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Sample records for active catalyst precursor

  1. Stable amorphous georgeite as a precursor to a high-activity catalyst

    NASA Astrophysics Data System (ADS)

    Kondrat, Simon A.; Smith, Paul J.; Wells, Peter P.; Chater, Philip A.; Carter, James H.; Morgan, David J.; Fiordaliso, Elisabetta M.; Wagner, Jakob B.; Davies, Thomas E.; Lu, Li; Bartley, Jonathan K.; Taylor, Stuart H.; Spencer, Michael S.; Kiely, Christopher J.; Kelly, Gordon J.; Park, Colin W.; Rosseinsky, Matthew J.; Hutchings, Graham J.

    2016-03-01

    Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable—and hence little known and largely ignored—georgeite. The first three of these minerals are widely used as catalyst precursors for the industrially important methanol-synthesis and low-temperature water-gas shift (LTS) reactions, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite; with few exceptions it uses sodium carbonate as the carbonate source, but this also introduces sodium ions—a potential catalyst poison. Here we show that supercritical antisolvent (SAS) precipitation using carbon dioxide (refs 13, 14), a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts.

  2. Stable amorphous georgeite as a precursor to a high-activity catalyst.

    PubMed

    Kondrat, Simon A; Smith, Paul J; Wells, Peter P; Chater, Philip A; Carter, James H; Morgan, David J; Fiordaliso, Elisabetta M; Wagner, Jakob B; Davies, Thomas E; Lu, Li; Bartley, Jonathan K; Taylor, Stuart H; Spencer, Michael S; Kiely, Christopher J; Kelly, Gordon J; Park, Colin W; Rosseinsky, Matthew J; Hutchings, Graham J

    2016-03-01

    Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable--and hence little known and largely ignored--georgeite. The first three of these minerals are widely used as catalyst precursors for the industrially important methanol-synthesis and low-temperature water-gas shift (LTS) reactions, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite; with few exceptions it uses sodium carbonate as the carbonate source, but this also introduces sodium ions--a potential catalyst poison. Here we show that supercritical antisolvent (SAS) precipitation using carbon dioxide (refs 13, 14), a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts. PMID:26878237

  3. Nanostructured manganese oxides as highly active water oxidation catalysts: a boost from manganese precursor chemistry.

    PubMed

    Menezes, Prashanth W; Indra, Arindam; Littlewood, Patrick; Schwarze, Michael; Göbel, Caren; Schomäcker, Reinhard; Driess, Matthias

    2014-08-01

    We present a facile synthesis of bioinspired manganese oxides for chemical and photocatalytic water oxidation, starting from a reliable and versatile manganese(II) oxalate single-source precursor (SSP) accessible through an inverse micellar molecular approach. Strikingly, thermal decomposition of the latter precursor in various environments (air, nitrogen, and vacuum) led to the three different mineral phases of bixbyite (Mn2 O3 ), hausmannite (Mn3 O4 ), and manganosite (MnO). Initial chemical water oxidation experiments using ceric ammonium nitrate (CAN) gave the maximum catalytic activity for Mn2 O3 and MnO whereas Mn3 O4 had a limited activity. The substantial increase in the catalytic activity of MnO in chemical water oxidation was demonstrated by the fact that a phase transformation occurs at the surface from nanocrystalline MnO into an amorphous MnOx (1activities of water oxidation catalysts has been proposed by determining the amount of accessible manganese centers. PMID:25044528

  4. Nanostructured manganese oxides as highly active water oxidation catalysts: a boost from manganese precursor chemistry.

    PubMed

    Menezes, Prashanth W; Indra, Arindam; Littlewood, Patrick; Schwarze, Michael; Göbel, Caren; Schomäcker, Reinhard; Driess, Matthias

    2014-08-01

    We present a facile synthesis of bioinspired manganese oxides for chemical and photocatalytic water oxidation, starting from a reliable and versatile manganese(II) oxalate single-source precursor (SSP) accessible through an inverse micellar molecular approach. Strikingly, thermal decomposition of the latter precursor in various environments (air, nitrogen, and vacuum) led to the three different mineral phases of bixbyite (Mn2 O3 ), hausmannite (Mn3 O4 ), and manganosite (MnO). Initial chemical water oxidation experiments using ceric ammonium nitrate (CAN) gave the maximum catalytic activity for Mn2 O3 and MnO whereas Mn3 O4 had a limited activity. The substantial increase in the catalytic activity of MnO in chemical water oxidation was demonstrated by the fact that a phase transformation occurs at the surface from nanocrystalline MnO into an amorphous MnOx (1activities of water oxidation catalysts has been proposed by determining the amount of accessible manganese centers.

  5. The effect of catalyst preparation on the performance of alumina-supported ruthenium catalysts. I. The impact of catalytic precursor on particle size and catalytic activity

    SciTech Connect

    Mieth, J.A.; Schwarz, J.A. )

    1989-07-01

    The effect of preparation method and the choice of metallic precursor on the performance of a series of Ru/Al{sub 2}O{sub 3} catalysts were studied. Wet impregnation and incipient wetness were the methods employed; ruthenium nitrosylnitrate and ruthenium trichloride were the reagents. In the latter case, either Ru(III)/Ru(IV) chlorospecies or mixtures of Ru(II) hydrazine complexes were the catalytic precursors. The series of Ru/Al{sub 2}O{sub 3} catalysts, with metal loadings from 0.7-5% by weight, were subjected to a battery of performance tests: CO temperature-programmed reaction, steady-state CO hydrogenation, and temperature-programmed surface reaction. The methanation activity and carbon deposited during steady-state reaction varied systematically with the dispersion of Ru on the alumina. High rates of methane production were found on catalysts containing a large reservoir of carbon-containing reaction intermediates. The performance of these catalysts depended on the precursor used in their preparation. The effects of weight loading, method of preparation, and variations in the impregnant pH were small within a group prepared from a common precursor.

  6. Characterization of different precursors and activated vanadium phosphate catalysts by [sup 31]P NMR spin echo mapping

    SciTech Connect

    Sananes, M.T. Univ. of Liverpool ); Tuel, A.; Volta, J.C. ); Hutchings, G.J. )

    1994-07-01

    In a previous publication, the authors emphasized the use of the spin echo mapping technique applied to [sup 31]P NMR to obtain information on the valence state of vanadium in different environments of phosphorus for several VPO reference structures. In this paper, the authors describe the use of this technique, combined with knowledge of reference phases, to study VPO catalysts prepared from different precursors and used for the oxidation of n-butane into maleic anhydride. 9 refs., 2 figs., 1 tab.

  7. Sulfate as a precursor of catalyst poisoning

    SciTech Connect

    Mador, I.L.; Rosan, A.M.; Crissey, R.K.

    1984-05-01

    The poisoning of noble metal catalysts of hydrogenation reactions by sulfur in various forms is discussed. The specific reaction investigated was the hydrogenation of phenol to cyclohexanone over palladium. Catalyst pretreatments with NaHSO/sub 4/, PdSO/sub 4/, H/sub 2/, and He produced catalyst activities varying from inactive to unimpaired.

  8. Catalyst activator

    DOEpatents

    McAdon, Mark H.; Nickias, Peter N.; Marks, Tobin J.; Schwartz, David J.

    2001-01-01

    A catalyst activator particularly adapted for use in the activation of metal complexes of metals of Group 3-10 for polymerization of ethylenically unsaturated polymerizable monomers, especially olefins, comprising two Group 13 metal or metalloid atoms and a ligand structure including at least one bridging group connecting ligands on the two Group 13 metal or metalloid atoms.

  9. Temperature-programmed sulfiding of precursor cobalt oxide genesis of highly active sites on sulfided cobalt catalyst for hydrogenation and isomerization

    SciTech Connect

    Inamura, Kazuhiro; Takyu, Toshiyuki ); Okamoto, Yasuaki; Nagata, Kozo; Imanaka, Toshinobu )

    1992-02-01

    It was found that the method of sulfidation of cobalt oxide strongly affects the catalytic activities and selectivities of the resultant cobalt sulfide catalyst, as well as the calcination temperature of the cobalt oxide. When cobalt oxide was sulfided at 673 K by a temperature-programmed sulfiding method (a heating rate of 6 K/min), catalytic activities for the hydrogenation of butadiene and the isomerization of 1-butene were considerably enhanced compared with those for cobalt sulfide prepared by isothermal sulfidation at 673 K. Results of temperature-programmed sulfiding (TPS), temperature-programmed reduction (TPR), and X-ray diffraction (XRD) suggest that the catalysts showing high catalytic activities after sulfidation are partially sulfided at 673 K and consist of the unsulfided cobalt core phases (CoO or metallic Co). The sulfidation property of precursor cobalt oxides has been studied using TPS, simulating the sulfidation process of the cobalt sulfide catalysts. Two distinctly different kinds of sulfidation process are estimated by TPS measurements of the cobalt oxides. The calcination temperature of the precursor cobalt oxides strongly affects the sulfidation paths. They are differentiated in terms of the presence of a metallic Co intermediate. The relationship of the mechanism of sulfidation of the cobalt oxides to the generation of highly active sites is discussed.

  10. The fluxional amine gold(III) complex as an excellent catalyst and precursor of biologically active acyclic carbenes.

    PubMed

    Montanel-Pérez, Sara; Herrera, Raquel P; Laguna, Antonio; Villacampa, M Dolores; Gimeno, M Concepción

    2015-05-21

    A new amine gold(III) complex [Au(C6F5)2(DPA)]ClO4 with the di-(2-picolyl)amine (DPA) ligand has been synthesised. In the solid state the complex has a chiral amine nitrogen because the ligand coordinates to the gold centre through one nitrogen atom from a pyridine and through the NH moiety, whereas in solution it shows a fluxional behaviour with a rapid exchange between the pyridine sites. This complex can be used as an excellent synton to prepare new gold(III) carbene complexes by the reaction with isocyanide CNR. The resulting gold(III) derivatives have unprecedented bidentate C^N acyclic carbene ligands. All the complexes have been spectroscopically and structurally characterized. Taking advantage of the fluxional behaviour of the amine complex, its catalytic properties have been tested in several reactions with the formation of C-C and C-N bonds. The complex showed excellent activity with total conversion, without the presence of a co-catalyst, and with a catalyst loading as low as 0.1%. These complexes also present biological properties, and cytotoxicity studies have been performed in vitro against three tumour human cell lines, Jurkat (T-cell leukaemia), MiaPaca2 (pancreatic carcinoma) and A549 (lung carcinoma). Some of them showed excellent cytotoxic activity compared with the reference cisplatin.

  11. Hydrodeoxygenation of coal using organometallic catalyst precursors

    NASA Astrophysics Data System (ADS)

    Kirby, Stephen R.

    2002-04-01

    coals. Trends within the data were similar to those reported by other authors. Based on the conclusions from both the model compound studies and the coal analysis, predictions were made of the catalyst precursors' performance in the HDO of the three selected coals. It was concluded that CoMo-T2 is a desirable catalyst precursor for the HDO of coals (particularly low-rank coals), but that an optimum set of conditions must be determined to take full advantage of its HDO ability. (Abstract shortened by UMI.)

  12. The role of catalyst precursor anions in coal gasification

    SciTech Connect

    Abotsi, G.M.K.

    1992-08-28

    The aims of the proposed project are to enrich our understanding of the roles of various aqueous soluble catalyst precursor anions on the surface electrical properties of coal and to ascertain the influence of the surface charge on the adsorption, dispersion, and activities of calcium and potassium. These goals will be achieved by impregnating a North Dakota lignite (PSOC 1482) and its demineralized derivative with calcium or potassium catalyst precursors containing acetate (CH{sub 3}COO{sup {minus}}), chloride (Cl{sup {minus}}), nitrate (NO{sub 3}{sup {minus}}), sulfate (SO{sub 4}{sup 2{minus}}), and carbonate (CO{sub 3}{sup 2{minus}}) anions. Catalyst loading will be conducted under well-controlled conditions of solution pH and ionic strength. In the last quarter, the surface charge properties of the coal was determined as a function of acetate (CH{sub 3}COO{sup {minus}}), chloride (Cl{sup {minus}}), nitrate (NO{sup 3}{sup {minus}}), carbonate (CO{sub 3}{sup 2{minus}}) or sulfate (SO{sub 4}{sup 2{minus}})concentration using the respective potassium salts of these anions. In general, low anion concentrations (10{sup {minus}3} or 10{sup {minus}2} mol/L) had little effect on the zeta potentials of the coals. However, the surface charge densities of the coal become less negative at 10-1 mol/L of the nitrate, carbonate or sulfate anions. These trends suggest that the surface charge density of the coal is controlled by the adsorption of potassium ions (K{sup +}) onto the coal particles. The net negative charge on the coal panicles creates a repulsive force between the anions and the coal surface and prevents the anions from exerting any significant effect on the coal's electrokinetic properties.

  13. Supported Oxide Catalysts from Chelating Precursors

    NASA Astrophysics Data System (ADS)

    Prieto-Centurion, Dario

    Supported Fe catalysts and, in particular, Fe and substituted MFI zeolites have attracted industrial and academic attention due to their ability to promote selective catalytic reduction of NOx and selective partial oxidation of hydrocarbons. It is generally accepted that some form of highly dispersed, binuclear or atomically-isolated metal species are involved in the selective processes catalyzed these materials. Several studies have sought to reproduce the structures and reactivity of these substituted zeolites on dierent supports. Given that specialized reagents or preparation conditions that are required in some of these preparation methods, and that multiple surface structures are often formed, this dissertation aimed to develop a route to highly dispersed supported transition metals using commonly available reactants and synthesis routes. Described here is a straightforward and effective procedure to control dispersion and surface speciation of Fe on SiO2 and CeO2 through incipient wetness impregnation (IWI) of the support with aqueous, anionic complexes of Fe3+ and ethylenediaminetetraacetic acid (EDTA) followed by oxidative heat-treatment. On SiO2, this method preferentially creates isolated surface structures up to loading of 0.9 Fe nm-2 if using alkali counter-cations. This isolated species display classic 'single-site' behavior|constant turn over frequency (TOF) with increasing Fe surface density|in the oxidation of adamantane with H 2O2, indicating active sites are equally accessible and equally active within this range of surface density. Additionally, TOF increases linearly with electronegativity of the alkali counter-cation, suggesting electronic promotion. Conversely, IWI of unprotected Fe3+ produces agglomerates less active in this reaction. On CeO2, the sterics and negative charge imparted on Fe 3+ by EDTA4- inhibits incorporation of Fe into surface vacancies. Instead, formation of two-dimensional oligomeric structures which can undergo Fe3+-Fe2

  14. Photoacoustic infrared analysis of nickel catalysts precursors

    NASA Astrophysics Data System (ADS)

    Pasieczna, S.; Ryczkowski, J.

    2006-11-01

    Photoacoustic spectroscopy (FT-IR/PAS) has been used for identification of different forms of nickel precursors formed during CIM (classical impregnation method) and DIM (double impregnation method) process and different pH of the solution containing nickel ions.

  15. The role of catalyst precursor anions in coal gasification. Final technical report, September 1991--June 1994

    SciTech Connect

    Abotsi, G.M.K.

    1995-01-01

    The utilization of coal is currently limited by several factors, including the environmental impacts of coal use and the lack of cost-effective technologies to convert coal into useful gaseous and liquid products. Several catalysts have been evaluated for coal gasification and liquefaction. The activities of the catalysts are dependent on many factors such as the method of catalyst addition to the coal and the catalyst precursor type. Since catalyst addition to coal is frequently conducted in aqueous solution, the surface chemistry of colloidal coal particles will be expected to exert an influence on catalyst uptake. However, the effects of the various coal gasification catalyst precursors on the interfacial properties of coal during catalyst loading from solution has received little attention. The aim of this study is to ascertain the influence of the metal salts (i): calcium acetate (Ca(OOCCH{sub 3}){sub 2}), calcium chloride (CaCl{sub 2}) or calcium nitrate (Ca(NO{sub 3}){sub 2}) and (ii): potassium acetate (KOOCCH{sub 3}), potassium chloride (KCl), potassium nitrate (KNO{sub 3}), potassium carbonate (K{sub 2}CO{sub 3}) and potassium sulfate (K{sub 2}SO{sub 4}) on the electrokinetic and adsorptive properties of coal and determine the relationship, if any, between coal surface electrokinetic properties, and catalyst loading and eventually its effects on the reactivities of coal chars.

  16. Relation between hydrodesulfurization activity and the state of promoters in precursor calcined Ni-Co-Mo/Al/sub 2/O/sub 3/ catalysts

    SciTech Connect

    Caceres, C.; Fierro, J.L.G.; Agudo, A.L.; Severino, F.; Laine, J.

    1986-01-01

    Two series of NiCo-Mo/Al/sub 2/O/sub 3/ hydrodesulfurization (HDS) catalysts prepared by different procedures were investigated. In each series the Mo loading and the total content of promoters (Co + Ni) were kept constant but the Co/(Co + Ni) atomic ratio was varied from 0 to 1. The two series of catalysts were prepared by a sequential wet impregnation technique. In series I, the impregnations of both Mo and promoters were carried out at the pH of the impregnating aqueous solutions, employing an intermediate calcination; in series II, Mo was impregnated at pH 10, while the promoters were added in aqueous ethanol solutions without intermediate calcination. Catalysts in their calcined state were characterized by reduction in H/sub 2/ at 500/sup 0/C, O/sub 2/ chemisorption, and infrared spectroscopy of adsorbed NO. The HDS activity and the optimum Co/(Co + Ni) atomic ratio were different for the two series, in agreement with the previous studies, HDS activity being generally higher for series II than for series I. Dispersion of Mo (as estimated from O/sub 2/ chemisorption) and NO adsorption on Mo in reduced catalysts (as judged from the intensity of the band at about 1705 cm/sup -1/) were not substantially different for the two series of catalysts and did not correlate with HDS activity. However, adsorbed NO on promoters in oxidized catalysts (bands at about 1880 and 1800 cm/sup -1/) followed roughly the same trend as HDS activity, suggesting that the active sites may be related to the Co and Ni atoms adsorbing NO. Possible reasons for the differences between HDS activity of the two series are considered.

  17. Syntheses of biodiesel precursors: sulfonic acid catalysts for condensation of biomass-derived platform molecules.

    PubMed

    Balakrishnan, Madhesan; Sacia, Eric R; Bell, Alexis T

    2014-04-01

    Synthesis of transportation fuel from lignocellulosic biomass is an attractive solution to the green alternative-energy problem. The production of biodiesel, in particular, involves the process of upgrading biomass-derived small molecules to diesel precursors containing a specific carbon range (C11 -C23). Herein, a carbon-upgrading process utilizing an acid-catalyzed condensation of furanic platform molecules from biomass is described. Various types of sulfonic acid catalysts have been evaluated for this process, including biphasic and solid supported catalysts. A silica-bound alkyl sulfonic acid catalyst has been developed for promoting carbon-carbon bond formation of biomass-derived carbonyl compounds with 2-methylfuran. This hydrophobic solid acid catalyst exhibits activity and selectivity that are comparable to those of a soluble acid catalyst. The catalyst can be readily recovered and recycled, possesses appreciable hydrolytic stability in the presence of water, and retains its acidity over multiple reaction cycles. Application of this catalyst to biomass-derived platform molecules led to the synthesis of a variety of furanic compounds, which are potential biodiesel precursors.

  18. Spectroscopic studies of alumina-supported nickel catalysts precursors. Part I. Catalysts prepared from acidic solutions

    NASA Astrophysics Data System (ADS)

    Pasieczna-Patkowska, S.; Ryczkowski, J.

    2007-04-01

    Nickel alumina-supported catalysts were prepared from acidic solutions of nickel nitrate by the CIM and DIM methods (classical and double impregnation, respectively). The catalysts exhibited different nickel species due to the existence of various metal-support interaction strengths. As a consequence, the reducibility and other surface properties changed as a function of the preparation method. The aim of this work was to study the interaction between the metal precursor and the alumina surface by means of FT-IR (Fourier transform infrared) and FT-IR/PAS (FT-IR photoacoustic spectroscopy).

  19. Thermal Decomposition of Bulk K-CoMoSx Mixed Alcohol Catalyst Precursors and Effects on Catalyst Morphology and Performance

    SciTech Connect

    Menart, M. J.; Hensley, J. E.; Costelow, K. E.

    2012-09-26

    Cobalt molybdenum sulfide-type mixed alcohol catalysts were synthesized via calcination of precipitated bulk sulfides and studied with temperature programmed decomposition analysis. Precursors containing aqueous potassium were also considered. Precipitates thermally decomposed in unique events which released ammonia, carbon dioxide, and sulfur. Higher temperature treatments led to more crystalline and less active catalysts in general with ethanol productivity falling from 203 to 97 g (kg cat){sup -1} h{sup -1} when the calcination temperature was increased from 375 to 500 C. The addition of potassium to the precursor led to materials with crystalline potassium sulfides and good catalytic performance. In general, less potassium was required to promote alcohol selectivity when added before calcination. At calcination temperatures above 350 C, segregated cobalt sulfides were observed, suggesting that thermally decomposed sulfide precursors may contain a mixture of molybdenum and cobalt sulfides instead of a dispersed CoMoS type of material. When dimethyl disulfide was fed to the precursor during calcination, crystalline cobalt sulfides were not detected, suggesting an important role of free sulfur during decomposition.

  20. Ni-based heterogeneous catalyst from a designed molecular precursor for the efficient electrochemical water oxidation.

    PubMed

    Kuznetsov, Denis A; Konev, Dmitry V; Komarova, Natal'ya S; Ionov, Andrey M; Mozhchil, Rais N; Fedyanin, Ivan V

    2016-07-28

    Bimetallic Ni-Mo alkoxide was synthesized and exploited as the single-source precursor for the solution-processed deposition of the mixed-oxide layers on different conducting surfaces. Upon potential cycling in 1 M NaOH, these composites convert, in situ, into highly porous NiOx/NiOOH catalysts characterized by the high electrocatalytic activity for water oxidation under both basic (pH 13.6) and near neutral (pH 9.2) conditions. PMID:27354324

  1. Copper complexes as catalyst precursors in the electrochemical hydrogen evolution reaction.

    PubMed

    Kügler, Merle; Scholz, Julius; Kronz, Andreas; Siewert, Inke

    2016-04-28

    Herein, we report the synthesis and species distribution of copper(ii) complexes based on two different ligand scaffolds and the application of the two complexes in the electrochemical proton reduction catalysis. The ligands bind to one or two copper(II) ions and the pH-dependent mono/dinuclear equilibrium depends on the steric bulk of the ligands. The two water soluble copper(II) complexes were investigated for their activities in the electrochemical hydrogen evolution reaction (HER). In both complexes the copper(ii) ions have a N4-coordination environment composed of N-heterocycles, although in different coordination geometries (SPY-5 and TBPY-5). The solutions of the complexes were highly active catalysts in water at acidic pH but the complexes decompose under catalytic conditions. They act as precursors for highly active copper(0) and Cu2O deposits at the electrode surface, which are in turn the active catalysts. The absence or presence of the ligands has neither an influence on the catalytic activity of the solutions nor an influence on the activity of the deposit formed during controlled potential electrolysis. Finally, we can draw some conclusions on the stability of copper catalysts in the aqueous electrochemical HER. PMID:26986849

  2. Subeutectic Synthesis of Epitaxial Si-NWs with Diverse Catalysts Using a Novel Si Precursor

    PubMed Central

    2010-01-01

    The applicability of a novel silicon precursor with respect to reasonable nanowire (NW) growth rates, feasibility of epitaxial NW growth and versatility with respect to diverse catalysts was investigated. Epitaxial growth of Si-NWs was achieved using octochlorotrisilane (OCTS) as Si precursor and Au as catalyst. In contrast to the synthesis approach with SiCl4 as precursor, OCTS provides Si without the addition of H2. By optimizing the growth conditions, effective NW synthesis is shown for alternative catalysts, in particular, Cu, Ag, Ni, and Pt with the latter two being compatible to complementary metal-oxide-semiconductor technology. As for these catalysts, the growth temperatures are lower than the lowest liquid eutectic; we suggest that the catalyst particle is in the solid state during NW growth and that a solid-phase diffusion process, either in the bulk, on the surface, or both, must be responsible for NW nucleation. PMID:20843058

  3. Silica coated noble metal nanoparticle hydrosols as supported catalyst precursors.

    PubMed

    Kong, Tung Shing Adam; Yu, Kai Man Kerry; Tsang, Shik Chi

    2006-04-01

    Synthesis of well-defined nanoparticles has been intensively pursued not only for their fundamental scientific interest, but also for many technological applications. One important development of the nanomaterial is in the area of chemical catalysis. We have now developed a new aqueous-based method for the synthesis of silica encapsulated noble metal nanoparticles in controlled dimensions. Thus, colloid stable silica encapsulated approximately 5 nm platinum nanoparticle is synthesized by a multi-step method. The thickness of the silica coating could be controlled using a different amount of silica precursor. These particles supported on a high surface area alumina are also demonstrated to display a superior hydrogenation activity and stability against metal sintering after thermal activation.

  4. Ruthenium-based olefin metathesis catalysts bearing pH-responsive ligands: External control of catalyst solubility and activity

    NASA Astrophysics Data System (ADS)

    Balof, Shawna Lynn

    2011-12-01

    Sixteen novel, Ru-based olefin metathesis catalysts bearing pH responsive ligands were synthesized. The pH-responsive groups employed with these catalysts included dimethylamino (NMe2) modified NHC ligands as well as N-donor dimethylaminopyridine (DMAP) and 3-(o-pyridyl)propylidene ligands. These pH-responsive ligands provided the means by which the solubility and/or activity profiles of the catalysts produced could be controlled via acid addition. The main goal of this dissertation was to design catalyst systems capable of performing ring opening metathesis (ROMP) and ring closing metathesis (RCM) reactions in both organic and aqueous media. In an effort to quickly gain access to new catalyst structures, a template synthesis for functionalized NHC ligand precursors was designed, in addition to other strategies, to obtain ligand precursors with ancillary NMe2 groups. Kinetic studies for the catalysts produced from these precursors showed external control of catalyst solubility was afforded via protonation of the NMe2 groups of their NHC ligands. Additionally, this protonation afforded external control of catalyst propagation rates for several catalysts. This is the first known independent external control for the propagation rates of ROMP catalysts. The incorporation of pH-responsive N-donor ligands into catalyst structures also provided the means for the external control of metathesis activity, as the protonation of these ligands resulted in an increased initiation rate based on their fast and irreversible dissociation from the metal center. The enhanced external control makes these catalysts applicable to a wide range of applications, some of which have been explored by us and/or through collaboration. Three of the catalysts designed showed remarkable metathesis activity in aqueous media. These catalysts displayed comparable RCM activity in aqueous media to a class of water-soluble catalysts reported by Grubbs et al., considered to be the most active catalyst for

  5. The role of catalyst precursor anions in coal gasification. Third quarterly report

    SciTech Connect

    Abotsi, G.M.K.

    1992-08-28

    The aims of the proposed project are to enrich our understanding of the roles of various aqueous soluble catalyst precursor anions on the surface electrical properties of coal and to ascertain the influence of the surface charge on the adsorption, dispersion, and activities of calcium and potassium. These goals will be achieved by impregnating a North Dakota lignite (PSOC 1482) and its demineralized derivative with calcium or potassium catalyst precursors containing acetate (CH{sub 3}COO{sup {minus}}), chloride (Cl{sup {minus}}), nitrate (NO{sub 3}{sup {minus}}), sulfate (SO{sub 4}{sup 2{minus}}), and carbonate (CO{sub 3}{sup 2{minus}}) anions. Catalyst loading will be conducted under well-controlled conditions of solution pH and ionic strength. In the last quarter, the surface charge properties of the coal was determined as a function of acetate (CH{sub 3}COO{sup {minus}}), chloride (Cl{sup {minus}}), nitrate (NO{sup 3}{sup {minus}}), carbonate (CO{sub 3}{sup 2{minus}}) or sulfate (SO{sub 4}{sup 2{minus}})concentration using the respective potassium salts of these anions. In general, low anion concentrations (10{sup {minus}3} or 10{sup {minus}2} mol/L) had little effect on the zeta potentials of the coals. However, the surface charge densities of the coal become less negative at 10-1 mol/L of the nitrate, carbonate or sulfate anions. These trends suggest that the surface charge density of the coal is controlled by the adsorption of potassium ions (K{sup +}) onto the coal particles. The net negative charge on the coal panicles creates a repulsive force between the anions and the coal surface and prevents the anions from exerting any significant effect on the coal`s electrokinetic properties.

  6. Non-platinum group metal oxgyen reduction catalysts and their mechanism in both acid and alkaline media: The effect of the catalyst precursor and the ionomer on oxygen reduction

    NASA Astrophysics Data System (ADS)

    Robson, Michael H.

    Non-platinum catalysts are an attractive strategy for lowering the cost of fuel cells, but much more development is needed in order to replace platinum, especially at the cathode where oxygen is reduced. Research groups worldwide have donated material for a study in which precursor structure to catalyst activity correlations are made. The donated samples have been divided into three classes based on their precursor; macrocyclic chelates, small molecule, and polymeric precursors. The precursor is one activity-dictating factor among many, but it is one of the most influential. It was found that macrocyclic chelates on average produced the most active catalysts, having the highest limiting, diffusion-limited, kinetic, and exchange current densities, as well as the lowest overpotentials and H2O2 production. This suggests that the M-N4 atomic structure of the precursor remains largely static throughout heat treatment, as the M-Nx motif is the accepted active site conformation. The other classes were somewhat less active, but the breadth of precursor materials that range in structure and functionality, as well as low associated costs, make them attractive precursor materials. Careful precursor selection based on this analysis was applied to a new generation of catalyst derived from iron salt and 4-aminoantipyrine. An extensive investigation of the reduction of oxygen on the material performed in both acid and alkaline media, and it was found that reduction follows a two-step pathway. While the peroxide reducing step is also very fast, the first step is so rapid that, even at low active site density, the material is almost as active as platinum if all diffusion limitations are removed. In addition to bottom-up catalyst design, the catalyst:ionomer complex, by which catalyst is incorporated into the membrane electrode assembly, also affects reductive kinetics. A series of novel anionically conductive ionomers have been evaluated using a well-described cyanamide derived

  7. Influence of the metal precursor on the catalytic behavior of Pt/ceria catalysts in the preferential oxidation of CO in the presence of H₂ (PROX).

    PubMed

    Jardim, Erika O; Rico-Francés, Soledad; Coloma, Fernando; Anderson, James A; Silvestre-Albero, Joaquín; Sepúlveda-Escribano, Antonio

    2015-04-01

    The effect of the metal precursor (presence or absence of chlorine) on the preferential oxidation of CO in the presence of H2 over Pt/CeO2 catalysts has been studied. The catalysts are prepared using (Pt(NH3)4)(NO3)2 and H2PtCl6, as precursors, in order to ascertain the effect of the chlorine species on the chemical properties of the support and on the catalytic behavior of these systems in the PROX reaction. The results show that chloride species exert an important effect on the redox properties of the oxide support due to surface chlorination. Consequently, the chlorinated catalyst exhibits a poorer catalytic activity at low temperatures compared with the chlorine-free catalyst, and this is accompanied by a higher selectivity to CO2 even at high reaction temperatures. It is proposed that the CO oxidation mechanism follows different pathways on each catalyst.

  8. Influence of the metal precursor on the catalytic behavior of Pt/ceria catalysts in the preferential oxidation of CO in the presence of H₂ (PROX).

    PubMed

    Jardim, Erika O; Rico-Francés, Soledad; Coloma, Fernando; Anderson, James A; Silvestre-Albero, Joaquín; Sepúlveda-Escribano, Antonio

    2015-04-01

    The effect of the metal precursor (presence or absence of chlorine) on the preferential oxidation of CO in the presence of H2 over Pt/CeO2 catalysts has been studied. The catalysts are prepared using (Pt(NH3)4)(NO3)2 and H2PtCl6, as precursors, in order to ascertain the effect of the chlorine species on the chemical properties of the support and on the catalytic behavior of these systems in the PROX reaction. The results show that chloride species exert an important effect on the redox properties of the oxide support due to surface chlorination. Consequently, the chlorinated catalyst exhibits a poorer catalytic activity at low temperatures compared with the chlorine-free catalyst, and this is accompanied by a higher selectivity to CO2 even at high reaction temperatures. It is proposed that the CO oxidation mechanism follows different pathways on each catalyst. PMID:25531415

  9. Non-precious metal catalysts prepared from precursor comprising cyanamide

    SciTech Connect

    Chung, Hoon Taek; Zelenay, Piotr

    2015-10-27

    Catalyst comprising graphitic carbon and methods of making thereof; said graphitic carbon comprising a metal species, a nitrogen-containing species and a sulfur containing species. A catalyst for oxygen reduction reaction for an alkaline fuel cell was prepared by heating a mixture of cyanamide, carbon black, and a salt selected from an iron sulfate salt and an iron acetate salt at a temperature of from about 700.degree. C. to about 1100.degree. C. under an inert atmosphere. Afterward, the mixture was treated with sulfuric acid at elevated temperature to remove acid soluble components, and the resultant mixture was heated again under an inert atmosphere at the same temperature as the first heat treatment step.

  10. Hydrogen activation by magnesia catalysts

    SciTech Connect

    Yulin Gu; Brenner, A. )

    1992-07-01

    Hydrogen activation by magnesia catalysts was investigated by studying H{sub 2}-D{sub 2} exchange. The number of active sites, surface composition, rate, and mechanism of the reaction were investigated as a function of the activation temperature. Behavior of a commercial magnesia and a catalyst synthesized from Mg(OH){sub 2} were similar, although the latter catalyst had a much larger surface area. The upper limit for the number of active sites was determined in the classical manner by using selective poisoning by CO. A novel technique involving monitoring the stoichiometric reaction between magnesia and D{sub 2}(g) enabled the very unusual determination of the lower limit for the number of active sites. Thus, the true number of active sites is bracketed within the upper and lower limits. Maximal activity occurred after activation at 700 C. The number of active sites is about 10{sup 12}/cm{sup 2}, which is 10{sup 3}-fold higher than formerly reported on the basis of EPR data. The turnover frequency at 273 K and a partial pressure of 20 Torr of an equimolar mixture of H{sub 2}-D{sub 2} is 4 s{sup {minus}1}, roughly 10{sup 3}-fold less than previously reported. The site density and activity are now consistent with expected values, rather than the anomalous values previously reported. The hydroxyl coverage of the surface was determined in a novel manner using thermogravimetric analysis over the temperature range of 300 to 1,400 K. The catalysts are of low activity when the surface is either of very high or very low hydroxyl content. A mechanism in which the active site includes an ensemble consisting of a Mg{sup 2+} center and neighboring surface OH and O{sup 2{minus}} is proposed.

  11. Hydrodeoxygenation in low-rank coal liquefaction systems using novel organometallic catalyst precursors

    SciTech Connect

    Kirby, S.R.; Song, C.; Schobert, H.H.

    1996-12-31

    Oxygen functionalities, especially phenols, are undesirable components of coal derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial alternative would be the removal of these functionalities, or the prevention of their formation, during the liquefaction process. Organometallic precursors of Co, Ni and Mo have been studied as catalysts. To ascertain the hydrodeoxygenation properties of these catalysts under liquefaction conditions, model compounds were investigated. Anthrone, Dibutylmethyl phenol, dinaphthyl ether and xanthene were studied to provide a comparison of conversions of deoxygenated products. Studies of the deoxygenating abilities of these catalyst precursors in coal liquefaction systems have also been performed. Improvements in conversion and product quality are observed. Both these factors are dependent on the coal used.

  12. Diphenylamido Precursors to Bisalkoxide Molybdenum Olefin Metathesis Catalysts

    PubMed Central

    Sinha, Amritanshu; Müller, Peter; Hoveyda, Amir H.

    2008-01-01

    We have found that Mo(NAr)(CHR′)(NPh2)2 (R′ = t-Bu or CMe2Ph) and Mo(NAr′)(CHCMe2Ph)(NPh2)2 (Ar = 2,6-i-Pr2C6H3; Ar′ = 2,6-Me2C6H3) can be prepared through addition of two equivalents of LiNPh2 to Mo(NR″)(CHR′)(OTf)2(dme) species (R″ = Ar or Ar′ dme = 1,2-dimethoxyethane), although yields are low. A high yield route consists of addition of LiNPh2 to bishexafluro-t-butoxide species. An X-ray structure of Mo(NAr)(CHCMe2Ph)(NPh2)2 reveals that the two diphenylamido groups are oriented in a manner that allows an 18 electron count to be achieved. The diphenylamido complexes react readily with t-BuOH and (CF3)2MeCOH, but not readily with the sterically demanding biphenol H2[Biphen] (Biphen2- = 3,3′-Di-t-butyl-5,5′,6,6′-tetramethyl-1,1′-Biphenyl-2,2′-diolate). The diphenylamido complexes do react with various 3,3′-disubstituted binaphthols to yield binaphtholate catalysts that can be prepared in situ and employed for a simple asymmetric ring-closing metathesis reaction. In several cases conversions and enantioselectivities were comparable to reactions in which isolated catalysts were employed. PMID:19030118

  13. Anodic Deposition of a Robust Iridium-Based Water-Oxidation Catalyst from Organometallic Precursors

    SciTech Connect

    Blakemore, James D; Schley, Nathan D; Olack, G.; Incarvito, Christopher D; Brudvig, Gary W; Crabtree, Robert H

    2011-01-01

    Artificial photosynthesis, modeled on natural light-driven oxidation of water in Photosystem II, holds promise as a sustainable source of reducing equivalents for producing fuels. Few robust water-oxidation catalysts capable of mediating this difficult four-electron, four-proton reaction have yet been described. We report a new method for generating an amorphous electrodeposited material, principally consisting of iridium and oxygen, which is a robust and long-lived catalyst for water oxidation, when driven electrochemically. The catalyst material is generated by a simple anodic deposition from Cp*Ir aqua or hydroxo complexes in aqueous solution. This work suggests that organometallic precursors may be useful in electrodeposition of inorganic heterogeneous catalysts.

  14. Heterogenized Water Oxidation Catalysts Prepared by Immobilizing Kläui-Type Organometallic Precursors.

    PubMed

    Pastori, Gabriele; Wahab, Khaja; Bucci, Alberto; Bellachioma, Gianfranco; Zuccaccia, Cristiano; Llorca, Jordi; Idriss, Hicham; Macchioni, Alceo

    2016-09-12

    An efficient heterogenized water oxidation catalyst (2_TiO2 ) has been synthesized by immobilizing the Kläui-type organometallic precursor [Cp*Ir{P(O)(OH)2 }3 ]Na (2, Cp*=1,2,3,4,5-pentamethylcyclopentadienyl ligand) onto rutile TiO2 . Iridium is homogeneously distributed at the molecular and atomic/small cluster level in 2_TiO2 and 2'_TiO2 (solid catalyst recovered after the first catalytic run), respectively, as indicated by STEM-HAADF (scanning transmission electron microscopy - high angle annular dark field) studies. 2'_TiO2 exhibits TOF values up to 23.7 min(-1) in the oxidation of water to O2 driven by NaIO4 at nearly neutral pH, and a TON only limited by the amount of NaIO4 used, as indicated by multiple run experiments. Furthermore, while roughly 40 % leaching is observed during the first catalytic run, 2'_TiO2 does not undergo any further leaching even when in contact with strongly basic solutions and completely maintains its activity for thousands of cycles. NMR studies, in combination with ICP-OES (inductively coupled plasma optical emission spectrometry), indicate that the activation of 2_TiO2 occurs through the initial oxidative dissociation of PO4 (3-) , ultimately leading to active centers in which a 1:1 P/Ir ratio is present (derived from the removal of two PO4 (3-) units) likely missing the Cp* ligand. PMID:27246987

  15. Infrared investigations on metal-support interactions in Ni-SiO{sub 2} catalyst precursors: Role of silica

    SciTech Connect

    Ghuge, K.D.; Babu, G.P.

    1995-02-01

    In a Ni-silica catalyst system prepared by the precipitation/deposition method the silica is reported to play a role in forming the {open_quotes}support{close_quotes} to nickel carbonate (or hydroxide) species. The support formed is identified as various types of nickel silicate species and also as the species comprising -Ni-O-Si- linkages. Further, the support is shown to (i) provide the definite porous structure to the catalyst and (ii) influence the reducibility of nickel species. Also, in nickel catalyst system prepared by impregnation method, formation of silicate species on surface and its influence on reduction of nickel and restriction in metal sintering is well established. However, the mechanism of silica conversion to support species and influence on metal dispersion, the formation of a definite porous network and catalytic activity in Ni-silica catalyst system prepared by precipitation is not well established. In this paper Ni-silica catalyst precursors were prepared by adding separate solutions of nickel sulfate and sodium carbonate simultaneously to the precipitation vessel containing a silica slurry as described by Nitta et al. and maintaining a SiO{sub 2}/Ni ratio of 0.5, precipitation temperature = 92{degrees}C, and pH = 8.5. 15 refs., 1 fig., 1 tab.

  16. An evaluation of Pt sulfite acid (PSA) as precursor for supported Pt catalysts

    SciTech Connect

    Regalbuto, J.R.; Ansel, O.; Miller, J.T.

    2010-11-12

    As a catalyst precursor, platinum sulfite acid (PSA) is easy to use and not relatively expensive, and is a potentially attractive precursor for many types of supported catalysts. The ultimate usefulness for many catalyst applications will depend on the extent that Pt can be dispersed and sulfur eliminated. To our knowledge, there exists no detailed characterization in the catalysis literature of PSA and the nanoparticulate Pt phases derived from it during catalyst pretreatment. To this end a series of supports including alumina, silica, magnesia, niobia, titania, magnesia and carbon were contacted with PSA solutions and subsequently analyzed with extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) analysis, and x-ray photoelectron spectroscopy (XPS) to characterize the Pt species formed upon impregnation, calcination, and reduction. While all catalysts show retention of some S, reasonably small particle sizes with relatively little Pt-S can in some instances be produced using PSA. The amount of retained sulfur appears to decrease with decreasing surface acidity, although even the most acidic supports (niobia and silica) display some storage of S even while only Pt-O bands are observed after calcination or reoxidation. More sulfur was eliminated by high temperature calcinations followed by reduction in hydrogen, at the expense of increasing Pt particle size.

  17. Support chemistry, surface area, and preparation effects on sulfided NiMo catalyst activity

    SciTech Connect

    Gardner, T.J.; McLaughlin, L.I.; Sandoval, R.S.

    1996-06-01

    Hydrous Metal Oxides (HMOs) are chemically synthesized materials which contain a homogeneous distribution of ion exchangeable alkali cations that provide charge compensation to the metal-oxygen framework. In terms of the major types of inorganic ion exchangers defined by Clearfield, these amorphous HMO materials are similar to both hydrous oxides and layered oxide ion exchangers (e.g., alkali metal titanates). For catalyst applications, the HMO material serves as an ion exchangeable support which facilitates the uniform incorporation of catalyst precursor species. Following catalyst precursor incorporation, an activation step is required to convert the catalyst precursor to the desired active phase. Considerable process development activities at Sandia National Laboratories related to HMO materials have resulted in bulk hydrous titanium oxide (HTO)- and silica-doped hydrous titanium oxide (HTO:Si)-supported NiMo catalysts that are more active in model reactions which simulate direct coal liquefaction (e.g., pyrene hydrogenation) than commercial {gamma}-Al{sub 2}O{sub 3}-supported NiMo catalysts. However, a fundamental explanation does not exist for the enhanced activity of these novel catalyst materials; possible reasons include fundamental differences in support chemistry relative to commercial oxides, high surface area, or catalyst preparation effects (ion exchange vs. incipient wetness impregnation techniques). The goals of this paper are to identify the key factors which control sulfided NiMo catalyst activity, including those characteristics of HTO- and HTO:Si-supported NiMo catalysts which uniquely set them apart from conventional oxide supports.

  18. Nickel-carbon nanocomposites prepared using castor oil as precursor: A novel catalyst for ethanol steam reforming

    NASA Astrophysics Data System (ADS)

    Carreño, Neftalí L. V.; Garcia, Irene T. S.; Raubach, Cristiane W.; Krolow, Mateus; Santos, Cláudia C. G.; Probst, Luiz F. D.; Fajardo, Humberto V.

    A novel and simple method to prepare nickel-based catalysts for ethanol steam reforming is proposed. The present method was developed using castor oil as a precursor. The results clarify that the nickel-carbon (Ni/C) catalyst has a high activity for ethanol steam reforming. It was observed that the catalytic behavior could be modified according to the experimental conditions employed. Moreover, it is interesting to note that the increase in the catalytic activity of the Ni/C nanocomposite over time, at 500 and 600 °C of reaction temperature, may be associated with the formation of filamentous carbon. The preliminary results indicate that the novel methodology used, led to the obtainment of materials with important properties that can be extended to applications in different catalytic process.

  19. Stereoselective Catalysis Achieved through in Situ Desymmetrization of an Achiral Iron Catalyst Precursor.

    PubMed

    Manna, Cesar M; Kaur, Aman; Yablon, Lauren M; Haeffner, Fredrik; Li, Bo; Byers, Jeffery A

    2015-11-18

    Stereoselective catalysis is described that proceeds with catalyst control but without the need to synthesize preformed chiral catalysts or ligands. Iron-based catalysts were discovered to effect the stereoselective polymerization of lactides starting from a single achiral precursor and the proper choice of an achiral silanol additive. Spectroscopic analysis of the polymer revealed that the stereoselectivity originates from an enantiomorphic site rather than a chain end stereocontrol mechanism. Iron intermediates that are stereogenic at iron are proposed to form in situ as a result of desymmetrization that occurs from a change in the metal coordination number. The proposed mechanism is supported by a combination of spectroscopic measurements, model complexes, kinetic measurements, and DFT calculations.

  20. Alumoxane precursors to designer catalysts and catalyst supports: Catalytic oxidation of dichloromethane

    SciTech Connect

    Cook, R.L.; Wong, C.; Harlan, C.J.; Kareiva, A.; Barron, A.R.

    1997-12-31

    Carboxylato-alumoxanes are aluminum-oxygen macromolecules consisting of a boehmite-like core surrounded by a sheath of carboxylate groups. The alumoxanes may be processed like organic polymers yet when fired are readily transformed into ceramic oxides. The alumoxanes can be precisely doped at room temperature in aqueous solution with a range of metal cations to prepare novel catalyst and catalyst support materials. The ease of introduction of multiple cations into the alumina lattice via the alumoxane approach provides a method for fine-tuning catalyst support properties and the fabrication of new catalyst materials themselves. Manganese-doped alumina (Mn-Al{sub 2}O{sub 3}), formed via the doping of an alumoxane with Mn at room temperature, is presented as an example where the alumoxane route provides enhanced catalytic performance over traditional approaches for the low temperature catalytic oxidation of chlorinated hydrocarbons (CHCs). The Mn-Al{sub 2}O{sub 3} formed from the Mn-doped alumoxane is compared with MnO{sub 2}/Al{sub 2}O{sub 3} prepared by the incipient wetness method, and commercial Pt/Al{sub 2}O{sub 3} for the oxidation/destruction of dichloromethane (CH{sub 2}Cl{sub 2}).

  1. Photogeneration of active formate decomposition catalysts to produce hydrogen from formate and water

    DOEpatents

    King, Jr., Allen D.; King, Robert B.; Sailers, III, Earl L.

    1983-02-08

    A process for producing hydrogen from formate and water by photogenerating an active formate decomposition catalyst from transition metal carbonyl precursor catalysts at relatively low temperatures and otherwise mild conditions is disclosed. Additionally, this process may be expanded to include the generation of formate from carbon monoxide and hydroxide such that the result is the water gas shift reaction.

  2. Chemical Vapor Deposition of Nanocarbon on Electroless NiB Catalyst Using Ethanol Precursor

    NASA Astrophysics Data System (ADS)

    Tanaka, Toru; Sato, Tomomi; Karasawa, Yusuke; Ueno, Kazuyoshi

    2011-05-01

    Nanocarbon materials have been expected as post-Cu interconnect materials for large-scale integrated circuits (LSIs). In this paper, we present a nanocarbon deposition process using electroless plated NiB as the catalyst, which features conformal deposition on patterned dielectric surfaces. It was found that carbon nanotubes (CNTs) and graphitic films were deposited on the electroless NiB by atmospheric pressure chemical vapor deposition (CVD) using ethanol as the precursor. The graphitic quality estimated from the Raman spectra of the nanocarbon on the NiB catalyst was equivalent to that on a sputter-deposited pure Ni catalyst. The nanocarbon shape was dependent on NiB thickness, and CNTs were grown on 10-nm-thick NiB and graphitic films were grown on 30 nm or thicker NiB. The deposition temperature can be lowered to 505 °C, although the graphitic quality was degraded. It is considered that the electroless catalysts can be effective for nanocarbon deposition on patterned dielectric surfaces.

  3. Directed deposition of silicon nanowires using neopentasilane as precursor and gold as catalyst.

    PubMed

    Kämpken, Britta; Wulf, Verena; Auner, Norbert; Winhold, Marcel; Huth, Michael; Rhinow, Daniel; Terfort, Andreas

    2012-01-01

    In this work the applicability of neopentasilane (Si(SiH(3))(4)) as a precursor for the formation of silicon nanowires by using gold nanoparticles as a catalyst has been explored. The growth proceeds via the formation of liquid gold/silicon alloy droplets, which excrete the silicon nanowires upon continued decomposition of the precursor. This mechanism determines the diameter of the Si nanowires. Different sources for the gold nanoparticles have been tested: the spontaneous dewetting of gold films, thermally annealed gold films, deposition of preformed gold nanoparticles, and the use of "liquid bright gold", a material historically used for the gilding of porcelain and glass. The latter does not only form gold nanoparticles when deposited as a thin film and thermally annealed, but can also be patterned by using UV irradiation, providing access to laterally structured layers of silicon nanowires.

