. Probabilities of recombination are found to have an exponential trend with gas-surface system temperature. The MD simulations are used to determine the activation energy for Eley-Rideal recombination of oxygen on a specific silica active site which is an important input parameter for the FRC model.

Crystal structure of glycoside hydrolase family 127 β-L-arabinofuranosidase from Bifidobacterium longum

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

Ito, Tasuku; Saikawa, Kyo; Kim, Seonah

2014-04-25

Graphical abstract: - Highlights: • HypBA1 β-L-arabinofuranosidase belongs to glycoside hydrolase family 127. • Crystal structure of HypBA1 was determined. • HypBA1 consists of a catalytic barrel and two additional β-sandwich domains. • The active site contains a Zn{sup 2+} coordinated by glutamate and three cysteines. • A possible reaction mechanism involving cysteine as the nucleophile is proposed. - Abstract: Enzymes acting on β-linked arabinofuranosides have been unknown until recently, in spite of wide distribution of β-L-arabinofuranosyl oligosaccharides in plant cells. Recently, a β-L-arabinofuranosidase from the glycoside hydrolase family 127 (HypBA1) was discovered in the newly characterized degradation system ofmore » hydroxyproline-linked β-L-arabinooligosaccharides in the bacterium Bifidobacterium longum. Here, we report the crystal structure of HypBA1 in the ligand-free and β-L-arabinofuranose complex forms. The structure of HypBA1 consists of a catalytic barrel domain and two additional β-sandwich domains, with one β-sandwich domain involved in the formation of a dimer. Interestingly, there is an unprecedented metal-binding motif with Zn{sup 2+} coordinated by glutamate and three cysteines in the active site. The glutamate residue is located far from the anomeric carbon of the β-L-arabinofuranose ligand, but one cysteine residue is appropriately located for nucleophilic attack for glycosidic bond cleavage. The residues around the active site are highly conserved among GH127 members. Based on biochemical experiments and quantum mechanical calculations, a possible reaction mechanism involving cysteine as the nucleophile is proposed.« less

A Sinter-Resistant Catalytic System Based on Platinum Nanoparticles Supported on TiO2 Nanofibers and Covered by Porous Silica

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

Dai, Yunqian; Lim, Byungkwon; Yang, Yong

2010-10-25

Platinum is a key catalyst that is invaluable in many important industrial processes such as CO oxidation in catalytic converters, oxidation and reduction reactions in fuel cells, nitric acid production, and petroleum cracking.[1] Many of these applications utilize Pt nanoparticles supported on oxides or porous carbon.[2] However, in practical applications that involve high temperatures (typically higher than 3008C), the Pt nanoparticles tend to lose their specific surface area and thus catalytic activity during operation because of sintering. Recent studies have shown that a porous oxide shell can act as a physical barrier to prevent sintering of unsupported metal nanoparticles and,more » at the same time, provide channels for chemical species to reach the surface of the nanoparticles, thus allowing the catalytic reaction to occur. This concept has been demonstrated in several systems, including Pt@SiO2,[3] Pt@CoO,[4] Pt/CeO2@SiO2,[5] Pd@SiO2,[6] Au@SiO2,[7] Au@SnO2 [8] and Au@ZrO2 [9] core– shell nanostructures. Despite these results, a sinter-resistant system has not been realized in supported Pt nanoparticle catalysts.« less

Discovery and Characterization of the 3-Hydroxyacyl-ACP Dehydratase Component of the Plant Mitochondrial Fatty Acid Synthase System1[OPEN

PubMed Central

Okazaki, Yozo; Lithio, Andrew; Jin, Huanan

2017-01-01

We report the characterization of the Arabidopsis (Arabidopsis thaliana) 3-hydroxyacyl-acyl carrier protein dehydratase (mtHD) component of the mitochondrial fatty acid synthase (mtFAS) system, encoded by AT5G60335. The mitochondrial localization and catalytic capability of mtHD were demonstrated with a green fluorescent protein transgenesis experiment and by in vivo complementation and in vitro enzymatic assays. RNA interference (RNAi) knockdown lines with reduced mtHD expression exhibit traits typically associated with mtFAS mutants, namely a miniaturized morphological appearance, reduced lipoylation of lipoylated proteins, and altered metabolomes consistent with the reduced catalytic activity of lipoylated enzymes. These alterations are reversed when mthd-rnai mutant plants are grown in a 1% CO2 atmosphere, indicating the link between mtFAS and photorespiratory deficiency due to the reduced lipoylation of glycine decarboxylase. In vivo biochemical feeding experiments illustrate that sucrose and glycolate are the metabolic modulators that mediate the alterations in morphology and lipid accumulation. In addition, both mthd-rnai and mtkas mutants exhibit reduced accumulation of 3-hydroxytetradecanoic acid (i.e. a hallmark of lipid A-like molecules) and abnormal chloroplastic starch granules; these changes are not reversible by the 1% CO2 atmosphere, demonstrating two novel mtFAS functions that are independent of photorespiration. Finally, RNA sequencing analysis revealed that mthd-rnai and mtkas mutants are nearly equivalent to each other in altering the transcriptome, and these analyses further identified genes whose expression is affected by a functional mtFAS system but independent of photorespiratory deficiency. These data demonstrate the nonredundant nature of the mtFAS system, which contributes unique lipid components needed to support plant cell structure and metabolism. PMID:28202596

Catalytic molecularly imprinted polymer membranes: development of the biomimetic sensor for phenols detection.

PubMed

Sergeyeva, T A; Slinchenko, O A; Gorbach, L A; Matyushov, V F; Brovko, O O; Piletsky, S A; Sergeeva, L M; Elska, G V

2010-02-05

Portable biomimetic sensor devices for the express control of phenols content in water were developed. The synthetic binding sites mimicking active site of the enzyme tyrosinase were formed in the structure of free-standing molecularly imprinted polymer membranes. Molecularly imprinted polymer membranes with the catalytic activity were obtained by co-polymerization of the complex Cu(II)-catechol-urocanic acid ethyl ester with (tri)ethyleneglycoldimethacrylate, and oligourethaneacrylate. Addition of the elastic component oligourethaneacrylate provided formation of the highly cross-linked polymer with the catalytic activity in a form of thin, flexible, and mechanically stable membrane. High accessibility of the artificial catalytic sites for the interaction with the analyzed phenol molecules was achieved due to addition of linear polymer (polyethyleneglycol Mw 20,000) to the initial monomer mixture before the polymerization. As a result, typical semi-interpenetrating polymer networks (semi-IPNs) were formed. The cross-linked component of the semi-IPN was represented by the highly cross-linked catalytic molecularly imprinted polymer, while the linear one was represented by polyethyleneglycol Mw 20,000. Extraction of the linear polymer from the fully formed semi-IPN resulted in formation of large pores in the membranes' structure. Concentration of phenols in the analyzed samples was detected using universal portable device oxymeter with the oxygen electrode in a close contact with the catalytic molecularly imprinted polymer membrane as a transducer. The detection limit of phenols detection using the developed sensor system based on polymers-biomimics with the optimized composition comprised 0.063 mM, while the linear range of the sensor comprised 0.063-1 mM. The working characteristics of the portable sensor devices were investigated. Storage stability of sensor systems at room temperature comprised 12 months (87%). As compared to traditional methods of phenols detection the developed sensor system is characterized by simplicity of operation, compactness, and low cost. Copyright 2009 Elsevier B.V. All rights reserved.

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

Ertem, Mehmed Zahid; Suna, Yuki; Himeda, Yuichiro

Pentamethylcyclopentadienyl iridium (Cp*Ir) complexes with bidentate ligands consisting of a pyridine ring and an electron-rich diazole ring were prepared. Their catalytic activity towards CO 2 hydrogenation in 2.0 M KHCO 3 aqueous solutions (pH 8.5) at 50 °C, under 1.0 MPa CO 2/H 2 (1:1) have been reported as an alternative to photo- and electrochemical CO 2 reduction. Bidentate ligands incorporating an electron-rich diazole ring improved the catalytic performance of the Ir complexes compared to the bipyridine ligand. Complexes 2, 4 and 6, possessing both a hydroxy group and an uncoordinated NH group, which are proton-responsive and capable of generatingmore » pendent-bases in basic media, recorded high initial TOF values of 1300 h -1, 1550 h -1 and 2000 h -1, respectively. Here, spectroscopic and computational investigations revealed that the reversible deprotonation changes the electronic properties of the complexes and causes interactions between pendent base and substrate and/or solvent water molecules, resulting in the high catalytic performance in basic media.« less

Locking the Active Conformation of c-Src Kinase through the Phosphorylation of the Activation Loop

PubMed Central

Meng, Yilin; Roux, Benoît

2013-01-01

Molecular dynamics umbrella sampling simulations are used to compare the relative stability of the active conformation of the catalytic domain of c-Src kinase while the tyrosine 416 in the activation loop (A-loop) is either unphosphorylated or phosphorylated. When the A-loop is unphosphorylated, there is considerable flexiblity of the kinase. While the active conformation of the kinase is not forbidden and can be visited transiently, it is not the predominant state. This is consistent with the view that c-Src displays some catalytic activity even when the A-loop is unphosphorylated. In contrast, phosphorylation of the A-loop contributes to stabilize several structural features that are critical for catalysis, such as the hydrophobic regulatory spine, the HRD motif, and the electrostatic switch. In summary, the free energy landscape calculations demonstrate that phosphorylation of tyrosine 416 in the A-loop essentially “locks” the kinase into its catalytically competent conformation. PMID:24103328

Engineering a hyper-catalytic enzyme by photo-activated conformation modulation

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

Agarwal, Pratul K

2012-01-01

Enzyme engineering for improved catalysis has wide implications. We describe a novel chemical modification of Candida antarctica lipase B that allows modulation of the enzyme conformation to promote catalysis. Computational modeling was used to identify dynamical enzyme regions that impact the catalytic mechanism. Surface loop regions located distal to active site but showing dynamical coupling to the reaction were connected by a chemical bridge between Lys136 and Pro192, containing a derivative of azobenzene. The conformational modulation of the enzyme was achieved using two sources of light that alternated the azobenzene moiety in cis and trans conformations. Computational model predicted thatmore » mechanical energy from the conformational fluctuations facilitate the reaction in the active-site. The results were consistent with predictions as the activity of the engineered enzyme was found to be enhanced with photoactivation. Preliminary estimations indicate that the engineered enzyme achieved 8-52 fold better catalytic activity than the unmodulated enzyme.« less

Nanophase-separated Ni3Nb as an automobile exhaust catalyst.

PubMed

Tanabe, Toyokazu; Imai, Tsubasa; Tokunaga, Tomoharu; Arai, Shigeo; Yamamoto, Yuta; Ueda, Shigenori; Ramesh, Gubbala V; Nagao, Satoshi; Hirata, Hirohito; Matsumoto, Shin-Ichi; Fujita, Takeshi; Abe, Hideki

2017-05-01

Catalytic remediation of automobile exhaust has relied on precious metals (PMs) including platinum (Pt). Herein, we report that an intermetallic phase of Ni and niobium (Nb) ( i.e. , Ni 3 Nb) exhibits a significantly higher activity than that of Pt for the remediation of the most toxic gas in exhaust ( i.e. , nitrogen monoxide (NO)) in the presence of carbon monoxide (CO). When subjected to the exhaust-remediation atmosphere, Ni 3 Nb spontaneously evolves into a catalytically active nanophase-separated structure consisting of filamentous Ni networks (thickness < 10 nm) that are incorporated in a niobium oxide matrix ( i.e. , NbO x ( x < 5/2)). The exposure of the filamentous Ni promotes NO dissociation, CO oxidation and N 2 generation, and the NbO x matrix absorbs excessive nitrogen adatoms to retain the active Ni 0 sites at the metal/oxide interface. Furthermore, the NbO x matrix immobilizes the filamentous Ni at elevated temperatures to produce long-term and stable catalytic performance over hundreds of hours.

New Developments in the Field of Reaction Technology: The Multiparallel Reactor HPMR 50-96

PubMed Central

Allwardt, Arne; Wendler, Christian; Thurow, Kerstin

2005-01-01

Catalytic high-pressure reactions play an important role in classic bulk chemistry. The optimization of common reactions, the search for new and more effective catalysts, and the increasing use of catalytic pressure reactions in the field of drug development call for high-parallel reaction systems. A crucial task of current developments, apart from the parameters of pressure, temperature, and number of reaction chambers, is, in this respect, the systems' integration into complex laboratory automation environments. PMID:18924722

RNase MRP cleaves pre-tRNASer-Met in the tRNA maturation pathway.

PubMed

Saito, Yuichiro; Takeda, Jun; Adachi, Kousuke; Nobe, Yuko; Kobayashi, Junya; Hirota, Kouji; Oliveira, Douglas V; Taoka, Masato; Isobe, Toshiaki

2014-01-01

Ribonuclease mitochondrial RNA processing (RNase MRP) is a multifunctional ribonucleoprotein (RNP) complex that is involved in the maturation of various types of RNA including ribosomal RNA. RNase MRP consists of a potential catalytic RNA and several protein components, all of which are required for cell viability. We show here that the temperature-sensitive mutant of rmp1, the gene for a unique protein component of RNase MRP, accumulates the dimeric tRNA precursor, pre-tRNA(Ser-Met). To examine whether RNase MRP mediates tRNA maturation, we purified the RNase MRP holoenzyme from the fission yeast Schizosaccharomyces pombe and found that the enzyme directly and selectively cleaves pre-tRNA(Ser-Met), suggesting that RNase MRP participates in the maturation of specific tRNA in vivo. In addition, mass spectrometry-based ribonucleoproteomic analysis demonstrated that this RNase MRP consists of one RNA molecule and 11 protein components, including a previously unknown component Rpl701. Notably, limited nucleolysis of RNase MRP generated an active catalytic core consisting of partial mrp1 RNA fragments, which constitute "Domain 1" in the secondary structure of RNase MRP, and 8 proteins. Thus, the present study provides new insight into the structure and function of RNase MRP.

Atmospheric nanoparticles in photocatalytic and thermal production of atmospheric pollutants

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

Chianelli, R.R.; Yacaman, M.J.

1997-12-31

Atmospheric aerosols which occur above heavily polluted areas such as Mexico City are characterized and found to be complex materials which have the potential to accelerate important ozone-forming reactions photocatalytically and thermocatalytically. In addition, because the particles are respirable, they represent a considerable health hazard. The aerosols consist of two intermixed components. The first component consists of amorphous carbonaceous materials of variable composition with fullerene like materials dispersed throughout. The second component is an inorganic material consisting of nanoparticles of oxides and sulfides supported on clay minerals. This inorganic component has all of the characteristics of an airborne photocatalyst. Nanoparticlesmore » of Fe{sub 2}O{sub 3}, MnO{sub 2} and FeS{sub 2} have demonstrated catalytic properties, particularly when occurring in the nanoparticle range as they do in the subject aerosol materials. These materials have band-gaps which occur in the broad solar spectrum enhancing the photocatalytic adsorption of solar radiation beyond that of the wider band-gap aluminosilicate and titanate materials which also occur in the aerosols. In addition, the materials are acidic and probably are coated with moisture when suspended in air, further enhancing the catalytic ability to crack hydrocarbons and create free radicals.« less

Catalytic systems used for polymerization, biomass conversion, and enhancing diffusion

NASA Astrophysics Data System (ADS)

Pong, Frances

A significant amount of research has been dedicated towards the study and improvement of catalysts. A better understanding of how catalysts work can lead to developing more cost-efficient catalytic systems for a variety of applications. My research is focuses on catalytic systems used in three different fields, which are (i) organometallic polymerization catalysts, (ii) molecular motors and (iii) biomass conversion. Researchers have long studied and modified organometallic catalysts for use in the direct co- and homopolymerization of monomers with polar functional groups. The ability to add polar moieties to polymers, which can potentially yield materials with a wider range of physical properties, is highly desirable. In this study (i), a series of naphthoxyimine palladium(II) catalysts -- in which the naphthyl backbone had been functionalized with different moieties -- were synthesized and systematically studied to determine the ligand structure's impact on catalytic activity. The study showed that slight modifications of the naphthyl backbone led to significant changes in the polymer's molecular weight and polydispersity index. The catalysts were also displayed some ability to co-polymerize ethylene and functionalized norbornene. These positive results suggest that further exploration of naphthoxyimine palladium (II) catalysts may be fundamentally interesting. The effect of active, motile particles at the nanoscale has been vigorously researched during the past decade. By understanding how such active suspensions behave, researchers can gain new insights which can potentially provide new applications in many fields. Here (ii) the momentum transfer of active catalysts (Grubbs' 2nd generation catalyst with a hydrodynamic radius of 6A) to their immediate surroundings is observed in an organic suspension. This phenomenon, which has been coined "enhanced diffusion," has not been well studied at the angstrom scale until now. Diffusion-NMR spectroscopy surprisingly revealed that these angstrom sized catalysts nearly double the speed of diffusion of passive molecular tracers in their immediate surroundings. This result is particularly intriguing because in this size regime, the viscosity of the surroundings is expected to completely overcome the inertial forces of these catalysts. This study has prompted further diffusion-NMR studies of molecular catalysts and enzymes as molecular motors. Catalytic systems play a crucial role in the conversion of renewable biomasses into energy and useful materials. This field of research has become increasingly important and lucrative as fossil fuel sources continue to decline/destabilize in the face of increased worldwide demand for more resources. In this work (iii), the efficacy of a hydrogen-pressurized, biphasic catalytic system to convert linear sugar polyols to iodoalkanes was examined. These iodoalkanes can easily be converted to 1-alkenes which can then be used for the synthesis of low density polyethylene. The results indicated that the system products were relatively pure and that the catalytic layer had a degree of recyclability, hinting that such a system may be viable for industrial use.

Quantitative Analysis of Homogeneous Electrocatalytic Reactions at IDA Electrodes: The Example of [Ni(PPh2NBn2)2]2+

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

Liu, Fei; Parkinson, B. A.; Divan, Ralu

Interdigitated array (IDA) electrodes have been applied to study the EC’ (electron transfer reaction followed by a catalytic reaction) reactions and a new method of quantitative analysis of IDA results was developed. In this new method, currents on IDA generator and collector electrodes for an EC’ mechanism are derived from the number of redox cycles and the contribution of non-catalytic current. And the fractions of bipotential recycling species and catalytic-active species are calculated, which helps understanding the catalytic reaction mechanism. The homogeneous hydrogen evolution reaction catalyzed by [Ni(PPh2NBn2)2]2+ (where PPh2NBn2 is 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) electrocatalyst was examined and analyzed with IDA electrodes.more » Besides, the existence of reaction intermediates in the catalytic cycle is inferred from the electrochemical behavior of a glassy carbon disk electrodes and carbon IDA electrodes. This quantitative analysis of IDA electrode cyclic voltammetry currents can be used as a simple and straightforward method for determining reaction mechanism in other catalytic systems as well.« less

Performance Testing of the Vapor Phase Catalytic Ammonia Removal Engineering Development Unit

NASA Technical Reports Server (NTRS)

Flynn, Michael; Tleimat, Maher; Nalette, Tim; Quinn, Gregory

2005-01-01

This paper describes the results of performance testing of the Vapor Phase Catalytic Ammonia Removal (VPCAR) technology. The VPCAR technology is currently being developed by NASA as a Mars transit vehicle water recycling system. NASA has recently completed-a grant-to develop a next generation VPCAR system. This grant concluded with the shipment of the final deliverable to NASA on 8/31/03. This paper presents the results of mass, power, volume, and acoustic measurements for the delivered system. Product water purity analysis for a Mars transit mission and a simulated planetary base wastewater ersatz are also provided.

Upgrading of Intermediate Bio-Oil Produced by Catalytic Pyrolysis

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

Abdullah, Zia; Chadwell, Brad; Taha, Rachid

2015-06-30

The objectives of this project were to (1) develop a process to upgrade catalytic pyrolysis bio-oil, (2) investigate new upgrading catalysts suited for upgrading catalytic pyrolysis bio-oil, (3) demonstrate upgrading system operation for more than 1,000 hours using a single catalyst charge, and (4) produce a final upgraded product that can be blended to 30 percent by weight with petroleum fuels or that is compatible with existing petroleum refining operations. This project has, to the best of our knowledge, for the first time enabled a commercially viable bio-oil hydrotreatment process to produce renewable blend stock for transportation fuels.

Method and apparatus for controlling accidental releases of tritium

DOEpatents

Galloway, T.R.

1980-04-01

An improvement is described in a tritium control system based on a catalytic oxidation reactor wherein accidental releases of tritium into room air are controlled by flooding the catalytic oxidation reactor with hydrogen when the tritium concentration in the room air exceeds a specified limit. The sudden flooding with hydrogen heats the catalyst to a high temperature within seconds, thereby greatly increasing the catalytic oxidation rate of tritium to tritiated water vapor. Thus, the catalyst is heated only when needed. In addition to the heating effect, the hydrogen flow also swamps the tritium and further reduces the tritium release. 1 fig.

Method and apparatus for controlling accidental releases of tritium

DOEpatents

Galloway, Terry R. [Berkeley, CA

1980-04-01

An improvement in a tritium control system based on a catalytic oxidation reactor wherein accidental releases of tritium into room air are controlled by flooding the catalytic oxidation reactor with hydrogen when the tritium concentration in the room air exceeds a specified limit. The sudden flooding with hydrogen heats the catalyst to a high temperature within seconds, thereby greatly increasing the catalytic oxidation rate of tritium to tritiated water vapor. Thus, the catalyst is heated only when needed. In addition to the heating effect, the hydrogen flow also swamps the tritium and further reduces the tritium release.

A competing, dual mechanism for catalytic direct benzene hydroxylation from combined experimental-DFT studies.

PubMed

Vilella, Laia; Conde, Ana; Balcells, David; Díaz-Requejo, M Mar; Lledós, Agustí; Pérez, Pedro J

2017-12-01

A dual mechanism for direct benzene catalytic hydroxylation is described. Experimental studies and DFT calculations have provided a mechanistic explanation for the acid-free, Tp x Cu-catalyzed hydroxylation of benzene with hydrogen peroxide (Tp x = hydrotrispyrazolylborate ligand). In contrast with other catalytic systems that promote this transformation through Fenton-like pathways, this system operates through a copper-oxyl intermediate that may interact with the arene ring following two different, competitive routes: (a) electrophilic aromatic substitution, with the copper-oxyl species acting as the formal electrophile, and (b) the so-called rebound mechanism, in which the hydrogen is abstracted by the Cu-O moiety prior to the C-O bond formation. Both pathways contribute to the global transformation albeit to different extents, the electrophilic substitution route seeming to be largely favoured.