  4. Catalyst dispersion and activity under conditions of temperature-staged liquefaction. Final report

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1993-02-01

    This research program involves the investigation of the use of highly dispersed catalyst precursors for the pretreatment of coals by mild hydrogenation. During the course of this effort solvent preswelling of the coal was evaluated as a means of deeply impregnating catalysts into coal, active phases of catalysts under reaction conditions were studied and the impact of these techniques were evaluated during pretreatment and temperature-staged liquefaction. Two coals, a Texas subbituminous and a Utah high volatile A bituminous, were used to examine the effects of solvent swelling pretreatment and catalyst impregnation on conversion behavior at 275{degrees}C, representative of the first, low-temperature stage in a temperature-staged liquefaction reaction. Ferrous sulfate, iron pentacarbonyl, ammonium tetrathiomolybdate, and molybdenum hexacarbonyl were used as catalyst precursors. Without swelling pretreatment, impregnation of both coals increased conversion, mainly through increased yields of preasphaltenes.

  5. Catalyst dispersion and activity under conditions of temperature-staged liquefaction

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1993-02-01

    This research program involves the investigation of the use of highly dispersed catalyst precursors for the pretreatment of coals by mild hydrogenation. During the course of this effort solvent preswelling of the coal was evaluated as a means of deeply impregnating catalysts into coal, active phases of catalysts under reaction conditions were studied and the impact of these techniques were evaluated during pretreatment and temperature-staged liquefaction. Two coals, a Texas subbituminous and a Utah high volatile A bituminous, were used to examine the effects of solvent swelling pretreatment and catalyst impregnation on conversion behavior at 275[degrees]C, representative of the first, low-temperature stage in a temperature-staged liquefaction reaction. Ferrous sulfate, iron pentacarbonyl, ammonium tetrathiomolybdate, and molybdenum hexacarbonyl were used as catalyst precursors. Without swelling pretreatment, impregnation of both coals increased conversion, mainly through increased yields of preasphaltenes.

  6. Highly Stable and Active Catalyst for Sabatier Reactions

    NASA Technical Reports Server (NTRS)

    Hu, Jianli; Brooks, Kriston P.

    2012-01-01

    Highly active Ru/TiO2 catalysts for Sabatier reaction have been developed. The catalysts have shown to be stable under repeated shutting down/startup conditions. When the Ru/TiO2 catalyst is coated on the engineered substrate Fe-CrAlY felt, activity enhancement is more than doubled when compared with an identically prepared engineered catalyst made from commercial Degussa catalyst. Also, bimetallic Ru-Rh/TiO2 catalysts show high activity at high throughput.

  7. Dry reforming of methane on Ni-Mg-Al nano-spheroid oxide catalysts prepared by the sol-gel method from hydrotalcite-like precursors

    NASA Astrophysics Data System (ADS)

    González, Albert R.; Asencios, Yvan J. O.; Assaf, Elisabete M.; Assaf, José M.

    2013-09-01

    Nanocapsular hydrotalcites (layered double hydroxides - LDHs) were synthesized by the sol-gel method and used as precursors of nano-structured mixed oxides containing various nickel loads (4, 15 and 19 wt%). The best conditions for the preparation of LDHs were analyzed and the structures of the resulting mixed oxides were studied. The optimal nickel load and calcining conditions were optimized. Finally, the resulting catalysts were tested in the dry reforming of methane for 8 h at 800 °C under atmospheric pressure. These materials showed high activity and stability, and the coke deposits were minimal on the catalyst prepared under optimal conditions (19 wt% nickel load and thermal treatment at 650 °C). The best catalyst formed amorphous carbon, which seems not to be prejudicial to the reaction.

  8. Effect of cobalt precursors on the dispersion, reduction, and CO oxidation of CoO(x)/γ-Al2O3 catalysts calcined in N2.

    PubMed

    Zhang, Lingling; Dong, Lihui; Yu, Wujiang; Liu, Lianjun; Deng, Yu; Liu, Bin; Wan, Haiqin; Gao, Fei; Sun, Keqin; Dong, Lin

    2011-03-15

    The present work tentatively investigated the effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the physicochemical properties of CoO(x)/γ-Al(2)O(3) catalysts calcined in N(2). XRD, Raman, XPS, FTIR, and UV-vis DRS results suggested that CoO/γ-Al(2)O(3) was obtained from cobalt acetate precursors and CoO was dispersed on γ-Al(2)O(3) below its dispersion capacity of 1.50 mmol/(100 m(2) γ-Al(2)O(3)), whereas Co(3)O(4)/γ-Al(2)O(3) was obtained from cobalt nitrate precursors and Co(3)O(4) preferred to agglomerate above the dispersion capacity of 0.15 mmol/(100m(2) γ-Al(2)O(3)). Compared with Co(3)O(4)/γ-Al(2)O(3), CoO/γ-Al(2)O(3) catalysts were difficult to be reduced and easy to desorb oxygen species at low temperatures and presented high activities for CO oxidation as proved by H(2)-TPR, O(2)-TPD, and CO oxidation model reaction results. A surface incorporation model was proposed to explain the dispersion and reduction properties of CoO/γ-Al(2)O(3) catalysts.

  9. Effect of cobalt precursors on the dispersion, reduction, and CO oxidation of CoO(x)/γ-Al2O3 catalysts calcined in N2.

    PubMed

    Zhang, Lingling; Dong, Lihui; Yu, Wujiang; Liu, Lianjun; Deng, Yu; Liu, Bin; Wan, Haiqin; Gao, Fei; Sun, Keqin; Dong, Lin

    2011-03-15

    The present work tentatively investigated the effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the physicochemical properties of CoO(x)/γ-Al(2)O(3) catalysts calcined in N(2). XRD, Raman, XPS, FTIR, and UV-vis DRS results suggested that CoO/γ-Al(2)O(3) was obtained from cobalt acetate precursors and CoO was dispersed on γ-Al(2)O(3) below its dispersion capacity of 1.50 mmol/(100 m(2) γ-Al(2)O(3)), whereas Co(3)O(4)/γ-Al(2)O(3) was obtained from cobalt nitrate precursors and Co(3)O(4) preferred to agglomerate above the dispersion capacity of 0.15 mmol/(100m(2) γ-Al(2)O(3)). Compared with Co(3)O(4)/γ-Al(2)O(3), CoO/γ-Al(2)O(3) catalysts were difficult to be reduced and easy to desorb oxygen species at low temperatures and presented high activities for CO oxidation as proved by H(2)-TPR, O(2)-TPD, and CO oxidation model reaction results. A surface incorporation model was proposed to explain the dispersion and reduction properties of CoO/γ-Al(2)O(3) catalysts. PMID:21216407

  10. Dimethyl carbonate production via the oxidative carbonylation ofmethanol over Cu/SiO2 catalysts prepared via molecular precursor graftingand chemical vapor deposition approaches

    SciTech Connect

    Drake, Ian J.; Fujdala, Kyle L.; Bell, Alexis T.; Tilley, T. Don

    2004-09-27

    The influence of catalyst synthesis method and Cu source on the activity and selectivity of Cu/SiO2 catalysts for the gas-phase oxidative carbonylation of methanol to dimethyl carbonate (DMC) is reported. [CuOSi(O tBu)3]4, [CuO tBu]4, and CuCl were used as precursors to produce highly dispersed silica-supported copper. XANES and EXAFS characterization prior to reaction (but after thermal treatment under He) showed that Cu in the catalysts prepared with CuCl and [CuOSi(O tBu)3]4 was present primarily as isolated Cu(I) species, whereas [CuO tBu]4 produced 1-nm Cu particles. During the catalytic reaction, the Cu in catalysts prepared from CuCl and [CuOSi(O tBu)3]4 formed highly dispersed CuO moieties, whereas the Cu in catalysts prepared from [CuO tBu]4 formed a cuprous oxide layer over a Cu(0) core. For comparison, poorly dispersed Cu on silica was prepared via traditional incipient wetness impregnation with Cu(NO3)2. It was found that activity for DMC formation increased with increasing Cu dispersion. The selectivity for DMC formation (relative to CO) decreased with decreasing Cu dispersion when the original state of the Cu was Cu(0) directly preceding reaction conditions.

  11. Water-Soluble Pd Nanoparticles Synthesized from ω-Carboxyl-S-Alkanethiosulfate Ligand Precursors as Unimolecular Micelle Catalysts

    PubMed Central

    Gavia, Diego J.; Maung, May S.; Shon, Young-Seok

    2014-01-01

    This report describes a two-phase synthesis of water-soluble carboxylate-functionalized alkanethiolate-capped Pd nanoparticles from ω-carboxyl-S-alkanethiosulfate sodium salts. The two-phase methodology using the thiosulfate ligand passivation protocol allowed a highly specific control over the surface ligand coverage of these nanoparticles, which are lost in a one-phase aqueous system because of the base-catalyzed hydrolysis of thiosulfate to thiolate. Systematic synthetic variations investigated in this study included the concentration of ω-carboxyl-S-alkanethiosulfate ligand precursors and reducing agent, NaBH4, and the overall ligand chain length. The resulting water-soluble Pd nanoparticles were isolated and characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), 1H NMR, UV–vis, and FT-IR spectroscopy. Among different variations, a decrease in the molar equivalent of NaBH4 resulted in a reduction in the surface ligand density while maintaining a similar particle core size. Additionally, reducing the chain length of the thiosulfate ligand precursor also led to the formation of stable nanoparticles with a lower surface coverage. Since the metal core size of these Pd nanoparticle variations remained quite consistent, direct correlation studies between ligand properties and catalytic activities against hydrogenation/isomerization of allyl alcohol could be performed. Briefly, Pd nanoparticles dissolved in water favored the hydrogenation of allyl alcohol to 1-propanol whereas Pd nanoparticles heterogeneously dispersed in chloroform exhibited a rather high selectivity towards the isomerization product (propanal). The results suggested that the surrounding ligand environments, such as the ligand structure, conformation, and surface coverage, were crucial in determining the overall activity and selectivity of the Pd nanoparticle catalysts. PMID:24246150

  12. Effect of catalyst preparation on catalytic activity

    SciTech Connect

    Huang, Y.J.R.

    1987-01-01

    Design parameters have been identified for Ni/Al{sub 2}O{sub 3} catalysts prepared by wet impregnation and incipient wetness from nickel nitrate solution in contact with a {gamma}-Al{sub 2}O{sub 3} support. The metal dispersion, activity for C{sub 1}, C{sub 2}, and C{sub 3} formation under synthesis conditions, and the carbon deposited during reaction have been shown to be predictable based solely on the properties of the electrolytes from which these catalysts were formed. Regardless of the method of preparation, NiAl{sub 2}O{sub 4} was found to be the only active Ni species on low weight loading Ni/Al{sub 2}O{sub 3} catalysts; both Ni and NiAl{sub 2}O{sub 4} are present on high weight loading catalysts. The high-temperature methane peak observed only from CO-TRP spectra of low weight loading catalysts is due to NiAl{sub 2}O{sub 4}; the low-temperature peak that appears as the weight loading is increased is due to Ni. Steady-state reaction kinetics for CH{sub 4} production yield activation energies which increase with increasing weight loading. The apparent activation energies for catalysts with a single methane peak in their CO-TPR spectra were found to be normally distributed. The apparent activation energies for catalysts with two methane peaks in their CO-TPR spectra were found to also be normally distributed when the method of preparation was considered in testing the statistical nature of the distribution. Titration experiments of the carbon pool subsequent to steady-state reaction of H{sub 2} and CO in conjunction with temperature-programmed surface reaction were used to asses the impact of Ni speciation on the rate-determining in step in the methanation reaction. In situ ESCA experiments and microreactor studies were used to examined the existence of metal-support interaction between dispersed Ni and the Al{sub 2}O{sub 3} carrier.

  13. Surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process: N2 sorption and XPS studies

    NASA Astrophysics Data System (ADS)

    Nikolova, D.; Krstić, J.; Spasov, L.; Simeonov, D.; Lončarević, D.; Stefanov, Pl.; Jovanović, D.

    2011-12-01

    The effect of the type of the silica gel pore structure on the surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process has been examined applying N2 sorption and X-ray photoelectron spectroscopy techniques. The nickel catalyst precursors with identical composition (SiO2/Ni = 1.0) has been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the three types of silica gel with different pore structures. It is shown that the usage of the silica gel supports with different texture as source of SiO2 causes different location of Ni-species into the support pores and on the external surface area. The XPS data confirm the formation of surface species with different strength of interaction and different dispersion. These surface characteristics of the precursors will predetermine the formation of the active nickel metallic phase as well as the mass transfer of the reactants and products to and from the catalytic sites.

  14. Heterogeneous catalytic reduction of perchlorate in water with Re-Pd/C catalysts derived from an oxorhenium(V) molecular precursor.

    PubMed

    Zhang, Yunxia; Hurley, Keith D; Shapley, John R

    2011-02-21

    The molecular Re(V) complex, chlorobis(2-(2'-hydroxyphenyl)-2-oxazoline)-oxorhenium(V), Re(O)(hoz)(2)Cl, has been investigated as a suitable precursor, when combined with activated carbon powder containing 5 wt % Pd, to provide a heterogeneous catalyst for the reduction of aqueous perchlorate by hydrogen. Two general methods for catalyst preparation have been adopted: first, by a standard "incipient wetness" impregnation of the carbon powder with handling under largely aerobic conditions for convenience and, second, by a completely anaerobic procedure maintaining a hydrogen atmosphere during adsorption of the complex in water onto the powder. Both types of catalyst were efficient for the complete reduction of perchlorate to chloride within a few hours at room temperature over a range of initial concentrations (2-200 ppm) under 1 atm of H(2) and acidic conditions (pH 2.7-3.7). The perchlorate reduction profiles displayed pseudo-first-order kinetics, and the rates were insensitive to excess chloride. Complete reduction of perchlorate was observed even at pH 5.9 in a phosphate buffer over the course of two weeks. Under comparable conditions, chlorate reduction proceeded ca. 10 times more quickly than perchlorate reduction. The impregnated catalyst was examined by STEM/EDS, which revealed a wide distribution in Pd nanoparticle sizes and also suggested that the Re complex did not aggregate preferentially on or near the Pd particles. XPS of this material provided evidence for reduced Pd after the reaction, but only a +7 oxidation state was seen for the Re sites both pre- and postreduction. Elemental analyses of the catalyst materials taken pre- and postreduction showed variable amounts of Re loss (0-50%) but relatively unchanged amounts of nitrogen. These results show the need to maintain a reducing atmosphere during the preparation and operation of the catalyst in order to achieve optimum activity and stability. PMID:21226477

  15. Catalyst Activity Comparison of Alcohols over Zeolites

    SciTech Connect

    Ramasamy, Karthikeyan K.; Wang, Yong

    2013-01-01

    Alcohol transformation to transportation fuel range hydrocarbon on HZSM-5 (SiO2 / Al2O3 = 30) catalyst was studied at 360oC and 300psig. Product distributions and catalyst life were compared using methanol, ethanol, 1-propanol or 1-butanol as a feed. The catalyst life for 1-propanol and 1-butanol was more than double compared to that for methanol and ethanol. For all the alcohols studied, the product distributions (classified to paraffin, olefin, napthene, aromatic and naphthalene compounds) varied with time on stream (TOS). At 24 hours TOS, liquid product from 1-propanol and 1-butanol transformation primarily contains higher olefin compounds. The alcohol transformation process to higher hydrocarbon involves a complex set of reaction pathways such as dehydration, oligomerization, dehydrocyclization, and hydrogenation. Compared to ethylene generated from methanol and ethanol, oligomerization of propylene and butylene has a lower activation energy and can readily take place on weaker acidic sites. On the other hand, dehydrocyclization of propylene and butylene to form the cyclic compounds requires the sits with stronger acid strength. Combination of the above mentioned reasons are the primary reasons for olefin rich product generated in the later stage of the time on stream and for the extended catalyst life time for 1 propanol and 1 butanol compared to methanol and ethanol conversion over HZSM-5.

  16. Process of activation of a palladium catalyst system

    DOEpatents

    Sobolevskiy, Anatoly; Rossin, Joseph A.; Knapke, Michael J.

    2011-08-02

    Improved processes for activating a catalyst system used for the reduction of nitrogen oxides are provided. In one embodiment, the catalyst system is activated by passing an activation gas stream having an amount of each of oxygen, water vapor, nitrogen oxides, and hydrogen over the catalyst system and increasing a temperature of the catalyst system to a temperature of at least 180.degree. C. at a heating rate of from 1-20.degree./min. Use of activation processes described herein leads to a catalyst system with superior NOx reduction capabilities.

  17. Bismuth-palladium heterometallic carboxylate as a single-source precursor for the carbon-supported Pd-Bi/C catalysts.

    PubMed

    Li, Bo; Zhang, Haitao; Huynh, Lan; Diverchy, Chantal; Hermans, Sophie; Devillers, Michel; Dikarev, Evgeny V

    2009-07-01

    The heterometallic complex [Bi(2)Pd(2)(O(2)CCF(3))(10)(HO(2)CCF(3))(2)] (1) was obtained by the solid state reaction of Bi(III) trifluoroacetate/trifluoroacetic acid adduct with unsolvated trinuclear Pd(II) trifluoroacetate. The crystal structure of 1 consists of discrete tetranuclear molecules, in which two paddlewheel [BiPd(O(2)CCF(3))(4)] units are connected by two chelating-bridging trifluoroacetate ligands through bismuth ends. There are no metal-metal bonds in the tetrameric structure of 1, since both Bi...Pd (3.0843(4) A) and Bi...Bi (4.5074(4) A) distances are too long to be considered as bonding interactions. A study of the solution behavior revealed that not only the coordinated trifluoroacetic acid in 1 can be effectively replaced by other donor solvent molecules but also the tetranuclear complex can be cleaved in solution into discrete dinuclear Bi-Pd species. Complex 1 was used as precursor for the preparation of a bimetallic Pd-Bi carbon-supported catalyst. The preparation procedure included the modification of the carbon support to increase the number of oxygenated functions at its surface followed by grafting complex 1 via ligand exchange for surface carboxylates and activating thermally. The resulting catalyst, consisting of small supported metallic particles, was found to be more active than the reference materials prepared from multisource homometallic Pd and Bi precursors. PMID:19499893

  18. Pd/MgO: Catalyst characterization and phenol hydrogenation activity

    SciTech Connect

    Claus, P.; Berndt, H.; Mohr, C.; Radnik, J.; Shin, E.J.; Keane, M.A.

    2000-05-15

    The gas-phase hydrogenation of phenol has been studied over a 1% w/w Pd/MgO catalyst prepared by impregnation of MgO with (NH{sub 4}){sub 2}PdCl{sub 6}. The catalyst precursor was activated by precalcination in air at 473 K followed by reduction in hydrogen at 573 K. Temperature-programmed reduction/desorption has revealed the presence of ammonium carbonate and/or ammonium hydrogen carbonate on the active surface in addition to a metallic palladium component. Whereas the latter was not detectable by X-ray diffraction due to the high metal dispersion, transmission electron microscopy revealed that the mean palladium particle diameter is 1.3 {+-} 0.2 nm, which corresponds to a palladium dispersion of D{sub Pd} = 71%. Impregnation followed by calcination is shown to transform MgO to Mg(OH){sub 2} while the additional reduction step generates a surface phase that is composed of both needle-like Periclase MgO and Mg(OH){sub 2}. X-ray photoelectron spectrometric analyses of the activated catalyst has established the presence of zero-valent palladium which appears to be electron rich as a result of metal-support interaction; a degree of palladium charging is also evident as well as residual surface chlorine. The effects on fractional phenol conversion and reaction selectivity of varying such process variables as reaction time, temperature, and phenol molar feed rate are considered and the possibility of thermodynamic limitations is addressed. Hydrogenation was observed to proceed in a stepwise fashion with cyclohexanone as the partially hydrogenated product and cyclohexanol as the fully hydrogenated product. The catalyst delivered a 96% selectivity with respect to cyclohexanone production at 423 K but the cyclohexanone yield decreased at higher temperatures as conversion declined and cyclohexanol was increasingly preferred. Conversion and selectivity were both stable with prolonged catalyst use, i.e., time on stream in excess of 55 h.

  19. Kinetics of NiO and NiCl2 Hydrogen Reduction as Precursors and Properties of Produced Ni/Al2O3 and Ni-Pd/Al2O3 Catalysts

    PubMed Central

    Sokić, Miroslav; Kamberović, Željko; Nikolić, Vesna; Marković, Branislav; Korać, Marija; Anđić, Zoran; Gavrilovski, Milorad

    2015-01-01

    The objects of this investigation were the comparative kinetic analysis of the NiO and NiCl2 reduction by hydrogen during an induction period and elimination of the calcination during the synthesis of Ni/Al2O3 catalysts. The effect of temperature and time on NiO and NiCl2 reduction degrees was studied. Avrami I equation was selected as the most favorable kinetic model and used to determine activation energy of the NiO and NiCl2 reduction for the investigated temperature range (623–923 K) and time intervals (1–5 minutes). The investigation enabled reaching conclusions about the reaction ability and rate of the reduction processes. Afterward, Ni/Al2O3 catalysts were obtained by using oxide and chloride precursor for Ni. The catalysts were supported on alumina-based foam and prepared via aerosol route. Properties of the samples before and after low-temperature hydrogen reduction (633 K) were compared. Obtained results indicated that the synthesis of Ni/Al2O3 catalysts can be more efficient if chloride precursor for Ni is directly reduced by hydrogen during the synthesis process, without the calcination step. In addition, Ni-Pd/Al2O3 catalysts with different metal content were prepared by using chloride precursors. Lower reduction temperature was utilized and the chlorides were almost completely reduced at 533 K. PMID:25789335

  20. Hydrodenitrification catalyst and a method for improving the activity of the catalyst

    SciTech Connect

    Ryan, R. C.

    1985-03-12

    Hydroconversion catalysts containing Group VIII and/or Group VIB catalytically active metals on a support, and particularly those containing nickel and molybdenum on alumina, are improved in hydrodenitrification (HDN) activity by impregnation of additional molybdenum and/or tungsten carbonyls onto the catalyst by sublimation. Preferably from about 1 to 5% w molybdenum is added. The carbonyl impregnated catalyst is then dried, calcined and, generally sulfided before use in a hydrocarbon conversion process.

  1. Characterization of active sites in zeolite catalysts

    SciTech Connect

    Eckert, J.; Bug, A.; Nicol, J.M.

    1997-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Atomic-level details of the interaction of adsorbed molecules with active sites in catalysts are urgently needed to facilitate development of more effective and/or environmentally benign catalysts. To this end the authors have carried out neutron scattering studies combined with theoretical calculations of the dynamics of small molecules inside the cavities of zeolite catalysts. The authors have developed the use of H{sub 2} as a probe of adsorption sites by observing the hindered rotations of the adsorbed H{sub 2} molecule, and they were able to show that an area near the four-rings is the most likely adsorption site for H{sub 2} in zeolite A while adsorption of H{sub 2} near cations located on six-ring sites decreases in strength as Ni {approximately} Co > Ca > Zn {approximately} Na. Vibrational and rotational motions of ethylene and cyclopropane adsorption complexes were used as a measure for zeolite-adsorbate interactions. Preliminary studies of the binding of water, ammonia, and methylamines were carried out in a number of related guest-host materials.

  2. Chloride-Bridged Dinuclear Rhodium(III) Complexes Bearing Chiral Diphosphine Ligands: Catalyst Precursors for Asymmetric Hydrogenation of Simple Olefins.

    PubMed

    Kita, Yusuke; Hida, Shoji; Higashihara, Kenya; Jena, Himanshu Sekhar; Higashida, Kosuke; Mashima, Kazushi

    2016-07-11

    Efficient rhodium(III) catalysts were developed for asymmetric hydrogenation of simple olefins. A new series of chloride-bridged dinuclear rhodium(III) complexes 1 were synthesized from the rhodium(I) precursor [RhCl(cod)]2 , chiral diphosphine ligands, and hydrochloric acid. Complexes from the series acted as efficient catalysts for asymmetric hydrogenation of (E)-prop-1-ene-1,2-diyldibenzene and its derivatives without any directing groups, in sharp contrast to widely used rhodium(I) catalytic systems that require a directing group for high enantioselectivity. The catalytic system was applied to asymmetric hydrogenation of allylic alcohols, alkenylboranes, and unsaturated cyclic sulfones. Control experiments support the superiority of dinuclear rhodium(III) complexes 1 over typical rhodium(I) catalytic systems. PMID:27088539

  3. Activation of catalysts for synthesizing methanol from synthesis gas

    DOEpatents

    Blum, David B.; Gelbein, Abraham P.

    1985-01-01

    A method for activating a methanol synthesis catalyst is disclosed. In this method, the catalyst is slurried in an inert liquid and is activated by a reducing gas stream. The activation step occurs in-situ. That is, it is conducted in the same reactor as is the subsequent step of synthesizing methanol from a methanol gas stream catalyzed by the activated catalyst still dispersed in a slurry.

  4. Phosphine-Free EWG-Activated Ruthenium Olefin Metathesis Catalysts

    NASA Astrophysics Data System (ADS)

    Grela, Karol; Szadkowska, Anna; Michrowska, Anna; Bieniek, Michal; Sashuk, Volodymyr

    Hoveyda-Grubbs catalyst has been successfully fine-tuned by us in order to increase its activity and applicability by the introduction of electron-withdrawing groups (EWGs) to diminish donor properties of the oxygen atom. As a result, the stable and easily accessible nitro-substituted Hoveyda-Grubbs catalyst has found a number of successful applications in various research and industrial laboratories. Some other EWG-activated Hoveyda-type catalysts are commercially available. The results described herewith demonstrate that the activity of ruthenium (Ru) metathesis catalysts can be enhanced by introduction of EWGs without detriment to catalysts stability. Equally noteworthy is the observation that different Ru catalysts turned out to be optimal for different applications. This shows that no single catalyst outperforms all others in all possible applications.

  5. Fischer-Tropsch Cobalt Catalyst Activation and Handling Through Wax Enclosure Methods

    NASA Technical Reports Server (NTRS)

    Klettlinger, Jennifer L. S.; Yen, Chia H.; Nakley, Leah M.; Surgenor, Angela D.

    2016-01-01

    Fischer-Tropsch (F-T) synthesis is considered a gas to liquid process which converts syn-gas, a gaseous mixture of hydrogen and carbon monoxide, into liquids of various hydrocarbon chain length and product distributions. Cobalt based catalysts are used in F-T synthesis and are the focus of this paper. One key concern with handling cobalt based catalysts is that the active form of catalyst is in a reduced state, metallic cobalt, which oxidizes readily in air. In laboratory experiments, the precursor cobalt oxide catalyst is activated in a fixed bed at 350 ?C then transferred into a continuous stirred tank reactor (CSTR) with inert gas. NASA has developed a process which involves the enclosure of active cobalt catalyst in a wax mold to prevent oxidation during storage and handling. This improved method allows for precise catalyst loading and delivery into a CSTR. Preliminary results indicate similar activity levels in the F-T reaction in comparison to the direct injection method. The work in this paper was supported by the NASA Fundamental Aeronautics Subsonics Fixed Wing Project.

  6. Structural Characterization of Alumina-Supported Rh Catalysts: Effects of Ceriation and Zirconiation by using Metal–Organic Precursors

    PubMed Central

    Kroner, Anna B; Newton, Mark A; Tromp, Moniek; Russell, Andrea E; Dent, Andrew J; Evans, John

    2013-01-01

    The effects of the addition of ceria and zirconia on the structural properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ-Al2O3) are studied. Ceria and zirconia are deposited by using two preparation methods. Method I involves the deposition of ceria on γ-Al2O3 from Ce(acac)3, and the rhodium metal is subsequently added, whereas method II is based on a controlled surface reaction technique, that is, the decomposition of metal–organic M(acac)x (in which M=Ce, x=3 and M=Zr, x=4) on Rh/γ-Al2O3. The structures of the prepared catalyst materials are characterized ex situ by using N2 physisorption, transmission electron microscopy, high-angle annular dark-field scanning transmission election microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure spectroscopy (XAFS). All supported rhodium systems readily oxidize in air at room temperature. By using ceriated and zirconiated precursors, a larger rhodium-based metallic core fraction is obtained in comparison to the undoped rhodium catalysts, suggesting that ceria and zirconia protect the rhodium particles against extensive oxidation. XPS results indicate that after the calcination and reduction treatments, a small amount of chlorine is retained on the support of all rhodium catalysts. EXAFS analysis shows significant Rh—Cl interactions for Rh/Al2O3 and Rh/CeOx/Al2O3 (method I) catalysts. After reaction with H2/He in situ, for series of samples with 1.6 wt % Rh, the EXAFS first shell analysis affords a mean size of approximately 30 atoms. A broader spread is evident with a 4 wt % rhodium loading (ca. 30–110 atoms), with the incorporation of zirconium providing the largest particle sizes. PMID:23943563

  7. A novel semiconductor compatible path for nano-graphene synthesis using CBr4 precursor and Ga catalyst

    PubMed Central

    Wang, S. M.; Gong, Q.; Li, Y. Y.; Cao, C. F.; Zhou, H. F.; Yan, J. Y.; Liu, Q. B.; Zhang, L. Y.; Ding, G. Q.; Di, Z. F.; Xie, X. M.

    2014-01-01

    We propose a novel semiconductor compatible path for nano-graphene synthesis using precursors containing C-Br bonding and liquid catalyst. The unique combination of CBr4 as precursor and Ga as catalyst leads to efficient C precipitation at a synthesis temperature of 200°C or lower. The non-wetting nature of liquid Ga on tested substrates limits nano-scale graphene to form on Ga droplets and substrate surfaces at low synthesis temperatures of T ≤ 450°C and at droplet/substrate interfaces by C diffusion via droplet edges when T ≥ 400°C. Good quality interface nano-graphene is demonstrated and the quality can be further improved by optimization of synthesis conditions and proper selection of substrate type and orientation. The proposed method provides a scalable and transfer-free route to synthesize graphene/semiconductor heterostructures, graphene quantum dots as well as patterned graphene nano-structures at a medium temperature range of 400–700°C suitable for most important elementary and compound semiconductors. PMID:24722194

  8. Metal organic framework-mediated synthesis of highly active and stable Fischer-Tropsch catalysts.

    PubMed

    Santos, Vera P; Wezendonk, Tim A; Jaén, Juan José Delgado; Dugulan, A Iulian; Nasalevich, Maxim A; Islam, Husn-Ubayda; Chojecki, Adam; Sartipi, Sina; Sun, Xiaohui; Hakeem, Abrar A; Koeken, Ard C J; Ruitenbeek, Matthijs; Davidian, Thomas; Meima, Garry R; Sankar, Gopinathan; Kapteijn, Freek; Makkee, Michiel; Gascon, Jorge

    2015-03-05

    Depletion of crude oil resources and environmental concerns have driven a worldwide research on alternative processes for the production of commodity chemicals. Fischer-Tropsch synthesis is a process for flexible production of key chemicals from synthesis gas originating from non-petroleum-based sources. Although the use of iron-based catalysts would be preferred over the widely used cobalt, manufacturing methods that prevent their fast deactivation because of sintering, carbon deposition and phase changes have proven challenging. Here we present a strategy to produce highly dispersed iron carbides embedded in a matrix of porous carbon. Very high iron loadings (>40 wt %) are achieved while maintaining an optimal dispersion of the active iron carbide phase when a metal organic framework is used as catalyst precursor. The unique iron spatial confinement and the absence of large iron particles in the obtained solids minimize catalyst deactivation, resulting in high active and stable operation.

  9. Metal organic framework-mediated synthesis of highly active and stable Fischer-Tropsch catalysts

    NASA Astrophysics Data System (ADS)

    Santos, Vera P.; Wezendonk, Tim A.; Jaén, Juan José Delgado; Dugulan, A. Iulian; Nasalevich, Maxim A.; Islam, Husn-Ubayda; Chojecki, Adam; Sartipi, Sina; Sun, Xiaohui; Hakeem, Abrar A.; Koeken, Ard C. J.; Ruitenbeek, Matthijs; Davidian, Thomas; Meima, Garry R.; Sankar, Gopinathan; Kapteijn, Freek; Makkee, Michiel; Gascon, Jorge

    2015-03-01

    Depletion of crude oil resources and environmental concerns have driven a worldwide research on alternative processes for the production of commodity chemicals. Fischer-Tropsch synthesis is a process for flexible production of key chemicals from synthesis gas originating from non-petroleum-based sources. Although the use of iron-based catalysts would be preferred over the widely used cobalt, manufacturing methods that prevent their fast deactivation because of sintering, carbon deposition and phase changes have proven challenging. Here we present a strategy to produce highly dispersed iron carbides embedded in a matrix of porous carbon. Very high iron loadings (>40 wt %) are achieved while maintaining an optimal dispersion of the active iron carbide phase when a metal organic framework is used as catalyst precursor. The unique iron spatial confinement and the absence of large iron particles in the obtained solids minimize catalyst deactivation, resulting in high active and stable operation.

  10. Increasing the hydrogenation activity of commercial catalysts for selective hydrocracking

    SciTech Connect

    Khashagul`gova, N.S.; Freiman, L.L.; Zelentsov, Yu.N.

    1994-07-01

    The catalysts generally used in hydrodewaxing or selective hydrocracking of n-paraffins are zeolites with the pentasil structure: TsVK, TsVM, TsVN, and Ultrasil. For use in the production of high-quality transformer oils from paraffinic feedstocks, these catalysts have not only a high cracking activity but also an adequate hydrogenating activity. Catalysts containing a nickel-molybdenum complex (or nickel molybdate synthesized by a specific method) are higher in hydrogenating activity in comparison with catalysts in which the metals are introduced by coextrusion or impregnation. Precipitation of a nickel-molybdenum complex on a solid support (aluminosilicate or zeolite) tends to increase its hydrogenating activity, so that the content of the hydrogenating metals in the catalyst can be reduced. This report describes studies on catalysts based on TsVM and TsVN high-silica zeolites.

  11. TiO2 nanotubes supported NiW hydrodesulphurization catalysts: Characterization and activity

    NASA Astrophysics Data System (ADS)

    Palcheva, R.; Dimitrov, L.; Tyuliev, G.; Spojakina, A.; Jiratova, K.

    2013-01-01

    High surface area TiO2 nanotubes (Ti-NT) synthesized by alkali hydrothermal method were used as a support for NiW hydrodesulphurization catalyst. Nickel salt of 12-tungstophosphoric acid - Ni3/2PW12O40 was applied as oxide precursor of the active components. The catalyst was characterized by SBET, XRD, UV-vis DRS, Raman spectroscopy, XPS, TPR and HRTEM. The results obtained were compared with those for the NiW catalysts prepared over high surface area titania and alumina supports. A polytungstate phase evidenced by Raman spectroscopy was observed indicating the destruction of the initial heteropolyanion. The catalytic experiments revealed two times higher thiophene conversion on NiW catalyst supported on Ti-NT than those of catalysts supported on alumina and titania. Increased HDS activity of the NiW catalyst supported on Ti-NT could be related to a higher amount of W oxysulfide entities interacting with Ni sulfide particles as consequence of the electronic effects of the Ti-NT observed with XPS analysis.

  12. Enhancement of the aspartame precursor synthetic activity of an organic solvent-stable protease.

    PubMed

    Ogino, Hiroyasu; Tsuchiyama, Shotaro; Yasuda, Masahiro; Doukyu, Noriyuki

    2010-03-01

    The PST-01 protease is highly stable and catalyzes the synthesis of the aspartame precursor with high reaction yields in the presence of organic solvents. However, the synthesis rate using the PST-01 protease was slower than that observed when thermolysin was used. Structural comparison of both enzymes showed particular amino acid differences near the active center. These few residue differences in the PST-01 protease were mutated to match those amino acid types found in thermolysin. The mutated PST-01 proteases at the 114th residue from tyrosine to phenylalanine showed enhancement of synthetic activity. This activity was found to be similar to thermolysin. In addition, mutating the residue in the PST-01 protease with arginine and serine showed more improvement of the activity. The mutant PST-01 protease should be more useful than thermolysin for the synthesis of the aspartame precursor, because this enzyme has higher stability and activity in the presence of organic solvents. The results show the potential of organic solvent-stable enzymes as industrial catalysts.

  13. Activation of molecular catalysts using semiconductor quantum dots

    DOEpatents

    Meyer, Thomas J.; Sykora, Milan; Klimov, Victor I.

    2011-10-04

    Photocatalytic materials based on coupling of semiconductor nanocrystalline quantum dots (NQD) and molecular catalysts. These materials have capability to drive or catalyze non-spontaneous chemical reactions in the presence of visible radiation, ultraviolet radiation, or both. The NQD functions in these materials as a light absorber and charge generator. Following light absorption, the NQD activates a molecular catalyst adsorbed on the surface of the NQD via transfer of one or more charges (either electrons or electron-holes) from the NQD to the molecular catalyst. The activated molecular catalyst can then drive a chemical reaction. A photoelectrolytic device that includes such photocatalytic materials is also described.

  14. Method for regeneration and activity improvement of syngas conversion catalyst

    DOEpatents

    Lucki, Stanley J.; Brennan, James A.

    1980-01-01

    A method is disclosed for the treatment of single particle iron-containing syngas (synthes.s gas) conversion catalysts comprising iron, a crystalline acidic aluminosilicate zeolite having a silica to alumina ratio of at least 12, a pore size greater than about 5 Angstrom units and a constraint index of about 1-12 and a matrix. The catalyst does not contain promoters and the treatment is applicable to either the regeneration of said spent single particle iron-containing catalyst or for the initial activation of fresh catalyst. The treatment involves air oxidation, hydrogen reduction, followed by a second air oxidation and contact of the iron-containing single particle catalyst with syngas prior to its use for the catalytic conversion of said syngas. The single particle iron-containing catalysts are prepared from a water insoluble organic iron compound.

  15. Performance of supported catalysts based on a new copper vanadate-type precursor for catalytic oxidation of toluene.

    PubMed

    Palacio, L A; Silva, E R; Catalão, R; Silva, J M; Hoyos, D A; Ribeiro, F R; Ribeiro, M F

    2008-05-01

    A new copper vanadate precursor with the formula NH(4)[Cu(2.5)V(2)O(7)(OH)(2)] . H(2)O was synthesized and deposited on two different supports, ZSM-5 and amorphous SiO(2), by a hydrothermal method or by mechanical mixture. The catalytic behaviour was evaluated in the total oxidation of toluene and the characterization was performed by H(2)-temperature-programmed reduction (H(2)-TPR), thermogravimetric analysis, elemental analysis, UV-vis diffuse reflectance spectroscopy and X-ray diffraction. It was found that the copper vanadate phase comprises two mixed oxides, one of them crystalline, the Ziesite phase, and the other one amorphous. The supported catalysts presented a content of copper vanadate phase of about 9-11 wt.%. The copper vanadate deposited on ZSM-5 by the hydrothermal method evidences the best performance in the oxidation of toluene. This behaviour can be associated with the smaller size and higher dispersion of the particles on the support, which was confirmed by their better reducibility and higher band gap energy value compared with the other series of studied catalysts.

  16. Catalytic deactivation of methane steam reforming catalysts. I. Activation

    SciTech Connect

    Agnelli, M.E.; Demicheli, M.C.; Ponzi, E.N.

    1987-08-01

    An alumina-supported catalyst was studied both in its original state and after activation and sintering. Chemical composition and textural properties were determined, and crystalline compounds were identified. Active-phase and support transformations occurring during activation were determined by differential thermoanalysis (DTA), temperature-programmed reduction (TPR), and X-ray diffraction. The catalyst activated by means of various procedures was characterized by measuring crystallite size.

  17. Preparation of plutonium-bearing ceramics via mechanically activated precursor

    NASA Astrophysics Data System (ADS)

    Chizhevskaya, S. V.; Stefanovsky, S. V.

    2000-07-01

    The problem of excess weapons plutonium disposition is suggested to be solved by means of its incorporation in stable ceramics with high chemical durability and radiation resistivity. The most promising host phases for plutonium as well as uranium and neutron poisons (gadolinium, hafnium) are zirconolite, pyrochlore, zircon, zirconia [1,2], and murataite [3]. Their production requires high temperatures and a fine-grained homogeneous precursor to reach final waste form with high quality and low leachability. Currently various routes to homogeneous products preparation such as sol-gel technology, wet-milling, and grinding in a ball or planetary mill are used. The best result demonstrates sol-gel technology but this route is very complicated. An alternative technology for preparation of ceramic precursors is the treatment of the oxide batch with high mechanical energy [4]. Such a treatment produces combination of mechanical (fine milling with formation of various defects, homogenization) and chemical (split bonds with formation of active centers—free radicals, ion-radicals, etc.) effects resulting in higher reactivity of the activated batch.

  18. The role of catalyst activation on the activity and attrition of precipitated iron Fischer-Tropsch catalysts

    SciTech Connect

    Datye, A.K.; Shroff, M.D.; Harrington, M.S.; Coulter, K.E.; Sault, A.G.; Jackson, N.B.

    1995-12-31

    The results of this work indicate that magnetite is not catalytically active for Fischer-Tropsch Synthesis (FTS) in precipitated, unsupported iron catalysts, but the formation of the carbide phase is necessary to obtain FTS activity. The transformation of magnetite to carbide, though essential to obtain FTS activity, also causes the catalyst to break down. This can lead to severe problems during operation in a commercial slurry phase reactor. The results presented here imply that activation and attrition are simultaneous and complementary processes. In another study, we show that the catalyst can also under go attrition on a micron scale which is caused by lack of strength of the forces binding the catalyst primary particles in the agglomerates. Both these processes can make wax separation and product recovery extremely difficult. In this study, we have also shown that H{sub 2} reduction of this catalyst to metallic iron is detrimental to subsequent catalyst activity and causes a loss of surface area due to sintering of the iron crystallites. Reduction to metallic Fe also causes impurities such as S to segregate to the surface causing a complete loss of FTS activity. It has been shown that even submonolayer amounts of S can cause a dramatic decrease in FTS activity, hence reduction to metallic Fe should be avoided during activation of these catalysts. We have shown, however, that a mild H{sub 2} reduction to magnetite does not lead to S segregation to the surface, and is therefore acceptable.

  19. Highly active and highly selective aromatization catalyst

    SciTech Connect

    Santilli, D.S.; Long, J.J.; Lewis, R.T.

    1987-10-06

    This patent describes a reforming catalyst comprising an L zeolite containing platinum metal and at least one promoter metal selected from the group consisting of iron, cobalt, titanium, and rare earth metal. The catalyst has a platinum to promoter metal mole ratio of less than 10:1. The patent also includes a method of preparing the reforming catalyst of claim 1, comprising steps of: (a) forming an aqueous solution of alkali hydroxide, aluminum hydroxide, and ferric salt; (b) combining the solution with an aqueous solution of silica to form a thickening gel in a mother liquor; (c) heating the thickening gel to form an L zeolite; (d) cooling the gel containing the L zeolite; (e) decanting the mother liquor from the gel; (f) filtering the L zeolite from the gel; (g) washing the filtered L zeolite; (h) drying the washed L zeolite; (i) adding platinum to the dried L zeolite to form a catalyst; (j) drying the catalyst; and (k) calcining the dried catalyst.

  20. Effect of the support and the reduction temperature on the formation of metallic nickel phase in Ni/silica gel precursors of vegetable oil hydrogenation catalysts

    NASA Astrophysics Data System (ADS)

    Gabrovska, M.; Krstić, J.; Tzvetkov, P.; Tenchev, K.; Shopska, M.; Vukelić, N.; Jovanović, D.

    2011-12-01

    Ni/SiO2 materials with identical composition (SiO2/Ni = 1.0) have been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the silica gel, obtained at three different pH values. The present investigation was undertaken in an endeavor to study the effects of the silica gel support type and the reduction temperature on the formation and dispersion of the metallic nickel phase in the reduced Ni/SiO2 precursors of the vegetable oil hydrogenation catalyst. The physicochemical characterization of the unreduced and reduced precursors has been accomplished appropriately by powder X-ray diffraction, infrared spectroscopy, temperature programmed reduction and H2-chemisorption techniques. It can be stated that the texture peculiarities of the silica gels used as supports influence on the crystalline state and distribution of the deposited Ni-containing phases during the preparation of the precursors, on the reduction temperature of the investigated solids as well as on the bulk size and surface dispersion of the arising metallic nickel particles. It was shown that two types of Ni2+-species are formed during the synthesis procedure, namely basic nickel carbonate-like and Ni-phyllosilicate with different extent of presence, location and strength of interaction. The different location of these species is supposed to result in various strength of Ni-O and Ni-O-Si interaction, thus determining the overall reducibility of the precursors. It was specified that the Ni2+-species are strongly bonded to the surface of the silica gel obtained at neutral pH value and weakly bonded to the surface of those prepared in acidic and alkaline conditions. It was established that the precursor, derivates from the silica gel obtained at alkaline conditions, demonstrates both significant reduction of the Ni2+ ions at 430°C and finely dispersed metallic nickel particles on its surface. High dispersion of the metallic nickel might be the crucial reason for achieving of

  1. Methanol synthesis from CO2 hydrogenation over La-M-Cu-Zn-O (M = Y, Ce, Mg, Zr) catalysts derived from perovskite-type precursors

    NASA Astrophysics Data System (ADS)

    Zhan, Haijuan; Li, Feng; Gao, Peng; Zhao, Ning; Xiao, Fukui; Wei, Wei; Zhong, Liangshu; Sun, Yuhan

    2014-04-01

    A series of La-M-Cu-Zn-O (M = Y, Ce, Mg, Zr) based perovskite-type catalysts are prepared by sol-gel method and characterized by XRD, BET, TPR, N2O-adsorption, XPS and TPD techniques. The results indicate that all the catalysts exhibit La2CuO4 perovskite structure. The addition of Ce, Mg and Zr lead to smaller particles, lower reduction temperature, higher Cu dispersion, larger amount of hydrogen desorption at low temperature and more amount of basic sites. However, Y has less affects on the physicochemical properties. The catalysts derived from perovskite-type precursors show high selectivity for methanol, which is correlated with the Cuα+ species that exists in the reduced catalysts. More exposed Cu surface area is favorable for high CO2 conversion.