Catalytic destruction of groundwater contaminants in reactive extraction wells

DOEpatents

McNab, Jr., Walt W.; Reinhard, Martin

2002-01-01

A system for remediating groundwater contaminated with halogenated solvents, certain metals and other inorganic species based on catalytic reduction reactions within reactive well bores. The groundwater treatment uses dissolved hydrogen as a reducing agent in the presence of a metal catalyst, such a palladium, to reduce halogenated solvents (as well as other substituted organic compounds) to harmless species (e.g., ethane or methane) and immobilize certain metals to low valence states. The reactive wells function by removing water from a contaminated water-bearing zone, treating contaminants with a well bore using catalytic reduction, and then reinjecting the treated effluent into an adjacent water-bearing zone. This system offers the advantages of a compact design with a minimal surface footprint (surface facilities) and the destruction of a broad suite of contaminants without generating secondary waste streams.

Catalytical Properties of Free and Immobilized Aspergillus niger Tannase.

PubMed

Flores-Maltos, Abril; Rodríguez-Durán, Luis V; Renovato, Jacqueline; Contreras, Juan C; Rodríguez, Raúl; Aguilar, Cristóbal N

2011-01-01

A fungal tannase was produced, recovered, and immobilized by entrapment in calcium alginate beads. Catalytical properties of the immobilized enzyme were compared with those of the free one. Tannase was produced intracellularly by the xerophilic fungus Aspergillus niger GH1 in a submerged fermentation system. Enzyme was recovered by cell disruption and the crude extract was partially purified. The catalytical properties of free and immobilized tannase were evaluated using tannic acid and methyl gallate as substrates. K(M) and V(max) values for free enzyme were very similar for both substrates. But, after immobilization, K(M) and V(max) values increased drastically using tannic acid as substrate. These results indicated that immobilized tannase is a better biocatalyst than free enzyme for applications on liquid systems with high tannin content, such as bioremediation of tannery or olive-mill wastewater.

Catalytical Properties of Free and Immobilized Aspergillus niger Tannase

PubMed Central

Flores-Maltos, Abril; Rodríguez-Durán, Luis V.; Renovato, Jacqueline; Contreras, Juan C.; Rodríguez, Raúl; Aguilar, Cristóbal N.

2011-01-01

A fungal tannase was produced, recovered, and immobilized by entrapment in calcium alginate beads. Catalytical properties of the immobilized enzyme were compared with those of the free one. Tannase was produced intracellularly by the xerophilic fungus Aspergillus niger GH1 in a submerged fermentation system. Enzyme was recovered by cell disruption and the crude extract was partially purified. The catalytical properties of free and immobilized tannase were evaluated using tannic acid and methyl gallate as substrates. K M and V max values for free enzyme were very similar for both substrates. But, after immobilization, K M and V max values increased drastically using tannic acid as substrate. These results indicated that immobilized tannase is a better biocatalyst than free enzyme for applications on liquid systems with high tannin content, such as bioremediation of tannery or olive-mill wastewater. PMID:21918717

Recent Advances in the Application of Magnetic Nanoparticles as a Support for Homogeneous Catalysts

PubMed Central

Govan, Joseph; Gun’ko, Yurii K.

2014-01-01

Magnetic nanoparticles are a highly valuable substrate for the attachment of homogeneous inorganic and organic containing catalysts. This review deals with the very recent main advances in the development of various nanocatalytic systems by the immobilisation of homogeneous catalysts onto magnetic nanoparticles. We discuss magnetic core shell nanostructures (e.g., silica or polymer coated magnetic nanoparticles) as substrates for catalyst immobilisation. Then we consider magnetic nanoparticles bound to inorganic catalytic mesoporous structures as well as metal organic frameworks. Binding of catalytically active small organic molecules and polymers are also reviewed. After that we briefly deliberate on the binding of enzymes to magnetic nanocomposites and the corresponding enzymatic catalysis. Finally, we draw conclusions and present a future outlook for the further development of new catalytic systems which are immobilised onto magnetic nanoparticles. PMID:28344220

Chemiluminescence analyzer of NOx as a high-throughput screening tool in selective catalytic reduction of NO

PubMed Central

Oh, Kwang Seok; Woo, Seong Ihl

2011-01-01

A chemiluminescence-based analyzer of NOx gas species has been applied for high-throughput screening of a library of catalytic materials. The applicability of the commercial NOx analyzer as a rapid screening tool was evaluated using selective catalytic reduction of NO gas. A library of 60 binary alloys composed of Pt and Co, Zr, La, Ce, Fe or W on Al2O3 substrate was tested for the efficiency of NOx removal using a home-built 64-channel parallel and sequential tubular reactor. The NOx concentrations measured by the NOx analyzer agreed well with the results obtained using micro gas chromatography for a reference catalyst consisting of 1 wt% Pt on γ-Al2O3. Most alloys showed high efficiency at 275 °C, which is typical of Pt-based catalysts for selective catalytic reduction of NO. The screening with NOx analyzer allowed to select Pt-Ce(X) (X=1–3) and Pt–Fe(2) as the optimal catalysts for NOx removal: 73% NOx conversion was achieved with the Pt–Fe(2) alloy, which was much better than the results for the reference catalyst and the other library alloys. This study demonstrates a sequential high-throughput method of practical evaluation of catalysts for the selective reduction of NO. PMID:27877438

Hydrophobic Shielding Drives Catalysis of Hydride Transfer in a Family of F420H2-Dependent Enzymes.

PubMed

Mohamed, A Elaaf; Condic-Jurkic, Karmen; Ahmed, F Hafna; Yuan, Peng; O'Mara, Megan L; Jackson, Colin J; Coote, Michelle L

2016-12-13

A family of flavin/deazaflavin-dependent oxidoreductases (FDORs) from mycobacteria has been recently characterized and found to play a variety of catalytic roles, including the activation of prodrugs such as the candidate anti-tuberculosis drug pretomanid (PA-824). However, our understanding of the catalytic mechanism used by these enzymes is relatively limited. To address this, we have used a combination of quantum mechanics and molecular dynamics calculations to study the catalytic mechanism of the activation of pretomanid by the deazaflavin-dependent nitroreductase (Ddn) from Mycobacterium tuberculosis. The preferred pathway involves an initial hydride transfer step from the deprotonated cofactor (i.e., F 420 H - ), with subsequent protonation, before a series of spontaneous intramolecular reactions to form the final reactive nitrogen species. The most likely proton source is a hydroxonium ion within the solvent accessible active site. Intriguingly, catalysis of the rate-determining hydride transfer step is aided by three tyrosine residues that form a hydrophobic barrier around the active site that, upon reaction, is then disrupted to allow increased water accessibility to facilitate the subsequent proton transfer step. The catalytic mechanism we propose is consistent with previous experimental observations of the Ddn enzyme and will inform the design of improved prodrugs in the future.

Synthesis of urease hybrid nanoflowers and their enhanced catalytic properties.

PubMed

Somturk, Burcu; Yilmaz, Ismail; Altinkaynak, Cevahir; Karatepe, Aslıhan; Özdemir, Nalan; Ocsoy, Ismail

2016-05-01

Increasing numbers of materials have been extensively used as platforms for enzyme immobilization to enhance catalytic activity and stability. Although stability of enzyme was accomplished with immobilization approaches, activity of the most of the enzymes was declined after immobilization. Herein, we synthesize the flower shaped-hybrid nanomaterials called hybrid nanoflower (HNF) consisting of urease enzyme and copper ions (Cu(2+)) and report a mechanistic elucidation of enhancement in both activity and stability of the HNF. We demonstrated how experimental factors influence morphology of the HNF. We proved that the HNF (synthesized from 0.02mgmL(-1) urease in 10mM PBS (pH 7.4) at +4°C) exhibited the highest catalytic activity of ∼2000% and ∼4000% when stored at +4°C and RT, respectively compared to free urease. The highest stability was also achieved by this HNF by maintaining 96.3% and 90.28% of its initial activity within storage of 30 days at +4°C and RT, respectively. This dramatically enhanced activity is attributed to high surface area, nanoscale-entrapped urease and favorable urease conformation of the HNF. The exceptional catalytic activity and stability properties of HNF can be taken advantage of to use it in fields of biomedicine and chemistry. Copyright © 2015 Elsevier Inc. All rights reserved.

Environmental Technology Verification: Test Report of Mobile Source Selective Catalytic Reduction--Nett Technologies, Inc., BlueMAX 100 version A urea-based selective catalytic reduction technology

EPA Science Inventory

Nett Technologies’ BlueMAX 100 version A Urea-Based SCR System utilizes a zeolite catalyst coating on a cordierite honeycomb substrate for heavy-duty diesel nonroad engines for use with commercial ultra-low–sulfur diesel fuel. This environmental technology verification (ETV) repo...

40 CFR 63.1567 - What are my requirements for inorganic HAP emissions from catalytic reforming units?

Code of Federal Regulations, 2010 CFR

2010-07-01

... ppmv. (iv) If you are required to use a colormetric tube sampling system to demonstrate continuous... limitations and work practice standards must I meet? You must: (1) Meet each emission limitation in Table 22 to this subpart that applies to you. If you operate a catalytic reforming unit in which different...

40 CFR Table 40 to Subpart Uuu of... - Requirements for Installation, Operation, and Maintenance of Continuous Opacity Monitoring...

Code of Federal Regulations, 2013 CFR

2013-07-01

... Systems 40 Table 40 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 40 Table 40 to Subpart UUU of Part 63—Requirements for Installation, Operation, and Maintenance of...

40 CFR Table 40 to Subpart Uuu of... - Requirements for Installation, Operation, and Maintenance of Continuous Opacity Monitoring...

Code of Federal Regulations, 2014 CFR

2014-07-01

... Systems 40 Table 40 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 40 Table 40 to Subpart UUU of Part 63—Requirements for Installation, Operation, and Maintenance of...

40 CFR Table 40 to Subpart Uuu of... - Requirements for Installation, Operation, and Maintenance of Continuous Opacity Monitoring...

Code of Federal Regulations, 2012 CFR

2012-07-01

... Systems 40 Table 40 to Subpart UUU of Part 63 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY...: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU, Table 40 Table 40 to Subpart UUU of Part 63—Requirements for Installation, Operation, and Maintenance of...

Low-temperature catalytic gasification of food processing wastes. 1995 topical report

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

Elliott, D.C.; Hart, T.R.

The catalytic gasification system described in this report has undergone continuing development and refining work at Pacific Northwest National Laboratory (PNNL) for over 16 years. The original experiments, performed for the Gas Research Institute, were aimed at developing kinetics information for steam gasification of biomass in the presence of catalysts. From the fundamental research evolved the concept of a pressurized, catalytic gasification system for converting wet biomass feedstocks to fuel gas. Extensive batch reactor testing and limited continuous stirred-tank reactor tests provided useful design information for evaluating the preliminary economics of the process. This report is a follow-on to previousmore » interim reports which reviewed the results of the studies conducted with batch and continuous-feed reactor systems from 1989 to 1994, including much work with food processing wastes. The discussion here provides details of experiments on food processing waste feedstock materials, exclusively, that were conducted in batch and continuous- flow reactors.« less

A novel liquid organic hydrogen carrier system based on catalytic peptide formation and hydrogenation

PubMed Central

Hu, Peng; Fogler, Eran; Diskin-Posner, Yael; Iron, Mark A.; Milstein, David

2015-01-01

Hydrogen is an efficient green fuel, but its low energy density when stored under high pressure or cryogenically, and safety issues, presents significant disadvantages; hence finding efficient and safe hydrogen carriers is a major challenge. Of special interest are liquid organic hydrogen carriers (LOHCs), which can be readily loaded and unloaded with considerable amounts of hydrogen. However, disadvantages include high hydrogen pressure requirements, high reaction temperatures for both hydrogenation and dehydrogenation steps, which require different catalysts, and high LOHC cost. Here we present a readily reversible LOHC system based on catalytic peptide formation and hydrogenation, using an inexpensive, safe and abundant organic compound with high potential capacity to store and release hydrogen, applying the same catalyst for loading and unloading hydrogen under relatively mild conditions. Mechanistic insight of the catalytic reaction is provided. We believe that these findings may lead to the development of an inexpensive, safe and clean liquid hydrogen carrier system. PMID:25882348

A PEG/copper(i) halide cluster as an eco-friendly catalytic system for C-N bond formation.

PubMed

Li, Cheng-An; Ji, Wei; Qu, Jian; Jing, Su; Gao, Fei; Zhu, Dun-Ru

2018-05-22

The catalytic activities of eight copper(i) halide clusters assembled from copper(i) halide and ferrocenyltelluroethers, 1-8, were investigated in C-N formation under various conditions. A catalytic procedure using poly(ethylene glycol) (PEG-400) as a greener alternative organic solvent has been developed. The PEG-400/5 system can achieve 99% targeted yield with a mild reaction temperature and short reaction time. After the isolation of the products by extraction with diethyl ether, this PEG-400/cluster system could be easily recycled. Spectroscopic studies elucidate a stepwise mechanism: firstly, proton-coupled electron transfer (PCET) involving the transfer of an electron from Cu+ and a proton from imidazole results in the formation of a labile penta-coordinated Cu2+ and aryl radical; the following effective electron transfer from the ferrocene unit reduces Cu2+ and forms the target product; finally, the ferrocenium unit is reduced by the I- anion. The merits of this eco-friendly synthesis are the efficient utilization of reagents and easy recyclability.

Inverse oxide/metal catalysts in fundamental studies and practical applications: A perspective of recent developments

DOE PAGES

Rodriguez, José A.; Liu, Ping; Graciani, Jesús; ...

2016-06-21

Inverse oxide/metal catalysts have shown to be excellent systems for studying the role of the oxide and oxide–metal interface in catalytic reactions. These systems can have special structural and catalytic properties due to strong oxide–metal interactions difficult to attain when depositing a metal on a regular oxide support. Oxide phases that are not seen or are metastable in a bulk oxide can become stable in an oxide/metal system opening the possibility for new chemical properties. Using these systems, it has been possible to explore fundamental properties of the metal–oxide interface (composition, structure, electronic state), which determine catalytic performance in themore » oxidation of CO, the water–gas shift and the hydrogenation of CO 2 to methanol. Recently, there has been a significant advance in the preparation of oxide/metal catalysts for technical or industrial applications. In conclusion, one goal is to identify methods able to control in a precise way the size of the deposited oxide particles and their structure on the metal substrate.« less

Surface-immobilized DNAzyme-type biocatalysis

NASA Astrophysics Data System (ADS)

Stefan, Loic; Lavergne, Thomas; Spinelli, Nicolas; Defrancq, Eric; Monchaud, David

2014-02-01

The structure of the double helix of deoxyribonucleic acid (DNA, also called duplex-DNA) was elucidated sixty years ago by Watson, Crick, Wilkins and Franklin. Since then, DNA has continued to hold a fascination for researchers in diverse fields including medicine and nanobiotechnology. Nature has indeed excelled in diversifying the use of DNA: beyond its canonical role of repository of genetic information, DNA could also act as a nanofactory able to perform some complex catalytic tasks in an enzyme-mimicking manner. The catalytic capability of DNA was termed DNAzyme; in this context, a peculiar DNA structure, a quadruple helix also named quadruplex-DNA, has recently garnered considerable interest since its autonomous catalytic proficiency relies on its higher-order folding that makes it suitable to interact efficiently with hemin, a natural cofactor of many enzymes. Quadruplexes have thus been widely studied for their hemoprotein-like properties, chiefly peroxidase-like activity, i.e., their ability to perform hemin-mediated catalytic oxidation reactions. Recent literature is replete with applications of quadruplex-based peroxidase-mimicking DNAzyme systems. Herein, we take a further leap along the road to biochemical applications, assessing the actual efficiency of catalytic quadruplexes for the detection of picomolar levels of surface-bound analytes in an enzyme-linked immunosorbent (ELISA)-type assay. To this end, we exploit an innovative strategy based on the functionalization of DNA by a multitasking platform named RAFT (for regioselectivity addressable functionalized template), whose versatility enables the grafting of DNA whatever its nature (duplex-DNA, quadruplex-DNA, etc.). We demonstrate that the resulting biotinylated RAFT/quadruplex systems indeed acquire catalytic properties that allow for efficient luminescent detection of picomoles of surface-bound streptavidin. We also highlight some of the pitfalls that have to be faced during optimization, notably demonstrating that highly optimized experimental conditions can make DNA pre-catalysts catalytically competent whatever their secondary structures.

Liquid Hydrogenation of Maleic Anhydride with Pd/C Catalyst at Low Pressure and Temperature in Batch Reactor.

PubMed

Kim, Ji Sun; Baek, Jae Ho; Ryu, Young Bok; Hong, Seong-Soo; Lee, Man Sig

2015-01-01

Succinic acid (SA) produced from hydrogenation of maleic anhydride (MAN) is used widely in manufacturing of pharmaceuticals, agrochemicals, surfactants and detergent, green solvent and biodegradable plastic. In this study, we performed that liquid hydrogenation of MAN to SA with 5 wt% Pd supported on activated carbon (Pd/C) at low pressure and temperature. The synthesis of SA was performed in aqueous solution while varying temperature, pressure, catalytic amount and agitation speed. We confirmed that the composition of the products consisting of SA, maleic acid (MA), fumaric acid (FA) and malic acid (MLA) depends on the process. The catalytic characteristics were analyzed by TGA, TEM.

Contact structure for use in catalytic distillation

DOEpatents

Jones, Jr., Edward M.

1984-01-01

A method for conducting catalytic chemical reactions and fractionation of the reaction mixture comprising feeding reactants into a distillation column reactor contracting said reactant in liquid phase with a fixed bed catalyst in the form of a contact catalyst structure consisting of closed porous containers containing the catatlyst for the reaction and a clip means to hold and support said containers, which are disposed above, i.e., on the distillation trays in the tower. The trays have weir means to provide a liquid level on the trays to substantially cover the containers. In other words, the trays function in their ordinary manner with the addition thereto of the catalyst. The reaction mixture is concurrently fractionated in the column.

Peroxiredoxins in Plants and Cyanobacteria

PubMed Central

2011-01-01

Abstract Peroxiredoxins (Prx) are central elements of the antioxidant defense system and the dithiol-disulfide redox regulatory network of the plant and cyanobacterial cell. They employ a thiol-based catalytic mechanism to reduce H2O2, alkylhydroperoxide, and peroxinitrite. In plants and cyanobacteria, there exist 2-CysPrx, 1-CysPrx, PrxQ, and type II Prx. Higher plants typically contain at least one plastid 2-CysPrx, one nucleo-cytoplasmic 1-CysPrx, one chloroplast PrxQ, and one each of cytosolic, mitochondrial, and plastidic type II Prx. Cyanobacteria express variable sets of three or more Prxs. The catalytic cycle consists of three steps: (i) peroxidative reduction, (ii) resolving step, and (iii) regeneration using diverse electron donors such as thioredoxins, glutaredoxins, cyclophilins, glutathione, and ascorbic acid. Prx proteins undergo major conformational changes in dependence of their redox state. Thus, they not only modulate cellular reactive oxygen species- and reactive nitrogen species-dependent signaling, but depending on the Prx type they sense the redox state, transmit redox information to binding partners, and function as chaperone. They serve in context of photosynthesis and respiration, but also in metabolism and development of all tissues, for example, in nodules as well as during seed and fruit development. The article surveys the current literature and attempts a mostly comprehensive coverage of present day knowledge and concepts on Prx mechanism, regulation, and function and thus on the whole Prx systems in plants. Antioxid. Redox Signal. 15, 1129–1159. PMID:21194355

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

Betancourt, Luis E.; Guzman-Blas, Rolando; Luo, Si

A robust electrodeposition method consisting of the rotating disk slurry electrode (RoDSE) technique to obtain Au nanoparticles highly dispersed on a conductive carbonaceous support, i.e., Vulcan XC-72R, for ethanol electrooxidation reaction in alkaline media was developed. Ceria was used as a cocatalyst using a Ce(III)-EDTA impregnation method in order to enhance the catalytic activity and improve the catalyst’s overall stability. Furthermore, the RoDSE method used to obtain highly dispersed Au nanoparticles does not require the use of a reducing agent or stabilizing agent, and the noble-metal loading was controlled by the addition and tuning of the metal precursor concentration. Inductivelymore » coupled plasma and thermogravimetric analysis indicated that the Au loading in the catalyst was 9 %. We determined the particle size and characteristic Au fcc crystal facets by X-ray diffraction. The morphology of the catalyst was also investigated using electron microscopy techniques. In addition, X-ray absorption spectroscopy was used to corroborate the presence and identify the oxidation state of Ce in the system and to observe if there are any electronic interactions within the 8 % Au/CeO x/C system. Cyclic voltammetry of electrodeposited 9 % Au/C and Ce-promoted 8 % Au/C showed a higher catalytic current density for ethanol oxidation when compared with commercially available catalysts (20 % Au/C) of a higher precious metal loading. Additionally, we report a higher stability toward the ethanol electrooxidation process, which was corroborated by 1 mV/s linear sweep voltammetry and chronoamperometric studies.« less

Uniform Free-Energy Profiles of the P-O Bond Formation and Cleavage Reactions Catalyzed by DNA Polymerases β and λ.

PubMed

Klvaňa, Martin; Bren, Urban; Florián, Jan

2016-12-29

Human X-family DNA polymerases β (Polβ) and λ (Polλ) catalyze the nucleotidyl-transfer reaction in the base excision repair pathway of the cellular DNA damage response. Using empirical valence bond and free-energy perturbation simulations, we explore the feasibility of various mechanisms for the deprotonation of the 3'-OH group of the primer DNA strand, and the subsequent formation and cleavage of P-O bonds in four Polβ, two truncated Polλ (tPolλ), and two tPolλ Loop1 mutant (tPolλΔL1) systems differing in the initial X-ray crystal structure and nascent base pair. The average calculated activation free energies of 14, 18, and 22 kcal mol -1 for Polβ, tPolλ, and tPolλΔL1, respectively, reproduce the trend in the observed catalytic rate constants. The most feasible reaction pathway consists of two successive steps: specific base (SB) proton transfer followed by rate-limiting concerted formation and cleavage of the P-O bonds. We identify linear free-energy relationships (LFERs) which show that the differences in the overall activation and reaction free energies among the eight studied systems are determined by the reaction free energy of the SB proton transfer. We discuss the implications of the LFERs and suggest pK a of the 3'-OH group as a predictor of the catalytic rate of X-family DNA polymerases.