  2. Microwave-hydrothermal synthesis and characterization of nanostructured copper substituted ZnM2O4 (M = Al, Ga) spinels as precursors for thermally stable Cu catalysts

    NASA Astrophysics Data System (ADS)

    Conrad, Franziska; Massue, Cyriac; Kühl, Stefanie; Kunkes, Edward; Girgsdies, Frank; Kasatkin, Igor; Zhang, Bingsen; Friedrich, Matthias; Luo, Yuan; Armbrüster, Marc; Patzke, Greta R.; Behrens, Malte

    2012-03-01

    Nanostructured CuxZn1-xAl2O4 with a Cu : Zn ratio of ¼ : ¾ has been prepared by a microwave-assisted hydrothermal synthesis at 150 °C and used as a precursor for Cu/ZnO/Al2O3-based catalysts. The spinel nanoparticles exhibit an average size of approximately 5 nm and a high specific surface area (above 250 m2 g-1). Cu nanoparticles of an average size of 3.3 nm can be formed by reduction of the spinel precursor in hydrogen and the accessible metallic Cu(0) surface area of the reduced catalyst was 8 m2 g-1. The catalytic performance of the material in CO2 hydrogenation and methanol steam reforming was compared with conventionally prepared Cu/ZnO/Al2O3 reference catalysts. The observed lower performance of the spinel-based samples is attributed to a lack of synergetic interaction of the Cu nanoparticles with ZnO due to the incorporation of Zn2+ in the stable spinel lattice. Despite its lower performance, however, the nanostructured nature of the spinel catalyst was stable after thermal treatment up to 500 °C in contrast to other Cu-based catalysts. Furthermore, a large fraction of the re-oxidized copper migrates back into the spinel upon calcination of the reduced catalyst, thereby enabling a regeneration of sintered catalysts after prolonged usage at high temperatures. Similarly prepared samples with Ga instead of Al exhibit a more crystalline catalyst with a spinel particle size around 20 nm. The slightly decreased Cu(0) surface area of 3.2 m2 g-1 due to less copper incorporation is not a significant drawback for the methanol steam reforming.Nanostructured CuxZn1-xAl2O4 with a Cu : Zn ratio of ¼ : ¾ has been prepared by a microwave-assisted hydrothermal synthesis at 150 °C and used as a precursor for Cu/ZnO/Al2O3-based catalysts. The spinel nanoparticles exhibit an average size of approximately 5 nm and a high specific surface area (above 250 m2 g-1). Cu nanoparticles of an average size of 3.3 nm can be formed by reduction of the spinel precursor in hydrogen

  3. Aldehyde dehydrogenase activity promotes survival of human muscle precursor cells

    PubMed Central

    Jean, Elise; Laoudj-Chenivesse, Dalila; Notarnicola, Cécile; Rouger, Karl; Serratrice, Nicolas; Bonnieu, Anne; Gay, Stéphanie; Bacou, Francis; Duret, Cédric; Carnac, Gilles

    2011-01-01

    Abstract Aldehyde dehydrogenases (ALDH) are a family of enzymes that efficiently detoxify aldehydic products generated by reactive oxygen species and might therefore participate in cell survival. Because ALDH activity has been used to identify normal and malignant cells with stem cell properties, we asked whether human myogenic precursor cells (myoblasts) could be identified and isolated based on their levels of ALDH activity. Human muscle explant-derived cells were incubated with ALDEFLUOR, a fluorescent substrate for ALDH, and we determined by flow cytometry the level of enzyme activity. We found that ALDH activity positively correlated with the myoblast-CD56+ fraction in those cells, but, we also observed heterogeneity of ALDH activity levels within CD56-purified myoblasts. Using lentiviral mediated expression of shRNA we demonstrated that ALDH activity was associated with expression of Aldh1a1 protein. Surprisingly, ALDH activity and Aldh1a1 expression levels were very low in mouse, rat, rabbit and non-human primate myoblasts. Using different approaches, from pharmacological inhibition of ALDH activity by diethylaminobenzaldehyde, an inhibitor of class I ALDH, to cell fractionation by flow cytometry using the ALDEFLUOR assay, we characterized human myoblasts expressing low or high levels of ALDH. We correlated high ALDH activity ex vivo to resistance to hydrogen peroxide (H2O2)-induced cytotoxic effect and in vivo to improved cell viability when human myoblasts were transplanted into host muscle of immune deficient scid mice. Therefore detection of ALDH activity, as a purification strategy, could allow non-toxic and efficient isolation of a fraction of human myoblasts resistant to cytotoxic damage. PMID:19840193

  4. Functional activity of mitochondria in cultured neural precursor cells.

    PubMed

    Plotnikov, E Yu; Marei, M V; Podgornyi, O V; Aleksandrova, M A; Zorov, D B; Sukhikh, G T

    2006-01-01

    We studied mitochondrial transmembrane potential of neural precursor cells forming neurospheres in culture. Uneven energization of mitochondria in neurosphere cells was detected. Heterogeneity of cells by the mitochondrial potential increased with neurosphere enlargement during culturing. Decrease in the mitochondrial potential in the central cells in large spheres, presumably caused by insufficient diffusion of oxygen and nutrients, can provoke their damage and death. Population of cells with high mitochondrial potential responded to addition of the nuclear dye by a decrease in mitochondrial potential, which can indicate functioning of ABCG2 complex in these cells, characteristic of undifferentiated stem cells. These data will help to create optimum conditions for culturing of neural stem cells for the maintenance of their maximum functional and proliferative activity. PMID:16929986

  5. Engineering Vertically Aligned Carbon Nanotube Growth by Decoupled Thermal Treatment of Precursor and Catalyst

    SciTech Connect

    Meshot, E.; Plata, D; Tawfick, S; Zhang, Y; Verploegen, E; Hart, A

    2009-01-01

    We study synthesis of vertically aligned carbon nanotube (CNT) 'forests' by a decoupled method that facilitates control of the mean diameter and structural quality of the CNTs and enables tuning of the kinetics for efficient growth to forest heights of several millimeters. The growth substrate temperature (Ts) primarily determines the CNT diameter, whereas independent and rapid thermal treatment (Tp) of the C2H4/H2 reactant mixture significantly changes the growth rate and terminal forest height but does not change the CNT diameter. Synchrotron X-ray scattering is utilized for precise, nondestructive measurement of CNT diameter in large numbers of samples. CNT structural quality monotonically increases with Ts yet decreases with Tp, and forests grown by this decoupled method have significantly higher quality than those grown using a conventional single-zone tube furnace. Chemical analysis reveals that the thermal treatment generates a broad population of hydrocarbon species, and a nonmonotonic relationship between catalyst lifetime and Tp suggests that certain carbon species either enhance or inhibit CNT growth. However, the forest height kinetics, as measured in real-time during growth, are self-similar, thereby indicating that a common mechanism of growth termination may be present over a wide range of process conditions.

  6. The activation mechanism of Fe-based olefin metathesis catalysts

    NASA Astrophysics Data System (ADS)

    Poater, Albert; Pump, Eva; Vummaleti, Sai Vikrama Chaitanya; Cavallo, Luigi

    2014-08-01

    Density functional theory calculations have been used to describe the first turnover for olefin metathesis reaction of a homogenous Fe-based catalyst bearing a N-heterocyclic carbene ligand with methoxyethene as a substrate. Equal to conventional Ru-based catalysts, the activation of its Fe congener occurs through a dissociative mechanism, however with a more exothermic reaction energy profile. Predicted upper energy barriers were calculated to be on average ∼2 kcal/mol more beneficial for Fe catalyzed metathesis. Overall, this present computational study emphasises on advantages of Fe-based metathesis and gives a potential recipe for the design of an efficient Fe-based olefin metathesis catalysts.

  7. Active and Durable Hydrogen Evolution Reaction Catalyst Derived from Pd-Doped Metal-Organic Frameworks.

    PubMed

    Chen, Jitang; Xia, Guoliang; Jiang, Peng; Yang, Yang; Li, Ren; Shi, Ruohong; Su, Jianwei; Chen, Qianwang

    2016-06-01

    The water electrolysis is of critical importance for sustainable hydrogen production. In this work, a highly efficient and stable PdCo alloy catalyst (PdCo@CN) was synthesized by direct annealing of Pd-doped metal-organic frameworks (MOFs) under N2 atmosphere. In 0.5 M H2SO4 solution, PdCo@CN displays remarkable electrocatalytic performance with overpotential of 80 mV, a Tafel slope of 31 mV dec(-1), and excellent stability of 10 000 cycles. Our studies reveal that noble metal doped MOFs are ideal precursors for preparing highly active alloy electrocatalysts with low content of noble metal.

  8. Catalyst dispersion and activity under conditions of temperature- staged liquefaction

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1992-02-01

    The general objectives of this research are (1) to investigate the use of highly dispersed catalysts for the pretreatment of coal by mild hydrogenation, (2) to identify the active forms of catalysts under reaction conditions and (3) to clarify the mechanisms of catalysis. The ultimate objective is to ascertain if mild catalytic hydrogenation resulting in very limited or no coal solubilization is an advantageous pretreatment for the transformation of coal into transportable fuels. The experimental program will focus upon the development of effective methods of impregnating coal with catalysts, evaluating the conditions under which the catalysts are most active and establishing the relative impact of improved impregnation on conversion and product distributions obtained from coal hydrogenation.

  9. Effect of the conditions of preparing mixed oxide catalyst of Mo-V-Te-Nb-O composition on its activity in the oxidative dehydrogenation of ethane

    NASA Astrophysics Data System (ADS)

    Finashina, E. D.; Kucherov, A. V.; Kustov, L. M.

    2013-12-01

    It is shown that catalytic activity of mixed oxide catalyst of Mo-V-Te-Nb-O composition in oxidative dehydrogenation (OD) of ethane is determined to a substantial degree by the Nb-to-(C2O4)2- ratio in niobium-containing precursors. A pH value of 2.8 to 3.0 for a mixture is optimal when conducting the hydrothermal synthesis of a mixed oxide catalyst; this is achieved by using oxaloniobic acid as a niobium-containing precursor. It is determined that substituting antimony for tellurium results in a loss of catalyst activity during the OD of ethane. The optimum Te content in a catalyst is 0.17 mol %.

  10. Synthesis, characterization and catalytic activity of carbon-silica hybrid catalyst from rice straw

    NASA Astrophysics Data System (ADS)

    Janaun, J.; Safie, N. N.; Siambun, N. J.

    2016-07-01

    The hybrid-carbon catalyst has been studied because of its promising potential to have high porosity and surface area to be used in biodiesel production. Silica has been used as the support to produce hybrid carbon catalyst due to its mesoporous structure and high surface area properties. The chemical synthesis of silica-carbon hybrid is expensive and involves more complicated preparation steps. The presence of natural silica in rice plants especially rice husk has received much attention in research because of the potential as a source for solid acid catalyst synthesis. But study on rice straw, which is available abundantly as agricultural waste is limited. In this study, rice straw undergone pyrolysis and functionalized using fuming sulphuric acid to anchor -SO3H groups. The presence of silica and the physiochemical properties of the catalyst produced were studied before and after sulphonation. The catalytic activity of hybrid carbon silica acid catalyst, (H-CSAC) in esterification of oleic acid with methanol was also studied. The results showed the presence of silica-carbon which had amorphous structure and highly porous. The carbon surface consisted of higher silica composition, had lower S element detected as compared to the surface that had high carbon content but lower silica composition. This was likely due to the fact that Si element which was bonded to oxygen was highly stable and unlikely to break the bond and react with -SO3H ions. H-CSAC conversions were 23.04 %, 35.52 % and 34.2 7% at 333.15 K, 343.15 K and 353.15 K, respectively. From this research, rice straw can be used as carbon precursor to produce hybrid carbon-silica catalyst and has shown catalytic activity in biodiesel production. Rate equation obtained is also presented.

  11. Amyloid precursor protein controls cholesterol turnover needed for neuronal activity

    PubMed Central

    Pierrot, Nathalie; Tyteca, Donatienne; D'auria, Ludovic; Dewachter, Ilse; Gailly, Philippe; Hendrickx, Aurélie; Tasiaux, Bernadette; Haylani, Laetitia El; Muls, Nathalie; N'Kuli, Francisca; Laquerrière, Annie; Demoulin, Jean-Baptiste; Campion, Dominique; Brion, Jean-Pierre; Courtoy, Pierre J; Kienlen-Campard, Pascal; Octave, Jean-Noël

    2013-01-01

    Perturbation of lipid metabolism favours progression of Alzheimer disease, in which processing of Amyloid Precursor Protein (APP) has important implications. APP cleavage is tightly regulated by cholesterol and APP fragments regulate lipid homeostasis. Here, we investigated whether up or down regulation of full-length APP expression affected neuronal lipid metabolism. Expression of APP decreased HMG-CoA reductase (HMGCR)-mediated cholesterol biosynthesis and SREBP mRNA levels, while its down regulation had opposite effects. APP and SREBP1 co-immunoprecipitated and co-localized in the Golgi. This interaction prevented Site-2 protease-mediated processing of SREBP1, leading to inhibition of transcription of its target genes. A GXXXG motif in APP sequence was critical for regulation of HMGCR expression. In astrocytes, APP and SREBP1 did not interact nor did APP affect cholesterol biosynthesis. Neuronal expression of APP decreased both HMGCR and cholesterol 24-hydroxylase mRNA levels and consequently cholesterol turnover, leading to inhibition of neuronal activity, which was rescued by geranylgeraniol, generated in the mevalonate pathway, in both APP expressing and mevastatin treated neurons. We conclude that APP controls cholesterol turnover needed for neuronal activity. PMID:23554170

  12. Formation of Golgi-derived active zone precursor vesicles.

    PubMed

    Maas, Christoph; Torres, Viviana I; Altrock, Wilko D; Leal-Ortiz, Sergio; Wagh, Dhananjay; Terry-Lorenzo, Ryan T; Fejtova, Anna; Gundelfinger, Eckart D; Ziv, Noam E; Garner, Craig C

    2012-08-01

    Vesicular trafficking of presynaptic and postsynaptic components is emerging as a general cellular mechanism for the delivery of scaffold proteins, ion channels, and receptors to nascent and mature synapses. However, the molecular mechanisms leading to the selection of cargos and their differential transport to subneuronal compartments are not well understood, in part because of the mixing of cargos at the plasma membrane and/or within endosomal compartments. In the present study, we have explored the cellular mechanisms of active zone precursor vesicle assembly at the Golgi in dissociated hippocampal neurons of Rattus norvegicus. Our studies show that Piccolo, Bassoon, and ELKS2/CAST exit the trans-Golgi network on a common vesicle that requires Piccolo and Bassoon for its proper assembly. In contrast, Munc13 and synaptic vesicle proteins use distinct sets of Golgi-derived transport vesicles, while RIM1α associates with vesicular membranes in a post-Golgi compartment. Furthermore, Piccolo and Bassoon are necessary for ELKS2/CAST to leave the Golgi in association with vesicles, and a core domain of Bassoon is sufficient to facilitate formation of these vesicles. While these findings support emerging principles regarding active zone differentiation, the cellular and molecular analyses reported here also indicate that the Piccolo-Bassoon transport vesicles leaving the Golgi may undergo further changes in protein composition before arriving at synaptic sites.

  13. Pollution Control Meets Sustainability: Structure-Activity Studies on New Iron Oxide-Based CO Oxidation Catalysts.

    PubMed

    Schoch, Roland; Bauer, Matthias

    2016-08-01

    A new class of catalysts for the oxidation of CO based on iron oxide as a biocompatible, earth-abundant and non-toxic metal is presented. The catalytic activities achieved with these catalysts provide promising milestones towards the substitution of noble metals in CO oxidation catalysts. The catalysts can be obtained by using iron core-shell nanoparticle precursors. The metal used for the shell material determines whether the iron core is integrated in or isolated from the support. The active iron site is effectively integrated into the γ-Al2 O3 support if an aluminum shell is present in the core-shell precursor. When the metal used for the shell is different from the support, an isolated structure is formed. Using this directed synthesis approach, different iron oxide species can be obtained and their structural differences are linked to distinct catalytic activities, as demonstrated by combined in-depth analytical studies using XRD, X-ray absorption spectroscopy (XAS), UV/Vis, and Brunauer-Emmett-Teller (BET) analysis. The key species responsible for high catalytic activity is identified as isolated tetrahedrally coordinated Fe(III) centers, whereas aggregation leads to a reduction in activity.

  14. Sol-gel derived mesoporous cobalt silica catalyst: Synthesis, characterization and its activity in the oxidation of phenol

    NASA Astrophysics Data System (ADS)

    Andas, Jeyashelly; Adam, Farook; Rahman, Ismail Ab.

    2014-10-01

    Highly mesoporous cobalt silica rice husk catalysts with (5-15 wt.%) Co2+ loading were prepared via a simple sol-gel technique at room temperature. The successful insertion of cobalt ions into silica matrix was evidenced from FT-IR, NMR, XPS and AAS analyses. Preservation of the mesoporosity nature of silica upon incorporating Co2+ was confirmed from the N2-sorption studies. The topography and morphology viewed by TEM analysis differs as the cobalt concentration varies from 5 to 15 wt.%. Parallel pore channels and spherical nanoparticles of 9.44 nm were achieved for cobalt silica catalysts with 10 and 15 wt.% respectively. Cobalt catalysts were active in the liquid-phase oxidation of phenol with H2O2 as an oxygen source. The performances of the catalysts were greatly influenced by various parameters such as reaction temperature, catalyst amount, molar ratio of substrate to oxidant, nature of solvent, metal loading and homogeneous precursor salt. Water served as the best reaction medium for this oxidation system. The regeneration studies confirmed cobalt catalyst could be reused for five cycles without experiencing large loss in the conversion. Both leaching and reusability studies testified that the catalysts were truly heterogeneous.

  15. A highly active and coke-resistant steam reforming catalyst comprising uniform nickel-iron alloy nanoparticles.

    PubMed

    Koike, Mitsuru; Li, Dalin; Nakagawa, Yoshinao; Tomishige, Keiichi

    2012-12-01

    Doing fine with Ni-Fe: The calcination and reduction of a hydrotalcite precursor containing Ni and Fe ions gives uniform Ni-Fe alloy nanoparticles mixed with Mg(Ni, Fe, Al)O particles. The uniformity of the Ni-Fe alloy nanoparticles is connected to the catalyst's high activity and resistance to coke formation in toluene and phenol steam reforming reactions.

  16. Molybdenum(VI) catalysts obtained from η3-allyl dicarbonyl precursors: synthesis, characterization and catalytic performance in cyclooctene epoxidation.

    PubMed

    Gamelas, Carla A; Gomes, Ana C; Bruno, Sofia M; Almeida Paz, Filipe A; Valente, Anabela A; Pillinger, Martyn; Romão, Carlos C; Gonçalves, Isabel S

    2012-03-28

    The oxidative decarbonylation of the η(3)-allyl dicarbonyl complexes [Mo(η(3)-C(3)H(5))Cl(CO)(2)(L)] (L = 2,2'-bipyridine (bipy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (di-tBu-bipy) (2)) by reaction with aqueous tert-butylhydroperoxide (TBHP) or H(2)O(2) gave the following compounds in good to excellent yields: the oxo-bridged dimers [MoO(2)Cl(L)](2)O (L = bipy (3), di-tBu-bipy (6)) using TBHP(10 equiv.)/CH(3)CN/r.t.; the molybdenum oxide/bipyridine hybrid material {[MoO(3)(bipy)][MoO(3)(H(2)O)]}(n) (4) and the octanuclear complex [Mo(8)O(24)(di-tBu-bipy)(4)] (7) using TBHP(50 equiv.)/H(2)O/70 °C; the oxodiperoxo complexes MoO(O(2))(2)(L) (L = bipy (5), di-tBu-bipy (8)) using H(2)O(2)(10 equiv.)/CH(3)CN/r.t. The structure of 7·x(solvent) (where solvent = CH(2)Cl(2) and/or diethyl ether) was determined by single crystal X-ray diffraction. Despite possessing the same windmill-type complex as that described previously for 7·10CH(2)Cl(2), the crystal structure of 7·x(solvent) is unique due to differences in the crystal packing. Compounds 1-8 were examined as catalysts or catalyst precursors for the epoxidation of cyclooctene using aqueous TBHP or H(2)O(2) as oxidant at 55 or 70 °C. Reactions were performed without co-solvent or with the addition of water, ethanol or acetonitrile. Cyclooctene oxide was always the only reaction product. Solids recovered after 24 h reaction at 70 °C were identified by FT-IR spectroscopy as the hybrid 4 from (1,3-5)/TBHP, complex 5 from (1,3-5)/H(2)O(2), and complex 8 from (2,6-8)/H(2)O(2). With TBHP as oxidant, the highest epoxide yields (for 24 h reaction at 70 °C) were obtained using excess H(2)O as solvent (28-38% for 1,3-5; 87-98% for 2,6-8), while with H(2)O(2) as oxidant, the highest epoxide yields were obtained using CH(3)CN as solvent (54-81% for 3-8).

  17. Lessons from isolable nickel(I) precursor complexes for small molecule activation.

    PubMed

    Yao, Shenglai; Driess, Matthias

    2012-02-21

    density functional theory (DFT) calculations, the geometric and electronic structures of these complexes were established and their distinctive reactivity, including the unprecedented monooxygenase-like activity of a bis(μ-oxo)nickel-iron complex, was studied. The studies have further led to other heterobimetallic complexes containing a [NiO(2)M] core, which are useful for understanding the influence of the heterometal on structure-reactivity relationships. The activation of N(2)O led directly to the hydrogen-atom abstraction product bis(μ-hydroxo)nickel(II) species and prevented isolation of any intermediate. In contrast, the activation of elemental S, Se, and Te with the same nickel(I) reagent furnished activation products with superchalcogenido E(2)(-) (E is S, Se, or Te) and dichalcogenido E(2)(2-) ligand in different activation stages. The isolable supersulfidonickel(II) subunit may serve as a versatile building block for the synthesis of heterobimetallic disulfidonickel(II) complexes with a [NiS(2)M] core. In the case of white phosphorus, the P(4) molecule has been coordinated to the nickel(I) center of dinuclear β-diketiminatonickel(I) precursor complexes; however, the whole P(4) subunit is a weaker electron acceptor than the dichalcogen ligands E(2), thus remaining unreduced. This P(4) binding mode is rare and could open new doors for subsequent functionalization of P(4). Our advances in understanding how these small molecules are bound to a nickel(I) center and are activated for further transformation offer promise for designing new catalysts. These nickel-containing complexes offer exceptional potential for nickel-mediated transformations of organic molecules and as model compounds for mimicking active sites of nickel-containing metalloenzymes. PMID:21875073

  18. Spectroscopic investigation of heterogeneous Ziegler-Natta catalysts: Ti and Mg chloride tetrahydrofuranates, their interaction compound, and the role of the activator.

    PubMed

    Seenivasan, Kalaivani; Sommazzi, Anna; Bonino, Francesca; Bordiga, Silvia; Groppo, Elena

    2011-07-25

    X-ray powder diffraction (XRPD), Infrared, Raman, and UV/Vis spectroscopy have been used to investigate the structural, vibrational, and optical properties of Ti and Mg chloride tetrahydrofuranates as precursors of heterogeneous Ziegler-Natta catalysts for polyethylene production; as well as their interaction compound (pro-catalyst) and the final catalyst obtained after interaction with the AlR(3) activator. Although the structure of the precursors and of the pro-catalyst were well known, that of the catalyst (obtained by reaction of the pro-catalyst with AlR(3)) was not easily obtainable from XRPD data. IR and Raman spectroscopy provided important information on tetrahydrofuran (thf) coordination and on the ν(M-Cl) region; whereas UV/Vis spectroscopy gave the direct proof on both the formal oxidation state and the coordination environment of the active Ti sites. Those presented herein are among the first direct experimental data on the structure of the active Ti sites in Ziegler-Natta catalysts, and can be used to validate the many computational studies that have been increasing exponentially in the last few decades.

  19. A Geomagnetic Precursor Technique for Predicting the Solar Activity Cycle

    NASA Astrophysics Data System (ADS)

    Sobel, E. I.; Rabin, D. M.

    2015-12-01

    The Western hemisphere has been recording sunspot numbers since Galileo discovered sunspots in the early 17th century, and the roughly 11-year solar cycle has been recognized since the 19th century. However, predicting the strength of any particular cycle remains a relatively imprecise task. This project's aim was to update and improve a forecasting technique based on geomagnetic precursors of future solar activity The model is a refinement of R. J. Thompson's 1993 paper that relates the number of geomagnetically disturbed days, as defined by the aa and Ap indices, to the sum of the sunspot number in the current and the previous cycle, Rn + Rn-1.[1] The method exploits the fact that two cycles coexist for some period on the Sun near solar minimum and therefore that the number of sunspots and disturbed days during the declining phase of one cycle gives an indication of the following cycle's strength. We wrote and updated IDL software procedures to define disturbed days with varying threshold values and graphed Rn + Rn-1 against them. The aa threshold was derived from the Ap threshold. After comparing the graphs for Ap values from 20 to 50, an Ap threshold of 30 and the corresponding aa threshold of 44 were chosen as yielding the best correlation. Confidence regions were computed to provide a quantitative uncertainty on future predictions. The 80% confidence region gives a range of ±40 in sunspot number. [1] Thompson, R. J. (1993). A technique for predicting the amplitude of the solar cycle. Solar Physics, 148, 2, 383-388.

  20. IPS activity observed as a precursor of solar induced terrestrial activity. [solar wind density fluctuations

    NASA Technical Reports Server (NTRS)

    Cronyn, W. M.; Shawhan, S. D.; Rickard, J. J.; Mitchell, D. G.; Roelof, E. C.; Gotwols, B. L.

    1978-01-01

    A radio telescope designed to exploit the interplanetary scintillation (IPS) technique and locate, map, and track solar wind disturbances which result in geomagnetic disturbances, thereby providing a forecast capability, is described. Preliminary results from operation of the telescope include: (1) evidence for a precursor signal in the IPS activity with a 1-2 day lead time with respect to density enhancements which frequently give rise to geomagnetic activity; (2) detection of a spectral broadening signature which also serves as a precursor of geomagnetic activity; (3) out-of-the-ecliptic plasma density enhancements which were not detected by near-Earth, ecliptic plane spacecraft; (4) detection of 12 corotating density enhancements;(5) detection of over 80 sources which give detectable scintillation of which 45 have been used for detailed synoptic analysis and 9 for spectral analysis; and (6) measurement of 0-lag coefficient of 0.56 between density and IPS activity enhancements.

  1. Fe-Impregnated Mineral Colloids for Peroxide Activation: Effects of Mineral Substrate and Fe Precursor.

    PubMed

    Li, Yue; Machala, Libor; Yan, Weile

    2016-02-01

    Heterogeneous iron species at the mineral/water interface are important catalysts for the generation of reactive oxygen species at circumneutral pH. One significant pathway leading to the formation of such species arises from deposition of dissolved iron onto mineral colloids due to changes in redox conditions. This study investigates the catalytic properties of Fe impregnated on silica, alumina, and titania nanoparticles (as prototypical mineral colloids). Fe impregnation was carried out by immersing the mineral nanoparticles in dilute Fe(II) or Fe(III) solutions at pH 6 and 3, respectively, in an aerobic environment. The uptake of iron per unit surface area follows the order of nTiO2 > nAl2O3 > nSiO2 for both types of Fe precursors. Impregnation of mineral particles in Fe(II) solutions results in predominantly Fe(III) species due to efficient surface-mediated oxidation. The catalytic activity of the impregnated solids to produce hydroxyl radical (·OH) from H2O2 decomposition was evaluated using benzoic acid as a probe compound under dark conditions. Invariably, the rates of benzoic acid oxidation with different Fe-laden particles increase with the surface density of Fe until a critical density above which the catalytic activity approaches a plateau, suggesting active Fe species are formed predominantly at low surface loadings. The critical surface density of Fe varies with the mineral substrate as well as the aqueous Fe precursor. Fe impregnated on TiO2 exhibits markedly higher activity than its Al2O3 and SiO2 counterparts. The speciation of interfacial Fe is analyzed with diffuse reflectance UV-vis analysis and interpretation of the data in the context of benzoic oxidation rates suggests that the surface activity of the solids for ·OH generation correlates strongly with the isolated (i.e., mononuclear) Fe species. Therefore, iron dispersed on mineral colloids is a significant form of reactive iron surfaces in the aquatic environment.

  2. Fe-Impregnated Mineral Colloids for Peroxide Activation: Effects of Mineral Substrate and Fe Precursor.

    PubMed

    Li, Yue; Machala, Libor; Yan, Weile

    2016-02-01

    Heterogeneous iron species at the mineral/water interface are important catalysts for the generation of reactive oxygen species at circumneutral pH. One significant pathway leading to the formation of such species arises from deposition of dissolved iron onto mineral colloids due to changes in redox conditions. This study investigates the catalytic properties of Fe impregnated on silica, alumina, and titania nanoparticles (as prototypical mineral colloids). Fe impregnation was carried out by immersing the mineral nanoparticles in dilute Fe(II) or Fe(III) solutions at pH 6 and 3, respectively, in an aerobic environment. The uptake of iron per unit surface area follows the order of nTiO2 > nAl2O3 > nSiO2 for both types of Fe precursors. Impregnation of mineral particles in Fe(II) solutions results in predominantly Fe(III) species due to efficient surface-mediated oxidation. The catalytic activity of the impregnated solids to produce hydroxyl radical (·OH) from H2O2 decomposition was evaluated using benzoic acid as a probe compound under dark conditions. Invariably, the rates of benzoic acid oxidation with different Fe-laden particles increase with the surface density of Fe until a critical density above which the catalytic activity approaches a plateau, suggesting active Fe species are formed predominantly at low surface loadings. The critical surface density of Fe varies with the mineral substrate as well as the aqueous Fe precursor. Fe impregnated on TiO2 exhibits markedly higher activity than its Al2O3 and SiO2 counterparts. The speciation of interfacial Fe is analyzed with diffuse reflectance UV-vis analysis and interpretation of the data in the context of benzoic oxidation rates suggests that the surface activity of the solids for ·OH generation correlates strongly with the isolated (i.e., mononuclear) Fe species. Therefore, iron dispersed on mineral colloids is a significant form of reactive iron surfaces in the aquatic environment. PMID:26713453

  3. Results of catalyst testing using iron-based catalysts

    SciTech Connect

    Linehan, J.C.; Darab, J.G.; Matson, D.W.

    1993-03-01

    As coal liquefaction catalysts, iron-based products are generally inferior to the more expensive molybdenum, cobalt, or nickel-based materials. However, the lower costs of production and recovery (or in the case of some iron catalysts, non-recovery) give the iron-based materials a potential economic advantage over the more efficient precious and semi-precious metal catalysts for this application. Recent research has shown that a number of different iron-containing materials can be successfully utilized as coal liquefaction catalysts or as catalyst. Pyrrhotite (Fe[sub 1-x]S) or a similar iron-sulfide phase is commonly believed to be the active catalyst in coal liquefaction and model compound pyrolysis reactions, although no specific phase has been yet been isolated as the actual catalyst species. The active iron-containing catalyst is usually generated in situ from an iron-oxide precursor and an elemental sulfur source under reducing conditions in the reactor vessel. Most research has concentrated on the use of common iron-oxide phases such as hematite or goethite (and their derivatives) as the iron-bearing precursor, or on non-specific iron materials produced by the reaction of various iron salts and compounds in the coal or liquefaction reactor. To our knowledge there has been no systematic effort to determine the optimum iron-containing precursor phase for producing active coal liquefaction catalysts, despite the fact that there are over ten iron-(hydroxy)oxide phases which can be easily synthesized in the laboratory. We have undertaken a systematic study to identify the most active iron-oxide catalyst precursor phases, the co-catalysts, and the coal pretreatments which will provide optimum yields in coal liquefaction processes.

  4. Results of catalyst testing using iron-based catalysts

    SciTech Connect

    Linehan, J.C.; Darab, J.G.; Matson, D.W.

    1993-03-01

    As coal liquefaction catalysts, iron-based products are generally inferior to the more expensive molybdenum, cobalt, or nickel-based materials. However, the lower costs of production and recovery (or in the case of some iron catalysts, non-recovery) give the iron-based materials a potential economic advantage over the more efficient precious and semi-precious metal catalysts for this application. Recent research has shown that a number of different iron-containing materials can be successfully utilized as coal liquefaction catalysts or as catalyst. Pyrrhotite (Fe{sub 1-x}S) or a similar iron-sulfide phase is commonly believed to be the active catalyst in coal liquefaction and model compound pyrolysis reactions, although no specific phase has been yet been isolated as the actual catalyst species. The active iron-containing catalyst is usually generated in situ from an iron-oxide precursor and an elemental sulfur source under reducing conditions in the reactor vessel. Most research has concentrated on the use of common iron-oxide phases such as hematite or goethite (and their derivatives) as the iron-bearing precursor, or on non-specific iron materials produced by the reaction of various iron salts and compounds in the coal or liquefaction reactor. To our knowledge there has been no systematic effort to determine the optimum iron-containing precursor phase for producing active coal liquefaction catalysts, despite the fact that there are over ten iron-(hydroxy)oxide phases which can be easily synthesized in the laboratory. We have undertaken a systematic study to identify the most active iron-oxide catalyst precursor phases, the co-catalysts, and the coal pretreatments which will provide optimum yields in coal liquefaction processes.

  5. Enhanced optical precursors by Doppler effect via active Raman gain process.

    PubMed

    Peng, Yandong; Niu, Yueping; Zhang, Lida; Yang, Aihong; Jiang, Lin; Gong, Shangqing

    2012-08-15

    A scheme for enhancing precursor pulse by Doppler effect is proposed in a room-temperature active-Raman-gain medium. Due to abnormal dispersion between two gain peaks, main fields are advanced and constructively interfere with optical precursors, which leads to enhancement of the transient pulse at the rise edge of the input. Moreover, after Doppler averaging, the abnormal dispersion intensifies and the constructive interference between precursors and main fields is much strengthened, which boosts the transient spike. Simulation results demonstrate that the peak intensity of precursors could be enhanced nearly 20 times larger than that of the input.

  6. Enhanced optical precursors by Doppler effect via active Raman gain process.

    PubMed

    Peng, Yandong; Niu, Yueping; Zhang, Lida; Yang, Aihong; Jiang, Lin; Gong, Shangqing

    2012-08-15

    A scheme for enhancing precursor pulse by Doppler effect is proposed in a room-temperature active-Raman-gain medium. Due to abnormal dispersion between two gain peaks, main fields are advanced and constructively interfere with optical precursors, which leads to enhancement of the transient pulse at the rise edge of the input. Moreover, after Doppler averaging, the abnormal dispersion intensifies and the constructive interference between precursors and main fields is much strengthened, which boosts the transient spike. Simulation results demonstrate that the peak intensity of precursors could be enhanced nearly 20 times larger than that of the input. PMID:23381248

  7. Metal and Precursor Effect during 1-Heptyne Selective Hydrogenation Using an Activated Carbon as Support

    PubMed Central

    Lederhos, Cecilia R.; Badano, Juan M.; Carrara, Nicolas; Coloma-Pascual, Fernando; Almansa, M. Cristina; Liprandi, Domingo; Quiroga, Mónica

    2013-01-01

    Palladium, platinum, and ruthenium supported on activated carbon were used as catalysts for the selective hydrogenation of 1-heptyne, a terminal alkyne. All catalysts were characterized by temperature programmed reduction, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. TPR and XPS suggest that the metal in all catalysts is reduced after the pretreatment with H2 at 673 K. The TPR trace of the PdNRX catalyst shows that the support surface groups are greatly modified as a consequence of the use of HNO3 during the catalyst preparation. During the hydrogenation of 1-heptyne, both palladium catalysts were more active and selective than the platinum and ruthenium catalysts. The activity order of the catalysts is as follows: PdClRX > PdNRX > PtClRX ≫ RuClRX. This superior performance of PdClRX was attributed in part to the total occupancy of the d electronic levels of the Pd metal that is supposed to promote the rupture of the H2 bond during the hydrogenation reaction. The activity differences between PdClRX and PdNRX catalysts could be attributed to a better accessibility of the substrate to the active sites, as a consequence of steric and electronic effects of the superficial support groups. The order for the selectivity to 1-heptene is as follows: PdClRX = PdNRX > RuClRX > PtClRX, and it can be mainly attributed to thermodynamic effects. PMID:24348168

  8. Activity and Stability of Nanoscale Oxygen Reduction Catalysts

    SciTech Connect

    Shao-Horn, Yang

    2015-07-28

    Design of highly active and stable nanoscale catalysts for electro-oxidation of small organic molecules is of great importance to the development of efficient fuel cells. The amount and instability of Pt-based catalysts in the cathode limits the cost, efficiency and lifetime of proton exchange membrane fuel cells. We developed a microscopic understanding of the factors governing activity and stability in Pt and PtM alloys. Experimental efforts were focused on probing the size and shape dependence of ORR activity of Pt-based nanoparticles supported on carbon nanotubes. A microscopic understanding of the activity was achieved by correlating voltammetry and rotating ring disk electrodes to surface atomic and electronic structures, which were elucidated predominantly by high-resolution transmission electron microscopy (HRTEM), Scanning transmission electron microscopy energy dispersive X-ray Spectroscopy (STEM-EDS) and synchrotron X-ray absorption spectroscopy (XAS).

  9. [Catalyst research]. Final Report

    SciTech Connect

    Ian P Rothwell; David R McMillin

    2005-03-14

    Research results are the areas of catalyst precursor synthesis, catalyst fluxionality, catalyst stability, polymerization of {alpha}-olefins as well as the chemistry of Group IV and Group V metal centers with aryloxide and arylsulfide ligands.

  10. Design of a high activity and selectivity alcohol catalyst

    SciTech Connect

    Foley, H.C.; Mills, G.A.

    1993-02-17

    Preliminary investigations of these manganese oxide materials show that the different oxides exhibit different selectivity toward methanol and other products. It seems that there is a correlation between the initial O/Mn ratio of the oxide and methanol selectivity. These conclusions are supported by the results displayed in Figures 1 and 2. The main product of the manganese oxide-catalyzed CO hydrogenation is methanol except on Mao, which shows the lowest methanol selectivity, but the highest CO[sub 2] yield. Preliminarily, the results suggest that the higher the O/Mn ratio of the precursor oxide, the higher will be the methanol selectivity, while the CO[sub 2] and methane selectivities will be lower. The higher CO[sub 2] and C[sub 2], C[sub 3] and C[sub 4] hydrocarbon selectivities over the Mao catalyst compared to the other manganese oxides tested, indicates that Mao acts more like a water-gas shift and Fischer-Tropsch catalyst.

  11. [Ru(η5-C5H5)(η6-C10H8)]PF6 as a catalyst precursor for the one-pot direct C-H alkenylation of nitrogen heterocycles.

    PubMed

    Lynam, Jason M; Milner, Lucy M; Mistry, Neetisha S; Slattery, John M; Warrington, Sally R; Whitwood, Adrian C

    2014-03-21

    The ruthenium naphthalene complex [Ru(η(5)-C5H5)(η(6)-C10H8)](+) is a catalyst precursor for the direct C-H alkenylation of pyridine and related nitrogen heterocycles by terminal alkynes. Stoichiometric studies have demonstrated that the naphthalene ligand may be displaced by either pyridine, 4-methylpyridine or dimethylaminopyridine (DMAP) to give species [Ru(η(5)-C5H5)L3](+) (L = nitrogen-based ligand). Reaction of in situ-generated [Ru(η(5)-C5H5)(py)3](+) (py = pyridine) with PPh3 results in the formation of [Ru(η(5)-C5H5)(PPh3)(py)2](+), the active catalyst for direct alkenylation, some [Ru(η(5)-C5H5)(PPh3)2(py)](+) is also formed in this reaction. A one-pot procedure is reported which has allowed for the nature of the nitrogen heterocycle and phosphine ligand to be evaluated. The sterically demanding phosphine PCy3 inhibits catalysis, and only trace amounts of product are formed when precursors containing a pentamethylcyclopentadienyl group were used. The greatest conversion was observed with PMe3 when used as co-ligand with [Ru(η(5)-C5H5)(η(6)-C10H8)](+). PMID:24481140

  12. Studies of the activity of catalysts based on heteropolyacids

    NASA Astrophysics Data System (ADS)

    Turek, Wincenty; Lapkowski, Mieczyslaw; Debiec, Joanna; Krowiak, Agnieszka

    2005-10-01

    The catalytic activity of samples such as PPy(H 4SiW 12O 40), PPy(H 5PMo 10V 2O 40), PPy(H 2Fe(III)PMo 10V 2O 40), PPy(H 3Cu(II)PMo 10V 2O 40) has been examined in two different test reactions. The acid-base and oxidation-reduction properties were studied using the conversion of isopropyl alcohol to propene and acetone. Redox ability of catalysts was examined in the reaction of oxidation of allyl alcohol to glycidol. It was found that the activity of catalysts in the oxidation of allyl alcohol increases as the oxidation properties determined from the conversion of isopropyl alcohol increase. It was also observed that stronger oxidation-reduction properties of the catalyst result in a high rate of the consecutive reaction of glycidol to 3-hydroxypropanone. The phase composition of catalysts was determined by means of X-ray diffraction (XRD).

  13. Use of H2S to Probe the Active Sites in FeNC Catalysts for the Oxygen Reduction Reaction (ORR) in Acidic Media

    SciTech Connect

    Singh, Deepika; Mamtani, Kuldeep; Bruening, Christopher R.; Miller, Jeffrey T.; Ozkan, Umit S.

    2014-10-01

    H2S has been used as a probe molecule both in an “in situ” poisoning experiment and in intermediate-temperature heat-treatment steps during and after the preparation of FeNC catalysts in an attempt to analyze its effect on their ORR activity. The heat treatments were employed either on the ball-milled precursor of FeNC or after the Ar-NH3 high temperature heat treatments. ORR activity of the H2S-treated catalysts was seen to be significantly lower than the sulfur-free catalysts, whether the sulfur exposure was during a half-cell testing, or as an intermediate-temperature exposure to H2S. The incorporation of sulfur species and interaction of Fe with sulfur were confirmed by characterization using XPS, EXAFS, TPO, and TPD. This study provides crucial evidence regarding differences in active sites in FeNC versus nitrogen-containing carbon nanostructured (CNx) catalysts.

  14. Investigating the performance of CoxOy/activated carbon catalysts for ethyl acetate catalytic combustion

    NASA Astrophysics Data System (ADS)

    Xie, Hongmei; Zhao, Xiaoping; Zhou, Guilin; He, Xiaoling; Lan, Hai; Jiang, Zongxuan

    2015-01-01

    The catalytic properties of Co-supported activated carbon (AC) catalysts for ethyl acetate catalytic elimination in air were investigated. Results showed that air atmosphere promoted the generation of high-valence state cobalt oxides, and promote the production of reactive oxygen species (ROS) in the Co3O4/AC catalyst. ROS crucially functioned in improving the catalytic activity of Co3O4/AC catalysts. Therefore, CoACA catalyst prepared in air exhibited higher catalytic activity than CoACN catalyst prepared in nitrogen, and CoACA catalyst led to high ethyl acetate conversion (>93%) and stability at a low reaction temperature (210 °C).

  15. Particle size distribution and morphological changes in activated carbon-metal oxide hybrid catalysts prepared under different heating conditions.

    PubMed

    Barroso-Bogeat, A; Alexandre-Franco, M; Fernández-González, C; Gómez-Serrano, V

    2016-03-01

    In catalysis processes, activated carbon (AC) and metal oxides (MOs) are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and a MO in a single hybrid material entails changes not only in the composition, microstructure and texture but also in the morphology, which may largely influence the catalytic behaviour of the resulting product. This work is aimed at investigating the modifications in the morphology and particle size distribution (PSD) for AC-MO hybrid catalysts as a result of their preparation under markedly different heating conditions. From a commercial AC and six MO (Al2O3, Fe2O3, ZnO, SnO2, TiO2 and WO3) precursors, two series of such catalysts are prepared by wet impregnation, oven-drying at 120 ºC, and subsequent heat treatment at 200 ºC or 850 ºC in inert atmosphere. The resulting samples are characterized in terms of their morphology and PSD by scanning electron microscopy and ImageJ processing program. Obtained results indicate that the morphology, PSD and degree of dispersion of the supported catalysts are strongly dependent both on the MO precursor and the heat treatment temperature. With the temperature rise, trends are towards the improvement of crystallinity, the broadening of the PSD and the increase in the average particle size, thus suggesting the involvement of sintering mechanisms. Such effects are more pronounced for the Fe, Sn and W catalysts due to the reduction of the corresponding MOs by AC during the heat treatment at 850 ºC.

  16. Facile synthesis of a platinum-lead oxide nanocomposite catalyst with high activity and durability for ethanol electrooxidation.

    PubMed

    Yang, Wei-Hua; Wang, Hong-Hui; Chen, De-Hao; Zhou, Zhi-You; Sun, Shi-Gang

    2012-12-21

    Aimed at searching for highly active and stable nano-scale Pt-based catalysts that can improve significantly the energy conversion efficiency of direct ethanol fuel cells (DEFCs), a novel Pt-PbO(x) nanocomposite (Pt-PbO(x) NC) catalyst with a mean size of 3.23 nm was synthesized through a simple wet chemistry method without using a surfactant, organometallic precursors and high temperature. Electrocatalytic tests demonstrated that the as-prepared Pt-PbO(x) NC catalyst possesses a much higher catalytic activity and a longer durability than Pt nanoparticles (nm-Pt) and commercial Pt black catalysts for ethanol electrooxidation. For instance, Pt-PbO(x) NC showed an onset potential that was 30 mV and 44 mV less positive, together with a peak current density 1.7 and 2.6 times higher than those observed for nm-Pt and Pt black catalysts in the cyclic voltammogram tests. The ratio of current densities per unit Pt mass on Pt-PbO(x) NC, nm-Pt and Pt black catalysts is 27.3 : 3.4 : 1 for the long-term (2 hours) chronoamperometric experiments measured at -0.4 V (vs. SCE). In situ FTIR spectroscopic studies revealed that the activity of breaking C-C bonds of ethanol of the Pt-PbO(x) NC is as high as 5.17 times that of the nm-Pt, which illustrates a high efficiency of ethanol oxidation to CO(2) on the as-prepared Pt-PbO(x) NC catalyst.

  17. Recombinant human epidermal growth factor precursor is a glycosylated membrane protein with biological activity.

    PubMed Central

    Mroczkowski, B; Reich, M; Chen, K; Bell, G I; Cohen, S

    1989-01-01

    NIH 3T3 cells were transfected with cDNA corresponding to human kidney prepro-epidermal growth factor (preproEGF) under control of the inducible mouse metallothionein promoter. The synthesis of recombinant human EGF precursor by these cells has provided us with a model system for analysis of the structure and activity of this precursor. In transfected cells, the precursor was present as an intrinsic 170-kilodalton membrane protein as well as a soluble protein in the extracellular medium; both forms were N glycosylated. Glycosylation of the EGF precursor was determined by (i) the direct incorporation of [3H]mannose and [3H]glucosamine, (ii) metabolic labeling in the presence or absence of glycosylation inhibitors, (iii) enzymatic cleavage of the precursor by N-glycanase or endoglycosidase II, and (iv) lectin chromatography. Recombinant human preproEGF was purified by affinity chromatography, using wheat germ lectin and antibodies to human EGF. The intact precursor was biologically active. Purified preparations of preproEGF (i) competed with 125I-labeled EGF for binding to the EGF receptor in intact fibroblast cells, (ii) activated the intrinsic tyrosine kinase activity of the EGF receptor in membrane preparations, and (iii) sustained the growth of a mouse keratinocyte cell line that is dependent on EGF for growth. These results suggest that proteolytic processing of the precursor may not be essential for its biological function. Images PMID:2789334

  18. Monitoring Precursor 16S rRNAs of Acinetobacter spp. in Activated Sludge Wastewater Treatment Systems

    PubMed Central

    Oerther, Daniel B.; Pernthaler, Jakob; Schramm, Andreas; Amann, Rudolf; Raskin, Lutgarde

    2000-01-01

    Recently, Cangelosi and Brabant used oligonucleotide probes targeting the precursor 16S rRNA of Escherichia coli to demonstrate that the levels of precursor rRNA were more sensitive to changes in growth phase than the levels of total rRNA (G. A. Cangelosi and W. H. Brabant, J. Bacteriol. 179:4457–4463, 1997). In order to measure changes in the levels of precursor rRNA in activated sludge systems, we designed oligonucleotide probes targeting the 3′ region of the precursor 16S rRNA of Acinetobacter spp. We used these probes to monitor changes in the level of precursor 16S rRNA during batch growth of Acinetobacter spp. in Luria-Bertani (LB) medium, filtered wastewater, and in lab- and full-scale wastewater treatment systems. Consistent with the previous reports for E. coli, results obtained with membrane hybridizations and fluorescence in situ hybridizations with Acinetobacter calcoaceticus grown in LB medium showed a more substantial and faster increase in precursor 16S rRNA levels compared to the increase in total 16S rRNA levels during exponential growth. Diluting an overnight culture of A. calcoaceticus grown in LB medium with filtered wastewater resulted in a pattern of precursor 16S rRNA levels that appeared to follow diauxic growth. In addition, fluorescence in situ hybridizations with oligonucleotide probes targeting total 16S rRNA and precursor 16S rRNA showed that individual cells of A. calcoaceticus expressed highly variable levels of precursor 16S rRNA when adapting from LB medium to filtered sewage. Precursor 16S rRNA levels of Acinetobacter spp. transiently increased when activated sludge was mixed with influent wastewater in lab- and full-scale wastewater treatment systems. These results suggest that Acinetobacter spp. experience a change in growth activity within wastewater treatment systems. PMID:10788395

  19. Solution Structures of Highly Active Molecular Ir Water-Oxidation Catalysts from Density Functional Theory Combined with High-Energy X-ray Scattering and EXAFS Spectroscopy.

    PubMed

    Yang, Ke R; Matula, Adam J; Kwon, Gihan; Hong, Jiyun; Sheehan, Stafford W; Thomsen, Julianne M; Brudvig, Gary W; Crabtree, Robert H; Tiede, David M; Chen, Lin X; Batista, Victor S

    2016-05-01

    The solution structures of highly active Ir water-oxidation catalysts are elucidated by combining density functional theory, high-energy X-ray scattering (HEXS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. We find that the catalysts are Ir dimers with mono-μ-O cores and terminal anionic ligands, generated in situ through partial oxidation of a common catalyst precursor. The proposed structures are supported by (1)H and (17)O NMR, EPR, resonance Raman and UV-vis spectra, electrophoresis, etc. Our findings are particularly valuable to understand the mechanism of water oxidation by highly reactive Ir catalysts. Importantly, our DFT-EXAFS-HEXS methodology provides a new in situ technique for characterization of active species in catalytic systems. PMID:27087202

  20. Utilizing peroxide as precursor for the synthesis of CeO2/ZnO composite oxide with enhanced photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Lv, Zijian; Zhong, Qin; Ou, Man

    2016-07-01

    A facile synthesis method of CeO2/ZnO composite oxides with higher oxygen vacancy concentration was developed by a two-step precipitation method, in which peroxide was used as precursor. The photocatalytic activity of the catalysts under UV irradiation was studied in degradation of methylene blue (MB). All CeO2/ZnO photocatalysts exhibited higher photocatalytic performance than pure ZnO, and 1%CeO2/ZnO showed highest photocatalytic activity among the prepared catalysts. It was confirmed that the synergistic effect of CeO2 and oxygen vacancy caused the improved photocatalytic activity. Furthermore, the mechanism was investigated by introducing different additives, and it was found that the hydroxyl radicals played a crucial role in degradation process.

  1. Design of a high activity and selectivity alcohol catalyst

    SciTech Connect

    Foley, H.C.; Mills, G.A.

    1992-07-30

    In methanol dehydration by K-doped Rh-Mo/[gamma]-Al[sub 2]O[sub 3], while higher K levels reduced the dehydration propensity of the surface, at higher levels the potassium oxide layer formed after doping and calcining the surface interferes detrimentally with the Rh-Mo active metallic sites. Silica- and alumina-supported catalysts with 0.5% Rh loading were synthesized and tested for hydrogenation of CO.

  2. Effect of surface oxidation of the support on the thiophene hydrodesulfurization activity of Mo, Ni, and NiMo catalysts supported on activated carbon

    SciTech Connect

    Calafat, A. |; Lopez-Agudo, A.; Palacios, J.M.

    1996-08-01

    The present investigation attempts to provide a better understanding of the influence of the nature of the carbon support on the HDS activity of Mo, Ni, and NiMo catalysts. For this purpose a high purity activated carbon was subjected to oxidative treatments with HNO{sub 3} to modify its surface properties. NiMo catalysts supported on the resulting activated carbons were prepared and characterized by TPR, XRD, and SEM-EDX, and their activity for HDS of thiophene at 30 bars and 375{degrees}C was evaluated. The results obtained showed that oxidation of the carbon surface does not affect the HDS activity and other characteristics of the supported Mo phase. In contrast, the HDS activity of the Ni catalysts is enhanced by acid treatments of the carbon support. In this case, introduction of oxygen-containing functional groups (O{sub (s)}) leads to a strong interaction of O{sub (s)}-Ni during impregnation, which becomes essential to achieving and preserving high nickel dispersion. This effect on NiMo/C catalysts. The synergistic effect of the bimetallic catalysts is observed only when oxygen functional groups are present on the carbon surface, which are necessary for a good HDS activity, mainly because they enhance Ni-Mo interactions that produce the highly active Ni-Mo-S phase. A NiMoO{sub 4}-like phase formed during impregnation seems to be the precursor for the active sulfide phase over the present NiMo/C catalysts. 34 refs., 6 figs., 5 tabs.

  3. NREL Team Creates High-Activity, Durable Platinum Extended Surface Catalyst for Fuel Cells (Fact Sheet)

    SciTech Connect

    Not Available

    2011-02-01

    Researchers with NREL's Fuel Cell team showed that platinum can replace copper nanowires in such a way that high-surface-area and high-specific-activity catalysts are produced, potentially allowing for lower-cost catalysts.

  4. Structure and Activity of Pt-Ni Catalysts Supported on Modified Al2O3 for Ethanol Steam Reforming.

    PubMed

    Navarro, R M; Sanchez-Sanchez, M C; Fierro, J L G

    2015-09-01

    Modification of alumina with La-, Ce-, Zr- and Mg-oxides was studied with the aim to use them as supports of bimetallic Pt-Ni catalysts for the steam reforming of ethanol. Activity results showed that modifications of Al2O3 support with the incorporation of La, Ce, Zr or Mg oxides play an essential role in the catalytic behaviour of PtNi catalysts. Bimetallic PtNi catalyst supported on bare Al2O3 showed evolution of the reaction products with time on stream consisting in the increase of C2H4 production with concomitant decrease of CH4 and CO2 production. The addition of Mg or Zr to γ-A1203 did not inhibit the appearance of ethylene but delayed its production. In the case of Ce- or La-supported catalysts, the product selectivities were stable with time-on-stream, with no changes being observed in the product distribution for 24 h. Characterization results showed that La- and Ce-containing supports improves the Pt and Ni metal exposure values. The better stability achieved for Ce and La containing catalysts was inferred to be related with a participation/assistance of lanthanum and cerium entities in the gasification of coke deposits together with a modification of Pt and Ni dispersion which lower the probability of the nucleation of coke precursors on their surfaces. PMID:26716216

  5. Alumina-supported sulfided catalysts: V. Effect of P and F on the catalytic activity of hydrodesulfurization sulfided catalysts

    SciTech Connect

    Startsev, A.N.; Klimov, O.V.; Kalinkin, A.V.; Mastikhin, V.M.

    1994-07-01

    Phosphorus and flourine additives incorporated into the Ni-Mo/Al{sub 2}O{sub 3} sulfided catalysts on various stages of their preparation considerably lower the activation energy of the thiophene hydrogenolysis reaction. The interaction of promoting additives with the active component of the hydrodesulfurization catalyst is proved by XPS and {sup 31}P NMR. The effect of additives is discussed in terms of a synchronous mechanism involving interaction of reacting molecules in the coordination sphere of a bimetallic sulfide compound.

  6. Active and Durable Hydrogen Evolution Reaction Catalyst Derived from Pd-Doped Metal-Organic Frameworks.

    PubMed

    Chen, Jitang; Xia, Guoliang; Jiang, Peng; Yang, Yang; Li, Ren; Shi, Ruohong; Su, Jianwei; Chen, Qianwang

    2016-06-01

    The water electrolysis is of critical importance for sustainable hydrogen production. In this work, a highly efficient and stable PdCo alloy catalyst (PdCo@CN) was synthesized by direct annealing of Pd-doped metal-organic frameworks (MOFs) under N2 atmosphere. In 0.5 M H2SO4 solution, PdCo@CN displays remarkable electrocatalytic performance with overpotential of 80 mV, a Tafel slope of 31 mV dec(-1), and excellent stability of 10 000 cycles. Our studies reveal that noble metal doped MOFs are ideal precursors for preparing highly active alloy electrocatalysts with low content of noble metal. PMID:27112733

  7. Patched bimetallic surfaces are active catalysts for ammonia decomposition

    PubMed Central

    Guo, Wei; Vlachos, Dionisios G.

    2015-01-01

    Ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material's structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N−H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design. PMID:26443525

  8. Patched bimetallic surfaces are active catalysts for ammonia decomposition

    SciTech Connect

    Guo, Wei; Vlachos, Dionisios G.

    2015-10-07

    In this study, ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material’s structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.

  9. Patched bimetallic surfaces are active catalysts for ammonia decomposition.

    PubMed

    Guo, Wei; Vlachos, Dionisios G

    2015-10-07

    Ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material's structure. Core-shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core-shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.

  10. Sol immobilization technique: a delicate balance between activity, selectivity and stability for gold catalyst

    SciTech Connect

    Villa, Alberto; Wang, Di; Veith, Gabriel M; Prati, Laura

    2013-01-01

    Sol immobilization is a widely used method to prepare gold catalysts. The presence of the protective layer can have a significant influence on catalyst properties by mediating metal-support and reactantmetal interactions. This paper details the effect of a polyvinyl alcohol (PVA) protecting groups on the activity of a supported gold catalysts as well as its selectivity towards glycerol oxidation.

  11. Stable N-heterocyclic carbene (NHC)-palladium(0) complexes as active catalysts for olefin cyclopropanation reactions with ethyl diazoacetate.

    PubMed

    Martín, Carmen; Molina, Francisco; Alvarez, Eleuterio; Belderrain, Tomás R

    2011-12-23

    The Pd(0) complexes [(NHC)PdL(n)] (NHC=N-heterocyclic carbene ligand; L=styrene for n=2 or PR(3) for n=1) efficiently catalyse olefin cyclopropanation by using ethyl diazoacetate (EDA) as the carbene source with activities that improve on previously described catalytic systems based on this metal. Mechanistic studies have shown that all of these catalyst precursors deliver the same catalytic species in solution, that is, [(IPr)Pd(sty)], a 14e(-) unsaturated intermediate that further reacts with EDA to afford [(IPr)Pd(=CHCO(2)Et)(sty)], from which the cyclopropane is formed.

  12. Evaluation of photocatalytic activities of supported catalysts on NaX zeolite or activated charcoal.

    PubMed

    de Brites-Nóbrega, Fernanda F; Polo, Aldino N B; Benedetti, Angélica M; Leão, Mônica M D; Slusarski-Santana, Veronice; Fernandes-Machado, Nádia R C

    2013-12-15

    This study aimed to evaluate the photocatalytic activity of ZnO and Nb2O5 catalysts, both supported on NaX zeolite and activated charcoal (AC). The synergistic effect between oxide and support and the influence of solution pH (3, 7 and 9) on photocatalytic degradation of reactive blue 5G (C.I. 222) were analyzed. The catalysts Nb2O5/NaX, Nb2O5/AC and ZnO/NaX, ZnO/AC with 5 and 10% (wt%) were prepared by wet impregnation. The results showed that the catalysts exhibit quite different structural and textural properties. The synergic effect between ZnO and NaX support was higher than that with the activated charcoal, showing that these catalysts were more efficient. The most photoactive catalyst was 10% ZnO/NaX which showed 100% discoloration of the dye solution at pH 3, 7 and 9 after 0.5, 5 and 2h of irradiation, respectively. The hydrolytic nature of zeolite favored the formation of surface hydroxyl radicals, which increased the activity of the photocatalyst. Thus, catalysts supported on NaX zeolite are promising for use in photocatalysis.

  13. Synergistic "ping-pong" energy transfer for efficient light activation in a chromophore-catalyst dyad.

    PubMed

    Quaranta, Annamaria; Charalambidis, Georgios; Herrero, Christian; Margiola, Sofia; Leibl, Winfried; Coutsolelos, Athanassios; Aukauloo, Ally

    2015-10-01

    The synthesis of a porphyrin-Ru(II) polypyridine complex where the porphyrin acts as a photoactive unit and the Ru(II) polypyridine as a catalytic precursor is described. Comparatively, the free base porphyrin was found to outperform the ruthenium based chromophore in the yield of light induced electron transfer. Mechanistic insights indicate the occurrence of a ping-pong energy transfer from the (1)LC excited state of the porphyrin chromophore to the (3)MCLT state of the catalyst and back to the (3)LC excited state of the porphyrin unit. The latter, triplet-triplet energy transfer back to the chromophore, efficiently competes with fast radiationless deactivation of the excited state at the catalyst site. The energy thus recovered by the chromophore allows improved yield of formation of the oxidized form of the chromophore and concomitantly of the oxidation of the catalytic unit by intramolecular charge transfer. The presented results are among the rare examples where a porphyrin chromophore is successfully used to drive an oxidative activation process where reductive processes prevail in the literature.

  14. The influence of Mn species on the SO2 removal of Mn-based activated carbon catalysts

    NASA Astrophysics Data System (ADS)

    Qu, Yi-Fan; Guo, Jia-Xiu; Chu, Ying-Hao; Sun, Ming-Chao; Yin, Hua-Qiang

    2013-10-01

    Using Mn(NO3)2 as precursor, a series of Mn-based activated carbon catalysts were prepared by ultrasound-assisted excessive impregnation method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The influences of Mn species and nitric acid pretreatment on the removal role of SO2 were investigated. MnO and Mn3O4 coexist in catalysts calcined at 650 and 800 °C and exhibit best SO2 removal ability, whereas Mn2O3 formed in the catalyst calcined at 500 °C and shows poor activity. After treatment by nitric acid, the Cdbnd O of activated carbon support increases and the crystal size of MnO decreases, resulting in the enhancement of the catalytic activity. During reaction process, manganese oxides are gradually transferred into MnO2. And this change directly results in a decrease of activity. But the SO2 removal rate has been maintained in the range of 30-40%, indicating that MnO2 still has a certain SO2 removal ability.

  15. Immobilisation of homogeneous olefin polymerisation catalysts. Factors influencing activity and stability.

    PubMed

    Severn, John R; Chadwick, John C

    2013-07-01

    The activity and stability of homogeneous olefin polymerisation catalysts, when immobilised on a support, are dependent on both chemical and physical effects. Chemical factors affecting catalyst activity include the ease of formation of the active species, which is strongly dependent on the transition metal. Catalyst productivity is dependent on the balance between activity and stability. Immobilisation can lead to a lower proportion of active species and therefore lower initial polymerisation activity, but nevertheless give higher polymer yields in cases where increased catalyst stability is obtained. Important physical factors are support porosity and the ability of a support to undergo progressive fragmentation during polymerisation, facilitating monomer diffusion through the growing catalyst/polymer particle. This article illustrates the importance of these factors in olefin polymerisation with both early- and late-transition metal catalysts, with particular reference to the use of silica and magnesium chloride supports as well as to effects of immobilisation on polymer structure and properties. PMID:23467461

  16. Progress in Synthesis of Highly Active and Stable Nickel-Based Catalysts for Carbon Dioxide Reforming of Methane.

    PubMed

    Kawi, Sibudjing; Kathiraser, Yasotha; Ni, Jun; Oemar, Usman; Li, Ziwei; Saw, Eng Toon

    2015-11-01

    In recent decades, rising anthropogenic greenhouse gas emissions (mainly CO2 and CH4 ) have increased alarm due to escalating effects of global warming. The dry carbon dioxide reforming of methane (DRM) reaction is a sustainable way to utilize these notorious greenhouse gases. This paper presents a review of recent progress in the development of nickel-based catalysts for the DRM reaction. The enviable low cost and wide availability of nickel compared with noble metals is the main reason for persistent research efforts in optimizing the synthesis of nickel-based catalysts. Important catalyst features for the rational design of a coke-resistant nickel-based nanocatalyst for the DRM reaction are also discussed. In addition, several innovative developments based on salient features for the stabilization of nickel nanocatalysts through various means (which include functionalization with precursors, synthesis by plasma treatment, stabilization/confinement on mesoporous/microporous/carbon supports, and the formation of metal oxides) are highlighted. The final part of this review covers major issues and proposed improvement strategies pertaining to the rational design of nickel-based catalysts with high activity and stability for the DRM reaction.

  17. Progress in Synthesis of Highly Active and Stable Nickel-Based Catalysts for Carbon Dioxide Reforming of Methane.

    PubMed

    Kawi, Sibudjing; Kathiraser, Yasotha; Ni, Jun; Oemar, Usman; Li, Ziwei; Saw, Eng Toon

    2015-11-01

    In recent decades, rising anthropogenic greenhouse gas emissions (mainly CO2 and CH4 ) have increased alarm due to escalating effects of global warming. The dry carbon dioxide reforming of methane (DRM) reaction is a sustainable way to utilize these notorious greenhouse gases. This paper presents a review of recent progress in the development of nickel-based catalysts for the DRM reaction. The enviable low cost and wide availability of nickel compared with noble metals is the main reason for persistent research efforts in optimizing the synthesis of nickel-based catalysts. Important catalyst features for the rational design of a coke-resistant nickel-based nanocatalyst for the DRM reaction are also discussed. In addition, several innovative developments based on salient features for the stabilization of nickel nanocatalysts through various means (which include functionalization with precursors, synthesis by plasma treatment, stabilization/confinement on mesoporous/microporous/carbon supports, and the formation of metal oxides) are highlighted. The final part of this review covers major issues and proposed improvement strategies pertaining to the rational design of nickel-based catalysts with high activity and stability for the DRM reaction. PMID:26440576

  18. Development of a simple method for the preparation of novel egg-shell type Pt catalysts using hollow silica nanostructures as supporting precursors

    SciTech Connect

    Wang Jiexin; Chen Jianfeng

    2008-04-01

    A simple method for the preparation of novel egg-shell type platinum catalysts was developed and achieved by utilizing unique hollow silica nanostructures, i.e., hollow silica nanospheres and nanotubes, as supports. The observation by transmission electron microscopy indicated that the well-dispersed hollow silica supported Pt catalysts with a Pt particle diameter of 8-14 nm can be successfully prepared by wet impregnation process and heat treatment. The Pt-loaded hollow silica nanostructures were also characterized by inductively coupled plasma, X-ray diffraction, specific surface area, Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy and energy dispersive spectroscopy. It was thus demonstrated that a higher Pt loading amount (0.392%) could be obtained under the same conditions except the addition of ammonia, which was found to be more effective than that (0.061%) with the addition of HCl in the immobilization of Pt. In addition, the effect of soaking time, Pt precursor concentration and calcination temperature on the loading of Pt in hollow silica nanostructures were investigated as well.

  19. The structure and activity of titania supported cobalt catalysts

    SciTech Connect

    Ho Suiwen; Houalla, M.; Hercules, D.M. ); Cruz, J.M. )

    1992-05-01

    A series of titania supported cobalt catalysts (0.5-6%) were prepared by incipient wetness impregnation, and were characterized by ESCA, XRD, and hydrogen chemisorption. After calcination at 400 C, a surface CoTiO[sub 3]-like phase was the main species present in the 0.5 and 1% cobalt catalysts. For higher cobalt loadings, discrete Co[sub 3]O[sub 4] particles were formed in addition to surface CoTiO[sub 3]. ESCA indicates that after reduction the cobalt metal particle size (6-13 nm) increases with increasing cobalt loadings, but does not vary with reduction temperature (400-500 C). Hydrogen chemisorption was found to be activated and suppressed. The extent of hydrogen chemisorption suppression increases with increasing reduction temperature and decreasing cobalt particle size. The turnover frequency (based on cobalt dispersion derived from ESCA) for benzene and CO hydrogenation decreases with increasing reduction temperature and decreasing cobalt particle size. The decline in activity correlates with the extent of suppression of H[sub 2] chemisorption. The results were interpreted in terms of a decrease in the fraction of exposed surface cobalt due to site blocking by reduced TiO[sub 3] moieties.

  20. Exploring Pd adsorption, diffusion, permeation, and nucleation on bilayer SiO2/Ru as a function of hydroxylation and precursor environment: From UHV to catalyst preparation

    NASA Astrophysics Data System (ADS)

    Pomp, Sascha; Kaden, William E.; Sterrer, Martin; Freund, Hans-Joachim

    2016-10-01

    The hydroxylation-dependent permeability of bilayer SiO2 supported on Ru(0001) was investigated by XPS and TDS studies in a temperature range of 100 K to 600 K. For this, the thermal behavior of Pd evaporated at 100 K, which results in surface and sub-surface (Ru-supported) binding arrangements, was examined relative to the extent of pre-hydroxylation. Samples containing only defect-mediated hydroxyls showed no effect on Pd diffusion through the film at low temperature. If, instead, the concentration of strongly bound hydroxyl groups and associated weakly bound water molecules was enriched by an electron-assisted hydroxylation procedure, the probability for Pd diffusion through the film is decreased via a pore-blocking mechanism. Above room temperature, all samples showed similar behavior, reflective of particle nucleation above the film and eventual agglomeration with any metal atoms initially binding beneath the film. When depositing Pd onto the same SiO2/Ru model support via adsorption of [Pd(NH3)4]Cl2 from alkaline (pH 12) precursor solution, we observe notably different adsorption and nucleation mechanisms. The resultant Pd adsorption complexes follow established decomposition pathways to produce model catalyst systems compatible with those created exclusively within UHV despite lacking the ability to penetrate the film due to the increased size of the initial Pd precursor groups.

  1. Highly durable and active non-precious air cathode catalyst for zinc air battery

    NASA Astrophysics Data System (ADS)

    Chen, Zhu; Choi, Ja-Yeon; Wang, Haijiang; Li, Hui; Chen, Zhongwei

    The electrochemical stability of non-precious FeCo-EDA and commercial Pt/C cathode catalysts for zinc air battery have been compared using accelerated degradation test (ADT) in alkaline condition. Outstanding oxygen reduction reaction (ORR) stability of the FeCo-EDA catalyst was observed compared with the commercial Pt/C catalyst. The FeCo-EDA catalyst retained 80% of the initial mass activity for ORR whereas the commercial Pt/C catalyst retained only 32% of the initial mass activity after ADT. Additionally, the FeCo-EDA catalyst exhibited a nearly three times higher mass activity compared to that of the commercial Pt/C catalyst after ADT. Furthermore, single cell test of the FeCo-EDA and Pt/C catalysts was performed where both catalysts exhibited pseudolinear behaviour in the 12-500 mA cm -2 range. In addition, 67% higher peak power density was observed from the FeCo-EDA catalyst compared with commercial Pt/C. Based on the half cell and single cell tests the non-precious FeCo-EDA catalyst is a very promising ORR electrocatalyst for zinc air battery.

  2. Novel, high-activity hydroprocessing catalysts: Iron group phosphides

    NASA Astrophysics Data System (ADS)

    Wang, Xianqin

    A series of iron, cobalt and nickel transition metal phosphides was synthesized by means of temperature-programmed reduction (TPR) of the corresponding phosphates. The same materials, Fe2P, CoP and NO, were also prepared on a silica (SiO2) support. The phase purity of these catalysts was established by x-ray diffraction (XRD), and the surface properties were determined by N2 BET specific surface area (Sg) measurements and CO chemisorption. The activities of the silica-supported catalysts were tested in a three-phase trickle bed reactor for the simultaneous hydrodenitrogenation (HDN) of quinoline and hydrodesulfurization (HDS) of dibenzothiophene using a model liquid feed at realistic conditions (30 atm, 370°C). The reactivity studies showed that the nickel phosphide (Ni2P/SiO2) was the most active of the catalysts. Compared with a commercial Ni-Mo-S/gamma-Al 2O3 catalyst at the same conditions, Ni2P/silica had a substantially higher HDS activity (100% vs. 76%) and HDN activity (82% vs. 38%). Because of their good hydrotreating activity, an extensive study of the preparation of silica supported nickel phosphides, Ni2P/SiO 2, was carried out. The parameters investigated were the phosphorus content and the weight loading of the active phase. The most active composition was found to have a starting synthesis Ni/P ratio close to 1/2, and the best loading of this sample on silica was observed to be 18 wt.%. Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES) measurements were employed to determine the structures of the supported samples. The main phase before and after reaction was found to be Ni2P, but some sulfur was found to be retained after reaction. A comprehensive scrutiny of the HDN reaction mechanism was also made over the Ni2P/SiO2 sample (Ni/P = 1/2) by comparing the HDN activity of a series of piperidine derivatives of different structure. It was found that piperidine adsorption involved an alpha-H activation

  3. Correlations between mass activity and physicochemical properties of Fe/N/C catalysts for the ORR in PEM fuel cell via 57Fe Mössbauer spectroscopy and other techniques.

    PubMed

    Kramm, Ulrike I; Lefèvre, Michel; Larouche, Nicholas; Schmeisser, Dieter; Dodelet, Jean-Pol

    2014-01-22

    The aim of this work is to clarify the origin of the enhanced PEM-FC performance of catalysts prepared by the procedures described in Science 2009, 324, 71 and Nat. Commun. 2011, 2, 416. Catalysts were characterized after a first heat treatment in argon at 1050 °C (Ar) and a second heat treatment in ammonia at 950 °C (Ar + NH3). For the NC catalysts a variation of the nitrogen precursor was also implemented. (57)Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy, neutron activation analysis, and N2 sorption measurements were used to characterize all catalysts. The results were correlated to the mass activity of these catalysts measured at 0.8 V in H2/O2 PEM-FC. It was found that all catalysts contain the same FeN4-like species already found in INRS Standard (Phys. Chem. Chem. Phys. 2012, 14, 11673). Among all FeN4-like species, only D1 sites, assigned to FeN4/C, and D3, assigned to N-FeN2+2 /C sites, were active for the oxygen reduction reaction (ORR). The difference between INRS Standard and the new catalysts is simply that there are many more D1 and D3 sites available in the new catalysts. All (Ar + NH3)-type catalysts have a much larger porosity than Ar-type catalysts, while the maximum number of their active sites is only slightly larger after a second heat treatment in NH3. The large difference in activity between the Ar-type catalysts and the Ar + NH3 ones stems from the availability of the sites to perform ORR, as many sites of the Ar-type catalysts are secluded in the material, while they are available at the surface of the Ar + NH3-type catalysts.

  4. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction

    SciTech Connect

    Song, Chunshan; Schobert, H.H.

    1993-02-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on the development of novel bimetallic dispersed catalysts for temperature-programmed liquefaction. The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular that can be used in low precursors concentrations (< 1 %) but exhibit high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. The major technical approaches are, first, to prepare the desired heteronuclear organometallic molecules as catalyst precursors that contain covalently bound, two different metal atoms and sulfur in a single molecule. Such precursors will generate finely dispersed bimetallic catalysts such as Fe-Mo, Co-Mo and Ni-Mo binary sulfides upon thermal decomposition. The second major technical approach is to perform the liquefaction of coals unpregnated with the organometallic precursors under temperature-programmed conditions, where the programmed heat-up serves as a step for both catalyst activation and coal pretreatment or preconversion. Two to three different complexes for each of the Fe-Mo, Co-Mo, and Ni-Mo combinations will be prepared. Initial catalyst screening tests will be conducted using a subbituminous coal and a bituminous coal. Effects of coal rank and solvents will be examined with the selected bimetallic catalysts which showed much higher activity than the dispersed catalysts from conventional precursors.

  5. Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: Structure-Activity Relationships.

    PubMed

    Bernicke, Michael; Ortel, Erik; Reier, Tobias; Bergmann, Arno; Ferreira de Araujo, Jorge; Strasser, Peter; Kraehnert, Ralph

    2015-06-01

    Iridium oxide is the catalytic material with the highest stability in the oxygen evolution reaction (OER) performed under acidic conditions. However, its high cost and limited availability demand that IrO2 is utilized as efficiently as possible. We report the synthesis and OER performance of highly active mesoporous IrO2 catalysts with optimized surface area, intrinsic activity, and pore accessibility. Catalytic layers with controlled pore size were obtained by soft-templating with micelles formed from amphiphilic block copolymers poly(ethylene oxide)-b-poly(butadiene)-b-poly(ethylene oxide). A systematic study on the influence of the calcination temperature and film thickness on the morphology, phase composition, accessible surface area, and OER activity reveals that the catalytic performance is controlled by at least two independent factors, that is, accessible surface area and intrinsic activity per accessible site. Catalysts with lower crystallinity show higher intrinsic activity. The catalyst surface area increases linearly with film thickness. As a result of the templated mesopores, the pore surface remains fully active and accessible even for thick IrO2 films. Even the most active multilayer catalyst does not show signs of transport limitations at current densities as high as 75 mA cm(-2) . PMID:25958795

  6. Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: Structure-Activity Relationships.

    PubMed

    Bernicke, Michael; Ortel, Erik; Reier, Tobias; Bergmann, Arno; Ferreira de Araujo, Jorge; Strasser, Peter; Kraehnert, Ralph

    2015-06-01

    Iridium oxide is the catalytic material with the highest stability in the oxygen evolution reaction (OER) performed under acidic conditions. However, its high cost and limited availability demand that IrO2 is utilized as efficiently as possible. We report the synthesis and OER performance of highly active mesoporous IrO2 catalysts with optimized surface area, intrinsic activity, and pore accessibility. Catalytic layers with controlled pore size were obtained by soft-templating with micelles formed from amphiphilic block copolymers poly(ethylene oxide)-b-poly(butadiene)-b-poly(ethylene oxide). A systematic study on the influence of the calcination temperature and film thickness on the morphology, phase composition, accessible surface area, and OER activity reveals that the catalytic performance is controlled by at least two independent factors, that is, accessible surface area and intrinsic activity per accessible site. Catalysts with lower crystallinity show higher intrinsic activity. The catalyst surface area increases linearly with film thickness. As a result of the templated mesopores, the pore surface remains fully active and accessible even for thick IrO2 films. Even the most active multilayer catalyst does not show signs of transport limitations at current densities as high as 75 mA cm(-2) .

  7. Effect of Pd precursor status on sonochemical surface activation in Cu electroless deposition

    NASA Astrophysics Data System (ADS)

    Kim, Kanghoon; Jin, Seonok; Kwon, Oh Joong

    2016-02-01

    Pd surface activation via a sonochemical approach was studied by varying Pd precursor status in the aqueous solution. By aging a K2PdCl6 activation solution overnight with added NH4OH, the chlorinated Pd complex was changed to an ammonia-based Pd complex. The Pd surface activation carried out with the NH4OH complexing agent resulted in improved surface condition following Cu electroless deposition. The Cu thin film deposited on a substrate sonochemically activated with the aged, ammonia-based Pd complex showed improved surface roughness and resistivity compared to that for Cu films deposited via two other precursors (chlorinated Pd complex and ammonia-based complex) without aging. In addition, nitrogen purging during sonochemical activation improved Cu film quality.

  8. Colloidal nickel/gallium nanoalloys obtained from organometallic precursors in conventional organic solvents and in ionic liquids: noble-metal-free alkyne semihydrogenation catalysts

    NASA Astrophysics Data System (ADS)

    Schütte, Kai; Doddi, Adinarayana; Kroll, Clarissa; Meyer, Hajo; Wiktor, Christian; Gemel, Christian; van Tendeloo, Gustaaf; Fischer, Roland A.; Janiak, Christoph

    2014-04-01

    Efforts to replace noble-metal catalysts by low-cost alternatives are of constant interest. The organometallic, non-aqueous wet-chemical synthesis of various hitherto unknown nanocrystalline Ni/Ga intermetallic materials and the use of NiGa for the selective semihydrogenation of alkynes to alkenes are reported. Thermal co-hydrogenolysis of the all-hydrocarbon precursors [Ni(COD)2] (COD = 1,5-cyclooctadiene) and GaCp* (Cp* = pentamethylcyclopentadienyl) in high-boiling organic solvents mesitylene and n-decane in molar ratios of 1 : 1, 2 : 3 and 3 : 1 yields the nano-crystalline powder materials of the over-all compositions NiGa, Ni2Ga3 and Ni3Ga, respectively. Microwave induced co-pyrolysis of the same precursors without additional hydrogen in the ionic liquid [BMIm][BF4] (BMIm = 1-butyl-3-methyl-imidazolium) selectively yields the intermetallic phases NiGa and Ni3Ga from the respective 1 : 1 and 3 : 1 molar ratios of the precursors. The obtained materials are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), IR, powder X-ray diffraction (PXRD) and atomic absorption spectroscopy (AAS). The single-source precursor [Ni(GaCp*)(PMe3)3] with a fixed Ni : Ga stoichiometry of 1 : 1 was employed as well. In comparison with the co-hydrogenolytic dual precursor source approach it turned out to be less practical due to inefficient nickel incorporation caused by the parasitic formation of stable [Ni(PMe3)4]. The use of ionic liquid [BMIm][BF4] as a non-conventional solvent to control the reaction and stabilize the nanoparticles proved to be particularly advantageous and stable colloids of the nanoalloys NiGa and Ni3Ga were obtained. A phase-selective Ni/Ga colloid synthesis in conventional solvents and in the presence of surfactants such as hexadecylamine (HDA) was not feasible due to the undesired reactivity of HDA with GaCp* leading to inefficient gallium incorporation. Recyclable NiGa nanoparticles selectively

  9. Insights into properties of activated carbons prepared from different raw precursors by pyrophosphoric acid activation.

    PubMed

    Gao, Yuan; Yue, Qinyan; Gao, Baoyu

    2016-03-01

    Low-cost activated carbons (ACs) were prepared from four kinds of solid wastes: petroleum coke, Enteromorpha prolifera, lignin from papermaking black liquid and hair, by pyrophosphoric acid (H4P2O7) activation. Thermo-gravimetric analysis of the pyrolysis of H4P2O7-precursor mixtures implied that H4P2O7 had different influences on the pyrolysis behavior of the four raw materials. N2 adsorption/desorption isotherms, scanning electron microscopy, Fourier transform infrared spectroscopy and adsorption capacities for dyes were used to characterize the prepared activated carbons. AC derived from E. prolifera exhibited the highest surface area (1094m(2)/g) and maximum monolayer adsorption capacity for malachite green (1250mg/g). Kinetic studies showed that the experimental data were in agreement with the pseudo-second-order model. The adsorption isotherms were well described by the Langmuir isotherm model, indicating the adsorption of dye onto the ACs proceeded by monolayers. PMID:26969070

  10. Biphasic catalysis using amphiphilic polyphenols-chelated noble metals as highly active and selective catalysts

    PubMed Central

    Mao, Hui; Yu, Hong; Chen, Jing; Liao, Xuepin

    2013-01-01

    In the field of catalysis, it is highly desired to develop novel catalysts that combine the advantages of both homogeneous and heterogeneous catalysts. Here we disclose that the use of plant pholyphenol as amphiphilic large molecule ligand/stabilizer allows for the preparation of noble metal complex and noble metal nanoparticle catalysts. These catalysts are found to be highly selective and active in aqueous-organic biphasic catalysis of cinnamaldehyde and quinoline, and can be reused at least 3 times without significant loss of activity. Moreover, the catalytic activity and reusability of the catalysts can be rationally controlled by simply adjusting the content of polyphenols in the catalysts. Our strategy may be extended to design a wide range of aqueous-organic biphasic catalysis system. PMID:23863916

  11. Adsorption of N-nitrosodimethylamine precursors by powdered and granular activated carbon.

    PubMed

    Hanigan, David; Zhang, Jinwei; Herckes, Pierre; Krasner, Stuart W; Chen, Chao; Westerhoff, Paul

    2012-11-20

    Activated carbon (AC) has been shown to remove precursors of halogenated disinfection byproducts. Granular and powdered activated carbon (GAC, PAC) were investigated for their potential to adsorb N-nitrosodimethylamine (NDMA) precursors from blends of river water and effluent from a wastewater treatment plant (WWTP). At bench scale, waters were exposed to lignite or bituminous AC, either as PAC in bottle point experiments or as GAC in rapid small-scale column tests (RSSCTs). NDMA formation potential (FP) was used as a surrogate for precursor removal. NDMA FP was reduced by 37, 59, and 91% with 3, 8, and 75 mg/L of one PAC, respectively, with a 4-h contact time. In RSSCTs and in full-scale GAC contactors, NDMA FP removal always exceeded that of the bulk dissolved organic carbon (DOC) and UV absorbance at 254 nm. For example, whereas DOC breakthrough exceeded 90% of its influent concentration after 10,000 bed volumes of operation in an RSSCT, NDMA FP was less than 40% of influent concentration after the same bed life of the GAC. At full or pilot scale, high NDMA FP reduction ranging from >60 to >90% was achieved across GAC contactors, dependent upon the GAC bed life and/or use of a preoxidant (chlorine or ozone). In all experiments, NDMA formation was not reduced to zero, which suggests that although some precursors are strongly sorbed, others are not. This is among the first studies to show that AC is capable of adsorbing NDMA precursors, but further research is needed to better understand NDMA precursor chemical properties (e.g., hydrophobicity, molecular size) and evaluate how best to incorporate this finding into full-scale designs and practice.

  12. Adsorption of N-nitrosodimethylamine precursors by powdered and granular activated carbon.

    PubMed

    Hanigan, David; Zhang, Jinwei; Herckes, Pierre; Krasner, Stuart W; Chen, Chao; Westerhoff, Paul

    2012-11-20

    Activated carbon (AC) has been shown to remove precursors of halogenated disinfection byproducts. Granular and powdered activated carbon (GAC, PAC) were investigated for their potential to adsorb N-nitrosodimethylamine (NDMA) precursors from blends of river water and effluent from a wastewater treatment plant (WWTP). At bench scale, waters were exposed to lignite or bituminous AC, either as PAC in bottle point experiments or as GAC in rapid small-scale column tests (RSSCTs). NDMA formation potential (FP) was used as a surrogate for precursor removal. NDMA FP was reduced by 37, 59, and 91% with 3, 8, and 75 mg/L of one PAC, respectively, with a 4-h contact time. In RSSCTs and in full-scale GAC contactors, NDMA FP removal always exceeded that of the bulk dissolved organic carbon (DOC) and UV absorbance at 254 nm. For example, whereas DOC breakthrough exceeded 90% of its influent concentration after 10,000 bed volumes of operation in an RSSCT, NDMA FP was less than 40% of influent concentration after the same bed life of the GAC. At full or pilot scale, high NDMA FP reduction ranging from >60 to >90% was achieved across GAC contactors, dependent upon the GAC bed life and/or use of a preoxidant (chlorine or ozone). In all experiments, NDMA formation was not reduced to zero, which suggests that although some precursors are strongly sorbed, others are not. This is among the first studies to show that AC is capable of adsorbing NDMA precursors, but further research is needed to better understand NDMA precursor chemical properties (e.g., hydrophobicity, molecular size) and evaluate how best to incorporate this finding into full-scale designs and practice. PMID:23106335

  13. Patched bimetallic surfaces are active catalysts for ammonia decomposition

    DOE PAGES

    Guo, Wei; Vlachos, Dionisios G.

    2015-10-07

    In this study, ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material’s structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-Hmore » bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.« less

  14. Regioselective chromatic orthogonality with light-activated metathesis catalysts.

    PubMed

    Levin, Efrat; Mavila, Sudheendran; Eivgi, Or; Tzur, Eyal; Lemcoff, N Gabriel

    2015-10-12

    The ability to selectively guide consecutive chemical processes towards a preferred pathway by using light of different frequencies is an appealing concept. Herein we describe the coupling of two photochemical reactions, one the photoisomerization and consequent activation of a sulfur-chelated latent olefin-metathesis catalyst at 350 nm, and the other the photocleavage of a silyl protecting group at 254 nm. Depending on the steric stress exerted by a photoremovable neighboring chemical substituent, we demonstrate the selective formation of either five- or six-membered-ring frameworks by light-triggered ring-closing metathesis. The orthogonality of these light-induced reactions allows the initiation of these processes independently and in interchangeable order, according to the wavelength of light used to promote them.

  15. High catalytic activity and pollutants resistivity using Fe-AAPyr cathode catalyst for microbial fuel cell application

    PubMed Central

    Santoro, Carlo; Serov, Alexey; Villarrubia, Claudia W. Narvaez; Stariha, Sarah; Babanova, Sofia; Artyushkova, Kateryna; Schuler, Andrew J.; Atanassov, Plamen

    2015-01-01

    For the first time, a new generation of innovative non-platinum group metal catalysts based on iron and aminoantipyrine as precursor (Fe-AAPyr) has been utilized in a membraneless single-chamber microbial fuel cell (SCMFC) running on wastewater. Fe-AAPyr was used as an oxygen reduction catalyst in a passive gas-diffusion cathode and implemented in SCMFC design. This catalyst demonstrated better performance than platinum (Pt) during screening in “clean” conditions (PBS), and no degradation in performance during the operation in wastewater. The maximum power density generated by the SCMFC with Fe-AAPyr was 167 ± 6 μW cm−2 and remained stable over 16 days, while SCMFC with Pt decreased to 113 ± 4 μW cm−2 by day 13, achieving similar values of an activated carbon based cathode. The presence of S2− and showed insignificant decrease of ORR activity for the Fe-AAPyr. The reported results clearly demonstrate that Fe-AAPyr can be utilized in MFCs under the harsh conditions of wastewater. PMID:26563922

  16. Highly active copper-network catalyst for the direct aldol reaction.

    PubMed

    Ohta, Hidetoshi; Uozumi, Yasuhiro; Yamada, Yoichi M A

    2011-09-01

    The development of a highly active solid-phase catechol-copper network catalyst for direct aldol reaction is described. The catalyst was prepared from an alkyl-chain-linked bis(catechol) and a copper(II) complex. The direct aldol reaction between carbonyl compounds (aldehydes and ketones) and methyl isocyanoacetate was carried out using 0.1-1 mol% [Cu] catalyst to give the corresponding oxazolines at yields of up to 99% and a trans/cis ratio of >99:1. The catalyst was reused with no loss of catalytic activity. A plausible reaction pathway is also described. PMID:21751405

  17. Fischer-Tropsch activity for non-promoted cobalt-on-alumina catalysts

    DOEpatents

    Singleton, Alan H.; Oukaci, Rachid; Goodwin, James G.

    2001-01-01

    Cobalt catalysts, and processes employing these inventive catalysts, for hydrocarbon synthesis. The inventive catalyst comprises cobalt on an alumina support and is not promoted with any noble or near noble metals. In one aspect of the invention, the alumina support preferably includes a dopant in an amount effective for increasing the activity of the inventive catalyst. The dopant is preferably a titanium dopant. In another aspect of the invention, the cobalt catalyst is preferably reduced in the presence of hydrogen at a water vapor partial pressure effective to increase the activity of the cobalt catalyst for hydrocarbon synthesis. The water vapor partial pressure is preferably in the range of from 0 to about 0.1 atmospheres.

  18. Highly active gold-based catalyst for the reaction of benzaldehyde with ethyl diazoacetate.

    PubMed

    Fructos, Manuel R; Díaz-Requejo, M Mar; Pérez, Pedro J

    2009-09-14

    The gold complex [IPrAu(NCMe)]BF(4) catalyzes the reaction of ethyl diazoacetate with benzaldehyde to give mixtures of ethyl 3-oxo-3-phenylpropanoate and ethyl 3-hydroxy-2-phenylacrylate in the first example of a group 11 metal-based catalyst for this transformation; the catalyst activity is improved by a factor of 2500 compared to those of previously reported iron-based catalysts.

  19. Correlation between Fischer-Tropsch catalytic activity and composition of catalysts

    PubMed Central

    2011-01-01

    This paper presents the synthesis and characterization of monometallic and bimetallic cobalt and iron nanoparticles supported on alumina. The catalysts were prepared by a wet impregnation method. Samples were characterized using temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), CO-chemisorption, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM-EDX) and N2-adsorption analysis. Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed microreactor at 543 K and 1 atm, with H2/CO = 2 v/v and space velocity, SV = 12L/g.h. The physicochemical properties and the FTS activity of the bimetallic catalysts were analyzed and compared with those of monometallic cobalt and iron catalysts at similar operating conditions. H2-TPR analysis of cobalt catalyst indicated three temperature regions at 506°C (low), 650°C (medium) and 731°C (high). The incorporation of iron up to 30% into cobalt catalysts increased the reduction, CO chemisorption and number of cobalt active sites of the catalyst while an opposite trend was observed for the iron-riched bimetallic catalysts. The CO conversion was 6.3% and 4.6%, over the monometallic cobalt and iron catalysts, respectively. Bimetallic catalysts enhanced the CO conversion. Amongst the catalysts studied, bimetallic catalyst with the composition of 70Co30Fe showed the highest CO conversion (8.1%) while exhibiting the same product selectivity as that of monometallic Co catalyst. Monometallic iron catalyst showed the lowest selectivity for C5+ hydrocarbons (1.6%). PMID:22047220

  20. Linking structure to function: The search for active sites in non-platinum group metal oxygen reduction reaction catalysts

    DOE PAGES

    Holby, Edward F.; Zelenay, Piotr

    2016-05-17

    Atomic-scale structures of oxygen reduction reaction (ORR) active sites in non-platinum group metal (non-PGM) catalysts, made from pyrolysis of carbon, nitrogen, and transition-metal (TM) precursors have been the subject of continuing discussion in the fuel cell electrocatalysis research community. We found that quantum chemical modeling is a path forward for understanding of these materials and how they catalyze the ORR. Here, we demonstrate through literature examples of how such modeling can be used to better understand non-PGM ORR active site relative stability and activity and how such efforts can also aid in the interpretation of experimental signatures produced by thesemore » materials.« less

  1. Hydrocarbon synthesis catalyst and method of preparation

    DOEpatents

    Sapienza, Richard S.; Sansone, Michael J.; Slegeir, William A. R.

    1983-08-02

    A catalyst for the synthesis of hydrocarbons from carbon monoxide and hydrogen composed of palladium or platinum and cobalt supported on a solid phase is disclosed. The catalyst is prepared by heating a heterogeneous component of the palladium or platinum deposited on the solid support in a solution of cobalt carbonyl or precursors thereof. The catalyst exhibits excellent activity, stability in air, and produces highly desirable product fractions even with dilute gaseous reactants. The catalyst is preferably used in dilute slurry form, which is desirable from a heat transfer standpoint.

  2. Hydrocarbon synthesis catalyst and method of preparation

    DOEpatents

    Sapienza, R.S.; Sansone, M.J.; Slegeir, W.A.R.

    1983-08-02

    A catalyst for the synthesis of hydrocarbons from carbon monoxide and hydrogen composed of palladium or platinum and cobalt supported on a solid phase is disclosed. The catalyst is prepared by heating a heterogeneous component of the palladium or platinum deposited on the solid support in a solution of cobalt carbonyl or precursors thereof. The catalyst exhibits excellent activity, stability in air, and produces highly desirable product fractions even with dilute gaseous reactants. The catalyst is preferably used in dilute slurry form, which is desirable from a heat transfer standpoint. 9 figs.

  3. Comparison of preparation methods for ceria catalyst and the effect of surface and bulk sulfates on its activity toward NH3-SCR.

    PubMed

    Chang, Huazhen; Ma, Lei; Yang, Shijian; Li, Junhua; Chen, Liang; Wang, Wei; Hao, Jiming

    2013-11-15

    A series of CeO2 catalysts prepared with sulfate (S) and nitrate (N) precursors by hydrothermal (H) and precipitation (P) methods were investigated in selective catalytic reduction of NOx by NH3 (NH3-SCR). The catalytic activity of CeO2 was significantly affected by the preparation methods and the precursor type. CeO2-SH, which was prepared by hydrothermal method with cerium (IV) sulfate as a precursor, showed excellent SCR activity and high N2 selectivity in the temperature range of 230-450 °C. Based on the results obtained by temperature-programmed reduction (H2-TPR), transmission infrared spectra (IR) and thermal gravimetric analysis (TGA), the excellent performance of CeO2-SH was correlated with the surface sulfate species formed in the hydrothermal reaction. These results indicated that sulfate species bind with Ce(4+) on the CeO2-SH catalyst, and the specific sulfate species, such as Ce(SO4)2 or CeOSO4, were formed. The adsorption of NH3 was promoted by these sulfate species, and the probability of immediate oxidation of NH3 to N2O on Ce(4+) was reduced. Accordingly, the selective oxidation of NH3 was enhanced, which contributed to the high N2 selectivity in the SCR reaction. However, the location of sulfate on the CeO2-SP catalyst was different. Plenty of sulfate species were likely deposited on CeO2-SP surface, covering the active sites for NO oxidation, which resulted in poor SCR activity in the test temperature range. Moreover, the resistance to alkali metals, such as Na and K, was improved over the CeO2-SH catalyst.

  4. Removal of N-nitrosodimethylamine precursors with powdered activated carbon adsorption.

    PubMed

    Beita-Sandí, Wilson; Ersan, Mahmut Selim; Uzun, Habibullah; Karanfil, Tanju

    2016-01-01

    The main objective of this study was to examine the roles of powdered activated carbon (PAC) characteristics (i.e., surface chemistry, pore size distribution, and surface area) in the removal of N-nitrosodimethylamine (NDMA) formation potential (FP) in surface and wastewater-impacted waters. Also, the effects of natural attenuation of NDMA precursors in surface waters, NDMA FP concentration, and carbon dose on the removal of NDMA FP by PAC were evaluated. Finally, the removal of NDMA FP by PAC at two full-scale DWTPs was monitored. Wastewater-impacted and surface water samples were collected to conduct adsorption experiments using different PACs and activated carbon fibers (ACFs) with a wide range of physicochemical characteristics. The removal efficiency of NDMA FP by PAC was significantly higher in wastewater-impacted than surface waters. Adsorbable NDMA precursors showed a size distribution in the waters tested; the adsorbable fraction included precursors accessing the pore size regions of 10-20 Å and <10 Å. Basic carbons showed higher removal of NDMA FP than acidic carbons on a surface area basis. The overall removal of NDMA FP by PAC on a mass basis depended on the surface area, pore size distribution and pHPZC. Thus, PACs with hybrid characteristics (micro and mesoporous), higher surface areas, and basic surface chemistry are more likely to be effective for NDMA precursor control by PAC adsorption. The application of PAC in DWTPs for taste and odor control resulted in an additional 20% removal of NDMA FP for the PAC doses of 7-10 mg/L. The natural attenuation of NDMA precursors through a combination of processes (biodegradation, photolysis and adsorption) decreased their adsorbability and removal by PAC adsorption.

  5. Removal of N-nitrosodimethylamine precursors with powdered activated carbon adsorption.

    PubMed

    Beita-Sandí, Wilson; Ersan, Mahmut Selim; Uzun, Habibullah; Karanfil, Tanju

    2016-01-01

    The main objective of this study was to examine the roles of powdered activated carbon (PAC) characteristics (i.e., surface chemistry, pore size distribution, and surface area) in the removal of N-nitrosodimethylamine (NDMA) formation potential (FP) in surface and wastewater-impacted waters. Also, the effects of natural attenuation of NDMA precursors in surface waters, NDMA FP concentration, and carbon dose on the removal of NDMA FP by PAC were evaluated. Finally, the removal of NDMA FP by PAC at two full-scale DWTPs was monitored. Wastewater-impacted and surface water samples were collected to conduct adsorption experiments using different PACs and activated carbon fibers (ACFs) with a wide range of physicochemical characteristics. The removal efficiency of NDMA FP by PAC was significantly higher in wastewater-impacted than surface waters. Adsorbable NDMA precursors showed a size distribution in the waters tested; the adsorbable fraction included precursors accessing the pore size regions of 10-20 Å and <10 Å. Basic carbons showed higher removal of NDMA FP than acidic carbons on a surface area basis. The overall removal of NDMA FP by PAC on a mass basis depended on the surface area, pore size distribution and pHPZC. Thus, PACs with hybrid characteristics (micro and mesoporous), higher surface areas, and basic surface chemistry are more likely to be effective for NDMA precursor control by PAC adsorption. The application of PAC in DWTPs for taste and odor control resulted in an additional 20% removal of NDMA FP for the PAC doses of 7-10 mg/L. The natural attenuation of NDMA precursors through a combination of processes (biodegradation, photolysis and adsorption) decreased their adsorbability and removal by PAC adsorption. PMID:26584342

  6. Neuronal precursor-specific activity of a human doublecortin regulatory sequence.

    PubMed

    Karl, Claudia; Couillard-Despres, Sebastien; Prang, Peter; Munding, Matthias; Kilb, Werner; Brigadski, Tanja; Plötz, Sonja; Mages, Wolfgang; Luhmann, Heiko; Winkler, Jürgen; Bogdahn, Ulrich; Aigner, Ludwig

    2005-01-01

    The doublecortin (DCX) gene encodes a 40-kDa microtubule-associated protein specifically expressed in neuronal precursors of the developing and adult CNS. Due to its specific expression pattern, attention was drawn to DCX as a marker for neuronal precursors and neurogenesis, thereby underscoring the importance of its promoter identification and promoter analysis. Here, we analysed the human DCX regulatory sequence and confined it to a 3.5-kb fragment upstream of the ATG start codon. We demonstrate by transient transfection experiments that this fragment is sufficient and specific to drive expression of reporter genes in embryonic and adult neuronal precursors. The activity of this regulatory fragment overlapped with the expression of endogenous DCX and with the young neuronal markers class III beta-tubulin isotype and microtubule-associated protein Map2ab but not with glial or oligodendroglial markers. Electrophysiological data further confirmed the immature neuronal nature of these cells. Deletions within the 3.5-kb region demonstrated the relevance of specific regions containing transcription factor-binding sites. Moreover, application of neurogenesis-related growth factors in the neuronal precursor cultures suggested the lack of direct signalling of these factors on the DCX promoter construct. PMID:15663475

  7. Investigation of photocalalytic activity of ZnO prepared by spray pyrolis with various precursors

    NASA Astrophysics Data System (ADS)

    Bourfaa, F.; Lamri Zeggar, M.; A, A.; Aida, M. S.; Attaf, N.