Uniform Free-Energy Profiles of the P–O Bond Formation and Cleavage Reactions Catalyzed by DNA Polymerases β and λ

PubMed Central

2016-01-01

Human X-family DNA polymerases β (Polβ) and λ (Polλ) catalyze the nucleotidyl-transfer reaction in the base excision repair pathway of the cellular DNA damage response. Using empirical valence bond and free-energy perturbation simulations, we explore the feasibility of various mechanisms for the deprotonation of the 3′-OH group of the primer DNA strand, and the subsequent formation and cleavage of P–O bonds in four Polβ, two truncated Polλ (tPolλ), and two tPolλ Loop1 mutant (tPolλΔL1) systems differing in the initial X-ray crystal structure and nascent base pair. The average calculated activation free energies of 14, 18, and 22 kcal mol–1 for Polβ, tPolλ, and tPolλΔL1, respectively, reproduce the trend in the observed catalytic rate constants. The most feasible reaction pathway consists of two successive steps: specific base (SB) proton transfer followed by rate-limiting concerted formation and cleavage of the P–O bonds. We identify linear free-energy relationships (LFERs) which show that the differences in the overall activation and reaction free energies among the eight studied systems are determined by the reaction free energy of the SB proton transfer. We discuss the implications of the LFERs and suggest pKa of the 3′-OH group as a predictor of the catalytic rate of X-family DNA polymerases. PMID:27992186

Photolytic AND Catalytic Destruction of Organic Waste Water Pollutants

NASA Astrophysics Data System (ADS)

Torosyan, V. F.; Torosyan, E. S.; Kryuchkova, S. O.; Gromov, V. E.

2017-01-01

The system: water supply source - potable and industrial water - wastewater - sewage treatment - water supply source is necessary for water supply and efficient utilization of water resources. Up-to-date technologies of waste water biological treatment require for special microorganisms, which are technologically complex and expensive but unable to solve all the problems. Application of photolytic and catalytically-oxidizing destruction is quite promising. However, the most reagents are strong oxidizers in catalytic oxidation of organic substances and can initiate toxic substance generation. Methodic and scientific approaches to assess bread making industry influence on the environment have been developed in this paper in order to support forecasting and taking technological decisions concerning reduction of this influence. Destructive methods have been tested: ultra violet irradiation and catalytic oxidation for extraction of organic compounds from waste water by natural reagents.

A cell-free method for expressing and reconstituting membrane proteins enables functional characterization of the plant receptor-like protein kinase FERONIA.

PubMed

Minkoff, Benjamin B; Makino, Shin-Ichi; Haruta, Miyoshi; Beebe, Emily T; Wrobel, Russell L; Fox, Brian G; Sussman, Michael R

2017-04-07

There are more than 600 receptor-like kinases (RLKs) in Arabidopsis , but due to challenges associated with the characterization of membrane proteins, only a few have known biological functions. The plant RLK FERONIA is a peptide receptor and has been implicated in plant growth regulation, but little is known about its molecular mechanism of action. To investigate the properties of this enzyme, we used a cell-free wheat germ-based expression system in which mRNA encoding FERONIA was co-expressed with mRNA encoding the membrane scaffold protein variant MSP1D1. With the addition of the lipid cardiolipin, assembly of these proteins into nanodiscs was initiated. FERONIA protein kinase activity in nanodiscs was higher than that of soluble protein and comparable with other heterologously expressed protein kinases. Truncation experiments revealed that the cytoplasmic juxtamembrane domain is necessary for maximal FERONIA activity, whereas the transmembrane domain is inhibitory. An ATP analogue that reacts with lysine residues inhibited catalytic activity and labeled four lysines; mutagenesis demonstrated that two of these, Lys-565 and Lys-663, coordinate ATP in the active site. Mass spectrometric phosphoproteomic measurements further identified phosphorylation sites that were examined using phosphomimetic mutagenesis. The results of these experiments are consistent with a model in which kinase-mediated phosphorylation within the C-terminal region is inhibitory and regulates catalytic activity. These data represent a step further toward understanding the molecular basis for the protein kinase catalytic activity of FERONIA and show promise for future characterization of eukaryotic membrane proteins. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

The inhibition of cAMP-dependent protein kinase by full-length hepatitis C virus NS3/4A complex is due to ATP hydrolysis.

PubMed

Aoubala, M; Holt, J; Clegg, R A; Rowlands, D J; Harris, M

2001-07-01

Hepatitis C virus (HCV) is an important cause of chronic liver disease, but the molecular mechanisms of viral pathogenesis remain to be established. The HCV non-structural protein NS3 complexes with NS4A and has three enzymatic activities: a proteinase and a helicase/NTPase. Recently, catalytically inactive NS3 fragments containing an arginine-rich motif have been reported to interact with, and inhibit, the catalytic subunit of cAMP-dependent protein kinase (PKA C-subunit). Here we demonstrate that full-length, catalytically active NS3/4A, purified from recombinant baculovirus-infected insect cells, is also able to inhibit PKA C-subunit in vitro. This inhibition was abrogated by mutation of either the arginine-rich motif or the conserved helicase motif II, both of which also abolished NTPase activity. As PKA C-subunit inhibition was also enhanced by poly(U) (an activator of NS3 NTPase activity), we hypothesized that PKA C-subunit inhibition could be due to NS3/4A-mediated ATP hydrolysis. This was confirmed by experiments in which a constant ATP concentration was maintained by addition of an ATP regeneration system--under these conditions PKA C-subunit inhibition was not observed. Interestingly, the mutations also abrogated the ability of wild-type NS3/4A to inhibit the PKA-regulated transcription factor CREB in transiently transfected hepatoma cells. Our data are thus not consistent with the previously proposed model in which the arginine-rich motif of NS3 was suggested to act as a pseudosubstrate inhibitor of PKA C-subunit. However, in vivo effects of NS3/4A suggest that ATPase activity may play a role in viral pathology in the infected liver.

Simultaneous Detection of Electronic Structure Changes from Two Elements of a Bifunctional Catalyst Using Wavelength-Dispersive X-ray Emission Spectroscopy and in situ Electrochemistry

PubMed Central

Gul, Sheraz; Desmond Ng, Jia Wei; Alonso-Mori, Roberto; Kern, Jan; Sokaras, Dimosthenis; Anzenberg, Eitan; Lassalle-Kaiser, Benedikt; Gorlin, Yelena; Weng, Tsu-Chien; Zwart, Petrus H.; Zhang, Jin Z.; Bergmann, Uwe; Yachandra, Vittal K.; Jaramillo, Thomas F.; Yano, Junko

2015-01-01

Multielectron catalytic reactions, such as water oxidation, nitrogen reduction, or hydrogen production in enzymes and inorganic catalysts often involve multimetallic clusters. In these systems, the reaction takes place between metals or metals and ligands to facilitate charge transfer, bond formation/breaking, substrate binding, and release of products. In this study, we present a method to detect X-ray emission signals from multiple elements simultaneously, which allows for the study of charge transfer and the sequential chemistry occurring between elements. Kβ X-ray emission spectroscopy (XES) probes charge and spin states of metals as well as their ligand environment. A wavelength-dispersive spectrometer based on the von Hamos geometry was used to disperse Kβ signals of multiple elements onto a position detector, enabling an XES spectrum to be measured in a single-shot mode. This overcomes the scanning needs of the scanning spectrometers, providing data free from temporal and normalization errors and therefore ideal to follow sequential chemistry at multiple sites. We have applied this method to study MnOx-based bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In particular, we investigated the effects of adding a secondary element, Ni, to form MnNiOx and its impact on the chemical states and catalytic activity, by tracking the redox characteristics of each element upon sweeping the electrode potential. The detection scheme we describe here is general and can be applied to time-resolved studies of materials consisting of multiple elements, to follow the dynamics of catalytic and electron transfer reactions. PMID:25747045

Transition State Charge Stabilization and Acid-Base Catalysis of mRNA Cleavage by the Endoribonuclease RelE

PubMed Central

Dunican, Brian F.; Hiller, David A.; Strobel, Scott A.

2015-01-01

The bacterial toxin RelE is a ribosome-dependent endoribonuclease. It is part of a type II toxin-antitoxin system that contributes to antibiotic resistance and biofilm formation. During amino acid starvation RelE cleaves mRNA in the ribosomal A-site, globally inhibiting protein translation. RelE is structurally similar to microbial RNases that employ general acid-base catalysis to facilitate RNA cleavage. The RelE active-site is atypical for acid-base catalysis, in that it is enriched for positively charged residues and lacks the prototypical histidine-glutamate catalytic pair, making the mechanism of mRNA cleavage unclear. In this study we use a single-turnover kinetic analysis to measure the effect of pH and phosphorothioate substitution on the rate constant for cleavage of mRNA by wild-type RelE and seven active-site mutants. Mutation and thio-effects indicate a major role for stabilization of increased negative change in the transition state by arginine 61. The wild-type RelE cleavage rate constant is pH-independent, but the reaction catalyzed by many of the mutants is strongly pH dependent, suggestive of general acid-base catalysis. pH-rate curves indicate that wild-type RelE operates with the pKa of at least one catalytic residue significantly downshifted by the local environment. Mutation of any single active-site residue is sufficient to disrupt this microenvironment and revert the shifted pKa back above neutrality. pH-rate curves are consistent with K54 functioning as a general base and R81 as a general acid. The capacity of RelE to effect a large pKa shift and facilitate a common catalytic mechanism by uncommon means furthers our understanding of other atypical enzymatic active sites. PMID:26535789

Iridium complexes containing mesoionic C donors: selective C(sp3)-H versus C(sp2)-H bond activation, reactivity towards acids and bases, and catalytic oxidation of silanes and water.

PubMed

Petronilho, Ana; Woods, James A; Mueller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

2014-11-24

Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000 h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Simultaneous detection of electronic structure changes from two elements of a bifunctional catalyst using wavelength-dispersive X-ray emission spectroscopy and in situ electrochemistry.

PubMed

Gul, Sheraz; Ng, Jia Wei Desmond; Alonso-Mori, Roberto; Kern, Jan; Sokaras, Dimosthenis; Anzenberg, Eitan; Lassalle-Kaiser, Benedikt; Gorlin, Yelena; Weng, Tsu-Chien; Zwart, Petrus H; Zhang, Jin Z; Bergmann, Uwe; Yachandra, Vittal K; Jaramillo, Thomas F; Yano, Junko

2015-04-14

Multielectron catalytic reactions, such as water oxidation, nitrogen reduction, or hydrogen production in enzymes and inorganic catalysts often involve multimetallic clusters. In these systems, the reaction takes place between metals or metals and ligands to facilitate charge transfer, bond formation/breaking, substrate binding, and release of products. In this study, we present a method to detect X-ray emission signals from multiple elements simultaneously, which allows for the study of charge transfer and the sequential chemistry occurring between elements. Kβ X-ray emission spectroscopy (XES) probes charge and spin states of metals as well as their ligand environment. A wavelength-dispersive spectrometer based on the von Hamos geometry was used to disperse Kβ signals of multiple elements onto a position detector, enabling an XES spectrum to be measured in a single-shot mode. This overcomes the scanning needs of the scanning spectrometers, providing data free from temporal and normalization errors and therefore ideal to follow sequential chemistry at multiple sites. We have applied this method to study MnOx-based bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In particular, we investigated the effects of adding a secondary element, Ni, to form MnNiOx and its impact on the chemical states and catalytic activity, by tracking the redox characteristics of each element upon sweeping the electrode potential. The detection scheme we describe here is general and can be applied to time-resolved studies of materials consisting of multiple elements, to follow the dynamics of catalytic and electron transfer reactions.

Simultaneous detection of electronic structure changes from two elements of a bifunctional catalyst using wavelength-dispersive X-ray emission spectroscopy and in situ electrochemistry

DOE PAGES

Gul, Sheraz; Ng, Jia Wei Desmond; Alonso-Mori, Roberto; ...

2015-02-25

Multielectron catalytic reactions, such as water oxidation, nitrogen reduction, or hydrogen production in enzymes and inorganic catalysts often involve multimetallic clusters. In these systems, the reaction takes place between metals or metals and ligands to facilitate charge transfer, bond formation/breaking, substrate binding, and release of products. In this study, we present a method to detect X-ray emission signals from multiple elements simultaneously, which allows for the study of charge transfer and the sequential chemistry occurring between elements. Kβ X-ray emission spectroscopy (XES) probes charge and spin states of metals as well as their ligand environment. A wavelength-dispersive spectrometer based onmore » the von Hamos geometry was used to disperse Kβ signals of multiple elements onto a position detector, enabling an XES spectrum to be measured in a single-shot mode. This overcomes the scanning needs of the scanning spectrometers, providing data free from temporal and normalization errors and therefore ideal to follow sequential chemistry at multiple sites. We have applied this method to study MnOx-based bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In particular, we investigated the effects of adding a secondary element, Ni, to form MnNiOx and its impact on the chemical states and catalytic activity, by tracking the redox characteristics of each element upon sweeping the electrode potential. In conclusion, the detection scheme we describe here is general and can be applied to time-resolved studies of materials consisting of multiple elements, to follow the dynamics of catalytic and electron transfer reactions.« less

Evolution of catalytic RNA in the laboratory

NASA Technical Reports Server (NTRS)

Joyce, Gerald F.

1992-01-01

We are interested in the biochemistry of existing RNA enzymes and in the development of RNA enzymes with novel catalytic function. The focal point of our research program has been the design and operation of a laboratory system for the controlled evolution of catalytic RNA. This system serves as working model of RNA-based life and can be used to explore the catalytic potential of RNA. Evolution requires the integration of three chemical processes: amplification, mutation, and selection. Amplification results in additional copies of the genetic material. Mutation operates at the level of genotype to introduce variability, this variability in turn being expressed as a range of phenotypes. Selection operates at the level of phenotype to reduce variability by excluding those individuals that do not conform to the prevailing fitness criteria. These three processes must be linked so that only the selected individuals are amplified, subject to mutational error, to produce a progeny distribution of mutant individuals. We devised techniques for the amplification, mutation, and selection of catalytic RNA, all of which can be performed rapidly in vitro within a single reaction vessel. We integrated these techniques in such a way that they can be performed iteratively and routinely. This allowed us to conduct evolution experiments in response to artificially-imposed selection constraints. Our objective was to develop novel RNA enzymes by altering the selection constraints in a controlled manner. In this way we were able to expand the catalytic repertoire of RNA. Our long-range objective is to develop an RNA enzyme with RNA replicase activity. If such an enzyme had the ability to produce additional copies of itself, then RNA evolution would operate autonomously and the origin of life will have been realized in the laboratory.

A new approach for crystallization of copper(ii) oxide hollow nanostructures with superior catalytic and magnetic response

NASA Astrophysics Data System (ADS)

Singh, Inderjeet; Landfester, Katharina; Chandra, Amreesh; Muñoz-Espí, Rafael

2015-11-01

We report the synthesis of copper(ii) oxide hollow nanostructures at ambient pressure and close to room temperature by applying the soft templating effect provided by the confinement of droplets in miniemulsion systems. Particle growth can be explained by considering a mechanism that involves both diffusion and reaction control. The catalytic reduction of p-nitrophenol in aqueous media is used as a model reaction to prove the catalytic activity of the materials: the synthesized hollow structures show nearly 100 times higher rate constants than solid CuO microspheres. The kinetic behavior and the order of the reduction reaction change due to the increase of the surface area of the hollow structures. The synthesis also leads to modification of physical properties such as magnetism.We report the synthesis of copper(ii) oxide hollow nanostructures at ambient pressure and close to room temperature by applying the soft templating effect provided by the confinement of droplets in miniemulsion systems. Particle growth can be explained by considering a mechanism that involves both diffusion and reaction control. The catalytic reduction of p-nitrophenol in aqueous media is used as a model reaction to prove the catalytic activity of the materials: the synthesized hollow structures show nearly 100 times higher rate constants than solid CuO microspheres. The kinetic behavior and the order of the reduction reaction change due to the increase of the surface area of the hollow structures. The synthesis also leads to modification of physical properties such as magnetism. Electronic supplementary information (ESI) available: Associated structural and morphological analysis, XPS characterization, BET surface area, catalytic measurements, recycle tests of the catalyst, and magnetic characterizations. See DOI: 10.1039/c5nr05579b

Catalytic multi-stage liquefaction of coal at HTI: Bench-scale studies in coal/waste plastics coprocessing

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

Pradhan, V.R.; Lee, L.K.; Stalzer, R.H.

1995-12-31

The development of Catalytic Multi-Stage Liquefaction (CMSL) at HTI has focused on both bituminous and sub-bituminous coals using laboratory, bench and PDU scale operations. The crude oil equivalent cost of liquid fuels from coal has been curtailed to about $30 per barrel, thus achieving over 30% reduction in the price that was evaluated for the liquefaction technologies demonstrated in the late seventies and early eighties. Contrary to the common belief, the new generation of catalytic multistage coal liquefaction process is environmentally very benign and can produce clean, premium distillates with a very low (<10ppm) heteroatoms content. The HTI Staff hasmore » been involved over the years in process development and has made significant improvements in the CMSL processing of coals. A 24 month program (extended to September 30, 1995) to study novel concepts, using a continuous bench scale Catalytic Multi-Stage unit (30kg coal/day), has been initiated since December, 1992. This program consists of ten bench-scale operations supported by Laboratory Studies, Modelling, Process Simulation and Economic Assessments. The Catalytic Multi-Stage Liquefaction is a continuation of the second generation yields using a low/high temperature approach. This paper covers work performed between October 1994- August 1995, especially results obtained from the microautoclave support activities and the bench-scale operations for runs CMSL-08 and CMSL-09, during which, coal and the plastic components for municipal solid wastes (MSW) such as high density polyethylene (HDPE)m, polypropylene (PP), polystyrene (PS), and polythylene terphthlate (PET) were coprocessed.« less

Merging Visible Light Photoredox Catalysis with Metal Catalyzed C–H Activations: On the Role of Oxygen and Superoxide Ions as Oxidants

PubMed Central

2016-01-01

Conspectus The development of efficient catalytic systems for direct aromatic C–H bond functionalization is a long-desired goal of chemists, because these protocols provide environmental friendly and waste-reducing alternatives to classical methodologies for C–C and C–heteroatom bond formation. A key challenge for these transformations is the reoxidation of the in situ generated metal hydride or low-valent metal complexes of the primary catalytic bond forming cycle. To complete the catalytic cycle and to regenerate the C–H activation catalyst, (super)stoichiometric amounts of Cu(II) or Ag(I) salts have often been applied. Recently, “greener” approaches have been developed by applying molecular oxygen in combination with Cu(II) salts, internal oxidants that are cleaved during the reaction, or solvents or additives enabling the metal hydride reoxidation. All these approaches improved the environmental friendliness but have not overcome the obstacles associated with the overall limited functional group and substrate tolerance. Hence, catalytic processes that do not feature the unfavorable aspects described above and provide products in a streamlined as well as economically and ecologically advantageous manner would be desirable. In this context, we decided to examine visible light photoredox catalysis as a new alternative to conventionally applied regeneration/oxidation procedures. This Account summarizes our recent advances in this expanding area and will highlight the new concept of merging distinct redox catalytic processes for C–H functionalizations through the application of visible light photoredox catalysis. Photoredox catalysis can be considered as catalytic electron-donating or -accepting processes, making use of visible-light absorbing homogeneous and heterogeneous metal-based catalysts, as well as organic dye sensitizers or polymers. As a consequence, photoredox catalysis is, in principle, an ideal tool for the recycling of any given metal catalyst via a coupled electron transfer (ET) process. Here we describe our first successful endeavors to address the above challenges by combining visible light photoredox catalysis with different ruthenium, rhodium, or palladium catalyzed C–H activations. Since only small amounts of the oxidant are generated and are immediately consumed in these transformations, side reactions of substrates or products can be avoided. Thus, usually oxidant-sensible substrates can be used, which makes these methods highly suitable for complex molecular structure syntheses. Moreover, mechanistic studies shed light on new reaction pathways, intermediates, and in situ generated species. The successful development of our dual catalysis concept, consisting of combined visible light photoredox catalysis and metal catalyzed C–H functionalization, provides many new opportunities for further explorations in the field of C–H functionalization. PMID:27556812

Characterization of the catalytic center of the Ebola virus L polymerase.

PubMed

Schmidt, Marie Luisa; Hoenen, Thomas

2017-10-01

Ebola virus (EBOV) causes a severe hemorrhagic fever in humans and non-human primates. While no licensed therapeutics are available, recently there has been tremendous progress in developing antivirals. Targeting the ribonucleoprotein complex (RNP) proteins, which facilitate genome replication and transcription, and particularly the polymerase L, is a promising antiviral approach since these processes are essential for the virus life cycle. However, until now little is known about L in terms of its structure and function, and in particular the catalytic center of the RNA-dependent RNA polymerase (RdRp) of L, which is one of the most promising molecular targets, has never been experimentally characterized. Using multiple sequence alignments with other negative sense single-stranded RNA viruses we identified the putative catalytic center of the EBOV RdRp. An L protein with mutations in this center was then generated and characterized using various life cycle modelling systems. These systems are based on minigenomes, i.e. miniature versions of the viral genome, in which the viral genes are exchanged against a reporter gene. When such minigenomes are coexpressed with RNP proteins in mammalian cells, the RNP proteins recognize them as authentic templates for replication and transcription, resulting in reporter activity reflecting these processes. Replication-competent minigenome systems indicated that our L catalytic domain mutant was impaired in genome replication and/or transcription, and by using replication-deficient minigenome systems, as well as a novel RT-qPCR-based genome replication assay, we showed that it indeed no longer supported either of these processes. However, it still showed similar expression to wild-type L, and retained its ability to be incorporated into inclusion bodies, which are the sites of EBOV genome replication. We have experimentally defined the catalytic center of the EBOV RdRp, and thus a promising antiviral target regulating an essential aspect of the EBOV life cycle.