    2016-03-01

    Semiconductor photocatalysts such as ZnO has attracted much attention in recent years due to their various applications for the degradation of organic pollutants in water, air and in dye sensitized photovoltaic solar cell. In the present work, ZnO thin films were prepared by ultrasonic spray pyrolysis by using different precursors namely: acetate, chloride and zinc nitrate in order to investigate their influence on ZnO photocatalytic activity. The films crystalline structure was studied by mean of X- ray diffraction measurements (XRD) and the films surface morphology by Scanning Electron Microscopy (SEM). The films optical properties were studied by mean of UV-visible spectroscopy. The prepared films were tested for the degradation of the red reactive dye largely used in textile industry. As a result, we found that the zinc nitrate is the best precursor to prepare ZnO thin films suitable for a good photocatalytic activity.

  8. Aged nano-structured platinum based catalyst: effect of chemical treatment on adsorption and catalytic activity.

    PubMed

    Shim, Wang Geun; Nahm, Seung Won; Park, Hyuk Ryeol; Yun, Hyung Sun; Seo, Seong Gyu; Kim, Sang Chai

    2011-02-01

    To examine the effect of chemical treatment on the adsorption and catalytic activity of nanostructured platinum based catalyst, the aged commercial Pt/AC catalyst was pretreated with sulfuric acid (H2SO4) and a cleaning agent (Hexane). Several reliable methods such as nitrogen adsorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and inductively coupled plasma (ICP) were employed to characterize the aged Pt/AC catalyst and its chemically pretreated Pt/AC catalysts. The catalytic and adsorption activities of nano-structured heterogeneous Pt/AC catalyst were investigated on the basis of toluene oxidation and adsorption isotherm data. In addition, the adsorption isotherms of toluene were used to calculate the adsorption energy distribution functions for the parent catalyst and its pre-treated nano-structured Pt/AC catalysts. It was found that sulfuric acid aqueous treatment can enhance the catalytic performance of aged Pt/AC catalyst toward catalytic oxidation of toluene. It was also shown that a comparative analysis of the energy distribution functions for nano-structured Pt/AC catalysts as well as the pore size distribution provides valuable information about their structural and energetic heterogeneity.

  9. Serum of patients with active rheumatoid arthritis inhibits differentiation of osteochondrogenic precursor cells.

    PubMed

    Pathak, Janak L; Verschueren, Patrick; Lems, Willem F; Bravenboer, Nathalie; Klein-Nulend, Jenneke; Bakker, Astrid D; Luyten, Frank P

    2016-05-01

    Delayed fracture healing is frequently experienced in patients with systemic inflammation such as during rheumatoid arthritis (RA). The reasons for this are diverse, but could also be caused by inflammatory cytokines and/or growth factors in serum from patients with active disease. We hypothesized that serum from patients with active RA contains circulating inflammatory factors that inhibit differentiation of osteochondrogenic precursors. Serum was obtained from 15 patients with active RA (active RA-sera) and from the same patients in clinical remission 1 year later (remission RA-sera; controls). The effect of active RA-sera on osteochondrogenic differentiation of chondrogenic ATDC5 cells and primary human periosteum-derived progenitor cells (HPDC) was determined in micromass culture. In ATDC5 cells, active RA-sera reduced Ki67 transcription levels by 40% and cartilage matrix accumulation by 14% at day 14, and Alp transcription levels by 16%, and matrix mineralization by 17% at day 21 compared with remission RA-sera. In HPDCs, active RA-sera inhibited metabolic activity by 8%, SOX9 transcription levels by 14%, and cartilage matrix accumulation by 7% at day 7 compared with remission RA-sera. In conclusion, sera from patients with active RA negatively affect differentiation of osteochondrogenic precursors, and as a consequence may contribute to delayed fracture healing in these patients.

  10. Linking morphology with activity through the lifetime of pretreated PtNi nanostructured thin film catalysts

    DOE PAGES

    Cullen, David A.; Lopez-Haro, Miguel; Bayle-Guillemaud, Pascale; Debe, Mark; Steinbach, Andrew J.; Guetaz, L.

    2015-04-10

    In this study, the nanoscale morphology of highly active Pt3Ni7 nanostructured thin film fuel cell catalysts is linked with catalyst surface area and activity following catalyst pretreatments, conditioning and potential cycling. The significant role of fuel cell conditioning on the structure and composition of these extended surface catalysts is demonstrated by high resolution imaging, elemental mapping and tomography. The dissolution of Ni during fuel cell conditioning leads to highly complex, porous structures which were visualized in 3D by electron tomography. Quantification of the rendered surfaces following catalyst pretreatment, conditioning, and cycling shows the important role pore structure plays in surfacemore » area, activity, and durability.« less

  11. Linking morphology with activity through the lifetime of pretreated PtNi nanostructured thin film catalysts

    SciTech Connect

    Cullen, David A.; Lopez-Haro, Miguel; Bayle-Guillemaud, Pascale; Debe, Mark; Steinbach, Andrew J.; Guetaz, L.

    2015-04-10

    In this study, the nanoscale morphology of highly active Pt3Ni7 nanostructured thin film fuel cell catalysts is linked with catalyst surface area and activity following catalyst pretreatments, conditioning and potential cycling. The significant role of fuel cell conditioning on the structure and composition of these extended surface catalysts is demonstrated by high resolution imaging, elemental mapping and tomography. The dissolution of Ni during fuel cell conditioning leads to highly complex, porous structures which were visualized in 3D by electron tomography. Quantification of the rendered surfaces following catalyst pretreatment, conditioning, and cycling shows the important role pore structure plays in surface area, activity, and durability.

  12. Combinatorial Optimization of Heterogeneous Catalysts Used in the Growth of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Cassell, Alan M.; Verma, Sunita; Delzeit, Lance; Meyyappan, M.; Han, Jie

    2000-01-01

    Libraries of liquid-phase catalyst precursor solutions were printed onto iridium-coated silicon substrates and evaluated for their effectiveness in catalyzing the growth of multi-walled carbon nanotubes (MWNTs) by chemical vapor deposition (CVD). The catalyst precursor solutions were composed of inorganic salts and a removable tri-block copolymer (EO)20(PO)70(EO)20 (EO = ethylene oxide, PO = propylene oxide) structure-directing agent (SDA), dissolved in ethanol/methanol mixtures. Sample libraries were quickly assayed using scanning electron microscopy after CVD growth to identify active catalysts and CVD conditions. Composition libraries and focus libraries were then constructed around the active spots identified in the discovery libraries to understand how catalyst precursor composition affects the yield, density, and quality of the nanotubes. Successful implementation of combinatorial optimization methods in the development of highly active, carbon nanotube catalysts is demonstrated, as well as the identification of catalyst formulations that lead to varying densities and shapes of aligned nanotube towers.

  13. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction

    SciTech Connect

    Chunshan, Song; Kirby, S.; Schmidt, E.

    1995-12-31

    The objective of this project is to explore bimetallic dispersed catalysts for more efficient coal liquefaction. Coal liquefaction involves cleavage of methylene, dimethylene and ether bridges connecting various aromatic units and the reactions of various oxygen functional groups. This paper describes recent results on (1) hydrodeoxygenation of O-containing polycyclic model compounds using novel organometallic catalyst precursors; and (2) activity and selectivity of dispersed Fe catalysts from organometallic and inorganic precursors for hydrocracking of 4-(1-naphthylmethyl) bibenzyl. The results showed that some iron containing catalysts have higher activity in the sulfur-free form, contrary to conventional wisdom. Adding sulfur to Fe precursors with Cp-ligands decreased the activity of the resulting catalyst. This is in distinct contrast to the cases with iron pentacarbonyl and superfine Fe{sub 2}O{sub 3}, where S addition increased their catalytic activity substantially. A positive correlation between sulfur addition and increased activity can be seen, but a reversed trend between Fe cluster size and hydrocracking conversion could be observed, for carbonyl-type Fe precursors. It is apparent that the activity and selectivity of Fe catalysts for NMBB conversion depends strongly on both the type of ligand environment, the oxidation state and the number of intermetal bonds in the molecular precursor.

  14. Low temperature catalysts for methanol production

    DOEpatents

    Sapienza, R.S.; Slegeir, W.A.; O'Hare, T.E.; Mahajan, D.

    1986-09-30

    A catalyst and process useful at low temperatures (below about 160 C) and preferably in the range 80--120 C used in the production of methanol from carbon monoxide and hydrogen are disclosed. The catalyst is used in slurry form and comprises a complex reducing agent derived from the component structure NaH--RONa-M(OAc)[sub 2] where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1--6 carbon atoms. This catalyst is preferably used alone but is also effective in combination with a metal carbonyl of a group VI (Mo, Cr, W) metal. The preferred catalyst precursor is Nic (where M = Ni and R = tertiary amyl). Mo(CO)[sub 6] is the preferred metal carbonyl if such component is used. The catalyst is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

  15. Active Gold-Ceria and Gold-Ceria/titania Catalysts for CO Oxidation. From Single-Crystal Model Catalysts to Powder Catalysts

    SciTech Connect

    Rodriguez, Jose A.; Si, Rui; Evans, Jaime; Xu, Wenqian; Hanson, Jonathan C.; Tao, Jing; Zhu, Yimei

    2014-07-23

    We studied CO oxidation on model and powder catalysts of Au-CeO2 and Au-CeOx/TiO2. Phenomena observed in Au-CeO2(1 1 1) and Au-CeO2/TiO2(1 1 0) provided useful concepts for designing and preparing highly active and stable Au-CeOx/TiO2 powder catalysts for CO oxidation. Small particles of Au dispersed on CeO2(1 1 1) displayed high catalytic activity, making Au-CeO2(1 1 1) a better CO oxidation catalyst than Au-TiO2(1 1 0) or Au-MgO(1 0 0). An excellent support for gold was found after depositing nanoparticles of ceria on TiO2(1 1 0). The CeOx nanoparticles act as nucleation centers for gold, improving dispersion of the supported metal and helping in the creation of reaction sites efficient for the adsorption of CO and the dissociation of the O2 molecule. High-surface area catalysts were prepared by depositing gold on ceria nanorods and CeOx/TiO2 powders. The samples were tested for the low-temperature (10–70 °C) oxygen-rich (1%CO/4%O2/He) CO oxidation reaction after pre-oxidation (20%O2/He, 300 °C) and pre-reduction (5%H2/He, 300 °C) treatments. Moreover, synchrotron-based operando X-ray diffraction (XRD) and X-ray absorption (XAS) spectroscopy were used to study the Au-CeO2 and Au-CeOx/TiO2 catalysts under reaction conditions. Our operando findings indicate that the most active phase of these catalysts for low-temperature CO oxidation consist of small particles of metallic Au dispersed on CeO2 or CeOx/TiO2.

  16. Anatomical Location of LPA1 Activation and LPA Phospholipid Precursors in Rodent and Human Brain

    PubMed Central

    González de San Román, E; Manuel, I; Giralt, MT; Chun, J; Estivill-Torrús, G; Rodriguez de Fonseca, F; Santín, LJ; Ferrer, I; Rodriguez-Puertas, R

    2016-01-01

    Lysophosphatidic acid (LPA) is a signaling molecule that binds to six known G protein-coupled receptors (GPCRs): LPA1–LPA6. LPA evokes several responses in the CNS including cortical development and folding, growth of the axonal cone and its retraction process. Those cell processes involve survival, migration, adhesion proliferation, differentiation and myelination. The anatomical localization of LPA1 is incompletely understood, particularly with regard to LPA binding. Therefore, we have used functional [35S]GTPγS autoradiography to verify the anatomical distribution of LPA1 binding sites in adult rodent and human brain. The greatest activity was observed in myelinated areas of the white matter such as corpus callosum, internal capsule and cerebellum. MaLPA1-null mice (a variant of LPA1-null) lack [35S]GTPγS basal binding in white matter areas, where the LPA1 receptor is expressed at high levels, suggesting a relevant role of the activity of this receptor in the most myelinated brain areas. In addition, phospholipid precursors of LPA were localized by MALDI-IMS in both rodent and human brain slices identifying numerous species of phosphatides (PA) and phosphatidylcholines (PC). Both PA and PC species represent potential LPA precursors. The anatomical distribution of these precursors in rodent and human brain may indicate a metabolic relationship between LPA and LPA1 receptors. PMID:25857358

  17. Atomic Layer-by-Layer Deposition of Pt on Pd Nanocubes for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction

    SciTech Connect

    Xie, Shuifen; Choi, Sang; Lu, Ning; Roling, Luke T.; Herron, Jeffrey A.; Zhang, Lei; Park, Jinho; Wang, Jinguo; Kim, Moon J.; Xie, Zhaoxiong; Mavrikakis, Manos; Xia, Younan

    2014-06-11

    An effective strategy for reducing the Pt content while retaining the activity of a Pt-based catalyst is to deposit the Pt atoms as ultrathin skins of only a few atomic layers thick on nanoscale substrates made of another metal. During deposition, however, the Pt atoms often take an island growth mode because of a strong bonding between Pt atoms. Here we report a versatile route to the conformal deposition of Pt as uniform, ultrathin shells on Pd nanocubes in a solution phase. The introduction of the Pt precursor at a relatively slow rate and high temperature allowed the deposited Pt atoms to spread across the entire surface of a Pd nanocube to generate a uniform shell. The thickness of the Pt shell could be controlled from one to six atomic layers by varying the amount of Pt precursor added into the system. Compared to a commercial Pt/C catalyst, the Pd@PnL (n = 1-6) core-shell nanocubes showed enhancements in specific activity and durability toward the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations on model (100) surfaces suggest that the enhancement in specific activity can be attributed to the weakening of OH binding through ligand and strain effects, which, in turn, increases the rate of OH hydrogenation. A volcano-type relationship between the ORR specific activity and the number of Pt atomic layers was derived, in good agreement with the experimental results. Both theoretical and experimental studies indicate that the ORR specific activity was maximized for the catalysts based on Pd@Pt2-3L nanocubes. Because of the reduction in Pt content used and the enhancement in specific activity, the Pd@Pt1L nanocubes showed a Pt mass activity with almost three-fold enhancement relative to the Pt/C catalyst.

  18. Electrolyte-dependent electrosynthesis and activity of cobalt-based water oxidation catalysts.

    PubMed

    Surendranath, Yogesh; Dinca, Mircea; Nocera, Daniel G

    2009-02-25

    Electrolysis of Co(2+) in phosphate, methylphosphonate, and borate electrolytes effects the electrodeposition of an amorphous highly active water oxidation catalyst as a thin film on an inert anode. Electrodeposition of a catalytically competent species immediately follows oxidation of Co(2+) to Co(3+) in solution. Methylphosphonate and borate electrolytes support catalyst activity comparable to that observed for phosphate. Catalytic activity for O(2) generation in aqueous solutions containing 0.5 M NaCl is retained for catalysts grown from phosphate electrolyte.

  19. New melanogenesis and photobiological processes in activation and proliferation of precursor melanocytes after UV-exposure: ultrastructural differentiation of precursor melanocytes from Langerhans cells

    SciTech Connect

    Jimbow, K.; Uesugi, T.

    1982-02-01

    Photobiological processes involving new melanogenesis after exposure to ultraviolet (UV) light were experimentally studied in C57 black adult mice by histochemistry, cytochemistry, and autoradiography. The trunk and the plantar region of the foot, where no functioning melanocytes were present before exposure, were exposed to UV-A for 14 consecutive days. Both regions revealed a basically similar pattern for new melanogenesis which involved an activation of precursor melanocytes. Essentially all of ''indeterminate'' cells appeared to be precursor melanocytes, the fine structure of which could be differentiated even from poorly developed Langerhans cells. New melanogenesis was manifested by 4 stages of cellular and subcellular reactions of these cells as indicated by histochemistry of dihydroxyphenylalanine (dopa) and autoradiography of thymidine incorporation: (a) an initial lag in the activation of precursor melanocytes with development of Golgi cisternae and rough endoplasmic reticulum followed by formation of unmelanized melanosomes (day 0 to 2); (b) synthesis of active tyrosinase accumulated in Golgi cisternae and vesicles with subsequent formation of melanized melanosomes in these cells (day 3 to 5); (c) mitotic proliferation of many of these activated cells, followed by an exponential increase of new melanocytes (day 6 to 7); and (d) melanosome transfer with differentiation of 10 nm filaments and arborization of dendrites, but without any significant change in the melanocyte population (day 8 to 14). The melanosome transfer was, however, not obvious until after 7 days of exposure. The size of newly synthesized melanosomes was similar to that of tail skin where native melanocytes were present before exposure.

  20. Anatomical location of LPA1 activation and LPA phospholipid precursors in rodent and human brain.

    PubMed

    González de San Román, Estibaliz; Manuel, Iván; Giralt, María Teresa; Chun, Jerold; Estivill-Torrús, Guillermo; Rodríguez de Fonseca, Fernando; Santín, Luis Javier; Ferrer, Isidro; Rodríguez-Puertas, Rafael

    2015-08-01

    Lysophosphatidic acid (LPA) is a signaling molecule that binds to six known G protein-coupled receptors: LPA1 -LPA6 . LPA evokes several responses in the CNS, including cortical development and folding, growth of the axonal cone and its retraction process. Those cell processes involve survival, migration, adhesion proliferation, differentiation, and myelination. The anatomical localization of LPA1 is incompletely understood, particularly with regard to LPA binding. Therefore, we have used functional [(35) S]GTPγS autoradiography to verify the anatomical distribution of LPA1 binding sites in adult rodent and human brain. The greatest activity was observed in myelinated areas of the white matter such as corpus callosum, internal capsule and cerebellum. MaLPA1 -null mice (a variant of LPA1 -null) lack [(35) S]GTPγS basal binding in white matter areas, where the LPA1 receptor is expressed at high levels, suggesting a relevant role of the activity of this receptor in the most myelinated brain areas. In addition, phospholipid precursors of LPA were localized by MALDI-IMS in both rodent and human brain slices identifying numerous species of phosphatides and phosphatidylcholines. Both phosphatides and phosphatidylcholines species represent potential LPA precursors. The anatomical distribution of these precursors in rodent and human brain may indicate a metabolic relationship between LPA and LPA1 receptors. Lysophosphatidic acid (LPA) is a signaling molecule that binds to six known G protein-coupled receptors (GPCR), LPA1 to LPA6 . LPA evokes several responses in the central nervous system (CNS), including cortical development and folding, growth of the axonal cone and its retraction process. We used functional [(35) S]GTPγS autoradiography to verify the anatomical distribution of LPA1 -binding sites in adult rodent and human brain. The distribution of LPA1 receptors in rat, mouse and human brains show the highest activity in white matter myelinated areas. The basal and

  1. Anatomical location of LPA1 activation and LPA phospholipid precursors in rodent and human brain.

    PubMed

    González de San Román, Estibaliz; Manuel, Iván; Giralt, María Teresa; Chun, Jerold; Estivill-Torrús, Guillermo; Rodríguez de Fonseca, Fernando; Santín, Luis Javier; Ferrer, Isidro; Rodríguez-Puertas, Rafael

    2015-08-01

    Lysophosphatidic acid (LPA) is a signaling molecule that binds to six known G protein-coupled receptors: LPA1 -LPA6 . LPA evokes several responses in the CNS, including cortical development and folding, growth of the axonal cone and its retraction process. Those cell processes involve survival, migration, adhesion proliferation, differentiation, and myelination. The anatomical localization of LPA1 is incompletely understood, particularly with regard to LPA binding. Therefore, we have used functional [(35) S]GTPγS autoradiography to verify the anatomical distribution of LPA1 binding sites in adult rodent and human brain. The greatest activity was observed in myelinated areas of the white matter such as corpus callosum, internal capsule and cerebellum. MaLPA1 -null mice (a variant of LPA1 -null) lack [(35) S]GTPγS basal binding in white matter areas, where the LPA1 receptor is expressed at high levels, suggesting a relevant role of the activity of this receptor in the most myelinated brain areas. In addition, phospholipid precursors of LPA were localized by MALDI-IMS in both rodent and human brain slices identifying numerous species of phosphatides and phosphatidylcholines. Both phosphatides and phosphatidylcholines species represent potential LPA precursors. The anatomical distribution of these precursors in rodent and human brain may indicate a metabolic relationship between LPA and LPA1 receptors. Lysophosphatidic acid (LPA) is a signaling molecule that binds to six known G protein-coupled receptors (GPCR), LPA1 to LPA6 . LPA evokes several responses in the central nervous system (CNS), including cortical development and folding, growth of the axonal cone and its retraction process. We used functional [(35) S]GTPγS autoradiography to verify the anatomical distribution of LPA1 -binding sites in adult rodent and human brain. The distribution of LPA1 receptors in rat, mouse and human brains show the highest activity in white matter myelinated areas. The basal and

  2. Copper catalyst activation driven by photoinduced electron transfer: a prototype photolatent click catalyst.

    PubMed

    Harmand, Lydie; Cadet, Sarah; Kauffmann, Brice; Scarpantonio, Luca; Batat, Pinar; Jonusauskas, Gediminas; McClenaghan, Nathan D; Lastécouères, Dominique; Vincent, Jean-Marc

    2012-07-16

    PET cat. While the copper(II) tren ketoprofenate precatalyst 1 (see picture) is inactive at room temperature in methanol, it is quantitatively and rapidly reduced to its cuprous state upon light irradiation to provide a highly reactive click catalyst. By simply introducing air into the reaction medium the catalysis can be switched off and then switched on again by bubbling argon followed by irradiation. PMID:22777953

  3. Synthesis and characterizations of palladium catalysts with high activity and stability for formic acid oxidation by hydrogen reduction in ethylene glycol at room temperature

    NASA Astrophysics Data System (ADS)

    Wu, Meixia; Li, Muwu; Wu, Xin; Li, Yuexia; Zeng, Jianhuang; Liao, Shijun

    2015-10-01

    In this work, a Pd/C catalyst with high activity as well as excellent stability has been prepared by hydrogen gas reduction of Pd(II) precursor in ethylene glycol solution with the assistance of appropriate amount of sodium citrate. Pd nanoparticles with an average particle size of 3.8 nm and excellent uniformity are obtained. The Pd/C catalyst synthesized in this work shows an electrochemical surface area of 68.6 m2 g-1 and displays activities of 819 A g-1. Strikingly, the Pd/C catalyst also exhibits excellent stability, which has been confirmed by its slow activity decay under repeated potential cycles as well as chronoamperometric test. The activity for Pd/C at the 300th and 500th cycle remains at 5.5 and 2.4 mA cm-2, respectively, which is 25% and 11% of its initial value, respectively. The oxidation currents at the Pd/C and Pd/C-Citrate (control) at 0 V decrease to 44% and 25% of their initial values. Transmission electron microscopy observations on the Pd/C catalyst after 1000 potential cycles reveal that, in addition to carbon support corrosion, Pd agglomeration together with more serious Pd dissolution occur at the same time, leading to a decrease of the electrocatalytic performance.

  4. Performance of (CoPC)n catalyst in active lithium-thionyl chloride cells

    NASA Technical Reports Server (NTRS)

    Shah, Pinakin M.

    1990-01-01

    An experimental study was conducted with anode limited D size cells to characterize the performance of an active lithium-thionyl chloride (Li/SOCl2) system using the polymeric cobalt phthalocyanine, (CoPC)n, catalyst in carbon cathodes. The author describes the results of this experiment with respect to initial voltage delays, operating voltages, and capacities. The effectiveness of the preconditioning methods evolved to alleviate passivation effects on storage are also discussed. The results clearly demonstrated the superior high rate capability of cells with the catalyst. The catalyst did not adversely impact the performance of cells after active storage for up to 6 months, while retaining its beneficial influences.

  5. Microwave and Beam Activation of Nanostructured Catalysts for Environmentally Friendly, Energy Efficient Heavy Crude Oil Processing

    SciTech Connect

    2009-03-01

    This factsheet describes a study whose goal is initial evaluation and development of energy efficient processes which take advantage of the benefits offered by nanostructured catalysts which can be activated by microwave, RF, or radiation beams.

  6. Crystallographic dependence of CO activation on cobalt catalysts: HCP versus FCC.

    PubMed

    Liu, Jin-Xun; Su, Hai-Yan; Sun, Da-Peng; Zhang, Bing-Yan; Li, Wei-Xue

    2013-11-01

    Identifying the structure sensitivity of catalysts in reactions, such as Fischer-Tropsch synthesis from CO and H2 over cobalt catalysts, is an important yet challenging issue in heterogeneous catalysis. Based on a first-principles kinetic study, we find for the first time that CO activation on hexagonal close-packed (HCP) Co not only has much higher intrinsic activity than that of face centered-cubic (FCC) Co but also prefers a different reaction route, i.e., direct dissociation with HCP Co but H-assisted dissociation on the FCC Co. The origin is identified from the formation of various denser yet favorable active sites on HCP Co not available for FCC Co, due to their distinct crystallographic structure and morphology. The great dependence of the activity on the crystallographic structure and morphology of the catalysts revealed here may open a new avenue for better, stable catalysts with maximum mass-specific reactivity.

  7. High-valent chromium-oxo complex acting as an efficient catalyst precursor for selective two-electron reduction of dioxygen by a ferrocene derivative.

    PubMed

    Liu, Shuo; Mase, Kentaro; Bougher, Curt; Hicks, Scott D; Abu-Omar, Mahdi M; Fukuzumi, Shunichi

    2014-07-21

    Efficient catalytic two-electron reduction of dioxygen (O2) by octamethylferrocene (Me8Fc) produced hydrogen peroxide (H2O2) using a high-valent chromium(V)-oxo corrole complex, [(tpfc)Cr(V)(O)] (tpfc = tris(pentafluorophenyl)corrole) as a catalyst precursor in the presence of trifluoroacetic acid (TFA) in acetonitrile (MeCN). The facile two-electron reduction of [(tpfc)Cr(V)(O)] by 2 equiv of Me8Fc in the presence of excess TFA produced the corresponding chromium(III) corrole [(tpfc)Cr(III)(OH2)] via fast electron transfer from Me8Fc to [(tpfc)Cr(V)(O)] followed by double protonation of [(tpfc)Cr(IV)(O)](-) and facile second-electron transfer from Me8Fc. The rate-determining step in the catalytic two-electron reduction of O2 by Me8Fc in the presence of excess TFA is inner-sphere electron transfer from [(tpfc)Cr(III)(OH2)] to O2 to produce the chromium(IV) superoxo species [(tpfc)Cr(IV)(O2(•-))], followed by fast proton-coupled electron transfer reduction of [(tpfc)Cr(IV)(O2(•-))] by Me8Fc to yield H2O2, accompanied by regeneration of [(tpfc)Cr(III)(OH2)]. Thus, although the catalytic two-electron reduction of O2 by Me8Fc was started by [(tpfc)Cr(V)(O)], no regeneration of [(tpfc)Cr(V)(O)] was observed in the presence of excess TFA, regardless of the tetragonal chromium complex being to the left of the oxo wall. In the presence of a stoichiometric amount of TFA, however, disproportionation of [(tfpc)Cr(IV)(O)](-) occurred via the protonated species [(tpfc)Cr(IV)(OH)] to produce [(tpfc)Cr(III)(OH2)] and [(tpfc)Cr(V)(O)].

  8. Tuning complex transition metal hydroxide nanostructures as active catalysts for water oxidation by a laser-chemical route.

    PubMed

    Niu, Kai-Yang; Lin, Feng; Jung, Suho; Fang, Liang; Nordlund, Dennis; McCrory, Charles C L; Weng, Tsu-Chien; Ercius, Peter; Doeff, Marca M; Zheng, Haimei

    2015-04-01

    Diverse transition metal hydroxide nanostructures were synthesized by laser-induced hydrolysis in a liquid precursor solution for alkaline oxygen evolution reaction (OER). Several active OER catalysts with fine control of composition, structure, and valence state were obtained including (Lix)[Ni0.66Mn0.34(OH)2](NO3)(CO3) · mH2O, Lix[Ni0.67Co0.33(OH)2](NO3)0.25(ORO)0.35 · mH2O, etc. An operate overpotential less than 0.34 V at current density of 10 mA cm(-2) was achieved. Such a controllable laser-chemical route for assessing complex nanostructures in liquids opens many opportunities to design novel functional materials for advanced applications.

  9. Chelating bis-N-heterocyclic carbene complexes of iron(ii) containing bipyridyl ligands as catalyst precursors for oxidation of alcohols.

    PubMed

    Pinto, Mara F; Cardoso, Bernardo de P; Barroso, Sónia; Martins, Ana M; Royo, Beatriz

    2016-09-14

    Chelating bis-N-heterocyclic carbene (bis-NHC) complexes of iron(ii) containing pyridyl ligands have been prepared by the reaction of [FeCl2L] [L = bipy (1), phen (2)] with [LiN(SiMe3)2] and a bis(imidazolium) salt. The [Fe(bis-NHC)L(I)2] complexes were active pre-catalysts in the oxidation of 1-phenylethanol with tert-butyl hydroperoxide in neat conditions, affording a quantitative yield of acetophenone in 4.5 h. The catalyst could be reused up to six cycles giving a turnover number (TON) of 1500. Various secondary alcohols, both aromatic and aliphatic were selectivity oxidised to the corresponding ketones in excellent yields. Compound 1 is stable in acetonitrile solution for ca. 4 h, although after 16 h, it evolves to a mixture of [Fe(bis-NHC)(bipy)2]I2 (3), [Fe(bipy)3](2+) and bis-imidazolium salt. The molecular structure of 3 has been determined by X-ray diffraction studies. PMID:27506414

  10. Effect of the Pd/MWCNTs anode catalysts preparation methods on their morphology and activity in a direct formic acid fuel cell

    NASA Astrophysics Data System (ADS)

    Lesiak, B.; Mazurkiewicz, M.; Malolepszy, A.; Stobinski, L.; Mierzwa, B.; Mikolajczuk-Zychora, A.; Juchniewicz, K.; Borodzinski, A.; Zemek, J.; Jiricek, P.

    2016-11-01

    Impact of Pd/MWCNTs catalysts preparation method on the catalysts morphology and activity in a formic acid electrooxidation reaction was investigated. Three reduction methods of Pd precursor involving reduction in a high pressure microwave reactor (Pd1), reduction with NaBH4 (Pd2) and microwave-assisted polyol method (Pd3) were used in this paper. Crystallites size and morphology were studied using the scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), whereas elemental composition, Pd chemical state and functional groups content by the X-ray photoelectron spectroscopy (XPS). The prepared catalysts were tested in a direct formic acid fuel cell (DFAFC) as an anode material. The catalytic activity was correlated with a mean fraction of the total Pd atoms exposed at the surface (FE). The value of FE was calculated from the crystallites size distribution determined by the STEM measurements. Non-linear dependence of a current density versus FE, approaching the maximum at FE≈0.25 suggests that the catalytic process proceeded at Pd nanocrystallites faces, with inactive edges and corners. Pd2 catalyst exhibited highest activity due to its smallest Pd crystallites (3.2 nm), however the absence of Pd crystallites aggregation and low content of carbon in PdCx phase, i.e. x = 4 at.% may also affect the observed.

  11. Morphology-dependent bactericidal activities of Ag/CeO2 catalysts against Escherichia coli.

    PubMed

    Wang, Lian; He, Hong; Yu, Yunbo; Sun, Li; Liu, Sijin; Zhang, Changbin; He, Lian

    2014-06-01

    Silver-loaded CeO2 nanomaterials (Ag/CeO2) including Ag/CeO2 nanorods, nanocubes, nanoparticles were prepared with hydrothermal and impregnation methods. Catalytic inactivation of Escherichia coli with Ag/CeO2 catalysts through the formation of reactive oxygen species (ROS) was investigated. For comparison purposes, the bactericidal activities of CeO2 nanorods, nanocubes and nanoparticles were also studied. There was a 3-4 log order improvement in the inactivation of E. coli with Ag/CeO2 catalysts compared with CeO2 catalysts. Temperature-programmed reduction of H2 showed that Ag/CeO2 catalysts had higher catalytic oxidation ability than CeO2 catalysts, which was the reason for that Ag/CeO2 catalysts exhibited stronger bactericidal activities than CeO2 catalysts. Further, the bactericidal activities of CeO2 and Ag/CeO2 depend on their shapes. Results of 5,5-dimethyl-1-pyrroline-N-oxide spin-trapping measurements by electron spin resonance and addition of catalase as a scavenger indicated the formation of OH, O2(-), and H2O2, which caused the obvious bactericidal activity of catalysts. The stronger chemical bond between Ag and CeO2 nanorods led to lower Ag(+) elution concentrations. The toxicity of Ag(+) eluted from the catalysts did not play an important role during the bactericidal process. Experimental results also indicated that Ag/CeO2 induced the production of intracellular ROS and disruption of the cell wall and cell membrane. A possible production mechanism of ROS and bactericidal mechanism of catalytic oxidation were proposed.

  12. Causes of Activation and Deactivation of Modified Nanogold Catalysts during Prolonged Storage and Redox Treatments.

    PubMed

    Kolobova, Ekaterina; Kotolevich, Yulia; Pakrieva, Ekaterina; Mamontov, Grigory; Farías, Mario H; Bogdanchikova, Nina; Cortés Corberán, Vicente; Pestryakov, Alexey

    2016-01-01

    The catalytic properties of modified Au/TiO₂ catalysts for low-temperature CO oxidation are affected by deactivation and reactivation after long-term storage and by redox treatments. The effect of these phenomena on the catalysts was studied by HRTEM, BET, SEM, FTIR CO, XPS and H₂ TPR methods. The main cause for the deactivation and reactivation of catalytic properties is the variation in the electronic state of the supported gold, mainly, the proportion of singly charged ions Au⁺. The most active samples are those with the highest proportion of singly charged gold ions, while catalysts with a high content of trivalent gold ions are inactive at low-temperatures. Active states of gold, resistant to changes caused by the reaction process and storage conditions, can be stabilized by modification of the titanium oxide support with transition metals oxides. The catalyst modified with lanthanum oxide shows the highest stability and activity. PMID:27089310

  13. Causes of Activation and Deactivation of Modified Nanogold Catalysts during Prolonged Storage and Redox Treatments.

    PubMed

    Kolobova, Ekaterina; Kotolevich, Yulia; Pakrieva, Ekaterina; Mamontov, Grigory; Farías, Mario H; Bogdanchikova, Nina; Cortés Corberán, Vicente; Pestryakov, Alexey

    2016-04-13

    The catalytic properties of modified Au/TiO₂ catalysts for low-temperature CO oxidation are affected by deactivation and reactivation after long-term storage and by redox treatments. The effect of these phenomena on the catalysts was studied by HRTEM, BET, SEM, FTIR CO, XPS and H₂ TPR methods. The main cause for the deactivation and reactivation of catalytic properties is the variation in the electronic state of the supported gold, mainly, the proportion of singly charged ions Au⁺. The most active samples are those with the highest proportion of singly charged gold ions, while catalysts with a high content of trivalent gold ions are inactive at low-temperatures. Active states of gold, resistant to changes caused by the reaction process and storage conditions, can be stabilized by modification of the titanium oxide support with transition metals oxides. The catalyst modified with lanthanum oxide shows the highest stability and activity.

  14. Structure and activity of tellurium/molybdenum oxide acrylonitrile catalysts. [Ammoxidation

    SciTech Connect

    Bart, J.C.J.; Giordano, N.

    1980-08-01

    The tellurium/molybdenum mixed oxides ((TeMo)O) catalyst system was investigated as part of the development of an industrial cerium/tellurium/molybdenum mixed oxides catalyst for propylene ammoxidation Catalysts containing 25% active phase on silica were prepared, characterized by BET surface area measurement, mercury porosimetry, X-ray diffraction, and optical microscopy, and tested for the ammoxidation of propylene at 400/sup 0/-460/sup 0/C in a flow reactor. The results suggested that Te/sub 2/MoO/sub 7/ is the active phase. The mechanism probably involves activation of propylene on a tellurium site and oxygen insertion at isolated and highly distorted MoO/sub 6/ octahedral sites. The addition of cerium to the binary catalyst prevents the reductive degradation of (TeMo)O which occurs under reactor flow conditions by a phase-separation process.

  15. Sulphate-activated growth of bamboo-like carbon nanotubes over copper catalysts

    NASA Astrophysics Data System (ADS)

    Lin, Jarrn-Horng; Chen, Ching-Shiun; Zeng, Zhi-Yan; Chang, Chia-Wei; Chen, Hsiu-Wei

    2012-07-01

    A sulphate-activated mechanism is proposed to describe the growth of bamboo-like carbon nanotubes (CNTs) over copper catalysts using chemical vapour deposition with helium-diluted ethylene. Sulphate-assisted copper catalysts afford a high-yield growth of bamboo-like CNTs at a mild temperature, 800 °C however, non-sulphate-assisted copper catalysts, e.g., copper acetate and copper nitrate prepared catalysts, were inert to CNT growth and only gave amorphous carbons (a-C) surrounding copper nanoparticles under the same conditions. Nevertheless, the addition of sulphate ions in the preparation step for the two inert catalysts can activate their abilities for CNT growth with remarkable yields. Furthermore, Raman spectra analysis demonstrates a linear dependence between the concentration of sulphate ions in copper catalysts and the ratio of CNT-a-C in the as-grown carbon soot. The sulphate-activated effect on CNT growth over copper catalysts could be related to a three-way interaction of sulphate ions, copper nanoparticles and support. In situ TEM images of an as-grown CNT irradiated by electron beams without the inlet of carbon sources reveal a new pathway of carbon diffusion through the bulk of copper nanoparticles and an enlarged inner-wall thickness of the on-site CNT. This carbon diffusion model over copper catalysts can provide new insights into the CNT growth mechanism over non-magnetic metal catalysts.A sulphate-activated mechanism is proposed to describe the growth of bamboo-like carbon nanotubes (CNTs) over copper catalysts using chemical vapour deposition with helium-diluted ethylene. Sulphate-assisted copper catalysts afford a high-yield growth of bamboo-like CNTs at a mild temperature, 800 °C however, non-sulphate-assisted copper catalysts, e.g., copper acetate and copper nitrate prepared catalysts, were inert to CNT growth and only gave amorphous carbons (a-C) surrounding copper nanoparticles under the same conditions. Nevertheless, the addition of

  16. Effect of Support on the Activity of Ag-based Catalysts for Formaldehyde Oxidation

    PubMed Central

    Zhang, Jianghao; Li, Yaobin; Zhang, Yan; Chen, Min; Wang, Lian; Zhang, Changbin; He, Hong

    2015-01-01

    Ag-based catalysts with different supports (TiO2, Al2O3 and CeO2) were prepared by impregnation method and subsequently tested for the catalytic oxidation of formaldehyde (HCHO) at low temperature. The Ag/TiO2 catalyst showed the distinctive catalytic performance, achieving the complete HCHO conversion at around 95 °C. In contrast, the Ag/Al2O3 and Ag/CeO2 catalysts displayed much lower activity and the 100% conversion was reached at 110 °C and higher than 125 °C, respectively. The Ag-based catalysts were next characterized by several methods. The characterization results revealed that supports have the dramatic influence on the Ag particle sizes and dispersion. Kinetic tests showed that the Ag based catalyst on the TiO2, Al2O3 or CeO2 supports have the similar apparent activation energy of 65 kJ mol−1, indicating that the catalytic mechanism keep immutability over these three catalysts. Therefore, Ag particle size and dispersion was confirmed to be the main factor affecting the catalytic performance for HCHO oxidation. The Ag/TiO2 catalyst has the highest Ag dispersion and the smallest Ag particle size, accordingly presenting the best catalytic performance for HCHO oxidation. PMID:26263506

  17. Decoupling HZSM-5 catalyst activity from deactivation during upgrading of pyrolysis oil vapors.

    PubMed

    Wan, Shaolong; Waters, Christopher; Stevens, Adam; Gumidyala, Abhishek; Jentoft, Rolf; Lobban, Lance; Resasco, Daniel; Mallinson, Richard; Crossley, Steven

    2015-02-01

    The independent evaluation of catalyst activity and stability during the catalytic pyrolysis of biomass is challenging because of the nature of the reaction system and rapid catalyst deactivation that force the use of excess catalyst. In this contribution we use a modified pyroprobe system in which pulses of pyrolysis vapors are converted over a series of HZSM-5 catalysts in a separate fixed-bed reactor controlled independently. Both the reactor-bed temperature and the Si/Al ratio of the zeolite are varied to evaluate catalyst activity and deactivation rates independently both on a constant surface area and constant acid site basis. Results show that there is an optimum catalyst-bed temperature for the production of aromatics, above which the production of light gases increases and that of aromatics decrease. Zeolites with lower Si/Al ratios give comparable initial rates for aromatics production, but far more rapid catalyst deactivation rates than those with higher Si/Al ratios. PMID:25504857

  18. Surface state and catalytic activity and selectivity of nickel catalysts in hydrogenation reactions. III. Electronic and catalytic properties of nickel catalysts

    SciTech Connect

    Okamoto, Y.; Nitta, Y.; Imanaka, T.; Teranishi, S.

    1980-08-01

    Various nickel catalysts (nickle-boride, nickel-phosphide, Raney-nickel, Urushibara-nickel, and decomposed-nickel) were investigated to examine the relationships between catalytic and electronic properties of nickel catalysts modified by component elements (boron, phosphorus, aluminum, and zinc) in the catalysts. Based on the x-ray photoelectron spectroscopic results, a parameter ..delta..q was tentatively proposed to characterize the electronic properties of the catalysts. The specific activity (activity per surface area of nickel metal) for hydrogenation reaction, the adsorption equilibrium constant of acetophenone, the resistivity against poisoning, and the characteristic selectivities in hydrogenation of 1,2-butylene oxide were found to be summarized in terms of the parameter ..delta..q. It is suggested that a useful parameter to reflect the electronic properties of the nickel catalysts.

  19. Gc protein (vitamin D-binding protein): Gc genotyping and GcMAF precursor activity.

    PubMed

    Nagasawa, Hideko; Uto, Yoshihiro; Sasaki, Hideyuki; Okamura, Natsuko; Murakami, Aya; Kubo, Shinichi; Kirk, Kenneth L; Hori, Hitoshi

    2005-01-01

    The Gc protein (human group-specific component (Gc), a vitamin D-binding protein or Gc globulin), has important physiological functions that include involvement in vitamin D transport and storage, scavenging of extracellular G-actin, enhancement of the chemotactic activity of C5a for neutrophils in inflammation and macrophage activation (mediated by a GalNAc-modified Gc protein (GcMAF)). In this review, the structure and function of the Gc protein is focused on especially with regard to Gc genotyping and GcMAF precursor activity. A discussion of the research strategy "GcMAF as a target for drug discovery" is included, based on our own research. PMID:16302727

  20. Catalysts possessing augmented C-O and C-N hydrogenolysis activity. Preliminary progress report, August-September 1983

    SciTech Connect

    Massoth, F.E.; Shabtai, J.S.

    1983-10-31

    The aim of the proposed research is to synthesize and investigate new sulfided catalyst systems having higher carbon-heteroatom hydrogenolysis activity as compared to ring hydrogenation activity. A fundamental approach is planned to gain understanding of the basic catalytic properties which relate to hydrogenolysis, hydrogenation and cracking functions of the catalysts. This will involve preparation of new catalysts, characterization of their properties and model compound reactivity studies. In another part of the project, selected catalysts will be applied in studies of more complex O- and N-containing model compounds with the objective of providing fundamental data on the stereochemistry of HDO and HDN reactions. These data will be used to develop steric surface-reactant models for sulfided catalysts. These new catalysts should be of particular importance for upgrading of coal-derived liquids and solids, as well as other heavy feedstocks. The research is divided into four tasks: (1) catalyst preparation and activity testing; (2) catalyst characterization; (2) study of catalyst activity under hydroprocessing conditions; and (4) stereochemical studies. This report covers a period of only one month. Work was initiated on catalyst preparation. A brief literature search was made to ascertain what different preparation methods can be applied to supported sulfide catalysts besides the standard wetness method. Several Cr/Al/sub 2/O/sub 3/ catalysts containing Co or Ni were prepared by the standard impregnation method. 3 references.

  1. Method of treating intermetallic alloy hydrogenation/oxidation catalysts for improved impurity poisoning resistance, regeneration and increased activity

    DOEpatents

    Wright, Randy B.

    1992-01-01

    Alternate, successive high temperature oxidation and reduction treatments, in either order, of intermetallic alloy hydrogenation and intermetallic alloy oxidation catalysts unexpectedly improves the impurity poisoning resistance, regeneration capacity and/or activity of the catalysts. The particular alloy, and the final high temperature treatment given alloy (oxidation or reduction) will be chosen to correspond to the function of the catalyst (oxidation or hydrogenation).

  2. An Integrated Geospatial System for earthquake precursors assessment in Vrancea tectonic active zone in Romania

    NASA Astrophysics Data System (ADS)

    Zoran, Maria A.; Savastru, Roxana S.; Savastru, Dan M.

    2015-10-01

    With the development of space-based technologies to measure surface geophysical parameters and deformation at the boundaries of tectonic plates and large faults, earthquake science has entered a new era. Using time series satellite data for earthquake prediction, it is possible to pursue the behaviors of earthquake precursors in the future and to announce early warnings when the differences between the predicted value and the observed value exceed the pre-define threshold value. Starting with almost one week prior to a moderate or strong earthquake a transient thermal infrared rise in LST of several Celsius degrees (oC) and the increased OLR values higher than the normal have been recorded around epicentral areas, function of the magnitude and focal depth, which disappeared after the main shock. Also are recorded associated geomagnetic and ionospheric distrurbances. Vrancea tectonic active zone in Romania is characterized by a high seismic hazard in European- Mediterranean region, being responsible of strong or moderate intermediate depth and normal earthquakes generation on a confined epicentral area. Based on recorded geophysical parameters anomalies was developed an integrated geospatial system for earthquake precursors assessment in Vrancea active seismic zone. This system integrates derived from time series MODIS Terra/Aqua, NOAA-AVHRR, ASTER, Landsat TM/ETM satellite data multi geophysical parameters (land surface temperature -LST, outgoing long-wave radiation- OLR, and mean air temperature- AT as well as geomagnetic and ionospheric data in synergy with in-situ data for surveillance and forecasting of seismic events.

  3. Premature Graying as a Consequence of Compromised Antioxidant Activity in Hair Bulb Melanocytes and Their Precursors

    PubMed Central

    Shi, Ying; Luo, Long-Fei; Liu, Xiao-Ming; Zhou, Qiong; Xu, Shi-Zheng; Lei, Tie-Chi

    2014-01-01

    Intricate coordinated mechanisms that govern the synchrony of hair growth and melanin synthesis remain largely unclear. These two events can be uncoupled in prematurely gray hair, probably due to oxidative insults that lead to the death of oxidative stress-sensitive melanocytes. In this study, we examined the gene expression profiles of middle (bulge) and lower (hair bulb) segments that had been micro-dissected from unpigmented and from normally pigmented hair follicles from the same donors using quantitative real-time RT-PCR (qPCR) arrays. We found a significant down-regulation of melanogenesis-related genes (TYR, TYRP1, MITF, PAX3, POMC) in unpigmented hair bulbs and of marker genes typical for melanocyte precursor cells (PAX3, SOX10, DCT) in unpigmented mid-segments compared with their pigmented analogues. qPCR, western blotting and spin trapping assays revealed that catalase protein expression and hydroxyl radical scavenging activities are strongly repressed in unpigmented hair follicles. These data provide the first clear evidence that compromised antioxidant activity in gray hair follicles simultaneously affects mature hair bulb melanocytes and their immature precursor cells in the bulge region. PMID:24695442

  4. Antimicrobial Activity of Artemisinin and Precursor Derived from In Vitro Plantlets of Artemisia annua L.

    PubMed Central

    Appalasamy, Suganthi; Lo, Kiah Yann; Ch'ng, Song Jin; Nornadia, Ku; Othman, Ahmad Sofiman; Chan, Lai-Keng

    2014-01-01

    Artemisia annua L., a medicinal herb, produces secondary metabolites with antimicrobial property. In Malaysia due to the tropical hot climate, A. annua could not be planted for production of artemisinin, the main bioactive compound. In this study, the leaves of three in vitro A. annua L. clones were, extracted and two bioactive compounds, artemisinin and a precursor, were isolated by thin layer chromatography. These compounds were found to be effective in inhibiting the growth of Gram-positive and Gram-negative bacteria but not Candida albicans. Their antimicrobial activity was similar to that of antibactericidal antibiotic streptomycin. They were found to inhibit the growth of the tested microbes at the minimum inhibition concentration of 0.09 mg/mL, and toxicity test using brine shrimp showed that even the low concentration of 0.09 mg/mL was very lethal towards the brine shrimps with 100% mortality rate. This study hence indicated that in vitro cultured plantlets of A. annua can be used as the alternative method for production of artemisinin and its precursor with antimicrobial activities. PMID:24575401

  5. Supplemental activation method for high-efficiency electron-transfer dissociation of doubly protonated peptide precursors.

    PubMed

    Swaney, Danielle L; McAlister, Graeme C; Wirtala, Matthew; Schwartz, Jae C; Syka, John E P; Coon, Joshua J

    2007-01-15

    Electron-transfer dissociation (ETD) delivers the unique attributes of electron capture dissociation to mass spectrometers that utilize radio frequency trapping-type devices (e.g., quadrupole ion traps). The method has generated significant interest because of its compatibility with chromatography and its ability to: (1) preserve traditionally labile post-translational modifications (PTMs) and (2) randomly cleave the backbone bonds of highly charged peptide and protein precursor ions. ETD, however, has shown limited applicability to doubly protonated peptide precursors, [M + 2H]2+, the charge and type of peptide most frequently encountered in "bottom-up" proteomics. Here we describe a supplemental collisional activation (CAD) method that targets the nondissociated (intact) electron-transfer (ET) product species ([M + 2H]+*) to improve ETD efficiency for doubly protonated peptides (ETcaD). A systematic study of supplementary activation conditions revealed that low-energy CAD of the ET product population leads to the near-exclusive generation of c- and z-type fragment ions with relatively high efficiency (77 +/- 8%). Compared to those formed directly via ETD, the fragment ions were found to comprise increased relative amounts of the odd-electron c-type ions (c+*) and the even-electron z-type ions (z+). A large-scale analysis of 755 doubly charged tryptic peptides was conducted to compare the method (ETcaD) to ion trap CAD and ETD. ETcaD produced a median sequence coverage of 89%-a significant improvement over ETD (63%) and ion trap CAD (77%).

  6. An alternative approach to PEPPSI catalysts: from palladium isonitriles to highly active unsymmetrically substituted PEPPSI catalysts.

    PubMed

    Zeiler, Anna; Rudolph, Matthias; Rominger, Frank; Hashmi, A Stephen K

    2015-07-27

    A series of new pyridine-enhanced precatalyst preparation, stabilization, and initiation (PEPPSI)-type complexes bearing different types of carbene ligands was prepared by the modular and convergent template synthesis strategy. Nitrogen acyclic carbenes, saturated and unsaturated five-membered NHC, saturated six-membered NHCs, and five-membered N-heterocyclic oxo-carbene (NHOC) ligands on palladium were prepared this way. These new organometallic compounds then were tested in Suzuki and Negishi cross-coupling reactions by using substrates with one or two substituents in ortho-position of the new CC bond being formed. Both aryl chlorides and bromides were tested as coupling partners. In some cases, the new ligands gave results similar to Organ's successful IPr-based and IPent-based PEPPSI derivatives, with aryl bromides 0.05 mol % catalyst load still gave satisfactory results, with aryl chlorides 0.5 mol % were needed. PMID:26096141

  7. Renewable phenols production by catalytic microwave pyrolysis of Douglas fir sawdust pellets with activated carbon catalysts.

    PubMed

    Bu, Quan; Lei, Hanwu; Wang, Lu; Wei, Yi; Zhu, Lei; Liu, Yupeng; Liang, Jing; Tang, Juming

    2013-08-01

    The effects of different activated carbon (AC) catalysts based on various carbon sources on products yield and chemical compositions of upgraded pyrolysis oils were investigated using microwave pyrolysis of Douglas fir sawdust pellets. Results showed that high amounts of phenols were obtained (74.61% and 74.77% in the upgraded bio-oils by DARCO MRX (wood based) and DARCO 830 (lignite coal based) activated carbons, respectively). The catalysts recycling test of the selected catalysts indicated that the carbon catalysts can be reused for at least 3-4 times and produced high concentrations of phenol and phenolic compounds. The chemical reaction mechanism for phenolics production during microwave pyrolysis of biomass was analyzed. PMID:23765005

  8. Catalyst dispersion and activity under conditions of temperature-staged liquefaction

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1992-02-01

    The general objectives of this research are (1) to investigate the use of highly dispersed catalysts for the pretreatment of coal by mild hydrogenation, (2) to identify the active forms of the catalysts under reaction conditions and (3) to clarify the mechanisms of catalysis. The ultimate objective is to ascertain if mild catalytic hydrogenation resulting in very limited or no coal solubilization is an advantageous pretreatment for the transformation of coal into transportable fuels. The experimental program will focus upon the development of effective methods of impregnating coal with catalysts, evaluating the conditions under which the catalysts are most active and establishing the relative impact of improved impregnation on conversion and product distributions obtained from coal hydrogenation.

  9. Renewable phenols production by catalytic microwave pyrolysis of Douglas fir sawdust pellets with activated carbon catalysts.

    PubMed

    Bu, Quan; Lei, Hanwu; Wang, Lu; Wei, Yi; Zhu, Lei; Liu, Yupeng; Liang, Jing; Tang, Juming

    2013-08-01

    The effects of different activated carbon (AC) catalysts based on various carbon sources on products yield and chemical compositions of upgraded pyrolysis oils were investigated using microwave pyrolysis of Douglas fir sawdust pellets. Results showed that high amounts of phenols were obtained (74.61% and 74.77% in the upgraded bio-oils by DARCO MRX (wood based) and DARCO 830 (lignite coal based) activated carbons, respectively). The catalysts recycling test of the selected catalysts indicated that the carbon catalysts can be reused for at least 3-4 times and produced high concentrations of phenol and phenolic compounds. The chemical reaction mechanism for phenolics production during microwave pyrolysis of biomass was analyzed.

  10. Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts

    PubMed Central

    Sahraie, Nastaran Ranjbar; Kramm, Ulrike I.; Steinberg, Julian; Zhang, Yuanjian; Thomas, Arne; Reier, Tobias; Paraknowitsch, Jens-Peter; Strasser, Peter

    2015-01-01

    Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here we report a successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and 57Fe Mössbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the active-site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity. PMID:26486465

  11. Low Temperature Activation of Supported Metathesis Catalysts by Organosilicon Reducing Agents.

    PubMed

    Mougel, Victor; Chan, Ka-Wing; Siddiqi, Georges; Kawakita, Kento; Nagae, Haruki; Tsurugi, Hayato; Mashima, Kazushi; Safonova, Olga; Copéret, Christophe

    2016-08-24

    Alkene metathesis is a widely and increasingly used reaction in academia and industry because of its efficiency in terms of atom economy and its wide applicability. This reaction is notably responsible for the production of several million tons of propene annually. Such industrial processes rely on inexpensive silica-supported tungsten oxide catalysts, which operate at high temperatures (>350 °C), in contrast with the mild room temperature reaction conditions typically used with the corresponding molecular alkene metathesis homogeneous catalysts. This large difference in the temperature requirements is generally thought to arise from the difficulty in generating active sites (carbenes or metallacyclobutanes) in the classical metal oxide catalysts and prevents broader applicability, notably with functionalized substrates. We report here a low temperature activation process of well-defined metal oxo surface species using organosilicon reductants, which generate a large amount of active species at only 70 °C (0.6 active sites/W). This high activity at low temperature broadens the scope of these catalysts to functionalized substrates. This activation process can also be applied to classical industrial catalysts. We provide evidence for the formation of a metallacyclopentane intermediate and propose how the active species are formed.

  12. Low Temperature Activation of Supported Metathesis Catalysts by Organosilicon Reducing Agents

    PubMed Central

    2016-01-01

    Alkene metathesis is a widely and increasingly used reaction in academia and industry because of its efficiency in terms of atom economy and its wide applicability. This reaction is notably responsible for the production of several million tons of propene annually. Such industrial processes rely on inexpensive silica-supported tungsten oxide catalysts, which operate at high temperatures (>350 °C), in contrast with the mild room temperature reaction conditions typically used with the corresponding molecular alkene metathesis homogeneous catalysts. This large difference in the temperature requirements is generally thought to arise from the difficulty in generating active sites (carbenes or metallacyclobutanes) in the classical metal oxide catalysts and prevents broader applicability, notably with functionalized substrates. We report here a low temperature activation process of well-defined metal oxo surface species using organosilicon reductants, which generate a large amount of active species at only 70 °C (0.6 active sites/W). This high activity at low temperature broadens the scope of these catalysts to functionalized substrates. This activation process can also be applied to classical industrial catalysts. We provide evidence for the formation of a metallacyclopentane intermediate and propose how the active species are formed. PMID:27610418

  13. Low Temperature Activation of Supported Metathesis Catalysts by Organosilicon Reducing Agents.

    PubMed

    Mougel, Victor; Chan, Ka-Wing; Siddiqi, Georges; Kawakita, Kento; Nagae, Haruki; Tsurugi, Hayato; Mashima, Kazushi; Safonova, Olga; Copéret, Christophe

    2016-08-24

    Alkene metathesis is a widely and increasingly used reaction in academia and industry because of its efficiency in terms of atom economy and its wide applicability. This reaction is notably responsible for the production of several million tons of propene annually. Such industrial processes rely on inexpensive silica-supported tungsten oxide catalysts, which operate at high temperatures (>350 °C), in contrast with the mild room temperature reaction conditions typically used with the corresponding molecular alkene metathesis homogeneous catalysts. This large difference in the temperature requirements is generally thought to arise from the difficulty in generating active sites (carbenes or metallacyclobutanes) in the classical metal oxide catalysts and prevents broader applicability, notably with functionalized substrates. We report here a low temperature activation process of well-defined metal oxo surface species using organosilicon reductants, which generate a large amount of active species at only 70 °C (0.6 active sites/W). This high activity at low temperature broadens the scope of these catalysts to functionalized substrates. This activation process can also be applied to classical industrial catalysts. We provide evidence for the formation of a metallacyclopentane intermediate and propose how the active species are formed. PMID:27610418

  14. Low Temperature Activation of Supported Metathesis Catalysts by Organosilicon Reducing Agents

    PubMed Central

    2016-01-01

    Alkene metathesis is a widely and increasingly used reaction in academia and industry because of its efficiency in terms of atom economy and its wide applicability. This reaction is notably responsible for the production of several million tons of propene annually. Such industrial processes rely on inexpensive silica-supported tungsten oxide catalysts, which operate at high temperatures (>350 °C), in contrast with the mild room temperature reaction conditions typically used with the corresponding molecular alkene metathesis homogeneous catalysts. This large difference in the temperature requirements is generally thought to arise from the difficulty in generating active sites (carbenes or metallacyclobutanes) in the classical metal oxide catalysts and prevents broader applicability, notably with functionalized substrates. We report here a low temperature activation process of well-defined metal oxo surface species using organosilicon reductants, which generate a large amount of active species at only 70 °C (0.6 active sites/W). This high activity at low temperature broadens the scope of these catalysts to functionalized substrates. This activation process can also be applied to classical industrial catalysts. We provide evidence for the formation of a metallacyclopentane intermediate and propose how the active species are formed.

  15. Increased Asynchronous Release and Aberrant Calcium Channel Activation in Amyloid Precursor Protein Deficient Neuromuscular Synapses

    PubMed Central

    Yang, Li; Wang, Baiping; Long, Cheng; Wu, Gangyi; Zheng, Hui

    2007-01-01

    Despite the critical roles of the amyloid precursor protein (APP) in Alzheimer's disease pathogenesis, its physiological function remains poorly established. Our previous studies implicated a structural and functional activity of the APP family of proteins in the developing neuromuscular junction (NMJ). Here we performed comprehensive analyses of neurotransmission in mature neuromuscular synapse of APP deficient mice. We found that APP deletion led to reduced paired-pulse facilitation and increased depression of synaptic transmission with repetitive stimulation. Readily releasable pool size and total releasable vesicles were not affected, but probability of release was significantly increased. Strikingly, the amount of asynchronous release, a measure sensitive to presynaptic calcium concentration, was dramatically increased, and pharmacological studies revealed that it was attributed to aberrant activation of N- and L-type Ca2+ channels. We propose that APP modulates synaptic transmission at the NMJ by ensuring proper Ca2+ channel function. PMID:17919826

  16. Waste polyvinylchloride derived pitch as a precursor to develop carbon fibers and activated carbon fibers.

    PubMed

    Qiao, W M; Yoon, S H; Mochida, I; Yang, J H

    2007-01-01

    Polyvinylchloride (PVC) was successfully recycled through the solvent extraction from waste pipe with an extraction yield of ca. 86%. The extracted PVC was pyrolyzed by a two-stage process (260 and 410 degrees C) to obtain free-chlorine PVC based pitch through an effective removal of chlorine from PVC during the heat-treatment. As-prepared pitch (softening point: 220 degrees C) was spun, stabilized, carbonized into carbon fibers (CFs), and further activated into activated carbon fibers (ACFs) in a flow of CO2. As-prepared CFs show comparable mechanical properties to commercial CFs, whose maximum tensile strength and modulus are 862 MPa and 62 GPa, respectively. The resultant ACFs exhibit a high surface area of 1200 m2/g, narrow pore size distribution and a low oxygen content of 3%. The study provides an effective insight to recycle PVC from waste PVC and develop a carbon precursor for high performance carbon materials such as CFs and ACFs.

  17. Nitrogen-doped carbon nanotubes as a highly active metal-free catalyst for selective oxidation.

    PubMed

    Chizari, Kambiz; Deneuve, Adrien; Ersen, Ovidiu; Florea, Ileana; Liu, Yu; Edouard, David; Janowska, Izabela; Begin, Dominique; Pham-Huu, Cuong

    2012-01-01

    Catalytic reactions are generally carried out on supported metals or oxides, which act as an active phase and require impregnation and thermal treatment steps. During tests, the metal or oxide nanoparticles could be further sintered, which would induces deactivation. Direct incorporation of the active phase into the matrix of a support could be an elegant alternative to prevent catalyst deactivation. Here, we report that nitrogen-doped carbon nanotubes (N-CNTs) can be efficiently employed as a metal-free catalyst for oxidative reactions that allow the selective transformation of the harmful, gaseous H(2)S into solid sulfur. The catalyst exhibits a high stability during the test at high space velocity. The macroscopic shaping of the catalyst on the silicon carbide foam also increases its catalytic activity by improving the contact between the reactants and the catalyst. Such macroscopic shaping allows the avoidance of problems linked with transport and handling of nanoscopic materials and also reduces the pressure drop across the catalyst bed to a large extent.

  18. ALTERNATIVE ROUTES FOR CATALYST PREPARATION: USE OF ULTRASOUND AND MICROWAVE IRRADIATION FOR THE PREPARATION OF VANADIUM PHOSPHORUS OXIDE CATALYST AND THEIR ACTIVITY FOR HYDROCARBON OXIDATION

    EPA Science Inventory

    Vanadium phosphorus oxide (VPO) has been prepared using ultrasound and microwave irradiation methods and compared with the catalyst prepared by conventional method for both the phase composition and activity for hydrocarbon oxidation. It is found that ultrasound irradiation metho...

  19. Phenol removal onto novel activated carbons made from lignocellulosic precursors: influence of surface properties.

    PubMed

    Nabais, J M Valente; Gomes, J A; Suhas; Carrott, P J M; Laginhas, C; Roman, S

    2009-08-15

    The adsorption of phenol from dilute aqueous solutions onto new activated carbons (AC) was studied. The novel activated carbon was produced from lignocellulosic (LC) precursors of rapeseed and kenaf. Samples oxidised with nitric acid in liquid phase were also studied. The results have shown the significant potential of rapeseed and kenaf for the activated carbon production. The activated carbons produced by carbon dioxide activation were mainly microporous with BET apparent surface area up to 1350 m(2)g(-1) and pore volume 0.5 cm(3)g(-1). The effects of concentration (0.1-2 mM) and pH (3-13) were studied. The phenol adsorption isotherms at 25 degrees C followed the Freundlich model with maximum adsorption capacities of approximately 80 and 50 mg g(-1) for the pristine and oxidised activated carbons, respectively. The influence of pH on the adsorption has two trends for pH below and above 10. It was possible to conclude that when phenol is predominantly in the molecular form the most probable mechanism is based on the pi-pi dispersion interaction between the phenol aromatic ring and the delocalised pi electrons present in the activated carbon aromatic structure. When phenolate is the major component the electrostatic repulsion that occurs at high pH values is the most important aspect of the adsorption mechanism.

  20. Degradation of typical N-nitrosodimethylamine (NDMA) precursors and its formation potential in anoxic-aerobic (AO) activated sludge system.

    PubMed

    Wang, Lin; Li, Yongmei; He, Guodong

    2014-01-01

    N-nitrosodimethylamine (NDMA) is an emerging disinfection byproduct. Removal of its potential precursors is considered as an effective method to control NDMA. In this study, four typical NDMA precursors (dimethylamine (DMA), trimethylamine (TMA), dimethylformamide (DMFA) and dimethylaminobenzene (DMAB)) were selected, and their removal capacities by activated sludge were investigated. Batch experiments indicated that removal of NDMA precursors was better under aerobic condition than anoxic condition; and their specific degradation rates follow the order of DMA > TMA > DMFA > DMAB. In anoxic-aerobic (AO) activated sludge system, the optimal hydraulic retention time and sludge retention time were 10 h and 20 d, respectively, for the removal of both NDMA precursors (four selected NDMA precursors and NDMA formation potential (NDMA FP)) and nutrients. Our results also suggested that there was a positive correlation between NDMA FP and dissolved organic nitrogen (DON) in wastewater. The removal efficiency of NDMA FP was in the range of 46.8-72.5% in the four surveyed wastewater treatment plants except the one which adopted chemically enhanced primary process. The results revealed that the AO system had the advantage of removing NDMA FP. Our results are helpful for the knowledge of the removals of NDMA precursors during activated sludge treatment processes.

  1. Structure-Activity Relationship Studies of Cyclopropenimines as Enantioselective Brønsted Base Catalysts

    PubMed Central

    Bandar, Jeffrey S.; Barthelme, Alexandre P.; Mazori, Alon Y.; Lambert, Tristan H.

    2015-01-01

    We recently demonstrated that chiral cyclopropenimines are viable Brønsted base catalysts in enantioselective Michael and Mannich reactions. Herein, we describe a series of structure-activity relationship studies that provide an enhanced understanding of the effectiveness of certain cyclopropenimines as enantioselective Brønsted base catalysts. These studies underscore the crucial importance of dicyclohexylamino substituents in mediating both reaction rate and enantioselectivity. In addition, an unusual catalyst CH···O interaction, which provides both ground state and transition state organization, is discussed. Cyclopropenimine stability studies have led to the identification of new catalysts with greatly improved stability. Finally, additional demonstrations of substrate scope and current limitations are provided herein. PMID:26504512

  2. The effect of catalyst preparation on catalytic activity: Final report, December 1, 1983-November 31, 1986

    SciTech Connect

    Schwarz, J.A.

    1986-12-01

    The performance of catalysts has been shown to be strongly dependent on their methods of preparation. The objective of our research has been to examine the effect of preparation procedures including metal concentration and pH of the impregnation solution on the catalytic properties of supported-metal catalyst systems. Design parameters have been identified for Ni/Al/sub 2/O/sub 3/ catalysts propared by incipient wetness and wet impregnation from nickel nitrate solution in contact with a ..gamma..-Al/sub 2/O/sub 3/ support. The metal dispersion, activity for C/sub 1/, C/sub 2/, and C/sub 3/ formation under synthesis conditions, and the carbon deposited during reaction have been shown to be predictable based solely on the properties of the electrolytes from which these catalysts were formed.

  3. Rejuvenation of MPTP-induced human neural precursor cell senescence by activating autophagy

    SciTech Connect

    Zhu, Liang; Dong, Chuanming; Sun, Chenxi; Ma, Rongjie; Yang, Danjing; Zhu, Hongwen; Xu, Jun

    2015-08-21

    Aging of neural stem cell, which can affect brain homeostasis, may be caused by many cellular mechanisms. Autophagy dysfunction was found in aged and neurodegenerative brains. However, little is known about the relationship between autophagy and human neural stem cell (hNSC) aging. The present study used 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) to treat neural precursor cells (NPCs) derived from human embryonic stem cell (hESC) line H9 and investigate related molecular mechanisms involved in this process. MPTP-treated NPCs were found to undergo premature senescence [determined by increased senescence-associated-β-galactosidase (SA-β-gal) activity, elevated intracellular reactive oxygen species level, and decreased proliferation] and were associated with impaired autophagy. Additionally, the cellular senescence phenotypes were manifested at the molecular level by a significant increase in p21 and p53 expression, a decrease in SOD2 expression, and a decrease in expression of some key autophagy-related genes such as Atg5, Atg7, Atg12, and Beclin 1. Furthermore, we found that the senescence-like phenotype of MPTP-treated hNPCs was rejuvenated through treatment with a well-known autophagy enhancer rapamycin, which was blocked by suppression of essential autophagy gene Beclin 1. Taken together, these findings reveal the critical role of autophagy in the process of hNSC aging, and this process can be reversed by activating autophagy. - Highlights: • We successfully establish hESC-derived neural precursor cells. • MPTP treatment induced senescence-like state in hESC-derived NPCs. • MPTP treatment induced impaired autophagy of hESC-derived NPCs. • MPTP-induced hESC-derived NPC senescence was rejuvenated by activating autophagy.

  4. Active site densities, oxygen activation and adsorbed reactive oxygen in alcohol activation on npAu catalysts.

    PubMed

    Wang, Lu-Cun; Friend, C M; Fushimi, Rebecca; Madix, Robert J

    2016-07-01

    The activation of molecular O2 as well as the reactivity of adsorbed oxygen species is of central importance in aerobic selective oxidation chemistry on Au-based catalysts. Herein, we address the issue of O2 activation on unsupported nanoporous gold (npAu) catalysts by applying a transient pressure technique, a temporal analysis of products (TAP) reactor, to measure the saturation coverage of atomic oxygen, its collisional dissociation probability, the activation barrier for O2 dissociation, and the facility with which adsorbed O species activate methanol, the initial step in the catalytic cycle of esterification. The results from these experiments indicate that molecular O2 dissociation is associated with surface silver, that the density of reactive sites is quite low, that adsorbed oxygen atoms do not spill over from the sites of activation onto the surrounding surface, and that methanol reacts quite facilely with the adsorbed oxygen atoms. In addition, the O species from O2 dissociation exhibits reactivity for the selective oxidation of methanol but not for CO. The TAP experiments also revealed that the surface of the npAu catalyst is saturated with adsorbed O under steady state reaction conditions, at least for the pulse reaction. PMID:27376884

  5. Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation

    NASA Astrophysics Data System (ADS)

    He, Qian; Freakley, Simon J.; Edwards, Jennifer K.; Carley, Albert F.; Borisevich, Albina Y.; Mineo, Yuki; Haruta, Masatake; Hutchings, Graham J.; Kiely, Christopher J.

    2016-09-01

    The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviours after heat treatment of Au/FeOx materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. Correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeOx catalyst.

  6. Active sites and mechanisms for direct oxidation of benzene to phenol over carbon catalysts.

    PubMed

    Wen, Guodong; Wu, Shuchang; Li, Bo; Dai, Chunli; Su, Dang Sheng

    2015-03-23

    The direct oxidation of benzene to phenol with H2 O2 as the oxidizer, which is regarded as an environmentally friendly process, can be efficiently catalyzed by carbon catalysts. However, the detailed roles of carbon catalysts, especially what is the active site, are still a topic of debate controversy. Herein, we present a fundamental consideration of possible mechanisms for this oxidation reaction by using small molecular model catalysts, Raman spectra, static secondary ion mass spectroscopy (SIMS), DFT calculations, quasi in situ ATR-IR and UV spectra. Our study indicates that the defects, being favorable for the formation of active oxygen species, are the active sites for this oxidation reaction. Furthermore, one type of active defect, namely the armchair configuration defect was successfully identified.

  7. Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation

    PubMed Central

    He, Qian; Freakley, Simon J.; Edwards, Jennifer K.; Carley, Albert F.; Borisevich, Albina Y.; Mineo, Yuki; Haruta, Masatake; Hutchings, Graham J.; Kiely, Christopher J.

    2016-01-01

    The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviours after heat treatment of Au/FeOx materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. Correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeOx catalyst. PMID:27671143

  8. Absence of functional active zone protein Bassoon affects assembly and transport of ribbon precursors during early steps of photoreceptor synaptogenesis.

    PubMed

    Regus-Leidig, Hanna; tom Dieck, Susanne; Brandstätter, Johann Helmut

    2010-06-01

    The retinal photoreceptor ribbon synapse is a structurally and functionally unique type of chemical synapse, specialized for tonic release of neurotransmitter in the dark. It is characterized by the presynaptic ribbon, an electron-dense organelle at the active zone, which is covered by hundreds of synaptic vesicles. Recently we showed that photoreceptor ribbon complexes are assembled from non-membranous, spherical densities--the precursor spheres--during the first two postnatal weeks of photoreceptor synaptogenesis. A core component of the precursor spheres and a key player in attaching the ribbon to the active zone is the presynaptic cytomatrix protein Bassoon. In this study, we examined in a comprehensive light and electron microscopic analysis whether Bassoon plays a role in the formation of the precursor spheres using Bassoon mutant mice lacking functional Bassoon. We report that developing Bassoon mutant photoreceptors contain fewer and smaller precursor spheres and that transport of precursor spheres to nascent synapses is delayed compared to wild-type controls. Moreover, western blot analyses of homogenates from postnatal day 0 (P0) to P14 Bassoon mutant retinae exhibit lower RIBEYE and Piccolo protein levels compared to the wild type, indicating elevated protein degradation in the absence of Bassoon. Our findings reveal a novel function of Bassoon in the early formation and delivery of precursor spheres to nascent ribbon synaptic sites in addition to its known role in ribbon anchoring during later stages of photoreceptor ribbon synaptogenesis.

  9. Computational approaches to the determination of active site structures and reaction mechanisms in heterogeneous catalysts.

    PubMed

    Catlow, C R A; French, S A; Sokol, A A; Thomas, J M

    2005-04-15

    We apply quantum chemical methods to the study of active site structures and reaction mechanisms in mesoporous silica and metal oxide catalysts. Our approach is based on the use of both molecular cluster and embedded cluster (QM/MM) techniques, where the active site and molecular complex are described using density functional theory (DFT) and the embedding matrix simulated by shell model potentials. We consider three case studies: alkene epoxidation over the microporous TS-1 catalyst; methanol synthesis on ZnO and Cu/ZnO and C-H bond activation over Li-doped MgO.

  10. Computational approaches to the determination of active site structures and reaction mechanisms in heterogeneous catalysts.

    PubMed

    Catlow, C R A; French, S A; Sokol, A A; Thomas, J M

    2005-04-15

    We apply quantum chemical methods to the study of active site structures and reaction mechanisms in mesoporous silica and metal oxide catalysts. Our approach is based on the use of both molecular cluster and embedded cluster (QM/MM) techniques, where the active site and molecular complex are described using density functional theory (DFT) and the embedding matrix simulated by shell model potentials. We consider three case studies: alkene epoxidation over the microporous TS-1 catalyst; methanol synthesis on ZnO and Cu/ZnO and C-H bond activation over Li-doped MgO. PMID:15901543

  11. Potential of jackfruit peel as precursor for activated carbon prepared by microwave induced NaOH activation.

    PubMed

    Foo, K Y; Hameed, B H

    2012-05-01

    The feasibility of preparing activated carbon (JPAC) from jackfruit peel, an industrial residue abundantly available from food manufacturing plants via microwave-assisted NaOH activation was explored. The influences of chemical impregnation ratio, microwave power and radiation time on the properties of activated carbon were investigated. JPAC was examined by pore structural analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption isotherm, elemental analysis, surface acidity/basicity and zeta potential measurements. The adsorptive behavior of JPAC was quantified using methylene blue as model dye compound. The best conditions resulted in JPAC with a monolayer adsorption capacity of 400.06 mg/g and carbon yield of 80.82%. The adsorption data was best fitted to the pseudo-second-order equation, while the adsorption mechanism was well described by the intraparticle diffusion model. The findings revealed the versatility of jackfruit peels as good precursor for preparation of high quality activated carbon.

  12. Stress-strain sensor for monitoring seismic precursors and fault activities in the sand

    NASA Astrophysics Data System (ADS)

    Du, Qiujiao; Sun, Wei; Zeng, Zuoxun

    2016-04-01

    In this paper, a sensor to monitor stress-strain signals in a granular medium is used to detect seismic precursory information. Compared with the widely used sensors of borehole stress in the rock, the sensor has more convenient operation, higher output sensitivity, compactness and farther propagation effect. The stress and strain changes before Pu'er Ms6.4 earthquake in China are recorded by Beijing and Xinmin stations, and its corresponding fault activities are analyzed. Study indicates anomalous amplitude of strain signal reaches 10 times higher than that of ordinary background, and compressive oscillation and extensional oscillation occurred constantly before the earthquake. The method and results presented in the paper provide a new way for investigating seismic precursors for shallow-source earthquakes.

  13. Relationship of prodigiosin condensing enzyme activity to the biosynthesis of prodigiosin and its precursors in Serratia marcescens.

    PubMed

    Cho, L K; Lowe, J A; Maguire, R B; Tsang, J C

    1987-04-15

    Prodigiosin condensing enzyme (PCE) activities were present in Serratia marcescens wild type 08, mutants OF, WF and 9-3-3. Their specific activities exhibited different maxima and at different times during the late log phase or the early stationary phase of cell growth. The levels of prodigiosin and its precursors also showed a significant increase at this period. The results support that prodigiosin and/or its precursors are secondary metabolites. The ubiquity of the PCE activity in mutants deficient in prodigiosin biosynthesis suggest that this particular enzyme may also be present in non-pigmented clinical isolates.

  14. Nanoscaled palladium catalysts on activated carbon support "Sibunit" for fine organic synthesis

    NASA Astrophysics Data System (ADS)

    Simakova, I.; Koskin, A.; Deliy, I.; Simakov, A.

    2005-08-01

    The application of nanosized palladium catalysts has gained growing importance over the last few years. Palladiumbased catalytic methods for fine organic synthesis permits the replacement of traditional labor-consuming techniques in multi-step organic syntheses and provides an improvement from the standpoint of cost and environmental impact. The use of activated carbon "Sibunit" as a substrate for catalysts has been fostered by the substrate's high surface area, chemical inertness both in acidic and basic media, and at the same time by the absence of very strong acidic centers on its surface which could promote undesirable side reactions during the catalytic run. A conversion of alpha-pinene derivatives to commercial biologically active compounds and fragrances as well as sun screens with ultra violet filtering properties, involves a catalytic hydrogenation as a key intermediate step. The aim of the present work is to clarify the factors favoring the dispersion of Pd metal on carbon. The effect of reduction temperature and pretreatment of the carbon surface on metal size during preparation of Pd on "Sibunit" catalysts for selective verbenol conversion was studied. The electron microscopy method (TEM) was used to show the influence on Pd metal dispersion of carbon surface oxidation by the oxidant H2O2, HNO3. The catalytic activity of Pd/C catalyst samples in verbenol hydrogenation reaction was determined. Kinetic peculiarities of verbenol hydrogenation over the most active catalyst sample were obtained.

  15. Engineering catalytic activity via ion beam bombardment of catalyst supports for vertically aligned carbon nanotube growth

    DOE PAGES

    Islam, A. E.; Zakharov, D.; Stach, E. A.; Nikoleav, P.; Amama, P. B.; Sargent, G.; Saber, S.; Huffman, D.; Erford, M.; Semiatin, S. L.; et al

    2015-09-16

    Carbon nanotube growth depends on the catalytic activity of metal nanoparticles on alumina or silica supports. The control on catalytic activity is generally achieved by variations in water concentration, carbon feed, and sample placement on a few types of alumina or silica catalyst supports obtained via thin film deposition. We have recently expanded the choice of catalyst supports by engineering inactive substrates like c-cut sapphire via ion beam bombardment. The deterministic control on the structure and chemistry of catalyst supports obtained by tuning the degree of beam-induced damage have enabled better regulation of the activity of Fe catalysts only inmore » the ion beam bombarded areas and hence enabled controllable super growth of carbon nanotubes. A wide range of surface characterization techniques were used to monitor the catalytically active surface engineered via ion beam bombardment. The proposed method offers a versatile way to control carbon nanotube growth in patterned areas and also enhances the current understanding of the growth process. As a result, with the right choice of water concentration, carbon feed and sample placement, engineered catalyst supports may extend the carbon nanotube growth yield to a level that is even higher than the ones reported here, and thus offers promising applications of carbon nanotubes in electronics, heat exchanger, and energy storage.« less

  16. Engineering catalytic activity via ion beam bombardment of catalyst supports for vertically aligned carbon nanotube growth

    SciTech Connect

    Islam, A. E.; Zakharov, D.; Stach, E. A.; Nikoleav, P.; Amama, P. B.; Sargent, G.; Saber, S.; Huffman, D.; Erford, M.; Semiatin, S. L.; Maruyama, B.

    2015-09-16

    Carbon nanotube growth depends on the catalytic activity of metal nanoparticles on alumina or silica supports. The control on catalytic activity is generally achieved by variations in water concentration, carbon feed, and sample placement on a few types of alumina or silica catalyst supports obtained via thin film deposition. We have recently expanded the choice of catalyst supports by engineering inactive substrates like c-cut sapphire via ion beam bombardment. The deterministic control on the structure and chemistry of catalyst supports obtained by tuning the degree of beam-induced damage have enabled better regulation of the activity of Fe catalysts only in the ion beam bombarded areas and hence enabled controllable super growth of carbon nanotubes. A wide range of surface characterization techniques were used to monitor the catalytically active surface engineered via ion beam bombardment. The proposed method offers a versatile way to control carbon nanotube growth in patterned areas and also enhances the current understanding of the growth process. As a result, with the right choice of water concentration, carbon feed and sample placement, engineered catalyst supports may extend the carbon nanotube growth yield to a level that is even higher than the ones reported here, and thus offers promising applications of carbon nanotubes in electronics, heat exchanger, and energy storage.

  17. ZrO2 -Based Alternatives to Conventional Propane Dehydrogenation Catalysts: Active Sites, Design, and Performance.

    PubMed

    Otroshchenko, Tatyana; Sokolov, Sergey; Stoyanova, Mariana; Kondratenko, Vita A; Rodemerck, Uwe; Linke, David; Kondratenko, Evgenii V

    2015-12-21

    Non-oxidative dehydrogenation of propane to propene is an established large-scale process that, however, faces challenges, particularly in catalyst development; these are the toxicity of chromium compounds, high cost of platinum, and catalyst durability. Herein, we describe the design of unconventional catalysts based on bulk materials with a certain defect structure, for example, ZrO2 promoted with other metal oxides. Comprehensive characterization supports the hypothesis that coordinatively unsaturated Zr cations are the active sites for propane dehydrogenation. Their concentration can be adjusted by varying the kind of ZrO2 promoter and/or supporting tiny amounts of hydrogenation-active metal. Accordingly designed Cu(0.05 wt %)/ZrO2 -La2 O3 showed industrially relevant activity and durability over ca. 240 h on stream in a series of 60 dehydrogenation and oxidative regeneration cycles between 550 and 625 °C. PMID:26566072

  18. Copper on responsive polymer microgels: a recyclable catalyst exhibiting tunable catalytic activity.

    PubMed

    Wu, Qingshi; Cheng, Han; Chang, Aiping; Bai, Xue; Lu, Fan; Wu, Weitai

    2014-11-25

    Copper has been immobilized on a chitosan-based responsive polymer microgel by simply stirring the microgel dispersion with copper sulfate. The ensuing catalyst is highly active for a model azide-alkyne [3+2]-cycloaddition reaction, and can be recycled at least 5 times; the catalytic activity can be tuned via swelling-deswelling transitions of the polymer gels. PMID:25283806

  19. Fischer–Tropsch Synthesis: Characterization Rb Promoted Iron Catalyst

    SciTech Connect

    Sarkar,A.; Jacobs, G.; Ji, Y.; Hamdeh, H.; Davis, B.

    2008-01-01

    Rubidium promoted iron Fischer-Tropsch synthesis (FTS) catalysts were prepared with two Rb/Fe atomic ratios (1.44/100 and 5/100) using rubidium nitrate and rubidium carbonate as rubidium precursors. Results of catalytic activity and deactivation studies in a CSTR revealed that rubidium promoted catalysts result in a steady conversion with a lower deactivation rate than that of the corresponding unpromoted catalyst although the initial activity of the promoted catalyst was almost half that of the unpromoted catalyst. Rubidium promotion results in lower methane production, and higher CO2, alkene and 1-alkene fraction in FTS products. M{umlt o}ssbauer spectroscopic measurements of CO activated and working catalyst samples indicated that the composition of the iron carbide phase formed after carbidization was -Fe5 C2 for both promoted and unpromoted catalysts. However, in the case of the rubidium promoted catalyst, '-Fe2.2C became the predominant carbidic phase as FTS continued and the overall catalyst composition remained carbidic in nature. In contrast, the carbide content of the unpromoted catalyst was found to decline very quickly as a function of synthesis time. Results of XANES and EXAFS measurements suggested that rubidium was present in the oxidized state and that the compound most prevalent in the active catalyst samples closely resembled that of rubidium carbonate.

  20. A delafossite-based copper catalyst for sustainable Cl2 production by HCl oxidation.

    PubMed

    Mondelli, Cecilia; Amrute, Amol P; Schmidt, Timm; Pérez-Ramírez, Javier

    2011-07-01

    A copper catalyst based on a delafossite precursor (CuAlO(2)) displays high activity and extraordinary lifetime in the gas-phase oxidation of HCl to Cl(2), representing a cost-effective alternative to RuO(2)-based catalysts for chlorine recycling. PMID:21607240

  1. Ni/Fe-supported over hydrotalcites precursors as catalysts for clean and selective oxidation of Basic Yellow 11: reaction intermediates determination.

    PubMed

    Ovejero, G; Rodríguez, A; Vallet, A; García, J

    2013-01-01

    In this work, Basic Yellow 11 (BY 11) was employed as model compound to study catalytic wet air oxidation as a pre-treatment step to the conventional biological oxidation. Ni and Fe catalysts supported over hydrotalcite (HT) were prepared by incipient wetness and excess impregnation to obtain catalysts with different metal loadings (from 1 to 10 wt.%). HTs were synthesized by co-precipitation and characterized with XRD, X-ray fluorescence (XRF), BET, thermogravimetric analysis and SEM. Results showed that dye conversion increased with Ni and Fe content up to 7 wt.% and that the most effective catalyst were prepared by incipient wetness impregnation. The influence of metal loading in the catalyst, and the preparation method as well as the reaction conditions was investigated. A mechanism and reaction pathways for BY 11 during catalytic liquid phase oxidation have also been proposed.

  2. Ni/Fe-supported over hydrotalcites precursors as catalysts for clean and selective oxidation of Basic Yellow 11: reaction intermediates determination.

    PubMed

    Ovejero, G; Rodríguez, A; Vallet, A; García, J

    2013-01-01

    In this work, Basic Yellow 11 (BY 11) was employed as model compound to study catalytic wet air oxidation as a pre-treatment step to the conventional biological oxidation. Ni and Fe catalysts supported over hydrotalcite (HT) were prepared by incipient wetness and excess impregnation to obtain catalysts with different metal loadings (from 1 to 10 wt.%). HTs were synthesized by co-precipitation and characterized with XRD, X-ray fluorescence (XRF), BET, thermogravimetric analysis and SEM. Results showed that dye conversion increased with Ni and Fe content up to 7 wt.% and that the most effective catalyst were prepared by incipient wetness impregnation. The influence of metal loading in the catalyst, and the preparation method as well as the reaction conditions was investigated. A mechanism and reaction pathways for BY 11 during catalytic liquid phase oxidation have also been proposed. PMID:22960061

  3. High-activity PtRuPd/C catalyst for direct dimethyl ether fuel cells.

    PubMed

    Li, Qing; Wen, Xiaodong; Wu, Gang; Chung, Hoon T; Gao, Rui; Zelenay, Piotr

    2015-06-22

    Dimethyl ether (DME) has been considered as a promising alternative fuel for direct-feed fuel cells but lack of an efficient DME oxidation electrocatalyst has remained the challenge for the commercialization of the direct DME fuel cell. The commonly studied binary PtRu catalyst shows much lower activity in DME than methanol oxidation. In this work, guided by density functional theory (DFT) calculation, a ternary carbon-supported PtRuPd catalyst was designed and synthesized for DME electrooxidation. DFT calculations indicated that Pd in the ternary PtRuPd catalyst is capable of significantly decreasing the activation energy of the CO and CH bond scission during the oxidation process. As evidenced by both electrochemical measurements in an aqueous electrolyte and polymer-electrolyte fuel cell testing, the ternary catalyst shows much higher activity (two-fold enhancement at 0.5 V in fuel cells) than the state-of-the-art binary Pt50 Ru50 /C catalyst (HiSPEC 12100).

  4. The role of surface reactions on the active and selective catalyst design for bioethanol steam reforming

    NASA Astrophysics Data System (ADS)

    Benito, M.; Padilla, R.; Serrano-Lotina, A.; Rodríguez, L.; Brey, J. J.; Daza, L.

    In order to study the role of surface reactions involved in bioethanol steam reforming mechanism, a very active and selective catalyst for hydrogen production was analysed. The highest activity was obtained at 700 °C, temperature at which the catalyst achieved an ethanol conversion of 100% and a selectivity to hydrogen close to 70%. It also exhibited a very high hydrogen production efficiency, higher than 4.5 mol H 2 per mol of EtOH fed. The catalyst was operated at a steam to carbon ratio (S/C) of 4.8, at 700 °C and atmospheric pressure. No by-products, such as ethylene or acetaldehyde were observed. In order to consider a further application in an ethanol processor, a long-term stability test was performed under the conditions previously reported. After 750 h, the catalyst still exhibited a high stability and selectivity to hydrogen production. Based on the intermediate products detected by temperature programmed desorption and reaction (TPD and TPR) experiments, a reaction pathway was proposed. Firstly, the adsorbed ethanol is dehydrogenated to acetaldehyde producing hydrogen. Secondly, the adsorbed acetaldehyde is transformed into acetone via acetic acid formation. Finally, acetone is reformed to produce hydrogen and carbon dioxide, which were the final reaction products. The promotion of such reaction sequence is the key to develop an active, selective and stable catalyst, which is the technical barrier for hydrogen production by ethanol reforming.

  5. Vanadium(V) Complexes with Substituted 1,5-bis(2-hydroxybenzaldehyde)carbohydrazones and Their Use As Catalyst Precursors in Oxidation of Cyclohexane.

    PubMed

    Dragancea, Diana; Talmaci, Natalia; Shova, Sergiu; Novitchi, Ghenadie; Darvasiová, Denisa; Rapta, Peter; Breza, Martin; Galanski, Markus; Kožı́šek, Jozef; Martins, Nuno M R; Martins, Luísa M D R S; Pombeiro, Armando J L; Arion, Vladimir B

    2016-09-19

    Six dinuclear vanadium(V) complexes have been synthesized: NH4[(VO2)2((H)LH)] (NH4[1]), NH4[(VO2)2((t-Bu)LH)] (NH4[2]), NH4[(VO2)2((Cl)LH)] (NH4[3]), [(VO2)(VO)((H)LH)(CH3O)] (4), [(VO2)(VO)((t-Bu)LH)(C2H5O)] (5), and [(VO2)(VO)((Cl)LH)(CH3O)(CH3OH/H2O)] (6) (where (H)LH4 = 1,5-bis(2-hydroxybenzaldehyde)carbohydrazone, (t-Bu)LH4 = 1,5-bis(3,5-di-tert-butyl-2-hydroxybenzaldehyde)carbohydrazone, and (Cl)LH4 = 1,5-bis(3,5-dichloro-2-hydroxybenzaldehyde)carbohydrazone). The structures of NH4[1] and 4-6 have been determined by X-ray diffraction (XRD) analysis. In all complexes, the triply deprotonated ligand accommodates two V ions, using two different binding sites ONN and ONO separated by a diazine unit -N-N-. In two pockets of NH4[1], two identical VO2(+) entities are present, whereas, in those of 4-6, two different VO2(+) and VO(3+) are bound. The highest oxidation state of V ions was corroborated by X-ray data, indicating the presence of alkoxido ligand bound to VO(3+) in 4-6, charge density measurements on 4, magnetic susceptibility, NMR spectroscopy, spectroelectrochemistry, and density functional theory (DFT) calculations. All four complexes characterized by XRD form dimeric associates in the solid state, which, however, do not remain intact in solution. Compounds NH4[1], NH4[2], and 4-6 were applied as alternative selective homogeneous catalysts for the industrially significant oxidation of cyclohexane to cyclohexanol and cyclohexanone. The peroxidative (with tert-butyl hydroperoxide, TBHP) oxidation of cyclohexane was performed under solvent-free and additive-free conditions and under low-power microwave (MW) irradiation. Cyclohexanol and cyclohexanone were the only products obtained (high selectivity), after 1.5 h of MW irradiation. Theoretical calculations suggest a key mechanistic role played by the carbohydrazone ligand, which can undergo reduction, instead of the metal itself, to form an active reduced form of the catalyst. PMID:27563933

  6. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, October--December 1992

    SciTech Connect

    Song, Chunshan; Schobert, H.H.

    1993-02-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on the development of novel bimetallic dispersed catalysts for temperature-programmed liquefaction. The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular that can be used in low precursors concentrations (< 1 %) but exhibit high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. The major technical approaches are, first, to prepare the desired heteronuclear organometallic molecules as catalyst precursors that contain covalently bound, two different metal atoms and sulfur in a single molecule. Such precursors will generate finely dispersed bimetallic catalysts such as Fe-Mo, Co-Mo and Ni-Mo binary sulfides upon thermal decomposition. The second major technical approach is to perform the liquefaction of coals unpregnated with the organometallic precursors under temperature-programmed conditions, where the programmed heat-up serves as a step for both catalyst activation and coal pretreatment or preconversion. Two to three different complexes for each of the Fe-Mo, Co-Mo, and Ni-Mo combinations will be prepared. Initial catalyst screening tests will be conducted using a subbituminous coal and a bituminous coal. Effects of coal rank and solvents will be examined with the selected bimetallic catalysts which showed much higher activity than the dispersed catalysts from conventional precursors.

  7. Two Peptides Derived from the Nerve Growth Factor Precursor Are Biologically Active

    PubMed Central

    Dicou, Eleni; Pflug, Beth; Magazin, Marilyn; Lehy, Thérèse; Djakiew, Daniel; Ferrara, Pascual; Nerrière, Véronique; Harvie, Douglas

    1997-01-01

    This report provides evidence that the proregion of the NGF precursor protein contains two novel bioactive peptides. The presence of pairs of basic amino acid (aa) residues in the NGF proregion suggests that two or three peptides other than NGF may be generated by proteolytic cleavage. Synthetic peptides of 29 aa (LIP1) and 38aa (LIP2) corresponding to the sequences −71 to −43 and −40 to −3 of the proNGF, respectively, were used in this study. ELISA specific for these two peptides revealed their presence in the rat intestine. LIP1 was localized by immunohistochemistry in endocrine cells of the intestinal epithelium, and LIP2 was immunoprecipitated from an intestinal extract. We also provide evidence for the presence of specific receptors for LIP2 in several cell lines. Scatchard analysis indicated the presence of a low affinity binding site with a Kd of ∼10−7 M and a high affinity binding site of 10−9 M. Cross-linking studies revealed receptor forms of about 140 kD and 93 kD in a prostatic adenocarcinoma cell line. LIP1 and LIP2 induced rapid F-actin redistribution in PC12 cells within 2 min of incubation, which suggests a role of LIP1 and LIP2 in the process of neurite outgrowth. Furthermore, both propeptides induced rapid tyrosine phosphorylation of the Trk protein in both prostatic adenocarcinoma cells and PC12 cells, thus implicating trk in their mechanism of action. These results support our hypothesis that two peptides within the NGF precursor protein are biologically active. PMID:9015309

  8. Inflammatory Eicosanoids Increase Amyloid Precursor Protein Expression via Activation of Multiple Neuronal Receptors

    PubMed Central

    Herbst-Robinson, Katie J.; Liu, Li; James, Michael; Yao, Yuemang; Xie, Sharon X.; Brunden, Kurt R.

    2015-01-01

    Senile plaques comprised of Aβ peptides are a hallmark of Alzheimer’s disease (AD) brain, as are activated glia that release inflammatory molecules, including eicosanoids. Previous studies have demonstrated that amyloid precursor protein (APP) and Aβ levels can be increased through activation of thromboxane A2-prostanoid (TP) receptors on neurons. We demonstrate that TP receptor regulation of APP expression depends on Gαq-signaling and conventional protein kinase C isoforms. Importantly, we discovered that Gαq-linked prostaglandin E2 and leukotriene D4 receptors also regulate APP expression. Prostaglandin E2 and thromboxane A2, as well as total APP levels, were found to be elevated in the brains of aged 5XFAD transgenic mice harboring Aβ plaques and activated glia, suggesting that increased APP expression resulted from eicosanoid binding to Gαq-linked neuronal receptors. Notably, inhibition of eicosanoid synthesis significantly lowered brain APP protein levels in aged 5XFAD mice. These results provide new insights into potential AD therapeutic strategies. PMID:26672557

  9. PERK Activation Promotes Medulloblastoma Tumorigenesis by Attenuating Premalignant Granule Cell Precursor Apoptosis.

    PubMed

    Ho, Yeung; Li, Xiting; Jamison, Stephanie; Harding, Heather P; McKinnon, Peter J; Ron, David; Lin, Wensheng

    2016-07-01

    Evidence suggests that activation of pancreatic endoplasmic reticulum kinase (PERK) signaling in response to endoplasmic reticulum stress negatively or positively influences cell transformation by regulating apoptosis. Patched1 heterozygous deficient (Ptch1(+/-)) mice reproduce human Gorlin's syndrome and are regarded as the best animal model to study tumorigenesis of the sonic hedgehog subgroup of medulloblastomas. It is believed that medulloblastomas in Ptch1(+/-) mice results from the transformation of granule cell precursors (GCPs) in the developing cerebellum. Here, we determined the role of PERK signaling on medulloblastoma tumorigenesis by assessing its effects on premalignant GCPs and tumor cells. We found that PERK signaling was activated in both premalignant GCPs in young Ptch1(+/-) mice and medulloblastoma cells in adult mice. We demonstrated that PERK haploinsufficiency reduced the incidence of medulloblastomas in Ptch1(+/-) mice. Interestingly, PERK haploinsufficiency enhanced apoptosis of premalignant GCPs in young Ptch1(+/-) mice but had no significant effect on medulloblastoma cells in adult mice. Moreover, we showed that the PERK pathway was activated in medulloblastomas in humans. These results suggest that PERK signaling promotes medulloblastoma tumorigenesis by attenuating apoptosis of premalignant GCPs during the course of malignant transformation. PMID:27181404

  10. In Situ Observation of Active Oxygen Species in Fe-Containing Ni-Based Oxygen Evolution Catalysts: The Effect of pH on Electrochemical Activity.