Analysis and properties of the decarboxylation products of oleic acid by catalytic triruthenium dodecacarbonyl

USDA-ARS?s Scientific Manuscript database

Recently, ruthenium-catalyzed isomerization-decarboxylation of fatty acids to give alkene mixtures was reported. When the substrate was oleic acid, the reaction yielded a mixture consisting of heptadecene isomers. In this work, we report the compositional analysis of the mixture obtained by triruthe...

Catalytic ozonation of petroleum refinery wastewater utilizing Mn-Fe-Cu/Al2O 3 catalyst.

PubMed

Chen, Chunmao; Yoza, Brandon A; Wang, Yandan; Wang, Ping; Li, Qing X; Guo, Shaohui; Yan, Guangxu

2015-04-01

There is of great interest to develop an economic and high-efficient catalytic ozonation system (COS) for the treatment of biologically refractory wastewaters. Applications of COS require options of commercially feasible catalysts. Experiments in the present study were designed to prepare and investigate a novel manganese-iron-copper oxide-supported alumina-assisted COS (Mn-Fe-Cu/Al2O3-COS) for the pretreatment of petroleum refinery wastewater. The highly dispersed composite metal oxides on the catalyst surface greatly promoted the performance of catalytic ozonation. Hydroxyl radical mediated oxidation is a dominant reaction in Mn-Fe-Cu/Al2O3-COS. Mn-Fe-Cu/Al2O3-COS enhanced COD removal by 32.7% compared with a single ozonation system and by 8-16% compared with Mn-Fe/Al2O3-COS, Mn-Cu/Al2O3-COS, and Fe-Cu/Al2O3-COS. The O/C and H/C ratios of oxygen-containing polar compounds significantly increased after catalytic ozonation, and the biodegradability of petroleum refinery wastewater was significantly improved. This study illustrates potential applications of Mn-Fe-Cu/Al2O3-COS for pretreatment of biologically refractory wastewaters.

One-Pot Conversion of Carbohydrates into Furan Derivatives via Furfural and 5-Hydroxylmethylfurfural as Intermediates.

PubMed

Liu, Bing; Zhang, Zehui

2016-08-23

Recently, there has been growing interest in the transformation of renewable biomass into value-added fuels and chemicals. The catalytic conversion of naturally abundant carbohydrates can generate two-important furan chemicals: 5-hydroxymethylfurfural (HMF) from C6 carbohydrates and furfural from C5 carbohydrates. Both HMF and furfural have received great interest as precursors in the synthesis of commodity chemicals and liquid fuels. In recent years, a trend has emerged to integrate sequential catalytic processes involving multistep reactions for the direct one-pot transformation of carbohydrates into the aimed fuels and chemicals. One-pot reactions have remarkably unique and environmentally friendly benefits, including the fact that isolation and purification of intermediate compounds can be avoided. Herein, the present article aims to review recent advances in the one-pot conversion of carbohydrates into furan derivatives via furfural and HMF as intermediates. Special attention will be paid to the catalytic systems, mechanistic insight, reaction pathways, and catalyst stability. It is expected that this review will guide researchers to develop effective catalytic systems for the one-pot transformation of carbohydrates into furan derivatives. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Destruction of problematic airborne contaminants by hydrogen reduction using a Catalytically Active, Regenerable Sorbent (CARS)

NASA Technical Reports Server (NTRS)

Thompson, John O.; Akse, James R.

1993-01-01

Thermally regenerable sorbent beds were demonstrated to be a highly efficient means for removal of toxic airborne trace organic contaminants aboard spacecraft. The utilization of the intrinsic weight savings available through this technology was not realized since many of the contaminants desorbed during thermal regeneration are poisons to the catalytic oxidizer or form highly toxic oxidation by-products in the Trace Contaminant Control System (TCCS). Included in this class of compounds are nitrogen, sulfur, silicon, and halogen containing organics. The catalytic reduction of these problematic contaminants using hydrogen at low temperatures (200-300 C) offers an attractive route for their destruction since the by-products of such reactions, hydrocarbons and inorganic gases, are easily removed by existing technology. In addition, the catalytic oxidizer can be operated more efficiently due to the absence of potential poisons, and any posttreatment beds can be reduced in size. The incorporation of the catalyst within the sorbent bed further improves the system's efficiency. The demonstration of this technology provides the basis for an efficient regenerable TCCS for future NASA missions and can be used in more conventional settings to efficiently remove environmental pollutants.

Catalytic methods using molecular oxygen for treatment of PMMS and ECLSS waste streams, volume 2

NASA Technical Reports Server (NTRS)

Akse, James R.

1992-01-01

Catalytic oxidation has proven to be an effective addition to the baseline sorption, ion exchange water reclamation technology which will be used on Space Station Freedom (SSF). Low molecular weight, polar organics such as alcohols, aldehydes, ketones, amides, and thiocarbamides which are poorly removed by the baseline multifiltration (MF) technology can be oxidized to carbon dioxide at low temperature (121 C). The catalytic oxidation process by itself can reduce the Total Organic Carbon (TOC) to below 500 ppb for solutions designed to model these waste waters. Individual challenges by selected contaminants have shown only moderate selectivity towards particular organic species. The combined technology is applicable to the more complex waste water generated in the Process Materials Management System (PMMS) and Environmental Control and Life Support System (ECLSS) aboard SSF. During the phase 3 Core Module Integrated Facility (CMIF) water recovery tests at NASA MSFC, real hygiene waste water and humidity condensate were processed to meet potable specifications by the combined technology. A kinetic study of catalytic oxidation demonstrates that the Langmuir-Hinshelwood rate equation for heterogeneous catalysts accurately represent the kinetic behavior. From this relationship, activation energy and rate constants for acetone were determined.

Calixarenes and Their Biomimetic Applications

PubMed Central

Agrawal, Y. K.; Bhatt, Harshit

2004-01-01

The synthetic models for the structures, spectroscopic properties and catalytic activities of metalloprotein active sites have been reviewed. Calixarenes were used as new biomimetic catalysts because of their advantage of providing preorganiiation of the catalytic group, which can bind the substrate dynamically that results in fast turnover and fast release of the products. Functional and structural models based on calixarenes are presented and in addition importance of molecular recognition and non-covalent interactions e.g. hydrogen bonding and their role in biological systems are discussed with the help of synthetic systems. PMID:18365079

Recent Developments in Hydrogen Evolving Molecular Cobalt(II)-Polypyridyl Catalysts

PubMed Central

Queyriaux, N.; Jane, R. T.; Massin, J.; Artero, V.; Chavarot-Kerlidou, M.

2015-01-01

The search for efficient noble metal-free hydrogen-evolving catalysts is the subject of intense research activity. A new family of molecular cobalt(II)-polypyridyl catalysts has recently emerged. These catalysts prove more robust under reductive conditions than other cobalt-based systems and display high activities under fully aqueous conditions. This review discusses the design, characterization, and evaluation of these catalysts for electrocatalytic and light-driven hydrogen production. Mechanistic considerations are addressed and structure-catalytic activity relationships identified in order to guide the future design of more efficient catalytic systems. PMID:26688590

Bioinspired construction of multi-enzyme catalytic systems.

PubMed

Shi, Jiafu; Wu, Yizhou; Zhang, Shaohua; Tian, Yu; Yang, Dong; Jiang, Zhongyi

2018-06-18

Enzyme catalysis, as a green, efficient process, displays exceptional functionality, adaptivity and sustainability. Multi-enzyme catalysis, which can accomplish the tandem synthesis of valuable materials/chemicals from renewable feedstocks, establishes a bridge between single-enzyme catalysis and whole-cell catalysis. Multi-enzyme catalysis occupies a unique and indispensable position in the realm of biological reactions for energy and environmental applications. Two complementary strategies, i.e., compartmentalization and substrate channeling, have been evolved by living organisms for implementing the complex in vivo multi-enzyme reactions (MERs), which have been applied to construct multi-enzyme catalytic systems (MECSs) with superior catalytic activity and stabilities in practical biocatalysis. This tutorial review aims to present the recent advances and future prospects in this burgeoning research area, stressing the features and applications of the two strategies for constructing MECSs and implementing in vitro MERs. The concluding remarks are presented with a perspective on the construction of MECSs through rational combination of compartmentalization and substrate channeling.

A bioinspired catalytic aerobic oxidative C-H functionalization of primary aliphatic amines: synthesis of 1,2-disubstituted benzimidazoles.

PubMed

Nguyen, Khac Minh Huy; Largeron, Martine

2015-09-01

Aerobic oxidative CH functionalization of primary aliphatic amines has been accomplished with a biomimetic cooperative catalytic system to furnish 1,2-disubstituted benzimidazoles that play an important role as drug discovery targets. This one-pot atom-economical multistep process, which proceeds under mild conditions, with ambient air and equimolar amounts of each coupling partner, constitutes a convenient environmentally friendly strategy to functionalize non-activated aliphatic amines that remain challenging substrates for non-enzymatic catalytic aerobic systems. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of Creative Commons Attribution NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Efficient catalytic system for the direct transformation of lignocellulosic biomass to furfural and 5-hydroxymethylfurfural.

PubMed

Zhang, Luxin; Xi, Guoyun; Zhang, Jiaxin; Yu, Hongbing; Wang, Xiaochang

2017-01-01

A feasible approach was developed for the co-production of 5-hydroxymethylfurfural (5-HMF) and furfural from corncob via a new porous polytriphenylamine-SO 3 H (SPTPA) solid acid catalyst in lactone solvents. XRD, SEM, XPS, N 2 adsorption-desorption, elemental analysis, TG-DTA, acid-base titration and FTIR spectroscopy techniques were used to characterize the catalyst. This study demonstrates and optimizes the catalytic performance of SPTPA and solvent selection. SPTPA was found to exhibit superior catalytic ability in γ-valerolactone (GVL). Under the optimum reaction conditions, simultaneously encouraging yields of furfural (73.9%) and 5-HMF (32.3%) were achieved at 448K. The main advantages of this process include reasonable yields of both 5-HMF and furfural in the same reaction system, practical simplicity for the raw biomass utilization, and the use of a safe and environmentally benign solvent. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nanoscale zero-valent iron incorporated with nanomagnetic diatomite for catalytic degradation of methylene blue in heterogeneous Fenton system.

PubMed

Zha, Yiming; Zhou, Ziqing; He, Haibo; Wang, Tianlin; Luo, Liqiang

2016-01-01

Nanoscale zero-valent iron (nZVI) incorporated with nanomagnetic diatomite (DE) composite material was prepared for catalytic degradation of methylene blue (MB) in heterogeneous Fenton system. The material was constructed by two facile steps: Fe3O4 magnetic nanoparticles were supported on DE by chemical co-precipitation method, after which nZVI was incorporated into magnetic DE by liquid-phase chemical reduction strategy. The as-prepared catalyst was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, magnetic properties measurement and nitrogen adsorption-desorption isotherm measurement. The novel nZVI@Fe3O4-diatomite nanocomposites showed a distinct catalytic activity and a desirable effect for degradation of MB. MB could be completely decolorized within 8 min and the removal efficiency of total organic carbon could reach to 90% after reaction for 1 h.

Low pressure EGR system having full range capability

DOEpatents

Easley, Jr., William Lanier; Milam, David Michael; Roozenboom, Stephan Donald; Bond, Michael Steven; Kapic, Amir

2009-09-22

An exhaust treatment system for an engine is disclosed and may have an air induction circuit, an exhaust circuit, and an exhaust recirculation circuit. The air induction circuit may be configured to direct air into the engine. The exhaust circuit may be configured to direct exhaust from the engine and include a turbine driven by the exhaust, a particulate filter disposed in series with and downstream of the turbine, and a catalytic device disposed in series with and downstream of the particulate filter. The exhaust recirculation circuit may be configured to selectively redirect at least some of the exhaust from between the particulate filter and the catalytic device to the air induction circuit. The catalytic device is selected to create backpressure within the exhaust circuit sufficient to ensure that, under normal engine operating conditions above low idle, exhaust can flow into the air induction circuit without throttling of the air.

A Hydrogen Peroxide Hot-Jet Simulator for Wind-Tunnel Tests of Turbojet-Exit Models

NASA Technical Reports Server (NTRS)

Runckel, Jack F.; Swihart, John M.

1959-01-01

A turbojet-engine-exhaust simulator which utilizes a hydrogen peroxide gas generator has been developed for powered-model testing in wind tunnels with air exchange. Catalytic decomposition of concentrated hydrogen peroxide provides a convenient and easily controlled method of providing a hot jet with characteristics that correspond closely to the jet of a gas turbine engine. The problems associated with simulation of jet exhausts in a transonic wind tunnel which led to the selection of a liquid monopropellant are discussed. The operation of the jet simulator consisting of a thrust balance, gas generator, exit nozzle, and auxiliary control system is described. Static-test data obtained with convergent nozzles are presented and shown to be in good agreement with ideal calculated values.

Molecular characterization of 45 kDa aspartic protease of Trichinella spiralis.

PubMed

Park, Jong Nam; Park, Sang Kyun; Cho, Min Kyoung; Park, Mi-Kyung; Kang, Shin Ae; Kim, Dong-Hee; Yu, Hak Sun

2012-12-21

In a previous study, we identified an aspartic protease gene (Ts-Asp) from the Trichinella spiralis muscle stage larva cDNA library. The gene sequence of Ts-Asp was 1281 bp long and was found to encode a protein consisting of 405 amino acids, with a molecular mass of 45.248 kD and a pI of 5.95. The deduced Ts-Asp has a conserved catalytic motif with catalytic aspartic acid residues in the active site, a common characteristic of aspartic proteases. In addition, the deduced amino acid sequence of Ts-Asp was found to possess significant homology (above 50%) with aspartic proteases from nematode parasites. Results of phylogenetic analysis indicated a close relationship of Ts-Asp with cathepsin D aspartic proteases. For production of recombinant Ts-Asp (rTs-Asp), the pGEX4T expression system was used. Like other proteases, the purified rTs-Asp was able to digest collagen matrix in vitro. Abundant expression of Ts-Asp was observed in muscle stage larva. Ts-Asp was detected in ES proteins, and was able to elicit the production of specific antibodies. It is the first report of molecular characterization of aspartic protease isolated from T. spiralis. Copyright © 2012 Elsevier B.V. All rights reserved.

Catalytic conversion reactions in nanoporous systems with concentration-dependent selectivity: Statistical mechanical modeling

DOE PAGES

Garcia, Andres; Wang, Jing; Windus, Theresa L.; ...

2016-05-20

Statistical mechanical modeling is developed to describe a catalytic conversion reaction A → B c or B t with concentration-dependent selectivity of the products, B c or B t, where reaction occurs inside catalytic particles traversed by narrow linear nanopores. The associated restricted diffusive transport, which in the extreme case is described by single-file diffusion, naturally induces strong concentration gradients. Hence, by comparing kinetic Monte Carlo simulation results with analytic treatments, selectivity is shown to be impacted by strong spatial correlations induced by restricted diffusivity in the presence of reaction and also by a subtle clustering of reactants, A.

Thermodynamics and kinetics of RNA tertiary structure formation in the junctionless hairpin ribozyme.

PubMed

White, Neil A; Hoogstraten, Charles G

2017-09-01

The hairpin ribozyme consists of two RNA internal loops that interact to form the catalytically active structure. This docking transition is a rare example of intermolecular formation of RNA tertiary structure without coupling to helix annealing. We have used temperature-dependent surface plasmon resonance (SPR) to characterize the thermodynamics and kinetics of RNA tertiary structure formation for the junctionless form of the ribozyme, in which loops A and B reside on separate molecules. We find docking to be strongly enthalpy-driven and to be accompanied by substantial activation barriers for association and dissociation, consistent with the structural reorganization of both internal loops upon complex formation. Comparisons with the parallel analysis of a ribozyme variant carrying a 2'-O-methyl modification at the self-cleavage site and with published data in other systems reveal a surprising diversity of thermodynamic signatures, emphasizing the delicate balance of contributions to the free energy of formation of RNA tertiary structure. Copyright © 2017 Elsevier B.V. All rights reserved.

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

PubMed

Liu, Lichen; Corma, Avelino

2018-05-23

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal-support interaction, and metal-reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles) in a unifying manner.

Understanding Anionic "Ligandless" Palladium Species in the Mizoroki-Heck Reaction.

PubMed

Schroeter, Felix; Strassner, Thomas

2018-05-07

The anionic complex [NBu 4 ][Pd(DMSO)Cl 3 ], as a "ligandless" system, was shown to be an active catalyst in the Mizoroki-Heck coupling of aryl chlorides in the absence of strongly σ-donating ligands. To investigate the experimentally observed influence of halides and the amount of water on the catalytic activity, we employed a combination of experiments and theoretical calculations. The presence of water was shown to be critical for the formation of the active palladium(0) species by oxidation of in situ generated tributylamine. Oxidative addition to an anionic palladium(0) species was found to be the rate-determining step of the catalytic cycle. For the ensuing steps, both neutral and anionic pathways were considered. It was shown that, in the absence of strongly σ-donating neutral ligands, chloride ions stabilize the catalytic intermediates. Therefore, an anionic pathway is preferred, which explains the need for tetrabutylammonium chloride as an additive. The study of the influence of bromide ions on the catalytic activity revealed that the strongly exergonic displacement of the neutral substrates by bromide ions lowers the catalytic activity.

Catalytic processes for space station waste conversion

NASA Technical Reports Server (NTRS)

Schoonover, M. W.; Madsen, R. A.

1986-01-01

Catalytic techniques for processing waste products onboard space vehicles were evaluated. The goal of the study was the conversion of waste to carbon, wash water, oxygen and nitrogen. However, the ultimate goal is conversion to plant nutrients and other materials useful in closure of an ecological life support system for extended planetary missions. The resulting process studied involves hydrolysis at 250 C and 600 psia to break down and compact cellulose material, distillation at 100 C to remove water, coking at 450 C and atmospheric pressure, and catalytic oxidation at 450 to 600 C and atmospheric pressure. Tests were conducted with a model waste to characterize the hydrolysis and coking processes. An oxidizer reactor was sized based on automotive catalytic conversion experience. Products obtained from the hydrolysis and coking steps included a solid residue, gases, water condensate streams, and a volatile coker oil. Based on the data obtained, sufficient component sizing was performed to make a preliminary comparison of the catalytic technique with oxidation for processing waste for a six-man spacecraft. Wet oxidation seems to be the preferred technique from the standpoint of both component simplicity and power consumption.

Versatile Three-Dimensional Porous Cu@Cu2 O Aerogel Networks as Electrocatalysts and Mimicking Peroxidases.

PubMed

Ling, Pinghua; Zhang, Qiang; Cao, Tingting; Gao, Feng

2018-06-04

A facile strategy is presented to form 3D porous Cu@Cu 2 O aerogel networks by self-assembling Cu@Cu 2 O nanoparticles with the diameters of ca. 40 nm for constructing catalytic interfaces. Unexpectedly, the prepared Cu@Cu 2 O aerogel networks display excellent electrocatalytic activity to glucose oxidation at a low onset potential of ca. 0.25 V. Moreover, the Cu@Cu 2 O aerogels also can act as mimicking-enzymes including horseradish peroxidase and NADH peroxidase, and show obvious enzymatic catalytic activities to the oxidation of dopamine (DA), o-phenyldiamine (OPD), 3,3,5,5-tetramethylbenzidine (TMB), and dihydronicotinamide adenine dinucleotide (NADH) in the presence of H 2 O 2 . These 3D Cu@Cu 2 O aerogel networks are a new class of porous catalytic materials as mimic peroxidases and electrocatalysts and offer a novel platform to construct catalytic interfaces for promising applications in electrochemical sensors and artificial enzymatic catalytic systems. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Transient Catalytic Combustor Model With Detailed Gas and Surface Chemistry

NASA Technical Reports Server (NTRS)

Struk, Peter M.; Dietrich, Daniel L.; Mellish, Benjamin P.; Miller, Fletcher J.; Tien, James S.

2005-01-01

In this work, we numerically investigate the transient combustion of a premixed gas mixture in a narrow, perfectly-insulated, catalytic channel which can represent an interior channel of a catalytic monolith. The model assumes a quasi-steady gas-phase and a transient, thermally thin solid phase. The gas phase is one-dimensional, but it does account for heat and mass transfer in a direction perpendicular to the flow via appropriate heat and mass transfer coefficients. The model neglects axial conduction in both the gas and in the solid. The model includes both detailed gas-phase reactions and catalytic surface reactions. The reactants modeled so far include lean mixtures of dry CO and CO/H2 mixtures, with pure oxygen as the oxidizer. The results include transient computations of light-off and system response to inlet condition variations. In some cases, the model predicts two different steady-state solutions depending on whether the channel is initially hot or cold. Additionally, the model suggests that the catalytic ignition of CO/O2 mixtures is extremely sensitive to small variations of inlet equivalence ratios and parts per million levels of H2.

Catalytic oxidation of volatile organic compounds (VOCs) - A review

NASA Astrophysics Data System (ADS)

Kamal, Muhammad Shahzad; Razzak, Shaikh A.; Hossain, Mohammad M.

2016-09-01

Emission of volatile organic compounds (VOCs) is one of the major contributors to air pollution. The main sources of VOCs are petroleum refineries, fuel combustions, chemical industries, decomposition in the biosphere and biomass, pharmaceutical plants, automobile industries, textile manufacturers, solvents processes, cleaning products, printing presses, insulating materials, office supplies, printers etc. The most common VOCs are halogenated compounds, aldehydes, alcohols, ketones, aromatic compounds, and ethers. High concentrations of these VOCs can cause irritations, nausea, dizziness, and headaches. Some VOCs are also carcinogenic for both humans and animals. Therefore, it is crucial to minimize the emission of VOCs. Among the available technologies, the catalytic oxidation of VOCs is the most popular because of its versatility of handling a range of organic emissions under mild operating conditions. Due to that fact, there are numerous research initiatives focused on developing advanced technologies for the catalytic destruction of VOCs. This review discusses recent developments in catalytic systems for the destruction of VOCs. Review also describes various VOCs and their sources of emission, mechanisms of catalytic destruction, the causes of catalyst deactivation, and catalyst regeneration methods.

Quantitative Characterization of Major Hepatic UDP-Glucuronosyltransferase Enzymes in Human Liver Microsomes: Comparison of Two Proteomic Methods and Correlation with Catalytic Activity.