    PubMed

    Trześniewski, Bartek J; Diaz-Morales, Oscar; Vermaas, David A; Longo, Alessandro; Bras, Wim; Koper, Marc T M; Smith, Wilson A

    2015-12-01

    Ni-based oxygen evolution catalysts (OECs) are cost-effective and very active materials that can be potentially used for efficient solar-to-fuel conversion process toward sustainable energy generation. We present a systematic spectroelectrochemical characterization of two Fe-containing Ni-based OECs, namely nickel borate (Ni(Fe)-B(i)) and nickel oxyhydroxide (Ni(Fe)OOH). Our Raman and X-ray absorption spectroscopy results show that both OECs are chemically similar, and that the borate anions do not play an apparent role in the catalytic process at pH 13. Furthermore, we show spectroscopic evidence for the generation of negatively charged sites in both OECs (NiOO(-)), which can be described as adsorbed "active oxygen". Our data conclusively links the OER activity of the Ni-based OECs with the generation of those sites on the surface of the OECs. The OER activity of both OECs is strongly pH dependent, which can be attributed to a deprotonation process of the Ni-based OECs, leading to the formation of the negatively charged surface sites that act as OER precursors. This work emphasizes the relevance of the electrolyte effect to obtain catalytically active phases in Ni-based OECs, in addition to the key role of the Fe impurities. This effect should be carefully considered in the development of Ni-based compounds meant to catalyze the OER at moderate pHs. Complementarily, UV-vis spectroscopy measurements show strong darkening of those catalysts in the catalytically active state. This coloration effect is directly related to the oxidation of nickel and can be an important factor limiting the efficiency of solar-driven devices utilizing Ni-based OECs.

  11. NOx reduction Activity over Phosphate-supported Platinum Catalysts with Hydrogen under Oxygen-rich Condition

    NASA Astrophysics Data System (ADS)

    Itoh, M.; Takehara, M.; Saito, M.; Machida, K.

    2011-10-01

    The phosphate supported Pt catalysts (Pt/AlPO4, Pt/CePO4, Pt/CeP2O7, Pt/SnP2O7, Pt/TiP2O7, Pt/Zn3(PO4)2) were prepared by a conventional impregnation method to evaluate their selective catalytic reduction activity of NOx under excess oxygen condition. Among them, good NOx reduction activity was obtained on the Pt/AlPO4 catalyst. Specific adsorption species during the NOx reduction were checked by a diffuse reflectance infrared Fourier transform spectrum (DRIFTs) measurement to examine the reaction mechanism. Also NH3 temperature programmed desorption measurements were performed for all catalysts and their catalytic properties were discussed from the viewpoints of solid acidity.

  12. Enhanced Oxygen Reduction Activity In Acid By Tin-Oxide Supported Au Nanoparticle Catalysts

    SciTech Connect

    Baker,W.; Pietron, J.; Teliska, M.; Bouwman, P.; Ramaker, D.; Swider-Lyons, K.

    2006-01-01

    Gold nanoparticles supported on hydrous tin-oxide (Au-SnO{sub x}) are active for the four-electron oxygen reduction reaction in an acid electrolyte. The unique electrocatalytic of the Au-SnO is confirmed by the low amount of peroxide detected with rotating ring-disk electrode voltammetry and Koutecky-Levich analysis. In comparison, 10 wt % Au supported on Vulcan carbon and SnO{sub x} catalysts both produce significant peroxide in the acid electrolyte, indicating only a two-electron reduction reaction. Characterization of the Au-SnO{sub x} catalyst reveals a high-surface area, amorphous support with 1.7 nm gold metal particles. The high catalytic activity of the Au-SnO is attributed to metal support interactions. The results demonstrate a possible path to non-Pt catalysts for proton exchange membrane fuel cell cathodes.

  13. Kinetics studies of d-glucose hydrogenation over activated charcoal supported platinum catalyst

    NASA Astrophysics Data System (ADS)

    Ahmed, Muthanna J.

    2012-02-01

    The kinetics of the catalytic hydrogenation of d-glucose to produce d-sorbitol was studied in a three-phase laboratory scale reactor. The hydrogenation reactions were performed on activated charcoal supported platinum catalyst in the temperature range 25-65°C and in a constant pressure of 1 atm. The kinetic data were modeled by zero, first and second-order reaction equations. In the operating regimes studied, the results show that the hydrogenation reaction was of a first order with respect to d-glucose concentration. Also the activation energy of the reaction was determined, and found to be 12.33 kJ mole-1. A set of experiment was carried out to test the deactivation of the catalyst, and the results show that the deactivation is slow with the ability of using the catalyst for several times with a small decrease in product yield.

  14. Air Oxidation of Activated Carbon to Synthesize a Biomimetic Catalyst for Hydrolysis of Cellulose.

    PubMed

    Shrotri, Abhijit; Kobayashi, Hirokazu; Fukuoka, Atsushi

    2016-06-01

    Oxygenated carbon catalyzes the hydrolysis of cellulose present in lignocellulosic biomass by utilizing the weakly acidic functional groups on its surface. Here we report the synthesis of a biomimetic carbon catalyst by simple and economical air-oxidation of a commercially available activated carbon. Air- oxidation at 450-500 °C introduced 2000-2400 μmol g(-1) of oxygenated functional groups on the material with minor changes in the textural properties. Selectivity towards the formation of carboxylic groups on the catalyst surface increased with the increase in oxidation temperature. The degree of oxidation on carbon catalyst was found to be proportional to its activity for hydrolysis of cellulose. The hydrolysis of eucalyptus in the presence of carbon oxidized at 475 °C afforded glucose yield of 77 % and xylose yield of 67 %.

  15. Catalysts possessing augmented C-O and C-N hydrogenolysis activity. Progress report No. 3, April-June 1984

    SciTech Connect

    Massoth, F.E.; Shabtai, J.S.

    1984-07-01

    The aim this research project is to synthesize and investigate new sulfided catalyst systems having higher carbon-heteroatom hydrogenolysis activity as compared with ring hydrogenation activity. A fundamental approach is being applied to gain understanding of the basic catalytic properties which relate to hydrogenolysis, hydrogenation and cracking functions of the catalysts. This involves preparation of new catalysts, characterization of their properties and model compound reactivity studies. In another part of the project, selected catalysts are being applied in studies of more complex O- and N- containing model compounds with the objective of providing fundamental data on the stereochemistry of HDO and HDN reactions. These data will be used to develop steric surface-reactant models for sulfided catalysts. Supported noble metal catalysts containing Rh and Pd were prepared by incipient wetness impregnation of ..gamma..-Al/sub 2/O/sub 3/ using nitrate solutions. Catalysts containing also Co and Cr were similarly prepared. Catalyst activities for HDO and HDN were evaluated using the model compounds dibenzofuran and indole. Characterization work by ESCA and oxygen chemisorption, of CoMo catalysts, and stereochemical studies with several catalysts were also initiated. 15 references, 1 figure, 3 tables.

  16. Improved coal liquefaction using carbon-supported hydrogenation catalysts: Quarterly reports for the period 1 April-30 September 1986. [Mo/C catalyst

    SciTech Connect

    Scaroni, A.W.; Derbyshire, F.J.; Solar, J.M.; Abotsi, G.M.K.

    1986-09-01

    Characterization studies of sulfided Mo/C catalysts have been continued. The stoichiometry of unsupported molybdenum sulfide, prepared by laboratory procedures, was confirmed to have an S/Mo atomic ratio of 2.0 after reduction in hydrogen at 400/sup 0/C. Toluene chemisorption has been used as a technique to obtain some indication of the catalyst dispersion and the active surface areas of Mo/C catalysts. The measured toluene surface areas were found to correlate with the catalyst activities for coal asphaltene conversion. Investigations of the effect of hydrogen pressure (500 to 1500 psig) have been made of the activities of an Mo/Ambersorb XE-348 catalyst and an Mo/NH/sub 3/ pretreated Ambersorb XE-348 catalyst (pretreated for 1.5 h at 873 K) for coal liquids conversion. The catalyst prepared on the pretreated support showed higher activity for asphaltene conversion. For both catalysts, asphaltene conversion increased and coking propensity decreased with increasing H/sub 2/ pressure. Mo/C catalysts have been prepared on five different supports using a molybdenum acetylacetonate precursor. The supports were loaded by adsorption from aqueous solution rather than impregnation by the incipient wetness technique. Preliminary results indicate that some of the catalysts prepared by this procedure possess higher activities for thiophene HDS than those earlier reported using molybdenumtricarbonyltriacetonitrile as a precursor. 30 refs., 9 figs., 7 tabs.

  17. Non-directed, carbonate-mediated C-H activation and aerobic C-H oxygenation with Cp*Ir catalysts.

    PubMed

    Kerr, M E; Ahmed, I; Gunay, A; Venditto, N J; Zhu, F; Ison, E A; Emmert, M H

    2016-06-14

    The effect of oxidatively stable L- and X-type additives on the activity of Cp*Ir catalyst precursors in the C-H activation of arenes has been studied. Turnover numbers for C-H activation of up to 65 can thus be achieved, as determined by H/D exchange in MeOH-D4. In particular, carbonate additives are found to enhance the C-H activation reactivity of Cp*Ir(H2O)3(OTf)2 () more significantly than L-type ligands investigated in this study. Based on these studies, Cp*Ir/carbonate systems are developed that catalyze the aerobic Csp(3)-H oxygenation of alkyl arenes, employing air as oxidant.

  18. Nanocrystalline Ferrihydrite-Based Catalysts for Fischer-Tropsch Synthesis: Part II. Effects of Activation Gases on the Catalytic Performance.

    PubMed

    Rhim, Geun Bae; Hong, Seok Yong; Park, Ji Chan; Jung, Heon; Rhee, Young Woo; Chun, Dong Hyun

    2016-02-01

    Fischer-Tropsch synthesis (FTS) was carried out over nanocrystalline ferrihydrite-based (Fe9O2(OH)23) catalysts activated by different reducing agents: syngas (H2+CO), CO, and H2. The syngas activation successfully changed the ferrihydrite-based catalysts into an active and stable catalytic structure with chi-carbide (Fe2.5 C) and epsilon'-carbide (Fe2.2 C). The crystal structure of the catalysts obtained by syngas activation was similar to the structure obtained by CO activation; this similarity was probably due to the peculiar reduction behavior of the ferrihydrite-based catalysts, which exhibit much greater reducibility in CO atmosphere than in H2 atmosphere. The performance of the catalysts activated by syngas was much higher than the performance of the catalysts activated by H2 and was comparable to the performance of the catalysts activated by CO. This strongly demonstrates that the ferrihydrite-based catalysts are advantageous for industrial FTS processes because syngas can be commonly used for both activation pre-treatment and subsequent reaction.

  19. Nanocrystalline Ferrihydrite-Based Catalysts for Fischer-Tropsch Synthesis: Part II. Effects of Activation Gases on the Catalytic Performance.

    PubMed

    Rhim, Geun Bae; Hong, Seok Yong; Park, Ji Chan; Jung, Heon; Rhee, Young Woo; Chun, Dong Hyun

    2016-02-01

    Fischer-Tropsch synthesis (FTS) was carried out over nanocrystalline ferrihydrite-based (Fe9O2(OH)23) catalysts activated by different reducing agents: syngas (H2+CO), CO, and H2. The syngas activation successfully changed the ferrihydrite-based catalysts into an active and stable catalytic structure with chi-carbide (Fe2.5 C) and epsilon'-carbide (Fe2.2 C). The crystal structure of the catalysts obtained by syngas activation was similar to the structure obtained by CO activation; this similarity was probably due to the peculiar reduction behavior of the ferrihydrite-based catalysts, which exhibit much greater reducibility in CO atmosphere than in H2 atmosphere. The performance of the catalysts activated by syngas was much higher than the performance of the catalysts activated by H2 and was comparable to the performance of the catalysts activated by CO. This strongly demonstrates that the ferrihydrite-based catalysts are advantageous for industrial FTS processes because syngas can be commonly used for both activation pre-treatment and subsequent reaction. PMID:27433672

  20. Vessel-associated myogenic precursors control macrophage activation and clearance of apoptotic cells.

    PubMed

    Bosurgi, L; Brunelli, S; Rigamonti, E; Monno, A; Manfredi, A A; Rovere-Querini, P

    2015-01-01

    Swift and regulated clearance of apoptotic cells prevents the accumulation of cell remnants in injured tissues and contributes to the shift of macrophages towards alternatively activated reparatory cells that sustain wound healing. Environmental signals, most of which are unknown, in turn control the efficiency of the clearance of apoptotic cells and as such determine whether tissues eventually heal. In this study we show that vessel-associated stem cells (mesoangioblasts) specifically modulate the expression of genes involved in the clearance of apoptotic cells and in macrophage alternative activation, including those of scavenger receptors and of molecules that bridge dying cells and phagocytes. Mesoangioblasts, but not immortalized myoblasts or neural precursor cells, enhance CD163 membrane expression in vitro as assessed by flow cytometry, indicating that the effect is specific. Mesoangioblasts transplanted in acutely or chronically injured skeletal muscles determine the expansion of the population of CD163(+) infiltrating macrophages and increase the extent of CD163 expression. Conversely, macrophages challenged with mesoangioblasts engulf significantly better apoptotic cells in vitro. Collectively, the data reveal a feed-forward loop between macrophages and vessel-associated stem cells, which has implications for the skeletal muscle homeostatic response to sterile injury and for diseases in which homeostasis is jeopardized, including muscle dystrophies and inflammatory myopathies. PMID:24749786

  1. Waste polyvinylchloride derived pitch as a precursor to develop carbon fibers and activated carbon fibers.

    PubMed

    Qiao, W M; Yoon, S H; Mochida, I; Yang, J H

    2007-01-01

    Polyvinylchloride (PVC) was successfully recycled through the solvent extraction from waste pipe with an extraction yield of ca. 86%. The extracted PVC was pyrolyzed by a two-stage process (260 and 410 degrees C) to obtain free-chlorine PVC based pitch through an effective removal of chlorine from PVC during the heat-treatment. As-prepared pitch (softening point: 220 degrees C) was spun, stabilized, carbonized into carbon fibers (CFs), and further activated into activated carbon fibers (ACFs) in a flow of CO2. As-prepared CFs show comparable mechanical properties to commercial CFs, whose maximum tensile strength and modulus are 862 MPa and 62 GPa, respectively. The resultant ACFs exhibit a high surface area of 1200 m2/g, narrow pore size distribution and a low oxygen content of 3%. The study provides an effective insight to recycle PVC from waste PVC and develop a carbon precursor for high performance carbon materials such as CFs and ACFs. PMID:17157493

  2. Rejuvenation of MPTP-induced human neural precursor cell senescence by activating autophagy.

    PubMed

    Zhu, Liang; Dong, Chuanming; Sun, Chenxi; Ma, Rongjie; Yang, Danjing; Zhu, Hongwen; Xu, Jun

    2015-08-21

    Aging of neural stem cell, which can affect brain homeostasis, may be caused by many cellular mechanisms. Autophagy dysfunction was found in aged and neurodegenerative brains. However, little is known about the relationship between autophagy and human neural stem cell (hNSC) aging. The present study used 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) to treat neural precursor cells (NPCs) derived from human embryonic stem cell (hESC) line H9 and investigate related molecular mechanisms involved in this process. MPTP-treated NPCs were found to undergo premature senescence [determined by increased senescence-associated-β-galactosidase (SA-β-gal) activity, elevated intracellular reactive oxygen species level, and decreased proliferation] and were associated with impaired autophagy. Additionally, the cellular senescence phenotypes were manifested at the molecular level by a significant increase in p21 and p53 expression, a decrease in SOD2 expression, and a decrease in expression of some key autophagy-related genes such as Atg5, Atg7, Atg12, and Beclin 1. Furthermore, we found that the senescence-like phenotype of MPTP-treated hNPCs was rejuvenated through treatment with a well-known autophagy enhancer rapamycin, which was blocked by suppression of essential autophagy gene Beclin 1. Taken together, these findings reveal the critical role of autophagy in the process of hNSC aging, and this process can be reversed by activating autophagy. PMID:26159917

  3. Commercial runs show TiO/sub 2/ Claus catalyst retains activity

    SciTech Connect

    Nougayrede, J.; Philippe, A.; Quesmerel, E.; Vermeersch, R.

    1987-08-10

    Commercial data are given for the CRS 31 Claus catalyst, jointly developed by Rhone Poulenc and Societe Nationale Elf Aquitane (Production) (SNEA). The data confirm laboratory results that show the catalyst's ability to deliver more complete hydrolysis in the first reactor of Claus sulfur recovery plants, and its ability to maintain activity in the second and third reactors. The most important losses in sulfur yields in Claus plants generally come from COS and CS/sub 2/ formed in the thermal steps of the process in the first reactor, and from the low Claus activity of alumina-based catalysts in the second and third reactors. In the first reactor, loaded with alumina-based catalyst, hydrolysis is only partial. Low Claus activity in second and third reactors is caused by the inevitable sulfation of the alumina. Catalytic-activity decrease of aluminas is caused particularly by the presence of oxygen, even in trace amounts, in the Claus gases. Therefore, in the first reactor, the CS/sub 2/ hydrolysis rate is lowered in the subsequent reactors, the H/sub 2/ + SO/sub 2/ conversion significantly drops. The chemical composition of CRS 31, TiO/sub 2/ only, in the same operating conditions, causes a significant improvement in activity because of its increased resistance to sulfation. The economics of the process are given.

  4. HDS activity and characterization of zeolite-supported nickel sulfide catalysts

    SciTech Connect

    Welters, W.J.J.; Vorbeck, G.; Haan, J.W. de; Beer, V.H.J. de; Santen, R.A. van; Zandbergen, H.W.

    1994-11-01

    Catalysts of nickel sulfide supported on zeolite Y have been prepared (by impregnation or ion exchange) and characterized by means of thiophene hydrodesulfurization (HDS), sulfur analysis, temperature-programmed sulfiding, {sup 129}Xe-NMR, HREM and dynamic oxygen chemisorption. The catalysts show large differences in catalytic behavior dependent on the preparation method (impregnation vs ion exchange) and the pretreatment conditions (method of sulfidation). Especially the ion-exchanged catalysts show a high initial activity, but due to the presence of acid sites deactivation is very strong. The initial activity of these catalysts can be improved significantly by drying prior to sulfidation. In all cases sulfidation results in quantitative formation of nickel sulfide, with Ni{sub 3}S{sub 2} being the main product. Occasionally, also some NiS appears to be present. The major part of the nickel sulfide phase is invariably located on the outside of the zeolite particles. The fraction of nickel sulfide in the zeolite pores depends on the preparation method and the pretreatment conditions. The differences in catalytic activity are ascribed not only to variations in overall nickel sulfide dispersion but also to the acidity of the support, and the presence of very active small nickel sulfide clusters in the pores of the zeolite can have a strong influence on the thiophene HDS activity. 40 refs., 13 figs., 3 tabs.

  5. Highly Active Carbon Supported Pd-Ag Nanofacets Catalysts for Hydrogen Production from HCOOH.

    PubMed

    Wang, Wenhui; He, Ting; Liu, Xuehua; He, Weina; Cong, Hengjiang; Shen, Yangbin; Yan, Liuming; Zhang, Xuetong; Zhang, Jinping; Zhou, Xiaochun

    2016-08-17

    Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag{hcp}). Then, the Pd-Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd-Ag alloy nanofacets, such as Pd-Ag{111}, Pd-Ag{100}, and Pd-Ag{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd-Ag{hcp} > Pd-Ag{111} > Pd-Ag{100}. Particularly, the activity of Pd-Ag{hcp} is up to an extremely high value, i.e., TOF{hcp} = 19 000 ± 1630 h(-1) at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd-Ag alloy nanocatalyst. The initial activity of Pd-Ag{hcp} even reaches (3.13 ± 0.19) × 10(6) h(-1) at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst. PMID:27454194

  6. Highly Active Carbon Supported Pd-Ag Nanofacets Catalysts for Hydrogen Production from HCOOH.

    PubMed

    Wang, Wenhui; He, Ting; Liu, Xuehua; He, Weina; Cong, Hengjiang; Shen, Yangbin; Yan, Liuming; Zhang, Xuetong; Zhang, Jinping; Zhou, Xiaochun

    2016-08-17

    Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag{hcp}). Then, the Pd-Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd-Ag alloy nanofacets, such as Pd-Ag{111}, Pd-Ag{100}, and Pd-Ag{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd-Ag{hcp} > Pd-Ag{111} > Pd-Ag{100}. Particularly, the activity of Pd-Ag{hcp} is up to an extremely high value, i.e., TOF{hcp} = 19 000 ± 1630 h(-1) at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd-Ag alloy nanocatalyst. The initial activity of Pd-Ag{hcp} even reaches (3.13 ± 0.19) × 10(6) h(-1) at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst.

  7. Effect of KCl addition method on the Pt/KL catalyst for the aromatization of hexane

    SciTech Connect

    Dai, Lian-Xin; Sakashita, Haru; Tatsumi, Takashi )

    1994-05-01

    The influence of the method for loading platinum precursor and adding KCl, KCl loading content, calcination temperature, KCl addition procedure, various additives, and water washing on the activity and selectivity of Pt/KL catalysts for hexane reforming reaction has been investigated. The catalyst preparation methods involve ion exchange (IE), incipient wetness impregnation (IWI), and coimpregnation with KCl (IWI-KCl). The Pt/KL catalysts prepared by ion exchange with [Pt(NH[sub 3])[sub 4

  8. Coatings of active and heat-resistant cobalt-aluminium xerogel catalysts.

    PubMed

    Schubert, Miriam; Schubert, Lennart; Thomé, Andreas; Kiewidt, Lars; Rosebrock, Christopher; Thöming, Jorg; Roessner, Frank; Bäumer, Marcus

    2016-09-01

    The application of catalytically coated metallic foams in catalytic processes has a high potential for exothermic catalytic reactions such as CO2 methanation or Fischer-Tropsch synthesis due to good heat conductivity, improved turbulent flow properties and high catalyst efficiencies. But the preparation of homogenous catalyst coats without pore blocking is challenging with conventional wash coating techniques. Here, we report on a stable and additive free colloidal CoAlOOH suspension (sol) for the preparation of catalytically active Co/Al2O3 xerogel catalysts and coatings. Powders with 18wt% Co3O4 prepared from this additive free synthesis route show a catalytic activity in Fischer-Tropsch synthesis and CO2 methanation which is similar to a catalyst prepared by incipient wetness impregnation (IWI) after activating the material under flowing hydrogen at 430°C. Yet, the xerogel catalyst exhibits a much higher thermal stability as compared to the IWI catalyst, as demonstrated in catalytic tests after different heat agings between 430°C and 580°C. It was also found that the addition of polyethylene glycol (PEG) to the sol influences the catalytic properties of the formed xerogels negatively. Only non-reducible cobalt spinels were formed from a CoAlOOH sol with 20wt% PEG. Metallic foams with pores sizes between 450 and 1200μm were coated with the additive free CoAlOOH sol, which resulted in homogenous xerogel layers. First catalytic tests of the coated metal foams (1200μm) showed good performance in CO2 methanation. PMID:27240245

  9. Precursor B Cells Increase in the Lung during Airway Allergic Inflammation: A Role for B Cell-Activating Factor

    PubMed Central

    Malmhäll, Carina; Rådinger, Madeleine; Ramos-Ramirez, Patricia; Lu, You; Deák, Tünde; Semitekolou, Maria; Gaga, Mina; Sjöstrand, Margareta; Lötvall, Jan; Bossios, Apostolos

    2016-01-01

    Background B cells, key cells in allergic inflammation, differentiate in the bone marrow and their precursors include pro-B, pre-B and immature B cells. Eosinophil progenitor cells increase in the lung after allergen exposure. However, the existence and possible role of B cell precursors in the lung during allergic inflammation remains elusive. Methods A BALB/c mouse model of allergic airway inflammation was utilized to perform phenotypic and quantification analyses of pro-B and pre-B cells in the lung by flow cytometry. B cell maturation factors IL-7 and B cell-activating factor (BAFF) and their receptors (CD127 and BAFFR, BCMA, TACI, respectively) were also evaluated in the lung and serum. The effect of anti-BAFF treatment was investigated both in vivo (i.p. administration of BAFF-R-Ig fusion protein) and in vitro (colony forming cell assay). Finally, BAFF levels were examined in the bronchoalveolar lavage (BAL) of asthmatic patients and healthy controls. Results Precursor pro and pre-B cells increase in the lung after allergen exposure, proliferate in the lung tissue in vivo, express markers of chemotaxis (CCR10 and CXCR4) and co-stimulation (CD40, CD86) and are resistant to apoptosis (Bax). Precursor B cells express receptors for BAFF at baseline, while after allergen challenge both their ligand BAFF and the BCMA receptor expression increases in B cell precursors. Blocking BAFFR in the lung in vivo decreases eosinophils and proliferating precursor B cells. Blocking BAFFR in bone marrow cultures in vitro reduces pre-B colony formation units. BAFF is increased in the BAL of severe asthmatics. Conclusion Our data support the concept of a BAFF-mediated role for B cell precursors in allergic airway inflammation. PMID:27513955

  10. Hydrogenation of biofuels with formic acid over a palladium-based ternary catalyst with two types of active sites.

    PubMed

    Wang, Liang; Zhang, Bingsen; Meng, Xiangju; Su, Dang Sheng; Xiao, Feng-Shou

    2014-06-01

    A composite catalyst including palladium nanoparticles on titania (TiO2) and on nitrogen-modified porous carbon (Pd/TiO2@N-C) is synthesized from palladium salts, tetrabutyl titanate, and chitosan. N2 sorption isotherms show that the catalyst has a high BET surface area (229 m(2)  g(-1)) and large porosity. XPS and TEM characterization of the catalyst shows that palladium species with different chemical states are well dispersed across the TiO2 and nitrogen-modified porous carbon, respectively. The Pd/TiO2@N-C catalyst is very active and shows excellent stability towards hydrogenation of vanillin to 2-methoxy-4-methylphenol using formic acid as hydrogen source. This activity can be attributed to a synergistic effect between the Pd/TiO2 (a catalyst for dehydrogenation of formic acid) and Pd/N-C (a catalyst for hydrogenation of vanillin) sites.

  11. The catalytic activity of the iron-coated pumice particles used as heterogeneous catalysts in the oxidation of natural organic matter by H2O2.

    PubMed

    Alver, Alper; Karaarslan, Mihrican; Kılıç, Ahmet

    2016-08-01

    The oxidative removal of natural organic matter (NOM) from waters was investigated by hydrogen peroxide (H2O2) and iron-coated pumice particles in heterogeneous catalytic oxidation process (HCOP). Removal of trihalomethane (THM) precursors, which is formed THM by the reacts with chloride, was performed with the hydroxyl radicals. Coating the original pumice particles with iron oxides significantly enhanced the removal of NOM with peroxide. The studies were carried out in two sections: (1) decomposition of hydrogen peroxide in pure water with iron-coated pumice and (2) oxidation of THM Precursor (NOM) by hydrogen peroxide with iron-coated pumice. The monitored parameters in this study include dissolved organic carbon and trihalomethanes formation potential. The results show that iron-coated pumice catalyst significantly increased the removal efficiency of NOM in the HCOP. The results show that iron-coated pumice catalyst significantly increased the removal efficiency of NOM in the HCOP. Results show that the oxidation of NOM and remaining NOM with H2O2 is improved by the addition of iron-coated pumice particles which activate the H2O2 molecule, leading to the formation of hydroxyl radicals in a Fenton-like process.

  12. The catalytic activity of the iron-coated pumice particles used as heterogeneous catalysts in the oxidation of natural organic matter by H2O2.

    PubMed

    Alver, Alper; Karaarslan, Mihrican; Kılıç, Ahmet

    2016-08-01

    The oxidative removal of natural organic matter (NOM) from waters was investigated by hydrogen peroxide (H2O2) and iron-coated pumice particles in heterogeneous catalytic oxidation process (HCOP). Removal of trihalomethane (THM) precursors, which is formed THM by the reacts with chloride, was performed with the hydroxyl radicals. Coating the original pumice particles with iron oxides significantly enhanced the removal of NOM with peroxide. The studies were carried out in two sections: (1) decomposition of hydrogen peroxide in pure water with iron-coated pumice and (2) oxidation of THM Precursor (NOM) by hydrogen peroxide with iron-coated pumice. The monitored parameters in this study include dissolved organic carbon and trihalomethanes formation potential. The results show that iron-coated pumice catalyst significantly increased the removal efficiency of NOM in the HCOP. The results show that iron-coated pumice catalyst significantly increased the removal efficiency of NOM in the HCOP. Results show that the oxidation of NOM and remaining NOM with H2O2 is improved by the addition of iron-coated pumice particles which activate the H2O2 molecule, leading to the formation of hydroxyl radicals in a Fenton-like process. PMID:26881482

  13. Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts.

    PubMed

    Varnell, Jason A; Tse, Edmund C M; Schulz, Charles E; Fister, Tim T; Haasch, Richard T; Timoshenko, Janis; Frenkel, Anatoly I; Gewirth, Andrew A

    2016-01-01

    The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites.

  14. Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts

    NASA Astrophysics Data System (ADS)

    Varnell, Jason A.; Tse, Edmund C. M.; Schulz, Charles E.; Fister, Tim T.; Haasch, Richard T.; Timoshenko, Janis; Frenkel, Anatoly I.; Gewirth, Andrew A.

    2016-08-01

    The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites.

  15. Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts

    PubMed Central

    Varnell, Jason A.; Tse, Edmund C. M.; Schulz, Charles E.; Fister, Tim T.; Haasch, Richard T.; Timoshenko, Janis; Frenkel, Anatoly I.; Gewirth, Andrew A.

    2016-01-01

    The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites. PMID:27538720

  16. Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts.

    PubMed

    Varnell, Jason A; Tse, Edmund C M; Schulz, Charles E; Fister, Tim T; Haasch, Richard T; Timoshenko, Janis; Frenkel, Anatoly I; Gewirth, Andrew A

    2016-01-01

    The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites. PMID:27538720

  17. Ligand-free Heck reaction: Pd(OAc)2 as an active catalyst revisited.

    PubMed

    Yao, Qingwei; Kinney, Elizabeth P; Yang, Zhi

    2003-09-19

    Palladium acetate was shown to be an extremely active catalyst for the Heck reaction of aryl bromides. Both the base and the solvent were found to have a fundamental influence on the efficiency of the reaction, with K(3)PO(4) and N,N-dimethylacetamide being the optimal base and solvent, respectively. PMID:12968913

  18. The calculation of surface orbital energies for specific types of active sites on dispersed metal catalysts

    SciTech Connect

    Augustine, R.L.; Lahanas, K.M.; Cole, F.

    1992-11-01

    An angular overlap calculation has been used to determine the s, p, and d orbital energy levels of the different types of surface sites present on dispersed metal catalysts. These data can permit a Frontier Molecular Orbital treatment of specific site activities as long as the surface orbital availability for overlap with adsorbed substrates is considered along with its energy value and symmetry.

  19. The calculation of surface orbital energies for specific types of active sites on dispersed metal catalysts

    SciTech Connect

    Augustine, R.L.; Lahanas, K.M.; Cole, F.

    1992-01-01

    An angular overlap calculation has been used to determine the s, p, and d orbital energy levels of the different types of surface sites present on dispersed metal catalysts. These data can permit a Frontier Molecular Orbital treatment of specific site activities as long as the surface orbital availability for overlap with adsorbed substrates is considered along with its energy value and symmetry.

  20. Ligand-free Heck reaction: Pd(OAc)2 as an active catalyst revisited.

    PubMed

    Yao, Qingwei; Kinney, Elizabeth P; Yang, Zhi

    2003-09-19

    Palladium acetate was shown to be an extremely active catalyst for the Heck reaction of aryl bromides. Both the base and the solvent were found to have a fundamental influence on the efficiency of the reaction, with K(3)PO(4) and N,N-dimethylacetamide being the optimal base and solvent, respectively.

  1. PREPARATION, CHARACTERIZATION AND ACTIVITY OF AL2O3-SUPPORTED V2O5 CATALYSTS

    EPA Science Inventory

    A series of activated alumina supported vanadium oxide catalysts with various V2O5 loadings ranging from 5 to 25 wt% has been prepared by wet impregnation technique. A combination of various physico-chemical techniques such as BET surface areas, oxygen chemisorption, X-ray diffra...

  2. Alkene Isomerization Using a Solid Acid as Activator and Support for a Homogeneous Catalyst

    ERIC Educational Resources Information Center

    Seen, Andrew J.

    2004-01-01

    An upper-level undergraduate experiment that, in addition to introducing students to catalysis using an air sensitive transition-metal complex, introduces the use of a solid acid as an activator and support for the catalyst is developed. The increased stability acquired in the course of the process affords the opportunity to characterize the…

  3. Graphene-supported hemin as a highly active biomimetic oxidation catalyst.

    PubMed

    Xue, Teng; Jiang, Shan; Qu, Yongquan; Su, Qiao; Cheng, Rui; Dubin, Sergey; Chiu, Chin-Yi; Kaner, Richard; Huang, Yu; Duan, Xiangfeng

    2012-04-16

    Well supported: stable hemin-graphene conjugates formed by immobilization of monomeric hemin on graphene, showed excellent catalytic activity, more than 10 times better than that of the recently developed hemin-hydrogel system and 100 times better than that of unsupported hemin. The catalysts also showed excellent binding affinities and catalytic efficiencies approaching that of natural enzymes. PMID:22368046

  4. Preparation, characterization, and activity of α-Ti(HPO4)2 supported metallocene catalysts

    NASA Astrophysics Data System (ADS)

    Shi, Yasai; Yuan, Yuan; Xu, Qinghong; Yi, Jianjun

    2016-10-01

    A series of heterogeneous catalysts by loading metallocenes on surface of α-Ti(HPO4)2, a kind of solid acid, has been synthesized. Polymerization of alkenes, including ethylene and propylene, based on participation of the heterogeneous catalysts were studied and the results were compared to metallocenes supported on silica gel, α-Zr(HPO4)2 and clay. Higher catalytic activity, larger polymer molecular weight and narrow distribution of polymer molecular weight were obtained. Acidic strength of the support and its influence to metallocenes were studied to discover intrinsic factors in the polymerizations.

  5. Method for preparing high activity silica supported hydrotreating catalysts

    SciTech Connect

    Thompson, M.S.

    1986-03-04

    A method is described for preparing a silica supported hydrotreating catalyst containing from about 10-25%w molybdenum and from about 1-5%w nickel and/or cobalt as hydrogenation metals. The method consists of: (a) reacting a mixture of MoCl/sub 5/ and a compound selected from the group consisting of Ni(H/sub 2/O)/sub 6/Cl/sub 2/, Co(H/sub 2/O)/sub 6/Cl/sub 2/ and mixutres in amounts to provide a desired catalytic metals concentration of the support in the presence of a solubilizing amount of acetonitrile; (b) heating the mixture to between about 25/sup 0/ and 80/sup 0/C until most of the metal compounds have reacted and/or dissolved; (c) removing any undissolved solids from the solution; (d) impregnating the dried silica support with the hydrogenation metals-containing solution in one or more steps; and (e) drying the impregnated silica support at elevated temperature.

  6. Highly active cobalt phosphate and borate based oxygen evolving catalysts operating in neutral and natural waters

    SciTech Connect

    Esswein, AJ; Surendranath, Y; Reece, SY; Nocera, DG

    2011-02-01

    A high surface area electrode is functionalized with cobalt-based oxygen evolving catalysts (Co-OEC = electrodeposited from pH 7 phosphate, Pi, pH 8.5 methylphosphonate, MePi, and pH 9.2 borate electrolyte, Bi). Co-OEC prepared from MePi and operated in Pi and Bi achieves a current density of 100 mA cm(-2) for water oxidation at 442 and 363 mV overpotential, respectively. The catalyst retains activity in near-neutral pH buffered electrolyte in natural waters such as those from the Charles River (Cambridge, MA) and seawater (Woods Hole, MA). The efficacy and ease of operation of anodes functionalized with Co-OEC at appreciable current density together with its ability to operate in near neutral pH buffered natural water sources bodes well for the translation of this catalyst to a viable renewable energy storage technology.

  7. Method of treating intermetallic alloy hydrogenation/oxidation catalysts for improved impurity poisoning resistance, regeneration and increased activity

    DOEpatents

    Wright, R.B.

    1992-01-14

    Alternate, successive high temperature oxidation and reduction treatments, in either order, of intermetallic alloy hydrogenation and intermetallic alloy oxidation catalysts unexpectedly improves the impurity poisoning resistance, regeneration capacity and/or activity of the catalysts. The particular alloy, and the final high temperature treatment given alloy (oxidation or reduction) will be chosen to correspond to the function of the catalyst (oxidation or hydrogenation). 23 figs.

  8. Method for dispersing catalyst onto particulate material

    DOEpatents

    Utz, Bruce R.; Cugini, Anthony V.

    1992-01-01

    A method for dispersing finely divided catalyst precursors onto the surface of coal or other particulate material includes the steps of forming a wet paste mixture of the particulate material and a liquid solution containing a dissolved transition metal salt, for instance a solution of ferric nitrate. The wet paste mixture is in a state of incipient wetness with all of this solution adsorbed onto the surfaces of the particulate material without the presence of free moisture. On adding a precipitating agent such as ammonia, a catalyst precursor such as hydrated iron oxide is deposited on the surfaces of the coal. The catalyst is activated by converting it to the sulfide form for the hydrogenation or direct liquefaction of the coal.

  9. Earthquake prediction activities and Damavand earthquake precursor test site in Iran

    NASA Astrophysics Data System (ADS)

    Mokhtari, Mohammad

    2010-01-01

    Iran has long been known as one of the most seismically active areas of the world, and it frequently suffers destructive and catastrophic earthquakes that cause heavy loss of human life and widespread damage. The Alborz region in the northern part of Iran is an active EW trending mountain belt of 100 km wide and 600 km long. The Alborz range is bounded by the Talesh Mountains to the west and the Kopet Dagh Mountains to the east and consists of several sedimentary and volcanic layers of Cambrian to Eocene ages that were deformed during the late Cenozoic collision. Several active faults affect the central Alborz. The main active faults are the North Tehran and Mosha faults. The Mosha fault is one of the major active faults in the central Alborz as shown by its strong historical seismicity and its clear morphological signature. Situated in the vicinity of Tehran city, this 150-km-long N100° E trending fault represents an important potential seismic source. For earthquake monitoring and possible future prediction/precursory purposes, a test site has been established in the Alborz mountain region. The proximity to the capital of Iran with its high population density, low frequency but high magnitude earthquake occurrence, and active faults with their historical earthquake events have been considered as the main criteria for this selection. In addition, within the test site, there are hot springs and deep water wells that can be used for physico-chemical and radon gas analysis for earthquake precursory studies. The present activities include magnetic measurements; application of methodology for identification of seismogenic nodes for earthquakes of M ≥ 6.0 in the Alborz region developed by International Institute of Earthquake Prediction Theory and Mathematical Geophysics, IIEPT RAS, Russian Academy of Science, Moscow (IIEPT&MG RAS); a feasibility study using a dense seismic network for identification of future locations of seismic monitoring stations and application

  10. Cyanate as an Active Precursor of Ethyl Carbamate Formation in Sugar Cane Spirit.

    PubMed

    Galinaro, Carlos A; Ohe, Thiago H K; da Silva, Augusto C H; da Silva, Sebastião C; Franco, Douglas W

    2015-08-26

    The thermodynamic and kinetic aspects of ethyl carbamate (EC) formation through the reaction between cyanate and ethanol were investigated. The rate constant values for cyanate ion decay and EC formation are (8.0 ± 0.4) × 10(-5) and (8.9 ± 0.4) × 10(-5) s(-1), respectively, at 25 °C in 48% aqueous ethanolic solution at pH 4.5. Under the investigated experimental conditions, the rate constants are independent of the ethanol and cyanate concentrations but increase as the temperature increases (ΔH1(⧧) = 19.4 ± 1 kcal/mol, ΔS1(⧧) = −12.1 ± 1 cal/K, and ΔG1(⧧) = 23.0 ± 1 kcal/mol) and decrease as the solution pH increases. According to molecular modeling (DFT) that was performed to analyze the reaction mechanism, the isocyanic acid (HNCO) is the active EC precursor. The calculated ΔG1(⧧), ΔH1(⧧), and ΔS1(⧧) values are in very good agreement with the experimental ones.

  11. TRAP-positive osteoclast precursors mediate ROS/NO-dependent bactericidal activity via TLR4.

    PubMed

    Nishimura, Kazuaki; Shindo, Satoru; Movila, Alexandru; Kayal, Rayyan; Abdullah, Albassam; Savitri, Irma Josefina; Ikeda, Atsushi; Yamaguchi, Tsuguno; Howait, Mohammed; Al-Dharrab, Ayman; Mira, Abdulghani; Han, Xiaozhe; Kawai, Toshihisa

    2016-08-01

    Osteoclastogenesis was induced by RANKL stimulation in mouse monocytes to examine the possible bactericidal function of osteoclast precursors (OCp) and mature osteoclasts (OCm) relative to their production of NO and ROS. Tartrate-resistant acid phosphatase (TRAP)-positive OCp, but few or no OCm, phagocytized and killed Escherichia coli in association with the production of reactive oxygen species (ROS) and nitric oxide (NO). Phagocytosis of E. coli and production of ROS and NO were significantly lower in TRAP+ OCp derived from Toll-like receptor (TLR)-4 KO mice than that derived from wild-type (WT) or TLR2-KO mice. Interestingly, after phagocytosis, TRAP+ OCp derived from wild-type and TLR2-KO mice did not differentiate into OCm, even with continuous exposure to RANKL. In contrast, E. coli-phagocytized TRAP+ OCp from TLR4-KO mice could differentiate into OCm. Importantly, neither NO nor ROS produced by TRAP+ OCp appeared to be engaged in phagocytosis-induced suppression of osteoclastogenesis. These results suggested that TLR4 signaling not only induces ROS and NO production to kill phagocytized bacteria, but also interrupts OCm differentiation. Thus, it can be concluded that TRAP+ OCp, but not OCm, can mediate bactericidal activity via phagocytosis accompanied by the production of ROS and NO via TLR4-associated reprograming toward phagocytic cell type. PMID:27343691

  12. Concealed expansion of immature precursors underpins acute burst of adult HSC activity in foetal liver

    PubMed Central

    Ivanovs, Andrejs; Zhao, Suling; Medvinsky, Alexander

    2016-01-01

    One day prior to mass emergence of haematopoietic stem cells (HSCs) in the foetal liver at E12.5, the embryo contains only a few definitive HSCs. It is thought that the burst of HSC activity in the foetal liver is underpinned by rapid maturation of immature embryonic precursors of definitive HSCs, termed pre-HSCs. However, because pre-HSCs are not detectable by direct transplantations into adult irradiated recipients, the size and growth of this population, which represents the embryonic rudiment of the adult haematopoietic system, remains uncertain. Using a novel quantitative assay, we demonstrate that from E9.5 the pre-HSC pool undergoes dramatic growth in the aorta-gonad-mesonephros region and by E11.5 reaches the size that matches the number of definitive HSCs in the E12.5 foetal liver. Thus, this study provides for the first time a quantitative basis for our understanding of how the large population of definitive HSCs emerges in the foetal liver. PMID:27095492

  13. Cyanate as an Active Precursor of Ethyl Carbamate Formation in Sugar Cane Spirit.

    PubMed

    Galinaro, Carlos A; Ohe, Thiago H K; da Silva, Augusto C H; da Silva, Sebastião C; Franco, Douglas W

    2015-08-26

    The thermodynamic and kinetic aspects of ethyl carbamate (EC) formation through the reaction between cyanate and ethanol were investigated. The rate constant values for cyanate ion decay and EC formation are (8.0 ± 0.4) × 10(-5) and (8.9 ± 0.4) × 10(-5) s(-1), respectively, at 25 °C in 48% aqueous ethanolic solution at pH 4.5. Under the investigated experimental conditions, the rate constants are independent of the ethanol and cyanate concentrations but increase as the temperature increases (ΔH1(⧧) = 19.4 ± 1 kcal/mol, ΔS1(⧧) = −12.1 ± 1 cal/K, and ΔG1(⧧) = 23.0 ± 1 kcal/mol) and decrease as the solution pH increases. According to molecular modeling (DFT) that was performed to analyze the reaction mechanism, the isocyanic acid (HNCO) is the active EC precursor. The calculated ΔG1(⧧), ΔH1(⧧), and ΔS1(⧧) values are in very good agreement with the experimental ones. PMID:26248556

  14. Pt5Gd as a highly active and stable catalyst for oxygen electroreduction.

    PubMed

    Escudero-Escribano, María; Verdaguer-Casadevall, Arnau; Malacrida, Paolo; Grønbjerg, Ulrik; Knudsen, Brian P; Jepsen, Anders K; Rossmeisl, Jan; Stephens, Ifan E L; Chorkendorff, Ib

    2012-10-10

    The activity and stability of Pt(5)Gd for the oxygen reduction reaction (ORR) have been studied, using a combination of electrochemical measurements, angle-resolved X-ray photoelectron spectroscopy (AR-XPS), and density functional theory calculations. Sputter-cleaned, polycrystalline Pt(5)Gd shows a 5-fold increase in ORR activity, relative to pure Pt at 0.9 V, approaching the most active in the literature for catalysts prepared in this way. AR-XPS profiles after electrochemical measurements in 0.1 M HClO(4) show the formation of a thick Pt overlayer on the bulk Pt(5)Gd, and the enhanced ORR activity can be explained by means of compressive strain effects. Furthermore, these novel bimetallic electrocatalysts are highly stable, which, in combination with their enhanced activity, makes them very promising for the development of new cathode catalysts for fuel cells. PMID:22998588

  15. La-Sr-Ni-Co-O based perovskite-type solid solutions as catalyst precursors in the CO 2 reforming of methane

    NASA Astrophysics Data System (ADS)

    Valderrama, Gustavo; Kiennemann, Alain; Goldwasser, Mireya R.

    La 1- xSr xNi 0.4Co 0.6O 3 and La 0.8Sr 0.2Ni 1- yCo yO 3 solid solutions with perovskite-type structure were synthesized by the sol-gel resin method and used as catalytic precursors in the dry reforming of methane with CO 2 to syngas, between 873 and 1073 K at atmospheric pressure under continuous flow of reactant gases with CH 4/CO 2 = 1 ratio. These quaternary oxides were characterized by X-ray diffraction (XRD), BET specific surface area and temperature-programmed reduction (TPR) techniques. XRD analyses of the more intense diffraction peaks and cell parameter measurements showed formation of La-Sr-Ni-Co-O solid solutions with La 0.9Sr 0.1CoO 3 and/or La 0.9Sr 0.1NiO 3 as the main crystallographic phases present on the solids depending on the degree of substitution. TPR analyses showed that Sr doping decreases the temperature of reduction via formation of intermediary species producing Ni 0, Co 0 with particle sizes in the range of nanometers over the SrO and La 2O 3 phases. These metallic nano particles highly dispersed in the solid matrix are responsible for the high activity shown during the reaction and avoid carbon formation. The presence of Sr in doping quantities also promotes the secondary reactions of carbon formation and water-gas shift in a very small extension during the dry reforming reaction.

  16. Structure-activity correlations in a nickel-borate oxygen evolution catalyst.

    PubMed

    Bediako, D Kwabena; Lassalle-Kaiser, Benedikt; Surendranath, Yogesh; Yano, Junko; Yachandra, Vittal K; Nocera, Daniel G

    2012-04-18

    An oxygen evolution catalyst that forms as a thin film from Ni(aq)(2+) solutions containing borate electrolyte (Ni-B(i)) has been studied by in situ X-ray absorption spectroscopy. A dramatic increase in catalytic rate, induced by anodic activation of the electrodeposited films, is accompanied by structure and oxidation state changes. Coulometric measurements correlated with X-ray absorption near-edge structure spectra of the active catalyst show that the nickel centers in activated films possess an average oxidation state of +3.6, indicating that a substantial proportion of nickel centers exist in a formal oxidation state of Ni(IV). In contrast, nickel centers in nonactivated films exist predominantly as Ni(III). Extended X-ray absorption fine structure reveals that activated catalyst films comprise bis-oxo/hydroxo-bridged nickel centers organized into sheets of edge-sharing NiO(6) octahedra. Diminished long-range ordering in catalyst films is due to their ostensibly amorphous nature. Nonactivated films display a similar oxidic nature but exhibit a distortion in the local coordination geometry about nickel centers, characteristic of Jahn-Teller distorted Ni(III) centers. Our findings indicate that the increase in catalytic activity of films is accompanied by changes in oxidation state and structure that are reminiscent of those observed for conversion of β-NiOOH to γ-NiOOH and consequently challenge the long-held notion that the β-NiOOH phase is a more efficient oxygen-evolving catalyst. PMID:22417283

  17. Highly active trialkoxymolybdenum(VI) alkylidyne catalysts synthesized by a reductive recycle strategy.

    PubMed

    Zhang, Wei; Kraft, Stefan; Moore, Jeffrey S

    2004-01-14

    A systematic study of alkyne metathesis catalyzed by trialkoxymolybdenum(VI) alkylidyne complexes is reported, in which substrate functional groups, alkynyl substituents, and catalyst ligands are varied. Sterically hindered trisamidomolybdenum(VI) propylidyne complex 5 was prepared conveniently through a previously communicated reductive recycle strategy. Alcoholysis of 5 with various phenols/alcohols provides a set of active catalysts for alkyne metathesis at room temperature, among which the catalyst with p-nitrophenol as ligand shows the highest catalytic activity and is compatible with a variety of functional groups and solvents. A key finding that enabled the use of highly active molybdenum(VI) catalysts is replacement of the commonly used propynyl substituents on the starting alkyne substrates with butynyl groups. Under reduced pressure using 1,2,4-trichlorobenzene as an involatile solvent, the alkyne metathesis of butynyl substituted compounds proceeds well at 30 degrees C providing high yields (83%-97%) of dimers. Rationalization of the special role played by butynyl substrates is discussed.