PubMed

Achour, Brahim; Dantonio, Alyssa; Niosi, Mark; Novak, Jonathan J; Fallon, John K; Barber, Jill; Smith, Philip C; Rostami-Hodjegan, Amin; Goosen, Theunis C

2017-10-01

Quantitative characterization of UDP-glucuronosyltransferase (UGT) enzymes is valuable in glucuronidation reaction phenotyping, predicting metabolic clearance and drug-drug interactions using extrapolation exercises based on pharmacokinetic modeling. Different quantitative proteomic workflows have been employed to quantify UGT enzymes in various systems, with reports indicating large variability in expression, which cannot be explained by interindividual variability alone. To evaluate the effect of methodological differences on end-point UGT abundance quantification, eight UGT enzymes were quantified in 24 matched liver microsomal samples by two laboratories using stable isotope-labeled (SIL) peptides or quantitative concatemer (QconCAT) standard, and measurements were assessed against catalytic activity in seven enzymes ( n = 59). There was little agreement between individual abundance levels reported by the two methods; only UGT1A1 showed strong correlation [Spearman rank order correlation (Rs) = 0.73, P < 0.0001; R 2 = 0.30; n = 24]. SIL-based abundance measurements correlated well with enzyme activities, with correlations ranging from moderate for UGTs 1A6, 1A9, and 2B15 (Rs = 0.52-0.59, P < 0.0001; R 2 = 0.34-0.58; n = 59) to strong correlations for UGTs 1A1, 1A3, 1A4, and 2B7 (Rs = 0.79-0.90, P < 0.0001; R 2 = 0.69-0.79). QconCAT-based data revealed generally poor correlation with activity, whereas moderate correlations were shown for UGTs 1A1, 1A3, and 2B7. Spurious abundance-activity correlations were identified in the cases of UGT1A4/2B4 and UGT2B7/2B15, which could be explained by correlations of protein expression between these enzymes. Consistent correlation of UGT abundance with catalytic activity, demonstrated by the SIL-based dataset, suggests that quantitative proteomic data should be validated against catalytic activity whenever possible. In addition, metabolic reaction phenotyping exercises should consider spurious abundance-activity correlations to avoid misleading conclusions. Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics.

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

Kim, Moon-Jung; Lee, Byung Cheon; Division of Biotechnology, College of Life Sciences & Biotechnology, Korea University, Seoul 136-701

Thioredoxin (Trx) is a major thiol-disulfide reductase that plays a role in many biological processes, including DNA replication and redox signaling. Although selenocysteine (Sec)-containing Trxs have been identified in certain bacteria, their enzymatic properties have not been characterized. In this study, we expressed a selenoprotein Trx from Treponema denticola, an oral spirochete, in Escherichia coli and characterized this selenoenzyme and its natural cysteine (Cys) homologue using E. coli Trx1 as a positive control. {sup 75}Se metabolic labeling and mutation analyses showed that the SECIS (Sec insertion sequence) of T. denticola selenoprotein Trx is functional in the E. coli Sec insertion system with specificmore » selenium incorporation into the Sec residue. The selenoprotein Trx exhibited approximately 10-fold higher catalytic activity than the Sec-to-Cys version and natural Cys homologue and E. coli Trx1, suggesting that Sec confers higher catalytic activity on this thiol-disulfide reductase. Kinetic analysis also showed that the selenoprotein Trx had a 30-fold higher K{sub m} than Cys-containing homologues, suggesting that this selenoenzyme is adapted to work efficiently with high concentrations of substrate. Collectively, the results of this study support the hypothesis that selenium utilization in oxidoreductase systems is primarily due to the catalytic advantage provided by the rare amino acid, Sec. - Highlights: • The first characterization of a selenoprotein Trx is presented. • The selenoenzyme Trx exhibits 10-fold higher catalytic activity than Cys homologues. • Se utilization in Trx is primarily due to the catalytic advantage provided by Sec residue.« less

Poisoning of bubble propelled catalytic micromotors: the chemical environment matters

PubMed Central

Zhao, Guanjia; Sanchez, Samuel; Schmidt, Oliver G.

2013-01-01

Self-propelled catalytic microjets have attracted considerable attention in recent years and these devices have exhibited the ability to move in complex media. The mechanism of propulsion is via the Pt catalysed decomposition of H2O2 and it is understood that the Pt surface is highly susceptible to poisoning by sulphur-containing molecules. Here, we show that important extracellular thiols as well as basic organic molecules can significantly hamper the motion of catalytic microjet engines. This is due to two different mechanisms: (i) molecules such as dimethyl sulfoxide can quench the hydroxyl radicals produced at Pt surfaces and reduce the amount of oxygen gas generated and (ii) molecules containing –SH, –SSR, and –SCH3 moieties can poison the catalytically active platinum surface, inhibiting the motion of the jet engines. It is essential that the presence of such molecules in the environment be taken into consideration for future design and operation of catalytic microjet engines. We show this effect on catalytic micromotors prepared by both rolled-up and electrodeposition approaches, demonstrating that such poisoning is universal for Pt catalyzed micromotors. We believe that our findings will contribute significantly to this field to develop alternative systems or catalysts for self-propulsion when practical applications in the real environment are considered. PMID:23450281

Selective Transformation of Various Nitrogen-Containing Exhaust Gases toward N2 over Zeolite Catalysts.

PubMed

Zhang, Runduo; Liu, Ning; Lei, Zhigang; Chen, Biaohua

2016-03-23

In this review we focus on the catalytic removal of a series of N-containing exhaust gases with various valences, including nitriles (HCN, CH3CN, and C2H3CN), ammonia (NH3), nitrous oxide (N2O), and nitric oxides (NO(x)), which can cause some serious environmental problems, such as acid rain, haze weather, global warming, and even death. The zeolite catalysts with high internal surface areas, uniform pore systems, considerable ion-exchange capabilities, and satisfactory thermal stabilities are herein addressed for the corresponding depollution processes. The sources and toxicities of these pollutants are introduced. The important physicochemical properties of zeolite catalysts, including shape selectivity, surface area, acidity, and redox ability, are described in detail. The catalytic combustion of nitriles and ammonia, the direct catalytic decomposition of N2O, and the selective catalytic reduction and direct catalytic decomposition of NO are systematically discussed, involving the catalytic behaviors as well as mechanism studies based on spectroscopic and kinetic approaches and molecular simulations. Finally, concluding remarks and perspectives are given. In the present work, emphasis is placed on the structure-performance relationship with an aim to design an ideal zeolite-based catalyst for the effective elimination of harmful N-containing compounds.

Development and Testing of a Methane/Oxygen Catalytic Microtube Ignition System for Rocket Propulsion

NASA Technical Reports Server (NTRS)

Deans, Matthew

2012-01-01

This study sought to develop a catalytic ignition advanced torch system with a unique catalyst microtube design that could serve as a low energy alternative or redundant system for the ignition of methane and oxygen rockets. Development and testing of iterations of hardware was carried out to create a system that could operate at altitude and produce a torch. A unique design was created that initiated ignition via the catalyst and then propagated into external staged ignition. This system was able to meet the goals of operating across a range of atmospheric and altitude conditions with power inputs on the order of 20 to 30 watts with chamber pressures and mass flow rates typical of comparable ignition systems for a 100 lbf engine.

Development and Testing of a Methane/Oxygen Catalytic Microtube Ignition System for Rocket Propulsion

NASA Technical Reports Server (NTRS)

Deans, Matthew C.; Schneider, Steven J.

2012-01-01

This study sought to develop a catalytic ignition advanced torch system with a unique catalyst microtube design that could serve as a low energy alternative or redundant system for the ignition of methane and oxygen rockets. Development and testing of iterations of hardware was carried out to create a system that could operate at altitude and produce a torch. A unique design was created that initiated ignition via the catalyst and then propagated into external staged ignition. This system was able to meet the goals of operating across a range of atmospheric and altitude conditions with power inputs on the order of 20 to 30 watts with chamber pressures and mass flow rates typical of comparable ignition systems for a 100 Ibf engine.

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.

Crystal Structure of Haloalkane Dehalogenase LinB from Sphingomonas paucimobilis UT26 at 0.95 Å Resolution: Dynamics of Catalytic Residues

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

Oakley, Aaron J.; Klvana, Martin; Otyepka, Michal

We present the structure of LinB, a 33-kDa haloalkane dehalogenase from Sphingomonas paucimobilis UT26, at 0.95 {angstrom} resolution. The data have allowed us to directly observe the anisotropic motions of the catalytic residues. In particular, the side-chain of the catalytic nucleophile, Asp108, displays a high degree of disorder. It has been modeled in two conformations, one similar to that observed previously (conformation A) and one strained (conformation B) that approached the catalytic base (His272). The strain in conformation B was mainly in the C{sub {alpha}}-C{sub {beta}}-C{sub {gamma}} angle (126{sup o}) that deviated by 13.4{sup o} from the 'ideal' bond anglemore » of 112.6{sup o}. On the basis of these observations, we propose a role for the charge state of the catalytic histidine in determining the geometry of the catalytic residues. We hypothesized that double-protonation of the catalytic base (His272) reduces the distance between the side-chain of this residue and that of the Asp108. The results of molecular dynamics simulations were consistent with the structural data showing that protonation of the His272 side-chain nitrogen atoms does indeed reduce the distance between the side-chains of the residues in question, although the simulations failed to demonstrate the same degree of strain in the Asp108 C{sub {alpha}}-C{sub {beta}}-C{sub {gamma}} angle. Instead, the changes in the molecular dynamics structures were distributed over several bond and dihedral angles. Quantum mechanics calculations on LinB with 1-chloro-2,2-dimethylpropane as a substrate were performed to determine which active site conformations and protonation states were most likely to result in catalysis. It was shown that His272 singly protonated at N{sub {delta}1} and Asp108 in conformation A gave the most exothermic reaction ({Delta}H = -22 kcal/mol). With His272 doubly protonated at N{sub {delta}1} and N{sub {epsilon}2}, the reactions were only slightly exothermic or were endothermic. In all calculations starting with Asp108 in conformation B, the Asp108 C{sub {alpha}}-C{sub {beta}}-C{sub {gamma}} angle changed during the reaction and the Asp108 moved to conformation A. The results presented here indicate that the positions of the catalytic residues and charge state of the catalytic base are important for determining reaction energetics in LinB.« less

Metal-organic cooperative catalysis in C-H and C-C bond activation and its concurrent recovery.

PubMed

Park, Young Jun; Park, Jung-Woo; Jun, Chul-Ho

2008-02-01

The development of an efficient catalytic activation (cleavage) system for C-H and C-C bonds is an important challenge in organic synthesis, because these bonds comprise a variety of organic molecules such as natural products, petroleum oils, and polymers on the earth. Among many elegant approaches utilizing transition metals to activate C-H and C-C bonds facilely, chelation-assisted protocols based on the coordinating ability of an organic moiety have attracted great attention, though they have often suffered from the need for an intact coordinating group in a substrate. In this Account, we describe our entire efforts to activate C-H or C-C bonds adjacent to carbonyl groups by employing a new concept of metal-organic cooperative catalysis (MOCC), which enables the temporal installation of a 2-aminopyridyl group into common aldehydes or ketones in a catalytic way. Consequently, a series of new catalytic reactions such as alcohol hydroacylation, oxo-ester synthesis, C-C triple bond cleavage, hydrative dimerization of alkynes, and skeletal rearrangements of cyclic ketones was realized through MOCC. In particular, in the quest for an optimized MOCC system composed of a Wilkinson's catalyst (Ph 3P) 3RhCl and an organic catalyst (2-amino-3-picoline), surprising efficiency enhancements could be achieved when benzoic acid and aniline were introduced as promoters for the aldimine formation process. Furthermore, a notable accomplishment of C-C bond activation has been made using 2-amino-3-picoline as a temporary chelating auxiliary in the reactions of unstrained ketones with various terminal olefins and Wilkinson's catalyst. In the case of seven-membered cyclic ketones, an interesting ring contraction to five- or six-membered ones takes place through skeletal rearrangements initiated by the C-C bond activation of MOCC. On the other hand, the fundamental advances of these catalytic systems into recyclable processes could be achieved by immobilizing both metal and organic components using a hydrogen-bonded self-assembled system as a catalyst support. This catalyst-recovery system provides a homogeneous phase at high temperature during the reaction and a heterogeneous phase at room temperature after the reaction. The product could be separated conveniently from the self-assembly support system by decanting the upper layer. The immobilized catalysts of both 2-aminopyridine and rhodium metal species sustained high catalytic activity for up to the eight catalytic reactions. In conclusion, the successful incorporation of an organocatalytic cycle into a transition metal catalyzed reaction led us to find MOCC for C-H and C-C bond activation. In addition, the hydrogen-bonded self-assembled support has been developed for an efficient and effective recovery system of homogeneous catalysts and could be successful in immobilizing both metal and organic catalysts.

Fuel cell with interdigitated porous flow-field

DOEpatents

Wilson, Mahlon S.

1997-01-01

A polymer electrolyte membrane (PEM) fuel cell is formed with an improved system for distributing gaseous reactants to the membrane surface. A PEM fuel cell has an ionic transport membrane with opposed catalytic surfaces formed thereon and separates gaseous reactants that undergo reactions at the catalytic surfaces of the membrane. The fuel cell may also include a thin gas diffusion layer having first and second sides with a first side contacting at least one of the catalytic surfaces. A macroporous flow-field with interdigitated inlet and outlet reactant channels contacts the second side of the thin gas diffusion layer for distributing one of the gaseous reactants over the thin gas diffusion layer for transport to an adjacent one of the catalytic surfaces of the membrane. The porous flow field may be formed from a hydrophilic material and provides uniform support across the backside of the electrode assembly to facilitate the use of thin backing layers.

Fuel cell with interdigitated porous flow-field

DOEpatents

Wilson, M.S.

1997-06-24

A polymer electrolyte membrane (PEM) fuel cell is formed with an improved system for distributing gaseous reactants to the membrane surface. A PEM fuel cell has an ionic transport membrane with opposed catalytic surfaces formed thereon and separates gaseous reactants that undergo reactions at the catalytic surfaces of the membrane. The fuel cell may also include a thin gas diffusion layer having first and second sides with a first side contacting at least one of the catalytic surfaces. A macroporous flow-field with interdigitated inlet and outlet reactant channels contacts the second side of the thin gas diffusion layer for distributing one of the gaseous reactants over the thin gas diffusion layer for transport to an adjacent one of the catalytic surfaces of the membrane. The porous flow field may be formed from a hydrophilic material and provides uniform support across the backside of the electrode assembly to facilitate the use of thin backing layers. 9 figs.

Neptune's Triton: A moon rich in dry ice and carbon

NASA Technical Reports Server (NTRS)

Prentice, A. J. R.

1989-01-01

The encounter of the spacecraft Voyager 2 with Neptune and its large satellite Triton in August 1989 will provide a crucial test of ideas regarding the origin and chemical composition of the outer solar system. In this pre-encounter publication, the possibility is quantified that Titron is a captured moon which, like Pluto and Charon, originally condensed as a major planetesimal within the gas ring that was shed by the contracting protosolar cloud at Neptune's orbit. Ideas of supersonic convective turbulence are used to compute the gas pressure, temperature and rat of catalytic synthesis of CH4, CO2, and C(s) within the protosolar cloud, assuming that all C is initially present as CO. The calculations lead to a unique composition for Triton, Pluto, Charon: each body consists of, by mass, 18 1/2 percent solid CO2 ice, 4 percent graphite, 1/2 percent CH4 ice, 29 percent methanated water ice and 48 percent of anhydrous rock. This mix has a density consistent with that of the Pluto-Charon system and yields a predicted mean density for Triton of 2.20 + or - 0.5 g/cu cm, for satellite radius equal to 1,750 km.

Photocatalytic dehydrogenation of formic acid on CdS nanorods through Ni and Co redox mediation under mild conditions.

PubMed

Khan, Muhammad Abdullah; Rehman, Zia-Ur-; Nasir, Jamal Abdul; Hafeez, Muhammad; Arshad, Muhammad; Ali, Naveed Zafar; Teixieira, Ivo F; McPherson, Ian

2018-05-30

Selective release of hydrogen from formic acid (FA) is deemed feasible to solve issues associated with the release and storage of hydrogen. Here, we present a new efficient photocatalytic system consisting of CdS nanorods (NR), Ni, and Co to liberate hydrogen from formic acid. The optimised noble metal free catalytic system employs Ni/Co as a redox mediator to relay electrons and holes from CdS-NR to the Ni and Co respectively, which also deters the oxidation of CdS-NR. As a result, a high hydrogen production activity of 32.6 mmolh-1g-1 from the decomposition of FA was noted. Furthermore, the photocatalytic system exhibit sustained H2 production rate for 12 hours with sequential turnover numbers surpassing 4×103, 3×103 and 2×103 for Co-Ni/CdS-NR, Ni-CdS-NR and CoCl2/CdS-NR respectively. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Novel biocatalytic systems for maintaining the nucleotide balance based on adenylate kinase immobilized on carbon nanostructures.

PubMed

Hetmann, Anna; Wujak, Magdalena; Bolibok, Paulina; Zięba, Wojciech; Wiśniewski, Marek; Roszek, Katarzyna

2018-07-01

In this study graphene oxide (GO), carbon quantum dots (CQD) and carbon nanoonions (CNO) have been characterized and applied for the first time as a matrix for recombinant adenylate kinase (AK, EC 2.7.4.3) immobilization. AK is an enzyme fulfilling a key role in metabolic processes. This phosphotransferase catalyzes the interconversion of adenine nucleotides (ATP, ADP and AMP) and thereby participates in nucleotide homeostasis, monitors a cellular energy charge as well as acts as a component of purinergic signaling system. The AK activity in all obtained biocatalytic systems was higher as compared to the free enzyme. We have found that the immobilization on carbon nanostructures increased both activity and stability of AK. Moreover, the biocatalytic systems consisting of AK immobilized on carbon nanostructures can be easily and efficiently lyophilized without risk of desorption or decrease in the catalytic activity of the investigated enzyme. The positive action of AK-GO biocatalytic system in maintaining the nucleotide balance in in vitro cell culture was proved. Copyright © 2018 Elsevier B.V. All rights reserved.

Cross-catalytic hairpin assembly-based exponential signal amplification for CRET assay with low background noise.

PubMed

Yue, Shuzhen; Zhao, Tingting; Qi, Hongjie; Yan, Yongcun; Bi, Sai

2017-08-15

A toehold-mediated strand displacement (TMSD)-based cross-catalytic hairpin assembly (C-CHA) is demonstrated in this study, achieving exponential amplification of nucleic acids. Functionally, this system consists of four hairpins (H1, H2, H3 and H4) and one single-stranded initiator (I). Upon the introduction of I, the first CHA reaction (CHA1) is triggered, leading to the self-assembly of hybrid H1·H2 that then initiates the second CHA reaction (CHA2) to obtain the hybrid H3·H4. Since the single-stranded region in H3·H4 is identical to I, a new CHA1 is initiated, which thus achieves cross operation of CHA1 and CHA2 and exponential growth kinetics. Interestingly, because the C-CHA performs in a cascade manner, this system can be considered as multi-level molecular logic circuits with feedback mechanism. Moreover, through incorporating G-quadruplex subunits and fluorescein isothiocyanate (FITC) in the product of H1·H2, this C-CHA is readily utilized to fabricate a chemiluminescence resonance energy transfer (CRET) biosensing platform, achieving sensitive and selective detection of DNA and microRNA in real samples. Since the high background signal induced by FITC in the absence of initiator is greatly reduced through labeling quencher in H1, the signal-to-noise ratio and detection sensitivity are improved significantly. Therefore, our proposed C-CHA protocol holds a great potential for further applications in not only building complex autonomous systems but also the development of biosensing platforms and DNA nanotechnology. Copyright © 2017 Elsevier B.V. All rights reserved.

NAIM and site-specific functional group modification analysis of RNase P RNA: magnesium dependent structure within the conserved P1-P4 multihelix junction contributes to catalysis.

PubMed

Kaye, Nicholas M; Christian, Eric L; Harris, Michael E

2002-04-09

The tRNA processing endonuclease ribonuclease P contains an essential and highly conserved RNA molecule (RNase P RNA) that is the catalytic subunit of the enzyme. To identify and characterize functional groups involved in RNase P RNA catalysis, we applied self-cleaving ribozyme-substrate conjugates, on the basis of the RNase P RNA from Escherichia coli, in nucleotide analogue interference mapping (NAIM) and site-specific modification experiments. At high monovalent ion concentrations (3 M) that facilitate protein-independent substrate binding, we find that the ribozyme is largely insensitive to analogue substitution and that concentrations of Mg2+ (1.25 mM) well below that necessary for optimal catalytic rate (>100 mM) are required to produce interference effects because of modification of nucleotide bases. An examination of the pH dependence of the reaction rate at 1.25 mM Mg2+ indicates that the increased sensitivity to analogue interference is not due to a change in the rate-limiting step. The nucleotide positions detected by NAIM under these conditions are located exclusively in the catalytic domain, consistent with the proposed global structure of the ribozyme, and predominantly occur within the highly conserved P1-P4 multihelix junction. Several sensitive positions in J3/4 and J2/4 are proximal to a previously identified site of divalent metal ion binding in the P1-P4 element. Kinetic analysis of ribozymes with site-specific N7-deazaadenosine and deazaguanosine modifications in J3/4 was, in general, consistent with the interference results and also permitted the analysis of sites not accessible by NAIM. These results show that, in this region only, modification of the N7 positions of A62, A65, and A66 resulted in measurable effects on reaction rate and modification at each position displayed distinct sensitivities to Mg2+ concentration. These results reveal a restricted subset of individual functional groups within the catalytic domain that are particularly important for substrate cleavage and demonstrate a close association between catalytic function and metal ion-dependent structure in the highly conserved P1-P4 multihelix junction.

Structure-specificity relationships in Abp, a GH27 β-L-arabinopyranosidase from Geobacillus stearothermophilus T6.

PubMed

Lansky, Shifra; Salama, Rachel; Solomon, Hodaya V; Feinberg, Hadar; Belrhali, Hassan; Shoham, Yuval; Shoham, Gil

2014-11-01

L-Arabinose sugar residues are relatively abundant in plants and are found mainly in arabinan polysaccharides and in other arabinose-containing polysaccharides such as arabinoxylans and pectic arabinogalactans. The majority of the arabinose units in plants are present in the furanose form and only a small fraction of them are present in the pyranose form. The L-arabinan-utilization system in Geobacillus stearothermophilus T6, a Gram-positive thermophilic soil bacterium, has recently been characterized, and one of the key enzymes was found to be an intracellular β-L-arabinopyranosidase (Abp). Abp, a GH27 enzyme, was shown to remove β-L-arabinopyranose residues from synthetic substrates and from the native substrates sugar beet arabinan and larch arabinogalactan. The Abp monomer is made up of 448 amino acids, and based on sequence homology it was suggested that Asp197 is the catalytic nucleophile and Asp255 is the catalytic acid/base. In the current study, the detailed three-dimensional structure of wild-type Abp (at 2.28 Å resolution) and its catalytic mutant Abp-D197A with (at 2.20 Å resolution) and without (at 2.30 Å resolution) a bound L-arabinose product are reported as determined by X-ray crystallography. These structures demonstrate that the three-dimensional structure of the Abp monomer correlates with the general fold observed for GH27 proteins, consisting of two main domains: an N-terminal TIM-barrel domain and a C-terminal all-β domain. The two catalytic residues are located in the TIM-barrel domain, such that their carboxylic functional groups are about 5.9 Å from each other, consistent with a retaining mechanism. An isoleucine residue (Ile67) located at a key position in the active site is shown to play a critical role in the substrate specificity of Abp, providing a structural basis for the high preference of the enzyme towards arabinopyranoside over galactopyranoside substrates. The crystal structure demonstrates that Abp is a tetramer made up of two `open-pincers' dimers, which clamp around each other to form a central cavity. The four active sites of the Abp tetramer are situated on the inner surface of this cavity, all opening into the central space of the cavity. The biological relevance of this tetrameric structure is supported by independent results obtained from size-exclusion chromatography (SEC), dynamic light-scattering (DLS) and small-angle X-ray scattering (SAXS) experiments. These data and their comparison to the structural data of related GH27 enzymes are used for a more general discussion concerning structure-selectivity aspects in this glycoside hydrolase (GH) family.

The Sugar Model: Catalytic Flow Reactor Dynamics of Pyruvaldehyde Synthesis from Triose Catalyzed by Poly-L-Lysine Contained in a Dialyzer

NASA Technical Reports Server (NTRS)

Weber, Arthur L.; DeVincenzi, Donald (Technical Monitor)

2000-01-01

The formation of pyruvaldehyde from triose sugars was catalyzed by poly-L-lysine contained in a small dialyzer (100 MWCO) suspended in a much larger triose substrate reservoir. The polylysine confined in the dialyzer functioned as a catalytic flow reactor that constantly brought in triose from the substrate reservoir by diffusion to offset the drop in triose concentration within the reactor caused by its conversion to pyruvaldehyde. A 400 mM solution of poly-L-lysine contained in a 0.35 ml dialyzer placed in a 120 ml solution of triose substrate (pH 5.5, 40 C) generated pyruvaldehyde 11 -times faster than an a control reaction without the catalytic dialyzer. However, since the catalytic dialyzer's volume was 343-times smaller than the control reaction, the synthetic intensity (rate/volume) of pyruvaldehyde synthesis within the catalytic dialyzer was 3400-times greater than that of the control reaction and substrate solution. A similar result was obtained using a dialyzer with a 500 MWCO value. Acting as a catalytic flow reactor the polylysine catalytic dialyzer synthesized about 3.5 molecules of pyruvaldehyde per lysine residue in 7 days -- an amount of triose equal to twice the weight of the catalyst. At 7 days the catalytic activity of polylysine was 16% of its initial value, a result indicating catalyst-poisoning caused by reaction of pyruvaldehyde with the e-amino groups of polylysine. The dialyzer method of catalyst containment was selected it provides a simple, flexible, and easily manipulated experimental system for studying the dynamics and evolutionary development of confined autocatalytic processes related to the origin of life under anaerobic conditions.

A novel bifunctional pectinase from Penicillium oxalicum SX6 with separate pectin methylesterase and polygalacturonase catalytic domains.

PubMed

Tu, Tao; Bai, Yingguo; Luo, Huiying; Ma, Rui; Wang, Yaru; Shi, Pengjun; Yang, Peilong; Meng, Kun; Yao, Bin

2014-06-01

A multimodular pectinase of glycoside hydrolase family 28, S6A, was identified in Penicillium oxalicum SX6 that consists of an N-terminal catalytic domain of pectin methylesterase, a Thr/Ser-rich linker region, and a C-terminal catalytic domain of polygalacturonase. Recombinant S6A and its two derivatives, S6PE (the catalytic domain of pectin methylesterase) and S6PG (the catalytic domain of polygalacturonase), were produced in Pichia pastoris. S6A was a bifunctional protein and had both pectin methylesterase and polygalacturonase activities. Three enzymes showed similar biochemical properties, such as optimal pH and temperature (pH 5.0 and 50 °C) and excellent stability at pH 3.5-6.0 and 40 °C. Most metal ions tested (Na(+), K(+), Ca(2+), Li(+), Co(2+), Cr(3+), Ni(2+), Cu(2+), Mn(2+),Mg(2+), Fe(3+), Zn(2+), and Pb(2+)) enhanced the pectin methylesterase activities of S6PE and S6A, but had little or inhibitory effects on the polygalacturonase activities of S6A and S6PG. In comparison with most fungal pectin methylesterases, S6A had higher specific activity (271.1 U/mg) towards 70 % DM citrus pectin. When S6PE and S6PG were combined at the activity ratio of 1:4, the most significant synergistic effect was observed in citrus pectin degradation and degumming of sisal fiber, which is comparable with the performance of S6A (95 v.s. 100 % and 16.9 v.s. 17.2 %, respectively). To the best of our knowledge, this work represents the first report of gene cloning, heterologous expression, and biochemical characterization of a bifunctional pectinase with separate catalytic domains.

SnRK1 is differentially regulated in the cotyledon and embryo axe of bean (Phaseolus vulgaris L) seeds.

PubMed

Coello, Patricia; Martínez-Barajas, Eleazar

2014-07-01

SnRK1 activity is developmentally regulated in bean seeds and exhibits a transient increase with the highest value at 20 days after anthesis (DAA), which coincides with the beginning of protein and starch accumulation. The catalytic subunit of SnRK1 shows a consistent decrease throughout the seed development period. However, by 15 DAA a significant proportion of the catalytic subunit appears phosphorylated. The increase in activity and phosphorylation of the catalytic subunit coincides with a decrease in hexoses. However, SnRK1 activity is differentially regulated in the cotyledon and embryo axe, where a larger proportion of the catalytic subunit is phosphorylated. SnRK1 obtained from endosperm extract is inhibited by T6P and to a lesser extent by ADPG and UDPG, whereas the enzyme isolated from embryo is virtually insensitive to T6P but exhibits some inhibition by ADPG and UDPG. In cotyledon extracts, the effects of T6P and ADPG on SnRK1 activity are additive, whereas in embryo extract, T6P inhibits the enzyme only when ADPG is present. After fractionation on Sephacryl-S300, SnRK1 activity obtained from cotyledon extracts is detected as a single peak associated with a molecular weight of 250 kDa whereas that obtained form embryo axe extracts detected as 2 peaks associated with molecular weight of 250 and 180 kDa. In both cases, the catalytic subunit exhibits a wide distribution but is concentrated in the fractions with the highest activity. To analyse the composition of the complex, cotyledon and embryo extracts were treated with a reversible crosslinker (DSP). DSP induced the formation of complexes with molecular weights of 97 and 180 kDa in the cotyledon and embryo extracts, respectively. Since all the phosphorylated catalytic subunit is present in the complexes induced by DSP, it appears that the phosphorylation favors its interaction with other proteins. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

Copper-Catalyzed Electrophilic Amination of Organoaluminum Nucleophiles with O-Benzoyl Hydroxylamines.

PubMed

Zhou, Shuangliu; Yang, Zhiyong; Chen, Xu; Li, Yimei; Zhang, Lijun; Fang, Hong; Wang, Wei; Zhu, Xiancui; Wang, Shaowu

2015-06-19

A copper-catalyzed electrophilic amination of aryl and heteroaryl aluminums with N,N-dialkyl-O-benzoyl hydroxylamines that affords the corresponding anilines in good yields has been developed. The catalytic reaction proceeds very smoothly under mild conditions and exhibits good substrate scope. Moreover, the developed catalytic system is also well suited for heteroaryl aluminum nucleophiles, providing facile access to heteroaryl amines.

Environmental Technology Verification Test Report of Mobile Source Selective Catalytic Reduction, Johnson Matthey SCCRT, Version 1, Selective Catalytic Reduction Technology with a Catalyzed Continuously Regenerating Trap

EPA Science Inventory

The Johnson Matthey SCCRT, v.1 technology is a urea-based SCR system combined with a CCRT filter designed for on-highway light, medium, and heavy heavy-duty diesel, urban and non-urban, bus exhaust gas recirculation (EGR)-or non-EGR-equipped engines for use with commercial ultra-...

Contact structure for use in catalytic distillation

DOEpatents

Jones, E.M. Jr.

1984-03-27

A method is described for conducting catalytic chemical reactions and fractionation of the reaction mixture comprising feeding reactants into a distillation column reactor, contracting said reactant in liquid phase with a fixed bed catalyst in the form of a contact catalyst structure consisting of closed porous containers containing the catalyst for the reaction and a clip means to hold and support said containers, which are disposed above, i.e., on the distillation trays in the tower. The trays have weir means to provide a liquid level on the trays to substantially cover the containers. In other words, the trays function in their ordinary manner with the addition thereto of the catalyst. The reaction mixture is concurrently fractionated in the column. 7 figs.

Contact structure for use in catalytic distillation

DOEpatents

Jones, Jr., Edward M.

1985-01-01

A method and apparatus for conducting catalytic chemical reactions and fractionation of the reaction mixture, comprising and feeding reactants into a distillation column reactor contracting said reactant in a liquid phase with a fixed bed catalyst in the form of a contact catalyst structure, consisting of closed porous containers containing the catalyst for the reaction and a clip means to hold and support said containers, which are disposed above, i.e., on the distillation trays in the tower. The trays have weir means to provide a liquid level on the trays to substantially cover the containers. In other words, the trays function in their ordinary manner with the addition thereto of the catalyst. The reaction mixture is concurrently fractionated in the column.

Contact structure for use in catalytic distillation

DOEpatents

Jones, E.M. Jr.

1985-08-20

A method and apparatus are disclosed for conducting catalytic chemical reactions and fractionation of the reaction mixture, comprising and feeding reactants into a distillation column reactor contracting said reactant in a liquid phase with a fixed bed catalyst in the form of a contact catalyst structure, consisting of closed porous containers containing the catalyst for the reaction and a clip means to hold and support said containers, which are disposed above, i.e., on the distillation trays in the tower. The trays have weir means to provide a liquid level on the trays to substantially cover the containers. In other words, the trays function in their ordinary manner with the addition thereto of the catalyst. The reaction mixture is concurrently fractionated in the column. 7 figs.

Postassembly Transformation of a Catalytically Active Composite Material, Pt@ZIF-8, via Solvent-Assisted Linker Exchange.

PubMed

Stephenson, Casey J; Hupp, Joseph T; Farha, Omar K

2016-02-15

2-Methylimidazolate linkers of Pt@ZIF-8 are exchanged with imidazolate using solvent-assisted linker exchange (SALE) to expand the apertures of the parent material and create Pt@SALEM-2. Characterization of the material before and after SALE was performed. Both materials are active as catalysts for the hydrogenation of 1-octene, whereas the hydrogenation of cis-cyclohexene occurred only with Pt@SALEM-2, consistent with larger apertures for the daughter material. The largest substrate, β-pinene, proved to be unreactive with H2 when either material was employed as a candidate catalyst, supporting the contention that substrate molecules, for both composites, must traverse the metal-organic framework component in order to reach the catalytic nanoparticles.

RNase MRP Cleaves Pre-tRNASer-Met in the tRNA Maturation Pathway

PubMed Central

Adachi, Kousuke; Nobe, Yuko; Kobayashi, Junya; Hirota, Kouji; Oliveira, Douglas V.; Taoka, Masato; Isobe, Toshiaki

2014-01-01

Ribonuclease mitochondrial RNA processing (RNase MRP) is a multifunctional ribonucleoprotein (RNP) complex that is involved in the maturation of various types of RNA including ribosomal RNA. RNase MRP consists of a potential catalytic RNA and several protein components, all of which are required for cell viability. We show here that the temperature-sensitive mutant of rmp1, the gene for a unique protein component of RNase MRP, accumulates the dimeric tRNA precursor, pre-tRNASer-Met. To examine whether RNase MRP mediates tRNA maturation, we purified the RNase MRP holoenzyme from the fission yeast Schizosaccharomyces pombe and found that the enzyme directly and selectively cleaves pre-tRNASer-Met, suggesting that RNase MRP participates in the maturation of specific tRNA in vivo. In addition, mass spectrometry–based ribonucleoproteomic analysis demonstrated that this RNase MRP consists of one RNA molecule and 11 protein components, including a previously unknown component Rpl701. Notably, limited nucleolysis of RNase MRP generated an active catalytic core consisting of partial mrp1 RNA fragments, which constitute “Domain 1” in the secondary structure of RNase MRP, and 8 proteins. Thus, the present study provides new insight into the structure and function of RNase MRP. PMID:25401760

Iridium clusters in KLTL zeolite: Structure and catalytic selectivity for n-hexane aromatization

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

Triantafillou, N.D.; Miller, J.T.; Gates, B.C.

Catalysts consisting of Ir clusters in zeolite KLTL were prepared by reduction of [Ir(NH{sub 3}){sub 5}Cl]Cl{sub 2} in the zeolite with H{sub 2} at temperatures 300 or 500{degrees}C. The catalysts were tested for reactions of n-hexane and H{sub 2} at 400, 440 and 480{degrees}C and were characterized by temperature-programmed reduction, hydrogen chemisorption, transmission electron microscopy, infrared spectroscopy of adsorbed CO, and extended X-ray absorption fine structure spectroscopy. The clusters consist of 4 to 6 Ir atoms on average and are sufficiently small to reside within the pores of the zeolite. The infrared spectra characteristic of terminal CO suggest that themore » support environment is slightly basic and that the Ir clusters are electron rich relative to the bulk metal. Notwithstanding the small cluster size, the support basicity, and the confining geometry of the LTL zeolite pore structure, the catalytic performance is similar to those of other Ir catalysts, with a poor selectivity for aromatization and a high selectivity for hydrogenolysis. These results are consistent with the inference that the principal requirements for selective naphtha aromatization catalysts are both a nonacidic support and a metal with a low hydrogenolsis activity, i.e., Pt. 47 refs., 6 figs., 3 tabs.« less

Spacecraft nitrogen generation. [liquid hydrazine

NASA Technical Reports Server (NTRS)

Marshall, R. D.; Carlson, J. N.; Powell, J. D.; Kacholia, K. K.

1974-01-01

Two spacecraft nitrogen (N2) generation systems based on the catalytic dissociation of hydrazine (N2H4) were evaluated. In the first system, liquid N2H4 is catalytically dissociated to yield an N2 and hydrogen (H2) gas mixture. Separation of the N2/H2 gas mixture to yield N2 and a supply of H2 is accomplished using a polymer-electrochemical N2/H2 separator. In the second system, the N2/H2 gas mixture is separated in a two-stage palladium/silver (Pd/Ag) N2/H2 separator. The program culminated in the successful design, fabrication, and testing of a N2H4 catalytic dissociator, a polymer-electrochemical N2/H2 separator, and a two-stage Pd/Ag N2/H2 separator. The hardware developed was sized for an N2 delivery rate of 6.81 kg/d (15lb/day). Experimental results demonstrated that both spacecraft N2 generation systems are capable of producing 6.81 kg/d (15lb/day) of 99.9% pure N2 at a pressure greater than or equal to 1035 kN/m(2) (150 psia).

Iridium Complexes with Proton-Responsive Azole-Type Ligands as Effective Catalysts for CO 2 Hydrogenation

DOE PAGES

Ertem, Mehmed Zahid; Suna, Yuki; Himeda, Yuichiro; ...

2017-10-06

Pentamethylcyclopentadienyl iridium (Cp*Ir) complexes with bidentate ligands consisting of a pyridine ring and an electron-rich diazole ring were prepared. Their catalytic activity towards CO 2 hydrogenation in 2.0 M KHCO 3 aqueous solutions (pH 8.5) at 50 °C, under 1.0 MPa CO 2/H 2 (1:1) have been reported as an alternative to photo- and electrochemical CO 2 reduction. Bidentate ligands incorporating an electron-rich diazole ring improved the catalytic performance of the Ir complexes compared to the bipyridine ligand. Complexes 2, 4 and 6, possessing both a hydroxy group and an uncoordinated NH group, which are proton-responsive and capable of generatingmore » pendent-bases in basic media, recorded high initial TOF values of 1300 h -1, 1550 h -1 and 2000 h -1, respectively. Here, spectroscopic and computational investigations revealed that the reversible deprotonation changes the electronic properties of the complexes and causes interactions between pendent base and substrate and/or solvent water molecules, resulting in the high catalytic performance in basic media.« less

Missense variants in AIMP1 gene are implicated in autosomal recessive intellectual disability without neurodegeneration

PubMed Central

Iqbal, Zafar; Püttmann, Lucia; Musante, Luciana; Razzaq, Attia; Zahoor, Muhammad Yasir; Hu, Hao; Wienker, Thomas F; Garshasbi, Masoud; Fattahi, Zohreh; Gilissen, Christian; Vissers, Lisenka ELM; de Brouwer, Arjan PM; Veltman, Joris A; Pfundt, Rolph; Najmabadi, Hossein; Ropers, Hans-Hilger; Riazuddin, Sheikh; Kahrizi, Kimia; van Bokhoven, Hans

2016-01-01

AIMP1/p43 is a multifunctional non-catalytic component of the multisynthetase complex. The complex consists of nine catalytic and three non-catalytic proteins, which catalyze the ligation of amino acids to their cognate tRNA isoacceptors for use in protein translation. To date, two allelic variants in the AIMP1 gene have been reported as the underlying cause of autosomal recessive primary neurodegenerative disorder. Here, we present two consanguineous families from Pakistan and Iran, presenting with moderate to severe intellectual disability, global developmental delay, and speech impairment without neurodegeneration. By the combination of homozygosity mapping and next generation sequencing, we identified two homozygous missense variants, p.(Gly299Arg) and p.(Val176Gly), in the gene AIMP1 that co-segregated with the phenotype in the respective families. Molecular modeling of the variants revealed deleterious effects on the protein structure that are predicted to result in reduced AIMP1 function. Our findings indicate that the clinical spectrum for AIMP1 defects is broader than witnessed so far. PMID:26173967

Missense variants in AIMP1 gene are implicated in autosomal recessive intellectual disability without neurodegeneration.

PubMed

Iqbal, Zafar; Püttmann, Lucia; Musante, Luciana; Razzaq, Attia; Zahoor, Muhammad Yasir; Hu, Hao; Wienker, Thomas F; Garshasbi, Masoud; Fattahi, Zohreh; Gilissen, Christian; Vissers, Lisenka E L M; de Brouwer, Arjan P M; Veltman, Joris A; Pfundt, Rolph; Najmabadi, Hossein; Ropers, Hans-Hilger; Riazuddin, Sheikh; Kahrizi, Kimia; van Bokhoven, Hans

2016-03-01

AIMP1/p43 is a multifunctional non-catalytic component of the multisynthetase complex. The complex consists of nine catalytic and three non-catalytic proteins, which catalyze the ligation of amino acids to their cognate tRNA isoacceptors for use in protein translation. To date, two allelic variants in the AIMP1 gene have been reported as the underlying cause of autosomal recessive primary neurodegenerative disorder. Here, we present two consanguineous families from Pakistan and Iran, presenting with moderate to severe intellectual disability, global developmental delay, and speech impairment without neurodegeneration. By the combination of homozygosity mapping and next generation sequencing, we identified two homozygous missense variants, p.(Gly299Arg) and p.(Val176Gly), in the gene AIMP1 that co-segregated with the phenotype in the respective families. Molecular modeling of the variants revealed deleterious effects on the protein structure that are predicted to result in reduced AIMP1 function. Our findings indicate that the clinical spectrum for AIMP1 defects is broader than witnessed so far.

Structure of the protein phosphatase 2A holoenzyme.

PubMed

Xu, Yanhui; Xing, Yongna; Chen, Yu; Chao, Yang; Lin, Zheng; Fan, Eugene; Yu, Jong W; Strack, Stefan; Jeffrey, Philip D; Shi, Yigong

2006-12-15

Protein Phosphatase 2A (PP2A) plays an essential role in many aspects of cellular physiology. The PP2A holoenzyme consists of a heterodimeric core enzyme, which comprises a scaffolding subunit and a catalytic subunit, and a variable regulatory subunit. Here we report the crystal structure of the heterotrimeric PP2A holoenzyme involving the regulatory subunit B'/B56/PR61. Surprisingly, the B'/PR61 subunit has a HEAT-like (huntingtin-elongation-A subunit-TOR-like) repeat structure, similar to that of the scaffolding subunit. The regulatory B'/B56/PR61 subunit simultaneously interacts with the catalytic subunit as well as the conserved ridge of the scaffolding subunit. The carboxyterminus of the catalytic subunit recognizes a surface groove at the interface between the B'/B56/PR61 subunit and the scaffolding subunit. Compared to the scaffolding subunit in the PP2A core enzyme, formation of the holoenzyme forces the scaffolding subunit to undergo pronounced conformational rearrangements. This structure reveals significant ramifications for understanding the function and regulation of PP2A.

Structural basis for catalytic activation by the human ZNF451 SUMO E3 ligase

DOE PAGES

Cappadocia, Laurent; Pichler, Andrea; Lima, Christopher D.

2015-11-02

E3 protein ligases enhance transfer of ubiquitin-like (Ubl) proteins from E2 conjugating enzymes to substrates by stabilizing the thioester-charged E2~Ubl in a closed configuration optimally aligned for nucleophilic attack. In this paper, we report biochemical and structural data that define the N-terminal domain of the Homo sapiens ZNF451 as the catalytic module for SUMO E3 ligase activity. The ZNF451 catalytic module contains tandem SUMO-interaction motifs (SIMs) bridged by a Pro-Leu-Arg-Pro (PLRP) motif. The first SIM and PLRP motif engage thioester-charged E2~SUMO while the next SIM binds a second molecule of SUMO bound to the back side of E2. We showmore » that ZNF451 is SUMO2 specific and that SUMO modification of ZNF451 may contribute to activity by providing a second molecule of SUMO that interacts with E2. Finally, our results are consistent with ZNF451 functioning as a bona fide SUMO E3 ligase.« less

Structural basis for catalytic activation by the human ZNF451 SUMO E3 ligase

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

Cappadocia, Laurent; Pichler, Andrea; Lima, Christopher D.

E3 protein ligases enhance transfer of ubiquitin-like (Ubl) proteins from E2 conjugating enzymes to substrates by stabilizing the thioester-charged E2~Ubl in a closed configuration optimally aligned for nucleophilic attack. In this paper, we report biochemical and structural data that define the N-terminal domain of the Homo sapiens ZNF451 as the catalytic module for SUMO E3 ligase activity. The ZNF451 catalytic module contains tandem SUMO-interaction motifs (SIMs) bridged by a Pro-Leu-Arg-Pro (PLRP) motif. The first SIM and PLRP motif engage thioester-charged E2~SUMO while the next SIM binds a second molecule of SUMO bound to the back side of E2. We showmore » that ZNF451 is SUMO2 specific and that SUMO modification of ZNF451 may contribute to activity by providing a second molecule of SUMO that interacts with E2. Finally, our results are consistent with ZNF451 functioning as a bona fide SUMO E3 ligase.« less

Coordination polymer structure and revisited hydrogen evolution catalytic mechanism for amorphous molybdenum sulfide

PubMed Central

Tran, Phong D.; Tran, Thu V.; Orio, Maylis; Torelli, Stephane; Truong, Quang Duc; Nayuki, Keiichiro; Sasaki, Yoshikazu; Chiam, Sing Yang; Yi, Ren; Honma, Itaru; Barber, James; Artero, Vincent

2017-01-01

Molybdenum sulfides are very attractive noble-metal free electrocatalysts for the hydrogen evolution reaction (HER) from water. Atomic structure and identity of the catalytically active sites have been well established for crystalline molybdenum disulfide (c-MoS2) but not for amorphous molybdenum sulfide (a-MoSx) which displays significantly higher HER activity compared to its crystalline counterpart. Here we show that HER–active a-MoSx, prepared either as nanoparticles or as films, is a molecular–based coordination polymer consisting of discrete [Mo3S13]2– building blocks. Of the three terminal disulfide (S22–) ligands within these clusters, two are shared to form the polymer chain. The third one remains free and generates molybdenum hydride moieties as the active site under H2 evolution conditions. Such a molecular structure therefore provides a basis for revisiting the mechanism of a-MoSx catalytic activity, as well as explaining some of its special properties such as reductive activation and corrosion. Our findings open up new avenues for the rational optimisation of this HER electrocatalyst as an alternative to platinum. PMID:26974410

Iridium Complexes with Proton-Responsive Azole-Type Ligands as Effective Catalysts for CO2 Hydrogenation.

PubMed

Suna, Yuki; Himeda, Yuichiro; Fujita, Etsuko; Muckerman, James T; Ertem, Mehmed Z

2017-11-23

Pentamethylcyclopentadienyl iridium (Cp*Ir) complexes with bidentate ligands consisting of a pyridine ring and an electron-rich diazole ring were prepared. Their catalytic activity toward CO 2 hydrogenation in 2.0 m KHCO 3 aqueous solutions (pH 8.5) at 50 °C, under 1.0 MPa CO 2 /H 2 (1:1) have been reported as an alternative to photo- and electrochemical CO 2 reduction. Bidentate ligands incorporating an electron-rich diazole ring improved the catalytic performance of the Ir complexes compared to the bipyridine ligand. Complexes 2, 4, and 6, possessing both a hydroxy group and an uncoordinated NH group, which are proton-responsive and capable of generating pendent bases in basic media, recorded high initial turnover frequency values of 1300, 1550, and 2000 h -1 , respectively. Spectroscopic and computational investigations revealed that the reversible deprotonation changes the electronic properties of the complexes and causes interactions between pendent base and substrate and/or solvent water molecules, resulting in high catalytic performance in basic media. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The origin of light hydrocarbons

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

Mango, F.D.

2000-04-01

The light hydrocarbons (LHs) are probably intermediates in the catalytic decomposition of oil to gas. Two lines of evidence support this possibility. First, the reaction was duplicated experimentally under moderate conditions. Second, natural LHs exhibit the characteristics of catalytic products, in particular a proportionality between isomers: (xy{sub i})/(x{sub i}y) = {alpha} (where x and x{sub i} are isomers; y and y{sub i} are isomers that are structurally similar to x and x{sub i}; and {alpha} is a constant). All oils exhibit this relationship with coefficients of correlation reaching 0.99. Isomer ratios change systematically with concentrations, some approaching thermodynamic equilibrium, othersmore » not. The correlations reported are the strongest yet disclosed for the LHs. Isomers are related in triads (e.g., n-hexane {leftrightarrow} 2-methylpentane {leftrightarrow} 3-methylpentane), consistent with cyclopropane precursors. The LHs obtained experimentally are indistinguishable from natural LHs in (xy{sub i})/(x{sub i}y). These relationships are not explained by physical fractionations, equilibrium control, or noncatalytic modes of origin. A catalytic origin, on the other hand, has precedence, economy and experimental support.« less

Magnetic properties and transmission electron microscopy studies of Ni nanoparticles encapsulated in carbon nanocages and carbon nanotubes

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

He Chunnian; Zhao Naiqin; Shi Chunsheng

2008-08-04

Three types of carbon nanomaterials, including bamboo-shaped carbon nanotubes with Ni encapsulated and hollow and Ni catalytic particles filled carbon nanocages, have been prepared by methane catalytic decomposition at a relatively low temperature. Transmission electron microscopy observations showed that fascinating fullerene-like Ni-C (graphitic) core-shell nanostructures predominated. Detailed examination of high-resolution transmission electron microscopy showed that the walls of bamboo-shaped carbon nanotubes with quasi-cone catalytic particles encapsulated consisted of oblique graphene planes with respect to the tube axis. The Ni particles encapsulated in the carbon nanocages were larger than that encapsulated in carbon nanotubes, but the diameters of the cores ofmore » hollow carbon nanocages were less than that of Ni particles encapsulated in carbon nanotubes, suggesting that the sizes of catalyst particles played an important role during carbon nanomaterial growth. The magnetic properties of the carbon nanomaterials were measured, which showed relatively large coercive force (H{sub c} = 138.4 O{sub e}) and good ferromagnetism (M{sub r}/M{sub s} = 0.325)« less

Ozone and Ozone By-Products in the Cabins of Commercial Aircraft

PubMed Central

Weisel, Clifford; Weschler, Charles J.; Mohan, Kris; Vallarino, Jose; Spengler, John D.

2013-01-01

The aircraft cabin represents a unique indoor environment due to its high surface-to-volume ratio, high occupant density and the potential for high ozone concentrations at cruising altitudes. Ozone was continuously measured and air was sampled on sorbent traps, targeting carbonyl compounds, on 52 transcontinental U.S. or international flights between 2008 and 2010. The sampling was predominantly on planes that did not have ozone scrubbers (catalytic converters). Peak ozone levels on aircraft without catalytic convertors exceeded 100 ppb, with some flights having periods of more than an hour when the ozone levels were > 75ppb. Ozone was greatly reduced on relatively new aircraft with catalytic convertors, but ozone levels on two flights whose aircraft had older convertors were similar to those on planes without catalytic convertors. Hexanal, heptanal, octanal, nonanal, decanal and 6-methyl-5-hepten-2-one (6-MHO) were detected in the aircraft cabin at sub- to low ppb levels. Linear regression models that included the log transformed mean ozone concentration, percent occupancy and plane type were statistically significant and explained between 18 and 25% of the variance in the mixing ratio of these carbonyls. Occupancy was also a significant factor for 6-MHO, but not the linear aldehydes, consistent with 6-MHO’s formation from the reaction between ozone and squalene, which is present in human skin oils. PMID:23517299

Evolutionary Diversifaction of Aminopeptidase N in Lepidoptera by Conserved Clade-specific Amino Acid Residues

PubMed Central

Hughes, Austin L.

2015-01-01

Members of the aminopepidase N (APN) gene family of the insect order Lepidoptera (moths and butterflies) bind the naturally insecticidal Cry toxins produced by the bacterium Bacillus thuringiensis. Phylogenetic analysis of amino acid sequences of seven lepidopteran APN classes provided strong support for the hypothesis that lepidopteran APN2 class arose by gene duplication prior to the most recent common ancestor of Lepidoptera and Diptera. The Cry toxin-binding region (BR) of lepidopteran and dipteran APNs was subject to stronger purifying selection within APN classes than was the remainder of the molecule, reflecting conservation of catalytic site and adjoining residues within the BR. Of lepidopteran APN classes, APN2, APN6, and APN8 showed the strongest evidence of functional specialization, both in expression patterns and in the occurrence of conserved derived amino acid residues. The latter three APN classes also shared a convergently evolved conserved residue close to the catalytic site. APN8 showed a particularly strong tendency towards class-specific conserved residues, including one of the catalytic site residues in the BR and ten others in close vicinity to the catalytic site residues. The occurrence of class-specific sequences along with the conservation of enzymatic function is consistent with the hypothesis that the presence of Cry toxins in the environment has been a factor shaping the evolution of this multi-gene family. PMID:24675701

Cardiac HDAC6 Catalytic Activity is Induced in Response to Chronic Hypertension

PubMed Central

Lemon, Douglas D.; Horn, Todd R.; Cavasin, Maria A.; Jeong, Mark Y.; Haubold, Kurt W.; Long, Carlin S.; Irwin, David C.; McCune, Sylvia A.; Chung, Eunhee; Leinwand, Leslie A.; McKinsey, Timothy A.

2011-01-01

Small molecule histone deacetylase (HDAC) inhibitors block adverse cardiac remodeling in animal models of heart failure. The efficacious compounds target class I, class IIb and, to a lesser extent, class IIa HDACs. It is hypothesized that a selective inhibitor of a specific HDAC class (or an isoform within that class) will provide a favorable therapeutic window for the treatment of heart failure, although the optimal selectivity profile for such a compound remains unknown. Genetic studies have suggested that class I HDACs promote pathological cardiac remodeling, while class IIa HDACs are protective. In contrast, nothing is known about the function or regulation of class IIb HDACs in the heart. We developed assays to quantify catalytic activity of distinct HDAC classes in left and right ventricular cardiac tissue from animal models of hypertensive heart disease. Class I and IIa HDAC activity was elevated in some but not all diseased tissues. In contrast, catalytic activity of the class IIb HDAC, HDAC6, was consistently increased in stressed myocardium, but not in a model of physiologic hypertrophy. HDAC6 catalytic activity was also induced by diverse extracellular stimuli in cultured cardiac myocytes and fibroblasts. These findings suggest an unforeseen role for HDAC6 in the heart, and highlight the need for pre-clinical evaluation of HDAC6-selective inhibitors to determine whether this HDAC isoform is pathological or protective in the setting of cardiovascular disease. PMID:21539845

Nanoparticle mediated micromotor motion

NASA Astrophysics Data System (ADS)

Liu, Mei; Liu, Limei; Gao, Wenlong; Su, Miaoda; Ge, Ya; Shi, Lili; Zhang, Hui; Dong, Bin; Li, Christopher Y.

2015-03-01

In this paper, we report the utilization of nanoparticles to mediate the motion of a polymer single crystal catalytic micromotor. Micromotors have been fabricated by directly self-assembling functional nanoparticles (platinum and iron oxide nanoparticles) onto one or both sides of two-dimensional polymer single crystals. We show that the moving velocity of these micromotors in fluids can be readily tuned by controlling the nanoparticles' surface wettability and catalytic activity. A 3 times velocity increase has been achieved for a hydrophobic micromotor as opposed to the hydrophilic ones. Furthermore, we demonstrate that the catalytic activity of platinum nanoparticles inside the micromotor can be enhanced by their synergetic interactions with iron oxide nanoparticles and an electric field. Both strategies lead to dramatically increased moving velocities, with the highest value reaching ~200 μm s-1. By decreasing the nanoparticles' surface wettability and increasing their catalytic activity, a maximum of a ~10-fold increase in the moving speed of the nanoparticle based micromotor can be achieved. Our results demonstrate the advantages of using nanoparticles in micromotor systems.In this paper, we report the utilization of nanoparticles to mediate the motion of a polymer single crystal catalytic micromotor. Micromotors have been fabricated by directly self-assembling functional nanoparticles (platinum and iron oxide nanoparticles) onto one or both sides of two-dimensional polymer single crystals. We show that the moving velocity of these micromotors in fluids can be readily tuned by controlling the nanoparticles' surface wettability and catalytic activity. A 3 times velocity increase has been achieved for a hydrophobic micromotor as opposed to the hydrophilic ones. Furthermore, we demonstrate that the catalytic activity of platinum nanoparticles inside the micromotor can be enhanced by their synergetic interactions with iron oxide nanoparticles and an electric field. Both strategies lead to dramatically increased moving velocities, with the highest value reaching ~200 μm s-1. By decreasing the nanoparticles' surface wettability and increasing their catalytic activity, a maximum of a ~10-fold increase in the moving speed of the nanoparticle based micromotor can be achieved. Our results demonstrate the advantages of using nanoparticles in micromotor systems. Electronic supplementary information (ESI) available: Fig. S1-S5 and Video S1-S3. See DOI: 10.1039/c4nr07558g

Rapid starting methanol reactor system

DOEpatents

Chludzinski, Paul J.; Dantowitz, Philip; McElroy, James F.

1984-01-01

The invention relates to a methanol-to-hydrogen cracking reactor for use with a fuel cell vehicular power plant. The system is particularly designed for rapid start-up of the catalytic methanol cracking reactor after an extended shut-down period, i.e., after the vehicular fuel cell power plant has been inoperative overnight. Rapid system start-up is accomplished by a combination of direct and indirect heating of the cracking catalyst. Initially, liquid methanol is burned with a stoichiometric or slightly lean air mixture in the combustion chamber of the reactor assembly. The hot combustion gas travels down a flue gas chamber in heat exchange relationship with the catalytic cracking chamber transferring heat across the catalyst chamber wall to heat the catalyst indirectly. The combustion gas is then diverted back through the catalyst bed to heat the catalyst pellets directly. When the cracking reactor temperature reaches operating temperature, methanol combustion is stopped and a hot gas valve is switched to route the flue gas overboard, with methanol being fed directly to the catalytic cracking reactor. Thereafter, the burner operates on excess hydrogen from the fuel cells.

Design and functionalization of photocatalytic systems within mesoporous silica.

PubMed

Qian, Xufang; Fuku, Kojirou; Kuwahara, Yasutaka; Kamegawa, Takashi; Mori, Kohsuke; Yamashita, Hiromi

2014-06-01

In the past decades, various photocatalysts such as TiO2, transition-metal-oxide moieties within cavities and frameworks, or metal complexes have attracted considerable attention in light-excited catalytic processes. Owing to high surface areas, transparency to UV and visible light as well as easily modified surfaces, mesoporous silica-based materials have been widely used as excellent hosts for designing efficient photocatalytic systems under the background of environmental remediation and solar-energy utilization. This Minireview mainly focuses on the surface-chemistry engineering of TiO2/mesoporous silica photocatalytic systems and fabrication of binary oxides and nanocatalysts in mesoporous single-site-photocatalyst frameworks. Recently, metallic nanostructures with localized surface plasmon resonance (LSPR) have been widely studied in catalytic applications harvesting light irradiation. Accordingly, silver and gold nanostructures confined in mesoporous silica and their corresponding catalytic activity enhanced by the LSPR effect will be introduced. In addition, the integration of metal complexes within mesoporous silica materials for the construction of functional inorganic-organic supramolecular photocatalysts will be briefly described. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Combustion engine system

NASA Technical Reports Server (NTRS)

Houseman, John (Inventor); Voecks, Gerald E. (Inventor)

1986-01-01

A flow through catalytic reactor which selectively catalytically decomposes methanol into a soot free hydrogen rich product gas utilizing engine exhaust at temperatures of 200 to 650 C to provide the heat for vaporizing and decomposing the methanol is described. The reactor is combined with either a spark ignited or compression ignited internal combustion engine or a gas turbine to provide a combustion engine system. The system may be fueled entirely by the hydrogen rich gas produced in the methanol decomposition reactor or the system may be operated on mixed fuels for transient power gain and for cold start of the engine system. The reactor includes a decomposition zone formed by a plurality of elongated cylinders which contain a body of vapor permeable, methanol decomposition catalyst preferably a shift catalyst such as copper-zinc.

Treatment of hazardous landfill leachate using Fenton process followed by a combined (UASB/DHS) system.

PubMed

Ismail, Sherif; Tawfik, Ahmed

2016-01-01

Fenton process for pre-treatment of hazardous landfill leachate (HLL) was investigated. Total, particulate and soluble chemical oxygen demand (CODt, CODp and CODs) removal efficiency amounted to 67%, 47% and 64%, respectively, at pH value of 3.5, molar ratio (H2O2/Fe(2+)) of 5, H2O2 dosage of 25 ml/L and contact time of 15 min. Various treatment scenarios were attempted and focused on studying the effect of pre-catalytic oxidation process on the performance of up-flow anaerobic sludge blanket (UASB), UASB/down-flow hanging sponge (DHS) and DHS system. The results obtained indicated that pre-catalytic oxidation process improved the CODt removal efficiency in the UASB reactor by a value of 51.4%. Overall removal efficiencies of CODt, CODs and CODp were 80 ± 6%, 80 ± 7% and 78 ± 16% for UASB/DHS treating pre-catalytic oxidation effluent, respectively. The removal efficiencies of CODt, CODs and CODp were, respectively, decreased to 54 ± 2%, 49 ± 2% and 71 ± 16% for UASB/DHS system without pre-treatment. However, the results for the combined process (UASB/DHS) system is almost similar to those obtained for UASB reactor treating pre-catalytic oxidation effluent. The DHS system achieved average removal efficiencies of 52 ± 4% for CODt, 51 ± 4% for CODs and 52 ± 15% for CODp. A higher COD fractions removal was obtained when HLL was pre-treated by Fenton reagent. The combined processes provided a removal efficiency of 85 ± 1% for CODt, 85 ± 1% for CODs and 83 ± 8% for CODp. The DHS system is not only effective for organics degradation but also for ammonia oxidation. Almost complete ammonia (NH4-N) removal (92 ± 3.6%) was occurred and the nitrate production amounted to 37 ± 6 mg/L in the treated effluent. This study strongly recommends applying Fenton process followed by DHS system for treatment of HLL.

Catalytic Enantioselective Cyclization and C3-Fluorination of Polyenes

PubMed Central

Cochrane, Nikki A.; Nguyen, Ha; Gagne, Michel R.

2013-01-01

(xylyl-phanephos)Pt2+ in combination with XeF2 mediates the consecutive diastereoselective cation-olefin cyclization/fluorination of polyene substrates. Isolated yields were typically in the 60s while enantioselectivies reached as high as 87%. The data are consistent with a stereoretentive fluorination of a P2Pt-alkyl cation intermediate. PMID:23282101

Transition States and transition state analogue interactions with enzymes.

PubMed

Schramm, Vern L

2015-04-21

Enzymatic transition states have lifetimes of a few femtoseconds (fs). Computational analysis of enzyme motions leading to transition state formation suggests that local catalytic site motions on the fs time scale provide the mechanism to locate transition states. An experimental test of protein fs motion and its relation to transition state formation can be provided by isotopically heavy proteins. Heavy enzymes have predictable mass-altered bond vibration states without altered electrostatic properties, according to the Born-Oppenheimer approximation. On-enzyme chemistry is slowed in most heavy proteins, consistent with altered protein bond frequencies slowing the search for the transition state. In other heavy enzymes, structural changes involved in reactant binding and release are also influenced. Slow protein motions associated with substrate binding and catalytic site preorganization are essential to allow the subsequent fs motions to locate the transition state and to facilitate the efficient release of products. In the catalytically competent geometry, local groups move in stochastic atomic motion on the fs time scale, within transition state-accessible conformations created by slower protein motions. The fs time scale for the transition state motions does not permit thermodynamic equilibrium between the transition state and stable enzyme states. Isotopically heavy enzymes provide a diagnostic tool for fast coupled protein motions to transition state formation and mass-dependent conformational changes. The binding of transition state analogue inhibitors is the opposite in catalytic time scale to formation of the transition state but is related by similar geometries of the enzyme-transition state and enzyme-inhibitor interactions. While enzymatic transition states have lifetimes as short as 10(-15) s, transition state analogues can bind tightly to enzymes with release rates greater than 10(3) s. Tight-binding transition state analogues stabilize the rare but evolved enzymatic geometry to form the transition state. Evolution to efficient catalysis optimized this geometry and its stabilization by a transition state mimic results in tight binding. Release rates of transition state analogues are orders of magnitude slower than product release in normal catalytic function. During catalysis, product release is facilitated by altered chemistry. Compared to the weak associations found in Michaelis complexes, transition state analogues involve strong interactions related to those in the transition state. Optimum binding of transition state analogues occurs when the complex retains the system motions intrinsic to transition state formation. Conserved dynamic motion retains the entropic components of inhibitor complexes, improving the thermodynamics of analogue binding.

Phosphotungstic acid encapsulated in the mesocages of amine-functionalized metal-organic frameworks for catalytic oxidative desulfurization.

PubMed

Wang, Xu-Sheng; Huang, Yuan-Biao; Lin, Zu-Jin; Cao, Rong

2014-08-21

Highly dispersed Keggin-type phosphotungstic acid (H3PW12O40, PTA) encapsulated in the mesocages of amine-functionalized metal-organic frameworks MIL-101(Cr)-NH2 has been prepared by an anion-exchange method. PTA anions (PW12O40(3-)) are stabilized in the mesocages via the electrostatic interaction with amino groups of the MIL-101(Cr)-NH2. The obtained catalyst (denoted PTA@MIL-101(Cr)-NH2) exhibits high catalytic activity in the extractive and catalytic oxidative desulfurization (ECODS) system under mild conditions. Moreover, it can be easily recovered and recycled several times without leaching and loss of activity.

Modification of ferrierite through post-synthesis treatments. Acidic and catalytic properties

NASA Astrophysics Data System (ADS)

Brylewska, Kamila; Tarach, Karolina A.; Mozgawa, Włodzimierz; Olejniczak, Zbigniew; Filek, Urszula; Góra-Marek, Kinga

2016-12-01

The main emphasis of this work was placed on a detailed characterization of structural, textural and acidic properties of FER zeolites with different Si/Al ratios in terms of their activity in ethanol dehydration reaction. Subsequent dealumination and desilication procedures were found to be an efficient methods of a secondary system of mesopore generation in the ferrierite crystals with preservation of their microporous characteristics. Through ethanol dehydration both the acidic and the textural features have a significant influence on catalytic performance of hierarchical ferrierites. It was shown that higher catalytic activity and selectivity to ethylene is ensured by zeolites with highly preserved microporous characteristic, i.e. well-developed micropore area and intrinsic acidity.

Catalytic activity of platinum on ruthenium electrodes with modified (electro)chemical states.

PubMed

Park, Kyung-Won; Sung, Yung-Eun

2005-07-21

Using Pt on Ru thin-film electrodes with various (electro)chemical states designed by the sputtering method, the effect of Ru states on the catalytic activity of Pt was investigated. The chemical and electrochemical properties of Pt/Ru thin-film samples were confirmed by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. In addition, Pt nanoparticles on Ru metal or oxide for an actual fuel cell system showed an effect of Ru states on the catalytic activity of Pt in methanol electrooxidation. Finally, it was concluded that such an enhancement of methanol electrooxidation on the Pt is responsible for Ru metallic and/or oxidation sites compared to pure Pt without any Ru state.

Density Functional Theory Study of Oxygen Reduction Activity on Ultrathin Platinum Nanotubes

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

Matanovic, Ivana; Kent, Paul; Garzon, Fernando

2012-07-13

The structure, stability, and catalytic activity of a number of single- and double-wall platinum (n,m) nanotubes ranging in diameter from 0.3 to 2.0 nm were studied using plane-wave based density functional theory in the gas phase and water environment. The change in the catalytic activity toward the oxygen reduction reaction (ORR) with the size and chirality of the nanotube was studied by calculating equilibrium adsorption potentials for ORR intermediates and by constructing free energy diagrams in the ORR dissociative mechanism network. In addition, the stability of the platinum nanotubes is investigated in terms of electrochemical dissolution potentials and by determiningmore » the most stable state of the material as a function of pH and potential, as represented in Pourbaix diagrams. Our results show that the catalytic activity and the stability toward electrochemical dissolution depend greatly on the diameter and chirality of the nanotube. On the basis of the estimated overpotentials for ORR, we conclude that smaller, approximately 0.5 nm in diameter single-wall platinum nanotubes consistently show a huge, up to 400 mV larger overpotential than platinum, indicating very poor catalytic activity toward ORR. This is the result of substantial structural changes induced by the adsorption of any chemical species on these tubes. Single-wall n = m platinum nanotubes with a diameter larger than 1 nm have smaller ORR overpotentials than bulk platinum for up to 180 mV and thus show improved catalytic activity relative to bulk. We also predict that these nanotubes can endure the highest cell potentials but dissolution potentials are still for 110 mV lower than for the bulk, indicating a possible corrosion problem.« less

Structure of a catalytic dimer of the α- and β-subunits of the F-ATPase from Paracoccus denitrificans at 2.3 Å resolution

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

Morales-Ríos, Edgar; Montgomery, Martin G.; Leslie, Andrew G. W.

2015-09-23

The structure of the αβ heterodimer of the F-ATPase from the α-proteobacterium P. denitrificans has been determined at 2.3 Å resolution. It corresponds to the ‘open’ or ‘empty’ catalytic interface found in other F-ATPases. The structures of F-ATPases have predominantly been determined from mitochondrial enzymes, and those of the enzymes in eubacteria have been less studied. Paracoccus denitrificans is a member of the α-proteobacteria and is related to the extinct protomitochondrion that became engulfed by the ancestor of eukaryotic cells. The P. denitrificans F-ATPase is an example of a eubacterial F-ATPase that can carry out ATP synthesis only, whereas manymore » others can catalyse both the synthesis and the hydrolysis of ATP. Inhibition of the ATP hydrolytic activity of the P. denitrificans F-ATPase involves the ζ inhibitor protein, an α-helical protein that binds to the catalytic F{sub 1} domain of the enzyme. This domain is a complex of three α-subunits and three β-subunits, and one copy of each of the γ-, δ- and ∊-subunits. Attempts to crystallize the F{sub 1}–ζ inhibitor complex yielded crystals of a subcomplex of the catalytic domain containing the α- and β-subunits only. Its structure was determined to 2.3 Å resolution and consists of a heterodimer of one α-subunit and one β-subunit. It has no bound nucleotides, and it corresponds to the ‘open’ or ‘empty’ catalytic interface found in other F-ATPases. The main significance of this structure is that it aids in the determination of the structure of the intact membrane-bound F-ATPase, which has been crystallized.« less

Crystal structure analysis of a bacterial aryl acylamidase belonging to the amidase signature enzyme family

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

Lee, Saeyoung; Park, Eun-Hye; Ko, Hyeok-Jin

2015-11-13

The atomic structure of a bacterial aryl acylamidase (EC 3.5.1.13; AAA) is reported and structural features are investigated to better understand the catalytic profile of this enzyme. Structures of AAA were determined in its native form and in complex with the analgesic acetanilide, p-acetaminophenol, at 1.70 Å and 1.73 Å resolutions, respectively. The overall structural fold of AAA was identified as an α/β fold class, exhibiting an open twisted β-sheet core surrounded by α-helices. The asymmetric unit contains one AAA molecule and the monomeric form is functionally active. The core structure enclosing the signature sequence region, including the canonical Ser-cisSer-Lys catalytic triad,more » is conserved in all members of the Amidase Signature enzyme family. The structure of AAA in a complex with its ligand reveals a unique organization in the substrate-binding pocket. The binding pocket consists of two loops (loop1 and loop2) in the amidase signature sequence and one helix (α10) in the non-amidase signature sequence. We identified two residues (Tyr{sup 136} and Thr{sup 330}) that interact with the ligand via water molecules, and a hydrogen-bonding network that explains the catalytic affinity over various aryl acyl compounds. The optimum activity of AAA at pH > 10 suggests that the reaction mechanism employs Lys{sup 84} as the catalytic base to polarize the Ser{sup 187} nucleophile in the catalytic triad. - Highlights: • We determined the first structure of a bacterial aryl acylamidase (EC 3.5.1.13). • Structure revealed spatially distinct architecture of the substrate-binding pocket. • Hydrogen-bonding with Tyr{sup 136} and Thr{sup 330} mediates ligand-binding and substrate.« less

System and method for controlling an engine based on ammonia storage in multiple selective catalytic reduction catalysts

DOEpatents

Sun, MIn; Perry, Kevin L.

2015-11-20

A system according to the principles of the present disclosure includes a storage estimation module and an air/fuel ratio control module. The storage estimation module estimates a first amount of ammonia stored in a first selective catalytic reduction (SCR) catalyst and estimates a second amount of ammonia stored in a second SCR catalyst. The air/fuel ratio control module controls an air/fuel ratio of an engine based on the first amount, the second amount, and a temperature of a substrate disposed in the second SCR catalyst.

Polynuclear complexes of copper(I) halides: coordination chemistry and catalytic transformations of alkynes

NASA Astrophysics Data System (ADS)

Mykhalichko, B. M.; Temkin, Oleg N.; Mys'kiv, M. G.

2000-11-01

Characteristic features of the coordination chemistry of Cu(I) and mechanisms of catalytic conversions of alkynes in the CuCl-MCl-H2O-HC≡CR system (MCl is alkali metal or ammonium chloride or amine hydrochloride; R=H, CH2OH, CH=CH2, etc.) are analysed based on studies of the compositions and structures of copper(I) chloride (bromide) complexes, alkyne π-complexes and ethynyl organometallic polynuclear compounds formed in this system in solutions and in the crystalline state. The role of polynuclear complexes in various reactions of alkynes is discussed. The bibliography includes 149 references.

Fabrication of transition metal-containing nanostructures via polymer templates for a multitude of applications

NASA Astrophysics Data System (ADS)

Lu, Jennifer Qing

Nanostructures such as carbon nanotubes and semiconducting nanowires offer great technological promise due to their remarkable properties. The lack of a rational synthesis method prevents fabricating these nanostructures with desirable and consistent properties at predefined locations for device applications. In this thesis, employing polymer templates, a variety of highly ordered catalytically active transition metal nanostructures, ranging from single metallic nanoparticles of Fe, Co, Ni, Au and bimetallic nanoparticles of Ni/Fe and Co/Mo to Fe-rich silicon oxide nanodomains with uniform and tunable size and spacing have been successfully synthesized. These nanostructures have been demonstrated to be excellent catalyst systems for the synthesis of carbon nanotube and silicon nanowire. High quality, small diameter carbon nanotubes and nanowires with narrow size distribution have been successfully attained. Because these catalytically active nanostructures are uniformly distributed and do not agglomerate at the growth temperatures, uniform, high density and high quality carbon nanotube mats have been obtained. Since this polymer template approach is fully compatible with conventional top-down photolithography, lithographically selective growth of carbon nanotubes on a surface or suspended carbon nanotubes across trenches have been produced by using existing semiconductor processing. We have also shown the feasibility of producing carbon nanotubes and silicon nanowires at predefined locations on a wafer format and established a wafer-level carbon nanotube based device fabrication process. The ability of the polymer template approach to control catalyst systems at the nano-, micro- and macro-scales paves a pathway for commercialization of these 1D nanostructure-enabled devices. Beside producing well-defined, highly ordered discrete catalytically active metal-containing nanostructures by the polymer template approach, Au and Ag nanotextured surfaces have also been attained by using a self-assembled ferrocenylsilane-based inorganic block copolymer template. These Au and Ag nanotextured surfaces exhibit different surface plasmon behavior than the nanotextured surface. Greatly enhanced and uniform Raman scattering have been observed on Ag nanotextured surfaces. Highly sensitive Au nanotextured surfaces suggest their potential application as sensing surfaces for SPR-based biodetection. This simple fabrication technique of producing inorganic nanostructures with adjustable properties such as size, spacing and composition offers great promise for both fundamental research and technological development.

Models of the Protocellular Structures, Functions and Evolution

NASA Technical Reports Server (NTRS)

Pohorille, Andrew; New, Michael; Keefe, Anthony; Szostak, Jack W.; Lanyi, Janos F.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

In the absence of extinct or extant record of protocells, the most direct way to test our understanding of the origin of cellular life is to construct laboratory models that capture important features of protocellular systems. Such efforts are currently underway in a collaborative project between NASA-Ames, Harvard medical School and University of California. They are accompanied by computational studies aimed at explaining self-organization of simple molecules into ordered structures. The centerpiece of this project is a method for the in vitro evolution of protein enzymes toward arbitrary catalytic targets. A similar approach has already been developed for nucleic acids: First, a very large population of candidate molecules is generated using a random synthetic approach. Next, the small numbers of molecules that can accomplish the desired task are selected. These molecules are next vastly multiplied using the polymerase chain reaction. A mutagenic approach, in which the sequences of selected molecules are randomly altered, can yield further improvements in performance or alterations of specificities. Unfortunately, the catalytic potential of nucleic acids is rather limited. Proteins are more catalytically capable but cannot be directly amplified. In the new technique, this problem is circumvented by covalently linking each protein of the initial, diverse, pool to the RNA sequence that codes for it. Then, selection is performed on the proteins, but the nucleic acids are replicated. To date, we have obtained "a proof of concept" by evolving simple, novel proteins capable of selectively binding adenosine tri-phosphate (ATP). Our next goal is to create an enzyme that can phosphorylate amino acids and another to catalyze the formation of peptide bonds in the absence of nucleic acid templates. This latter reaction does not take place in contemporary cells. once developed, these enzymes will be encapsulated in liposomes so that they will function in a simulated cellular environment. To provide a continuous energy supply, usually needed to activate the substrates, an energy transduction complex which generates ATP from adenosine diphosphate, inorganic phosphate and light will be used. This system, consisting of two modern proteins, ATP synthase and bacteriorhodopsin, has already been built and shown to work efficiently. By coupling chemical synthesis to such a system, it will be possible to drive chemical reactions by light if only the substrates for these reactions are supplied.

Molybdenum-based additives to mixed-metal oxides for use in hot gas cleanup sorbents for the catalytic decomposition of ammonia in coal gases

DOEpatents

Ayala, Raul E.

1993-01-01

This invention relates to additives to mixed-metal oxides that act simultaneously as sorbents and catalysts in cleanup systems for hot coal gases. Such additives of this type, generally, act as a sorbent to remove sulfur from the coal gases while substantially simultaneously, catalytically decomposing appreciable amounts of ammonia from the coal gases.

Catalytic devices

DOEpatents

Liu, Ming; Zhang, Xiang

2018-01-23

This disclosure provides systems, methods, and apparatus related to catalytic devices. In one aspect, a device includes a substrate, an electrically insulating layer disposed on the substrate, a layer of material disposed on the electrically insulating layer, and a catalyst disposed on the layer of material. The substrate comprises an electrically conductive material. The substrate and the layer of material are electrically coupled to one another and configured to have a voltage applied across them.

Prokaryotic Argonautes - variations on the RNA interference theme.

PubMed

van der Oost, John; Swarts, Daan C; Jore, Matthijs M

2014-04-15

The discovery of RNA interference (RNAi) has been a major scientific breakthrough. This RNA-guided RNA interference system plays a crucial role in a wide range of regulatory and defense mechanisms in eukaryotes. The key enzyme of the RNAi system is Argonaute (Ago), an endo-ribonuclease that uses a small RNA guide molecule to specifically target a complementary RNA transcript. Two functional classes of eukaryotic Ago have been described: catalytically active Ago that cleaves RNA targets complementary to its guide, and inactive Ago that uses its guide to bind target RNA to down-regulate translation efficiency. A recent comparative genomics study has revealed that Argonaute-like proteins are also encoded by prokaryotic genomes. Interestingly, there is a lot of variation among these prokaryotic Argonaute (pAgo) proteins with respect to domain architecture: some resemble the eukaryotic Ago (long pAgo) containing a complete or disrupted catalytic site, while others are truncated versions (short pAgo) that generally contain an incomplete catalytic site. Prokaryotic Agos with an incomplete catalytic site often co-occur with (predicted) nucleases. Based on this diversity, and on the fact that homologs of other RNAi-related protein components (such as Dicer nucleases) have never been identified in prokaryotes, it has been predicted that variations on the eukaryotic RNAi theme may occur in prokaryotes.

Prokaryotic Argonautes - variations on the RNA interference theme

PubMed Central

van der Oost, John; Swarts, Daan C.; Jore, Matthijs M.

2014-01-01

The discovery of RNA interference (RNAi) has been a major scientific breakthrough. This RNA-guided RNA interference system plays a crucial role in a wide range of regulatory and defense mechanisms in eukaryotes. The key enzyme of the RNAi system is Argonaute (Ago), an endo-ribonuclease that uses a small RNA guide molecule to specifically target a complementary RNA transcript. Two functional classes of eukaryotic Ago have been described: catalytically active Ago that cleaves RNA targets complementary to its guide, and inactive Ago that uses its guide to bind target RNA to down-regulate translation efficiency. A recent comparative genomics study has revealed that Argonaute-like proteins are also encoded by prokaryotic genomes. Interestingly, there is a lot of variation among these prokaryotic Argonaute (pAgo) proteins with respect to domain architecture: some resemble the eukaryotic Ago (long pAgo) containing a complete or disrupted catalytic site, while others are truncated versions (short pAgo) that generally contain an incomplete catalytic site. Prokaryotic Agos with an incomplete catalytic site often co-occur with (predicted) nucleases. Based on this diversity, and on the fact that homologs of other RNAi-related protein components (such as Dicer nucleases) have never been identified in prokaryotes, it has been predicted that variations on the eukaryotic RNAi theme may occur in prokaryotes. PMID:28357239

Silver iodide microstructures of a uniform towerlike shape: morphology purification via a chemical dissolution, simultaneously boosted catalytic durability, and enhanced catalytic performances.

PubMed

Lei, Bin; Zhu, Mingshan; Chen, Penglei; Chen, Chuncheng; Ma, Wanhong; Li, Tiesheng; Liu, Minghua

2014-03-26

The fabrication of microstructures/nanostructures of a uniform yet well-defined morphology has attracted broad interest from a variety of fields of advanced functional materials, especially catalysts. Most of the conventional methods generally suffer from harsh synthesis conditions, requirement of bulky apparatus, or incapability of scalable production, etc. To meet these formidable challenges, it is strongly desired to develop a facile, cost-effective, scalable method to fulfill a morphology purification. By a precipitation reaction between AgNO3 and KI, we report that irregular AgI structures, or their mixture with towerlike AgI architectures could be fabricated. Compared to the former, the mixed structures exhibit enhanced catalytic reactivity toward the photodegradation of Methyl Orange pollutant. However, its catalytic durability, which is one of the most crucial criteria that are required by superior catalysts, is poor. We further show that the irregular structures could be facilely removed from the mixture via a KI-assisted chemical dissolution, producing AgI of a uniform towerlike morphology. Excitingly, after such simple morphology purification, our towerlike AgI displays not only a boosted catalytic durability but also an enhanced catalytic reactivity. Our chemical dissolution-based morphology purification protocol might be extended to other systems, wherein high-quality advanced functional materials of desired properties might be developed.

Preliminary X-ray crystallographic studies of BthTX-II, a myotoxic Asp49-phospholipase A{sub 2} with low catalytic activity from Bothrops jararacussu venom

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

Corrêa, L. C.; Marchi-Salvador, D. P.; Cintra, A. C. O.

2006-08-01

A myotoxic Asp49-PLA{sub 2} with low catalytic activity from B. jararacussu (BthTX-II) was crystallized in the monoclinic crystal system; a complete X-ray diffraction data set was collected and a molecular-replacement solution was obtained. The oligomeric structure of BthTX-II resembles those of the Asp49-PLA{sub 2} PrTX-III and all bothropic Lys49-PLA{sub 2}s. For the first time, a complete X-ray diffraction data set has been collected from a myotoxic Asp49-phospholipase A{sub 2} (Asp49-PLA{sub 2}) with low catalytic activity (BthTX-II from Bothrops jararacussu venom) and a molecular-replacement solution has been obtained with a dimer in the asymmetric unit. The quaternary structure of BthTX-II resemblesmore » the myotoxin Asp49-PLA{sub 2} PrTX-III (piratoxin III from B. pirajai venom) and all non-catalytic and myotoxic dimeric Lys49-PLA{sub 2}s. In contrast, the oligomeric structure of BthTX-II is different from the highly catalytic and non-myotoxic BthA-I (acidic PLA{sub 2} from B. jararacussu). Thus, comparison between these structures should add insight into the catalytic and myotoxic activities of bothropic PLA{sub 2}s.« less

Catalytic Combustion for Ultra-Low NOx Hydrogen Turbines

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

Etemad, Shahrokh; Baird, Benjamin; Alavandi, Sandeep

2011-06-30

Precision Combustion, Inc., (PCI) in close collaboration with Solar Turbines, Incorporated, has developed and demonstrated a combustion system for hydrogen fueled turbines that reduces NOx to low single digit level while maintaining or improving current levels of efficiency and eliminating emissions of carbon dioxide. Full scale Rich Catalytic Hydrogen (RCH1) injector was developed and successfully tested at Solar Turbines, Incorporated high pressure test facility demonstrating low single digit NOx emissions for hydrogen fuel in the range of 2200F-2750F. This development work was based on initial subscale development for faster turnaround and reduced cost. Subscale testing provided promising results for 42%more » and 52% H2 with NOx emissions of less than 2 ppm with improved flame stability. In addition, catalytic reactor element testing for substrate oxidation, thermal cyclic injector testing to simulate start-stop operation in a gas turbine environment, and steady state 15 atm. operation testing were performed successfully. The testing demonstrated stable and robust catalytic element component life for gas turbine conditions. The benefit of the catalytic hydrogen combustor technology includes capability of delivering near-zero NOx without costly post-combustion controls and without requirement for added sulfur control. In addition, reduced acoustics increase gas turbine component life. These advantages advances Department of Energy (DOE’s) objectives for achievement of low single digit NOx emissions, improvement in efficiency vs. postcombustion controls, fuel flexibility, a significant net reduction in Integrated Gasification Combined Cycle (IGCC) system net capital and operating costs, and a route to commercialization across the power generation field from micro turbines to industrial and utility turbines.« less

Drosophila immunity: analysis of PGRP-SB1 expression, enzymatic activity and function.

PubMed

Zaidman-Rémy, Anna; Poidevin, Mickael; Hervé, Mireille; Welchman, David P; Paredes, Juan C; Fahlander, Carina; Steiner, Hakan; Mengin-Lecreulx, Dominique; Lemaitre, Bruno

2011-02-18

Peptidoglycan is an essential and specific component of the bacterial cell wall and therefore is an ideal recognition signature for the immune system. Peptidoglycan recognition proteins (PGRPs) are conserved from insects to mammals and able to bind PGN (non-catalytic PGRPs) and, in some cases, to efficiently degrade it (catalytic PGRPs). In Drosophila, several non-catalytic PGRPs function as selective peptidoglycan receptors upstream of the Toll and Imd pathways, the two major signalling cascades regulating the systemic production of antimicrobial peptides. Recognition PGRPs specifically activate the Toll pathway in response to Lys-type peptidoglycan found in most Gram-positive bacteria and the Imd pathway in response to DAP-type peptidoglycan encountered in Gram-positive bacilli-type bacteria and in Gram-negative bacteria. Catalytic PGRPs on the other hand can potentially reduce the level of immune activation by scavenging peptidoglycan. In accordance with this, PGRP-LB and PGRP-SC1A/B/2 have been shown to act as negative regulators of the Imd pathway. In this study, we report a biochemical and genetic analysis of PGRP-SB1, a catalytic PGRP. Our data show that PGRP-SB1 is abundantly secreted into the hemolymph following Imd pathway activation in the fat body, and exhibits an enzymatic activity towards DAP-type polymeric peptidoglycan. We have generated a PGRP-SB1/2 null mutant by homologous recombination, but its thorough phenotypic analysis did not reveal any immune function, suggesting a subtle role or redundancy of PGRP-SB1/2 with other molecules. Possible immune functions of PGRP-SB1 are discussed.