  18. Enhanced activity of urea electrooxidation on nickel catalysts supported on tungsten carbides/carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Wang, Lu; Du, Tingting; Cheng, Jin; Xie, Xing; Yang, Bolun; Li, Mingtao

    2015-04-01

    Nickel nanoparticles with tungsten carbides supported on the multi-walled carbon nanotubes, noted as Ni-WC/MWCNT catalyst, is prepared through an impregnation method and used for the electrooxidation of urea in alkaline conditions. The micro-morphology and composition of the Ni-WC/MWCNT particles are determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The electrooxidation activity and conductivity of the catalyst are investigated by cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Characterization results indicate that the Ni nanoparticles are uniformly distributed on the WC/MWCNT framework, and the Ni-WC/MWCNT catalyst shows an improved activity for the urea electrooxidation. The current densities of Ni-WC/MWCNT are over 3 times and 15 times higher than those of the Ni-WC/C and Ni/C catalysts, respectively, and the electrochemical impedance also decreases markedly. The higher activity on Ni-WC/MWCNT is attributed to the support effect of MWCNT as well as the synergistic effect between Ni and WC.

  19. Activity of platinum/carbon and palladium/carbon catalysts promoted by Ni2 P in direct ethanol fuel cells.

    PubMed

    Li, Guoqiang; Feng, Ligang; Chang, Jinfa; Wickman, Björn; Grönbeck, Henrik; Liu, Changpeng; Xing, Wei

    2014-12-01

    Ethanol is an alternative fuel for direct alcohol fuel cells, in which the electrode materials are commonly based on Pt or Pd. Owing to the excellent promotion effect of Ni2 P that was found in methanol oxidation, we extended the catalyst system of Pt or Pd modified by Ni2 P in direct ethanol fuel cells. The Ni2 P-promoted catalysts were compared to commercial catalysts as well as to reference catalysts promoted with only Ni or only P. Among the studied catalysts, Pt/C and Pd/C modified by Ni2 P (30 wt %) showed both the highest activity and stability. Upon integration into the anode of a homemade direct ethanol fuel cell, the Pt-Ni2 P/C-30 % catalyst showed a maximum power density of 21 mW cm(-2) , which is approximately two times higher than that of a commercial Pt/C catalyst. The Pd-Ni2 P/C-30 % catalyst exhibited a maximum power density of 90 mW cm(-2) . This is approximately 1.5 times higher than that of a commercial Pd/C catalyst. The discharge stability on both two catalysts was also greatly improved over a 12 h discharge operation.

  20. ``Greener Shade of Ruthenium'': New Concepts of Activation, Immobilization, and Recovery of Ruthenium Catalysts For Green Olefin Metathesis

    NASA Astrophysics Data System (ADS)

    Michrowska, Anna; Gulajski, Lukasz; Grela, Karol

    The results described herewith demonstrate that the activity of ruthenium (Ru) metathesis catalysts can be enhanced by introduction of electron-withdrawing groups (EWGs) without detriment to catalysts stability. This principle can be used not only to increase the catalyst activity, but also to alter its physical-chemical properties, such as solubility in given medium or affinity to silica gel. An example of novel immobilisation strategy, based on this concept is presented. The ammonium-tagged Hoveyda-type catalysts can be successfully applied in aqueous media as well as in ionic liquids (IL). Substitution of a benzylidene fragment can be used not only to immobilize the organometallic complex in such media, but also to increase its catalytic activity by electronic activation. The high stability and good application profiles of such modified catalysts in conjunction with their facile removal from organic products can be expected to offer new opportunities in green applications of olefin metathesis.

  1. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation

    NASA Astrophysics Data System (ADS)

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-05-01

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method.

  2. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation.

    PubMed

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-05-20

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method.

  3. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation

    PubMed Central

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-01-01

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method. PMID:27198855

  4. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation.

    PubMed

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-01-01

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method. PMID:27198855

  5. Commitment and Differentiation of Osteoclast Precursor Cells by the Sequential Expression of C-Fms and Receptor Activator of Nuclear Factor κb (Rank) Receptors

    PubMed Central

    Arai, Fumio; Miyamoto, Takeshi; Ohneda, Osamu; Inada, Tomohisa; Sudo, Tetsuo; Brasel, Kenneth; Miyata, Takashi; Anderson, Dirk M.; Suda, Toshio

    1999-01-01

    Osteoclasts are terminally differentiated cells derived from hematopoietic stem cells. However, how their precursor cells diverge from macrophagic lineages is not known. We have identified early and late stages of osteoclastogenesis, in which precursor cells sequentially express c-Fms followed by receptor activator of nuclear factor κB (RANK), and have demonstrated that RANK expression in early-stage of precursor cells (c-Fms+RANK−) was stimulated by macrophage colony-stimulating factor (M-CSF). Although M-CSF and RANKL (ligand) induced commitment of late-stage precursor cells (c-Fms+RANK+) into osteoclasts, even late-stage precursors have the potential to differentiate into macrophages without RANKL. Pretreatment of precursors with M-CSF and delayed addition of RANKL showed that timing of RANK expression and subsequent binding of RANKL are critical for osteoclastogenesis. Thus, the RANK–RANKL system determines the osteoclast differentiation of bipotential precursors in the default pathway of macrophagic differentiation. PMID:10601350

  6. Synthesis and Hydrodeoxygenation Properties of Ruthenium Phosphide Catalysts

    SciTech Connect

    Bowker, Richard H.; Smith, Mica C.; Pease, Melissa; Slenkamp, Karla M.; Kovarik, Libor; Bussell, Mark E.

    2011-07-01

    Ru2P/SiO2 and RuP/SiO2 catalysts were prepared by the temperature-programmed reduction (TPR) of uncalcined precursors containing hypophosphite ion (H2PO2-) as the phosphorus source. The Ru2P/SiO2 and RuP/SiO2 catalysts had small average particle sizes (~4 nm) and high CO chemisorption capacities (90-110 umol/g). The Ru phosphide catalysts exhibited similar or higher furan (C4H4O) hydrodeoxygenation (HDO) activities than did a Ru/SiO2 catalyst, and the phosphide catalysts favored C4 hydrocarbon products while the Ru metal catalyst produced primarily C3 hydrocarbons.

  7. In situ generated highly active copper oxide catalysts for the oxygen evolution reaction at low overpotential in alkaline solutions.

    PubMed

    Liu, Xiang; Cui, Shengsheng; Qian, Manman; Sun, Zijun; Du, Pingwu

    2016-04-25

    Developing efficient water oxidation catalysts made up of earth-abundant elements has attracted much attention as a step toward for future clean energy production. Herein we report a simple one-step method to generate a low cost copper oxide catalyst film in situ from a copper(ii) ethylenediamine complex. The resulting catalyst has excellent activity toward the oxygen evolution reaction in alkaline solutions. A catalytic current density of 1.0 mA cm(-2) and 10 mA cm(-2) for the catalyst film requires the overpotentials of only ∼370 mV and ∼475 mV in 1.0 M KOH, respectively. This catalytic performance shows that the new catalyst is one of the best Cu-based heterogeneous OER catalysts to date. PMID:27020763

  8. Low-temperature catalyst activator: mechanism of dense carbon nanotube forest growth studied using synchrotron radiation

    PubMed Central

    Takashima, Akito; Izumi, Yudai; Ikenaga, Eiji; Ohkochi, Takuo; Kotsugi, Masato; Matsushita, Tomohiro; Muro, Takayuki; Kawabata, Akio; Murakami, Tomo; Nihei, Mizuhisa; Yokoyama, Naoki

    2014-01-01

    The mechanism of the one-order-of-magnitude increase in the density of vertically aligned carbon nanotubes (CNTs) achieved by a recently developed thermal chemical vapor deposition process was studied using synchrotron radiation spectroscopic techniques. In the developed process, a Ti film is used as the underlayer for an Fe catalyst film. A characteristic point of this process is that C2H2 feeding for the catalyst starts at a low temperature of 450°C, whereas conventional feeding temperatures are ∼800°C. Photoemission spectroscopy using soft and hard X-rays revealed that the Ti underlayer reduced the initially oxidized Fe layer at 450°C. A photoemission intensity analysis also suggested that the oxidized Ti layer at 450°C behaved as a support for nanoparticle formation of the reduced Fe, which is required for dense CNT growth. In fact, a CNT growth experiment, where the catalyst chemical state was monitored in situ by X-ray absorption spectroscopy, showed that the reduced Fe yielded a CNT forest at 450°C. Contrarily, an Fe layer without the Ti underlayer did not yield such a CNT forest at 450°C. Photoemission electron microscopy showed that catalyst annealing at the conventional feeding temperature of 800°C caused excess catalyst agglomeration, which should lead to sparse CNTs. In conclusion, in the developed growth process, the low-temperature catalyst activation by the Ti underlayer before the excess Fe agglomeration realised the CNT densification. PMID:25075343

  9. Reactivation of a Ruthenium-Based Olefin Metathesis Catalyst

    PubMed Central

    Tabari, Daniel S.; Tolentino, Daniel R.; Schrodi, Yann

    2013-01-01

    1st Generation Hoveyda-Grubbs olefin metathesis catalyst was purposely decomposed in the presence of ethylene yielding inorganic species that are inactive in the ring-closing metathesis (RCM) of benchmark substrate diethyldiallyl malonate (DEDAM). The decomposed catalyst was treated with 1-(3,5-diisopropoxyphenyl)-1-phenylprop-2-yn-1-ol (3) to generate an olefin metathesis active ruthenium indenylidene-ether complex in 43 % yield. This complex was also prepared independently by reacting RuCl2(p-cymene)(PCy3) with organic precursor 3. The activity of the isolated reactivated catalyst in the RCM of DEDAM is similar to that of the independently prepared complex. PMID:23355756

  10. Reactivation of a Ruthenium-Based Olefin Metathesis Catalyst.

    PubMed

    Tabari, Daniel S; Tolentino, Daniel R; Schrodi, Yann

    2013-01-14

    1(st) Generation Hoveyda-Grubbs olefin metathesis catalyst was purposely decomposed in the presence of ethylene yielding inorganic species that are inactive in the ring-closing metathesis (RCM) of benchmark substrate diethyldiallyl malonate (DEDAM). The decomposed catalyst was treated with 1-(3,5-diisopropoxyphenyl)-1-phenylprop-2-yn-1-ol (3) to generate an olefin metathesis active ruthenium indenylidene-ether complex in 43 % yield. This complex was also prepared independently by reacting RuCl(2)(p-cymene)(PCy(3)) with organic precursor 3. The activity of the isolated reactivated catalyst in the RCM of DEDAM is similar to that of the independently prepared complex.

  11. Influence of liquid medium on the activity of a low-alpha Fischer-Tropsch catalyst

    SciTech Connect

    Gormley, R.J.; Zarochak, M.F.; Deffenbaugh, P.W.; Rao, K.R.P.M.

    1995-12-31

    The purpose of this research was to measure activity, selectivity, and the maintenance of these properties in slurry autoclave experiments with a Fischer-Tropsch (FT) catalyst that was used in the {open_quotes}FT II{close_quotes} bubble-column test, conducted at the Alternative Fuels Development Unit (AFDU) at LaPorte, Texas during May 1994. The catalyst contained iron, copper, and potassium and was formulated to produce mainly hydrocarbons in the gasoline range with lesser production of diesel-range products and wax. The probability of chain growth was thus deliberately kept low. Principal goals of the autoclave work have been to find the true activity of this catalyst in a stirred tank reactor, unhindered by heat or mass transfer effects, and to obtain a steady conversion and selectivity over the approximately 15 days of each test. Slurry autoclave testing of the catalyst in heavier waxes also allows insight into operation of larger slurry bubble column reactors. The stability of reactor operation in these experiments, particularly at loadings exceeding 20 weight %, suggests the likely stability of operations on a larger scale.

  12. Activity and stability of pyrolyzed iron ethylenediaminetetraacetic acid as cathode catalyst in microbial fuel cells.

    PubMed

    Wang, Li; Liang, Peng; Zhang, Jian; Huang, Xia

    2011-04-01

    A low-cost and effective iron-chelated catalyst was developed as an electrocatalyst for the oxygen reduction reaction (ORR) in microbial fuel cells (MFCs). The catalyst was prepared by pyrolyzing carbon mixed iron-chelated ethylenediaminetetraacetic acid (PFeEDTA/C) in an argon atmosphere. Cyclic voltammetry measurements showed that PFeEDTA/C had a high catalytic activity for ORR. The MFC with a PFeEDTA/C cathode produced a maximum power density of 1122 mW/m(2), which was close to that with a Pt/C cathode (1166 mW/m(2)). The PFeEDTA/C was stable during an operation period of 31 days. Based on X-ray diffraction and X-ray photoelectron spectroscopy measurements, quaternary-N modified with iron might be the active site for the oxygen reduction reaction. The total cost of a PFeEDTA/C catalyst was much lower than that of a Pt catalyst. Thus, PFeEDTA/C can be a good alternative to Pt in MFC practical applications.

  13. Structure-activity relationship of CuO/MnO2 catalysts in CO oxidation

    NASA Astrophysics Data System (ADS)

    Qian, Kun; Qian, Zhaoxia; Hua, Qing; Jiang, Zhiquan; Huang, Weixin

    2013-05-01

    A series of CuO/MnO2 catalysts with different CuO loadings were synthesized by the incipient wetness impregnation method. The catalysts were characterized by N2 adsorption-desorption isotherms, powder X-ray diffraction, X-ray photoelectron spectroscopy, H2-temperature programmed reduction, CO-temperature programmed reduction and scanning electron microscope. The CuO/MnO2 catalysts with CuO loading of 1-40% exhibit almost the same catalytic performance toward CO oxidation while those with higher CuO loadings exhibit a much poorer catalytic activity. The structural characterization results demonstrate that the CuO-MnO2 interface is the active site for CO oxidation in CuO/MnO2 catalysts and CO oxidation over CuO/MnO2 probably follows the interfacial reaction mechanism in which CO chemisorbed on CuO reacts with oxygen species on MnO2 at the CuO-MnO2 interface.

  14. Synthesis and structural characterization of double metal cyanides of iron and zinc: catalyst precursors for the copolymerization of carbon dioxide and epoxides.

    PubMed

    Darensbourg, Donald J; Adams, M Jason; Yarbrough, Jason C; Phelps, Andrea L

    2003-12-01

    Several synthetic approaches for the preparation of double metal cyanide (DMC) derivatives of iron(II) and zinc(II) are described. These include (1) metathesis reactions of ZnCl(2) or ZnI(2) with KCpFe(CN)(2)CO in aqueous solution, (2) reactions of KCpFe(CN)(2)CO and its phosphine-substituted analogues with Zn(CH(3)CN)(4)(BF(4))(2) and subsequent displacement of acetonitrile at the zinc centers by the addition of a neutral (phosphine) or anionic (phenoxide) ligand, and (3) reactions of the protonated HCpFe(CN)(2)(phosphine) complexes with Zn(N(SiMe(3))(2))(2), followed by the addition of phenols. All structures are based on a diamond-shaped planar arrangement of the Fe(2)(CN)(4)Zn(2) core with various appended ligands at the metal sites. Although attempts to replace the iodide ligands in [CpFe(mu-CN)(2)PPh(3)ZnI(THF)](2) with acetate using silver acetate failed, two novel cationic mixed-metal cyanide salts based on the [CpFe(PPh(3))(mu-CN)(2)Zn(NC(5)H(5))](2)(2+) framework were isolated from pyridine solution and their structures were defined by X-ray crystallography. The anionic ligand bound to zinc in these derivatives, which serve as an anionic polymerization initiator, was shown to be central to the catalytic copolymerization reaction of CO(2)/epoxide to provide polycarbonates and cyclic carbonates. The structurally stabilized phosphine-strapped complexes [CpFe(mu-CN)(2)Zn(X)THF](2)(mu-dppp), where X = I or phenolate, were shown to be thermally stable under the conditions (80 degrees C) of the copolymerization reaction by in situ infrared spectroscopy. Both of these derivatives were proposed to serve as mimics for the heterogeneous DMC catalysts in the patent literature, with the derivative where the initiator is a phenolate being more active for the production of polycarbonates. PMID:14632496

  15. Catalyst suppliers consolidate further, offer more catalysts

    SciTech Connect

    Rhodes, A.K.

    1995-10-02

    The list of suppliers of catalysts to the petroleum refining industry has decreased by five since Oil and Gas Journal`s survey of refining catalysts and catalytic additives was last published. Despite the consolidation, the list of catalyst designations has grown to about 950 in this latest survey, compared to 820 listed in 1993. The table divides the catalysts by use and gives data on their primary differentiating characteristics, feedstock, products, form, bulk density,catalyst support, active agents, availability, and manufactures.

  16. Obatoclax regulates the proliferation and fusion of osteoclast precursors through the inhibition of ERK activation by RANKL.

    PubMed

    Oh, Ju Hee; Lee, Jae Yoon; Park, Jin Hyeong; No, Jeong Hyeon; Lee, Na Kyung

    2015-03-01

    Obatoclax, a pan-Bcl2 inhibitor, shows antitumor activities in various solid malignancies. Bcl2-deficient mice have shown the importance of Bcl2 in osteoclasts, as the bone mass of the mice was increased by the induced apoptosis of osteoclasts. Despite the importance of Bcl2, the effects of obatoclax on the proliferation and differentiation of osteoclast precursors have not been studied extensively. Here, we describe the anti-proliferative effects of obatoclax on osteoclast precursors and its negative role on fusion of the cells. Stimulation with low doses of obatoclax significantly suppressed the proliferation of osteoclast precursors in a dose-dependent manner while the apoptosis was markedly increased. Its stimulation was sufficient to block the activation of ERK MAP kinase by RANKL. The same was true when PD98059, an ERK inhibitor, was administered to osteoclast precursors. The activation of JNK1/2 and p38 MAP kinase, necessary for osteoclast differentiation, by RANKL was not affected by obatoclax. Interestingly, whereas the number of TRAP-positive mononuclear cells was increased by both obatoclax and PD98059, fused, multinucleated cells larger than 100 μm in diameter containing more than 20 nuclei were completely reduced. Consistently, obatoclax failed to regulate the expression of osteoclast marker genes, including c-Fos, TRAP, RANK and CtsK. Instead, the expression of DC-STAMP and Atp6v0d2, genes that regulate osteoclast fusion, by RANKL was significantly abrogated by both obatoclax and PD98059. Taken together, these results suggest that obatoclax down-regulates the proliferation and fusion of osteoclast precursors through the inhibition of the ERK1/2 MAP kinase pathway.

  17. N-Butyl-2,4-dinitro-anilinium p-toluenesulfonate as a highly active and selective esterification catalyst

    PubMed Central

    Sattenapally, Narsimha; Wang, Wei; Liu, Huimin; Gao, Yong

    2013-01-01

    N-Butyl-2,4-dinitro-anilinium p-toluenesulfonate (1) was found to be a very active esterification catalyst that promotes condensation of equal mole amount of carboxylic acids and alcohols under mild conditions. This catalyst is also highly selective towards carboxylic acid and alcohol substrates at ambient temperature. PMID:24357885

  18. N-Butyl-2,4-dinitro-anilinium p-toluenesulfonate as a highly active and selective esterification catalyst.

    PubMed

    Sattenapally, Narsimha; Wang, Wei; Liu, Huimin; Gao, Yong

    2013-11-27

    N-Butyl-2,4-dinitro-anilinium p-toluenesulfonate (1) was found to be a very active esterification catalyst that promotes condensation of equal mole amount of carboxylic acids and alcohols under mild conditions. This catalyst is also highly selective towards carboxylic acid and alcohol substrates at ambient temperature.

  19. Activation of Metal-Organic Precursors by Electron Bombardment in the Gas Phase for Enhanced Deposition of Solid Films.

    PubMed

    Sun, Huaxing; Qin, Xiangdong; Zaera, Francisco

    2012-09-01

    The incorporation of gas-phase electron-impact ionization and activation of metal-organic compounds into atomic layer deposition (ALD) processes is reported as a way to enhance film growth with stable precursors. Specifically, it is shown here that gas-phase activation of methylcyclopentadienylmanganese tricarbonyl, MeCpMn(CO)3, which was accomplished by using a typical nude ion gauge employed in many ultrahigh-vacuum (UHV) studies, enhances its dissociative adsorption on silicon surfaces, affording the design of ALD cycles with more extensive Mn deposition and at lower temperatures. Significantly higher Mn uptakes were demonstrated by X-ray photoelectron spectroscopy (XPS) on both silicon dioxide films and on Si(100) wafers Ar(+)-sputtered to remove their native oxide layer. The effectiveness of this electron-impact activation approach in ALD is explained in terms of the cracking patterns seen in mass spectrometry for the metal-organic precursor used.

  20. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, April--June 1995

    SciTech Connect

    Kirby, S.; Song, Chunshan; Schobert, H.H.

    1995-09-01

    Coal liquefaction involves cleavage of methylene, dimethylene and ether bridges connecting polycyclic aromatic units and the reactions of various oxygen functional groups. Here in this quarterly, we report on our continued effort on hydrodeoxygenation of O-containing polycyclic model compounds using novel organometallic catalyst precursors. Compounds containing oxygen functional groups, especially phenols, are undesirable components of coal-derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial alternative would be the removal of these compounds, or the prevention of their formation, during the liquefaction reaction itself, rather than as a separate processing step. A novel organometallic catalyst precursor containing Co and Mo has been studied as a potential hydrogenation catalyst for coal liquefaction. To ascertain the hydrodeoxygenation activity of this catalyst under liquefaction conditions, model compounds were investigated. Anthrone, 2,6-di-t-butyl-4-methyl-phenol, dinaphthyl ether, and xanthene were reacted in the presence of the Co-Mo catalyst precursor and a precursor containing only Mo over a range of temperatures, providing a comparison of conversions to deoxygenated products. These conversions give an indication of the hydrodeoxygenating abilities of organometallic catalyst precursors within a coal liquefaction system. For example, at 400{degrees}C dinaphthylether was converted 100% (4.5% O-containing products) in the presence of the Co-Mo organometallic precursor, compared to 76.5% conversion (7.4% O-products) in the presence of the Mo catalyst.

  1. Rac1 inhibition negatively regulates transcriptional activity of the amyloid precursor protein gene.

    PubMed

    Wang, Pi-Lin; Niidome, Tetsuhiro; Akaike, Akinori; Kihara, Takeshi; Sugimoto, Hachiro

    2009-07-01

    Rac1, a member of the Rho family GTPases, participates in a variety of cellular functions including lamellipodia formation, actin cytoskeleton organization, cell growth, apoptosis, and neuronal development. Recent studies have implicated Rac1 in cytoskeletal abnormalities, production of reactive oxygen species, and generation of the amyloid beta-peptide (Abeta) observed in Alzheimer's disease. In this study, we examined the relationship between Rac1 and amyloid precursor protein (APP), because the abnormal proteolytic processing of APP is a pathologic feature of Alzheimer's disease. In primary hippocampal neurons, the Rac1-specific inhibitor NSC23766 decreased both Rac1 activity and APP protein levels in a concentration-dependent manner. To elucidate how NSC23766 decreases APP protein levels, we examined the effects of NSC23766 on APP processing, degradation, and biosynthesis. NSC23766 did not increase the levels of the proteolytic products of APP, sAPPalpha, Abeta40, and Abeta42. The proteasome inhibitor lactacystin did not reverse the NSC23766-induced decrease in APP protein levels. NSC23766 did, however, decrease the levels of both APP mRNA and APP protein. Decreased levels of APP mRNA and protein were also observed when HEK293 cells were transfected with an expression vector containing a dominant-negative Rac1 mutant or with siRNA targeting Rac1. By overexpressing progressively deleted fragments of the APP promoter in HEK293 cells, we identified a Rac1 response site at positions -233 to -41 bp in the APP promoter. Taken together, our results suggest that Rac1 regulates transcription of the APP gene in primary hippocampal neurons.

  2. Promoting effect of vanadium on catalytic activity of Pt/Ce-Zr-O diesel oxidation catalysts.

    PubMed

    Huang, Haifeng; Jiang, Bo; Gu, Lei; Qi, Zhonghua; Lu, Hanfeng

    2015-07-01

    A series of Pt-V/Ce-Zr-O diesel oxidation catalysts was prepared using the impregnation method. The catalytic activity and sulfur resistance of Pt-V/Ce-Zr-O were investigated in the presence of simulated diesel exhaust. The effect of vanadium on the structure and redox properties of the catalysts was also investigated using the Brunauer-Emmett-Teller method, X-ray diffraction, H2 temperature-programmed reduction, CO temperature-programmed desorption, X-ray photoelectron spectroscopy, and Energy Dispersive Spectroscopy. Results showed that the Pt particles were well dispersed on the Ce-Zr-O carrier through the vanadium isolation effect, which significantly improved the oxidation activity toward CO and hydrocarbons. An electron-withdrawing phenomenon occurred from V to Pt, resulting in an increase in the metallic nature of platinum, which was beneficial to hydrocarbon molecular activation.

  3. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Final report

    SciTech Connect

    Chunshan Song; Schobert, H.H.; Parfitt, D.P.

    1997-11-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that dispersed catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on exploring novel bimetallic dispersed catalysts for coal liquefaction and the effectiveness of temperature-programmed liquefaction using dispersed catalysts. The primary objective of this research was to explore novel bimetallic dispersed catalysts from organometallic molecular precursors, that could be used in low concentrations but exhibit relatively high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. We have synthesized and tested various catalyst precursors in liquefaction of subbituminous and bituminous coals and in model compound studies to examine how do the composition and structure of the catalytic precursors affect their effectiveness for coal liquefaction under different reaction conditions, and how do these factors affect their catalytic functions for hydrogenation of polyaromatic hydrocarbons, for cleavage of C-C bonds in polycyclic systems such as 4-(1-naphthylmethyl)bibenzyl, for hydrogenolysis of C-O bond such as that in dinaphthylether, for hydrodeoxygenation of phenolic compounds and other oxygen-containing compounds such as xanthene, and for hydrodesulfurization of polycyclic sulfur compounds such as dibenzothiophene. The novel bimetallic and monometallic precursors synthesized and tested in this project include various Mo- and Fe-based compounds.

  4. Highly active non-PGM catalysts prepared from metal organic frameworks

    SciTech Connect

    Barkholtz, Heather M.; Chong, Lina; Kaiser, Zachary B.; Xu, Tao; Liu, Di -Jia

    2015-06-11

    Finding inexpensive alternatives to platinum group metals (PGMs) is essential for reducing the cost of proton exchange membrane fuel cells (PEMFCs). Numerous materials have been investigated as potential replacements of Pt, of which the transition metal and nitrogen-doped carbon composites (TM/Nx/C) prepared from iron doped zeolitic imidazolate frameworks (ZIFs) are among the most active ones in catalyzing the oxygen reduction reaction based on recent studies. In this report, we demonstrate that the catalytic activity of ZIF-based TM/Nx/C composites can be substantially improved through optimization of synthesis and post-treatment processing conditions. Ultimately, oxygen reduction reaction (ORR) electrocatalytic activity must be demonstrated in membrane-electrode assemblies (MEAs) of fuel cells. The process of preparing MEAs using ZIF-based non-PGM electrocatalysts involves many additional factors which may influence the overall catalytic activity at the fuel cell level. Evaluation of parameters such as catalyst loading and perfluorosulfonic acid ionomer to catalyst ratio were optimized. Our overall efforts to optimize both the catalyst and MEA construction process have yielded impressive ORR activity when tested in a fuel cell system.

  5. Highly active non-PGM catalysts prepared from metal organic frameworks

    DOE PAGES

    Barkholtz, Heather M.; Chong, Lina; Kaiser, Zachary B.; Xu, Tao; Liu, Di -Jia

    2015-06-11

    Finding inexpensive alternatives to platinum group metals (PGMs) is essential for reducing the cost of proton exchange membrane fuel cells (PEMFCs). Numerous materials have been investigated as potential replacements of Pt, of which the transition metal and nitrogen-doped carbon composites (TM/Nx/C) prepared from iron doped zeolitic imidazolate frameworks (ZIFs) are among the most active ones in catalyzing the oxygen reduction reaction based on recent studies. In this report, we demonstrate that the catalytic activity of ZIF-based TM/Nx/C composites can be substantially improved through optimization of synthesis and post-treatment processing conditions. Ultimately, oxygen reduction reaction (ORR) electrocatalytic activity must be demonstratedmore » in membrane-electrode assemblies (MEAs) of fuel cells. The process of preparing MEAs using ZIF-based non-PGM electrocatalysts involves many additional factors which may influence the overall catalytic activity at the fuel cell level. Evaluation of parameters such as catalyst loading and perfluorosulfonic acid ionomer to catalyst ratio were optimized. Our overall efforts to optimize both the catalyst and MEA construction process have yielded impressive ORR activity when tested in a fuel cell system.« less

  6. Catalysts possessing augmented C-O and C-N hydrogenolysis activity. Progress report No. 1, October-December 1983

    SciTech Connect

    Massoth, F.E.; Shabtai, J.S.

    1984-01-09

    The aim of the proposed research is to synthesize and investigate new sulfided catalyst systems having higher carbon-heteroatom hydrogenolysis activity as compared to ring hydrogenation activity. A fundamental approach is planned to gain understanding of the basic catalytic properties which relate to hydrogenolysis, hydrogenation and cracking functions of the catalysts. This will involve preparation of new catalysts, characterization of their properties and model compound reactivity studies. In another part of the project, selected catalysts will be applied in studies of more complex O- and N- containing model compounds with the objective of providing fundamental data on the stereochemistry of HDO and HDN reactions. These data will be used to develop steric surface-reactant models for sulfided catalysts. During this quarter additional catalysts were prepared by incipient wetness impregnation using solutions at various pH levels. Catalysts prepared by this method included: 3% and 6% Co, or 3% and 6% Ni with either 8% Mo or with 4.5% Cr supported on ..gamma.. alumina. Five catalysts were tested for hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) activity using model compounds indole and dibenzofuran. 5 references, 5 figures, 1 table.

  7. ALTERNATIVE ROUTES FOR CATALYST PREPARATION: USE OF ULTRASOUND AND MICROWAVE IRRADIATION FOR THE PREPARATION OF VANADIUM PHOSPHORUS OXIDE CATALYST AND ITS ACTIVITY FOR HYDROCARBON OXIDATION

    EPA Science Inventory

    Vanadium phosphorus oxide (VPO) is a well-known catalyst used for the vapor phase n-butane oxidation to maleic anhydride. It is prepared by a variety of methods, all of which, however, eventually result in the same active phase. The two main methods for the preparation of its pr...

  8. Optimization of Single and Bimetallic Noble Metal Catalysts by Strong Electrostatic Adsorption

    NASA Astrophysics Data System (ADS)

    Barnes, Sean E.

    Heterogeneous catalysts are used in over 90% of chemical processes today. These small metal particles maximize the number of active sites present, which leads to cheaper, more effective catalysts. However, the preparation of heterogeneous catalysts is still a "dark art". An alternate to dry impregnation is the method of Strong Electrostatic Adsorption (SEA). In this method the surface hydroxyl groups of the support can either protonate or deprotonate depending on the pH of the contacting solution. These surface groups then can then attract oppositely charged metal precursors. Preparation of catalysts by SEA leads to the anchoring of small, well dispersed, highly active metal particles. The aim of this work is to optimize the preparation via SEA of various supported catalysts systems, particularly Pt/carbon, Au supported on a variety of materials, and Au-Pd/carbon. Carbon supported metal catalysts are becoming increasingly important not just as electro catalyst in fuel cells, but for many aqueous phase biomass conversion reactions.

  9. Comparative dimerization of 1-butene with a variety of metal catalysts, and the investigation of a new catalyst for C=H bond activation.

    PubMed

    Small, Brooke L; Schmidt, Roland

    2004-02-20

    Catalytic dimerization of 1-butene by a variety of catalysts is carried out, and the products are analyzed by gas chromatography and mass spectrometry. Catalysts based on cobalt and iron can produce highly linear dimers, with the cobalt-based dimers exceeding 97 % linearity. Catalysts based on vanadium and aluminum prefer to make branched dimers, which are most often methyl-heptenes in the case of vanadium and almost exclusively 2-ethyl-1-butene in the case of aluminum. The vanadium catalyst also produces substantial amounts of dienes and alkanes, suggesting a competing hydrogenation/dehydrogenation pathway that appears to involve vinyl Cbond;H bond activation. Nickel catalysts are generally less selective than those based on iron or cobalt for making linear dimers, but they can make dimers with 60 % linearity. The major by-products for the nickel systems are trisubstituted internal olefins. An important side reaction that must be considered for dimerization reactions is 1-butene isomerization to 2-butene, which makes recycling the butene difficult for a linear dimerization process. Aluminum, iron, and vanadium systems promote very little isomerization, but nickel and cobalt systems tend to isomerize the undimerized substrate heavily. PMID:14978828

  10. Activation and regeneration of a NiMo/Al[sub 2]O[sub 3] hydrotreatment catalyst

    SciTech Connect

    Teixeira da Silva, V.L.S.; Schmal, M. ); Frety, R. . Inst. de Reserches sur la Catalyse)

    1994-07-01

    Activation and regeneration procedures applied to a nickel-molybdenum on alumina catalyst, both fresh and spent, were tested by the hydrodesulfurization of thiophene. Characterization techniques used included temperature programmed reduction and oxidation (TPR,TPO), diffuse reflectance spectroscopy (DRS), and X-ray diffraction (XRD). The fresh catalyst was treated by sulfiding, reoxidation, and resulfiding. This sequence was found to be more effective than one sulfiding step, possibly because of the formation of a nickel molybdate phase during reoxidation. The spent catalyst could not be regenerated completely although its original surface properties were attained. The loss of activity of the spent catalysts was alluded by TPO to result from nickel-molybdenum segregation which probably happened because of the excessive heat from burning the coke present on the catalyst.

  11. The effect of H2O and pretreatment on the activity of a Pt/SnO2 catalyst

    NASA Technical Reports Server (NTRS)

    Vannorman, John D.; Brown, Kenneth G.; Schryer, Jacqueline; Schryer, David R.; Upchurch, Billy T.; Sidney, Barry D.

    1990-01-01

    CO oxidation catalysts with high activity at 25 C to 100 C are important for long-life, closed-cycle operation of pulsed CO2 lasers. A reductive pretreatment with either CO or H2 has been shown to significantly enhance the activity of a commercially available platinum on tin (IV) oxide (Pt/SnO2) catalyst relative to an oxidative or inert pretreatment or no pretreatment. Pretreatment at temperatures of 175 C and above causes an initial dip in the observed CO2 yield before the steady-state yield is attained. This dip has been found to be caused by dehydration of the catalyst during pretreatment and is readily eliminated by humidifying the catalyst or the reaction gas mixture. It is hypothesized that the effect of humidification is to increase the concentration of OH groups on the catalyst surface which play a role in the reaction mechanism.

  12. Integrated Interpretation of Geophysical, Geotechnical, and Environmental Monitoring Data to Define Precursors for Landslide Activation

    NASA Astrophysics Data System (ADS)

    Uhlemann, S.; Chambers, J.; Merritt, A.; Wilkinson, P.; Meldrum, P.; Gunn, D.; Maurer, H.; Dixon, N.

    2014-12-01

    To develop a better understanding of the failure mechanisms leading to first time failure or reactivation of landslides, the British Geological Survey is operating an observatory on an active, shallow landslide in North Yorkshire, UK, which is a typical example of slope failure in Lias Group mudrocks. This group and the Whitby Mudstone Formation in particular, show one of the highest landslide densities in the UK. The observatory comprises geophysical (i.e., ERT and self-potential monitoring, P- and S-wave tomography), geotechnical (i.e. acoustic emission and inclinometer), and hydrological and environmental monitoring (i.e. weather station, water level, soil moisture, soil temperature), in addition to movement monitoring using real-time kinematic GPS. In this study we focus on the reactivation of the landslide at the end of 2012, after an exceptionally wet summer. We present an integrated interpretation of the different data streams. Results show that the two lobes (east and west), which form the main focus of the observatory, behave differently. While water levels, and hence pore pressures, in the eastern lobe are characterised by a continuous increase towards activation resulting in significant movement (i.e. metres), water levels in the western lobe are showing frequent drainage events and thus lower pore pressures and a lower level of movement (i.e. tens of centimetres). This is in agreement with data from the geoelectrical monitoring array. During the summer season, resistivities generally increase due to decreasing moisture levels. However, during the summer of 2012 this seasonal pattern was interrupted, with the reactivated lobe displaying strongly decreasing resistivities (i.e. increasing moisture levels). The self-potential and soil moisture data show clear indications of moisture accumulation prior to the reactivation, followed by continuous discharge towards the base of the slope. Using the different data streams, we present 3D volumetric images of

  13. Active Site Dependent Reaction Mechanism over Ru/CeO2 Catalyst toward CO2 Methanation.

    PubMed

    Wang, Fei; He, Shan; Chen, Hao; Wang, Bin; Zheng, Lirong; Wei, Min; Evans, David G; Duan, Xue

    2016-05-18

    Oxygen vacancy on the surface of metal oxides is one of the most important defects which acts as the reactive site in a variety of catalytic reactions. In this work, operando spectroscopy methodology was employed to study the CO2 methanation reaction catalyzed by Ru/CeO2 (with oxygen vacancy in CeO2) and Ru/α-Al2O3 (without oxygen vacancy), respectively, so as to give a thorough understanding on active site dependent reaction mechanism. In Ru/CeO2 catalyst, operando XANES, IR, and Raman were used to reveal the generation process of Ce(3+), surface hydroxyl, and oxygen vacancy as well as their structural evolvements under practical reaction conditions. The steady-state isotope transient kinetic analysis (SSITKA)-type in situ DRIFT infrared spectroscopy undoubtedly substantiates that CO2 methanation undergoes formate route over Ru/CeO2 catalyst, and the formate dissociation to methanol catalyzed by oxygen vacancy is the rate-determining step. In contrast, CO2 methanation undergoes CO route over Ru surface in Ru/α-Al2O3 with the absence of oxygen vacancy, demonstrating active site dependent catalytic mechanism toward CO2 methanation. In addition, the catalytic activity evaluation and the oscillating reaction over Ru/CeO2 catalyst further prove that the oxygen vacancy catalyzes the rate-determining step with a much lower activation temperature compared with Ru surface in Ru/α-Al2O3 (125 vs 250 °C).

  14. Zirconia supported catalysts for bioethanol steam reforming: Effect of active phase and zirconia structure

    NASA Astrophysics Data System (ADS)

    Benito, M.; Padilla, R.; Rodríguez, L.; Sanz, J. L.; Daza, L.

    Three new catalysts have been prepared in order to study the active phase influence in ethanol steam reforming reaction. Nickel, cobalt and copper were the active phases selected and were supported on zirconia with monoclinic and tetragonal structure, respectively. To characterize the behaviour of the catalysts in reaction conditions a study of catalytic activity with temperature was performed. The highest activity values were obtained at 973 K where nickel and cobalt based catalysts achieved an ethanol conversion of 100% and a selectivity to hydrogen close to 70%. Nickel supported on tetragonal zirconia exhibited the highest hydrogen production efficiency, higher than 4.5 mol H 2/mol EtOH fed. The influence of steam/carbon (S/C) ratio on product distribution was another parameter studied between the range 3.2-6.5. Nickel supported on tetragonal zirconia at S/C = 3.2 operated at 973 K without by-product production such as ethylene or acetaldehyde. In order to consider a further application in an ethanol processor, a long-term reaction experiment was performed at 973 K, S/C = 3.2 and atmospheric pressure. After 60 h, nickel supported on tetragonal zirconia exhibited high stability and selectivity to hydrogen production.

  15. Cationic tungsten-oxo-alkylidene-N-heterocyclic carbene complexes: highly active olefin metathesis catalysts.

    PubMed

    Schowner, Roman; Frey, Wolfgang; Buchmeiser, Michael R

    2015-05-20

    The synthesis, structure, and olefin metathesis activity of the first neutral and cationic W-oxo-alkylidene-N-heterocyclic carbene (NHC) catalysts are reported. Neutral W-oxo-alkylidene-NHC catalysts can be prepared in up to 90% isolated yield. Depending on the ligands used, they possess either an octahedral (Oh) or trigonal bipyramidal ligand sphere. They can be activated with excess AlCl3 to form cationic olefin metathesis-active W-complexes; however, these readily convert into neutral chloro-complexes. Well-defined, stable cationic species can be prepared by stoichiometric substitution of one chloro ligand in the parent, neutral W-oxo-alkylidene-NHC complexes with Ag(MeCN)2B(Ar(F))4 or NaB(Ar(F))4; B(Ar(F))4 = B(3,5-(CF3)2-C6H3)4. They are highly active olefin metathesis catalysts, allowing for turnover numbers up to 10,000 in various olefin metathesis reactions including alkenes bearing nitrile, sec-amine, and thioether groups. PMID:25938340

  16. Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation

    DOE PAGES

    He, Qian; Freakley, Simon J.; Edwards, Jennifer K.; Carley, Albert F.; Borisevich, Albina Y.; Mineo, Yuki; Haruta, Masatake; Hutchings, Graham J.; Kiely, Christopher J.

    2016-09-27

    The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviors after heat treatment of Au/FeOx materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to revealmore » the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. As a result, correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeOx catalyst.« less

  17. Cationic tungsten-oxo-alkylidene-N-heterocyclic carbene complexes: highly active olefin metathesis catalysts.

    PubMed

    Schowner, Roman; Frey, Wolfgang; Buchmeiser, Michael R

    2015-05-20

    The synthesis, structure, and olefin metathesis activity of the first neutral and cationic W-oxo-alkylidene-N-heterocyclic carbene (NHC) catalysts are reported. Neutral W-oxo-alkylidene-NHC catalysts can be prepared in up to 90% isolated yield. Depending on the ligands used, they possess either an octahedral (Oh) or trigonal bipyramidal ligand sphere. They can be activated with excess AlCl3 to form cationic olefin metathesis-active W-complexes; however, these readily convert into neutral chloro-complexes. Well-defined, stable cationic species can be prepared by stoichiometric substitution of one chloro ligand in the parent, neutral W-oxo-alkylidene-NHC complexes with Ag(MeCN)2B(Ar(F))4 or NaB(Ar(F))4; B(Ar(F))4 = B(3,5-(CF3)2-C6H3)4. They are highly active olefin metathesis catalysts, allowing for turnover numbers up to 10,000 in various olefin metathesis reactions including alkenes bearing nitrile, sec-amine, and thioether groups.

  18. Lewis acid activation of carbodicarbene catalysts for Rh-catalyzed hydroarylation of dienes.

    PubMed

    Roberts, Courtney C; Matías, Desirée M; Goldfogel, Matthew J; Meek, Simon J

    2015-05-27

    The activation of carbodicarbene (CDC)-Rh(I) pincer complexes by secondary binding of metal salts is reported for the catalytic site-selective hydro-heteroarylation of dienes (up to 98% yield and >98:2 γ:α). Reactions are promoted by 5 mol % of a readily available tridentate (CDC)-Rh complex in the presence of an inexpensive lithium salt. The reaction is compatible with a variety of terminal and internal dienes and tolerant of ester, alkyl halide, and boronate ester functional groups. X-ray data and mechanistic experiments provide support for the role of the metal salts on catalyst activation and shed light on the reaction mechanism. The increased efficiency (120 to 22 °C) made available by catalytic amounts of metal salts to catalysts containing C(0) donors is a significant aspect of the disclosed studies. PMID:25961506

  19. Catalytically Active and Spectator Ce(3+) in Ceria-Supported Metal Catalysts.

    PubMed

    Kopelent, René; van Bokhoven, Jeroen A; Szlachetko, Jakub; Edebeli, Jacinta; Paun, Cristina; Nachtegaal, Maarten; Safonova, Olga V

    2015-07-20

    Identification of active species and the rate-determining reaction steps are crucial for optimizing the performance of oxygen-storage materials, which play an important role in catalysts lowering automotive emissions, as electrode materials for fuel cells, and as antioxidants in biomedicine. We demonstrated that active Ce(3+) species in a ceria-supported platinum catalyst during CO oxidation are short-lived and therefore cannot be observed under steady-state conditions. Using time-resolved resonant X-ray emission spectroscopy, we quantitatively correlated the initial rate of Ce(3+) formation under transient conditions to the overall rate of CO oxidation under steady-state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce(3+) was present as spectators. This approach can be applied to various catalytic processes involving oxygen-storage materials and reducible oxides to distinguish between redox and nonredox catalytic mechanisms.

  20. Boryl (Hetero)aryne Precursors as Versatile Arylation Reagents: Synthesis through C–H Activation and Orthogonal Reactivity

    PubMed Central

    Demory, Emilien; Devaraj, Karthik; Orthaber, Andreas; Gates, Paul J; Pilarski, Lukasz T

    2015-01-01

    (Pinacolato)boryl ortho-silyl(hetero)aryl triflates are presented as a new class of building blocks for arylation. They demonstrate unique versatility by delivering boronate or (hetero)aryne reactivity chemoselectively in a broad range of transformations. This approach enables the unprecedented postfunctionalization of fluoride-activated (hetero)aryne precursors, for example, as substrates in transition-metal catalysis, and offers valuable new possibilities for aryl boronate postfunctionalization without the use of specialized protecting groups. PMID:26270451

  1. A General Method for Multimetallic Platinum Alloy Nanowires as Highly Active and Stable Oxygen Reduction Catalysts.

    PubMed

    Bu, Lingzheng; Ding, Jiabao; Guo, Shaojun; Zhang, Xu; Su, Dong; Zhu, Xing; Yao, Jianlin; Guo, Jun; Lu, Gang; Huang, Xiaoqing

    2015-11-25

    An unconventional class of high-performance Pt alloy multimetallic nanowires (NWs) is produced by a general method. The obtained PtNi NWs exhibit amazingly specific and mass oxygen reduction reaction (ORR) activities with improvement factors of 51.1 and 34.6 over commercial Pt/C catalysts, respectively, and are also stable in ORR conditions, making them among the most efficient electrocatalysts for ORR.

  2. Reductive alkylation of active methylene compounds with carbonyl derivatives, calcium hydride and a heterogeneous catalyst.

    PubMed

    Guyon, Carole; Duclos, Marie-Christine; Sutter, Marc; Métay, Estelle; Lemaire, Marc

    2015-07-01

    A one-pot two-step reaction (Knoevenagel condensation - reduction of the double bond) has been developed using calcium hydride as a reductant in the presence of a supported noble metal catalyst. The reaction between carbonyl compounds and active methylene compounds such as methylcyanoacetate, 1,3-dimethylbarbituric acid, dimedone and the more challenging dimethylmalonate, affords the corresponding monoalkylated products in moderate to good yields (up to 83%) with minimal reduction of the starting carbonyl compounds. PMID:26053131

  3. CATALYST ACTIVITY MAINTENANCE FOR THE LIQUID PHASE SYNTHESIS GAS-TO-DIMETHYL ETHER PROCESS PART II: DEVELOPMENT OF ALUMINUM PHOSPHATE AS THE DEHYDRATION CATALYST FOR THE SINGLE-STEP LIQUID PHASE SYNGAS-TO-DME PROCESS

    SciTech Connect

    Xiang-Dong Peng

    2002-05-01

    At the heart of the single-step liquid phase syngas-to-DME process (LPDME{trademark}) is a catalyst system that can be active as well as stable. In the Alternative Fuels I program, a dual-catalyst system containing a Cu-based commercial methanol synthesis catalyst (BASF S3-86) and a commercial dehydration material ({gamma}-alumina) was demonstrated. It provided the productivity and selectivity expected from the LPDME process. However, the catalyst system deactivated too rapidly to warrant a viable commercial process [1]. The mechanistic investigation in the early part of the DOE's Alternative Fuels II program revealed that the accelerated catalyst deactivation under LPDME conditions is due to detrimental interaction between the methanol synthesis catalyst and methanol dehydration catalyst [2,3]. The interaction was attributed to migration of Cu- and/or Zn-containing species from the synthesis catalyst to the dehydration catalyst. Identification of a dehydration catalyst that did not lead to this detrimental interaction while retaining adequate dehydration activity was elusive. Twenty-nine different dehydration materials were tested, but none showed the desired performance [2]. The search came to a turning point when aluminum phosphate was tested. This amorphous material is prepared by precipitating a solution containing Al(NO{sub 3}){sub 3} and H{sub 3}PO{sub 4} with NH{sub 4}OH, followed by washing, drying and calcination. The aluminum phosphate catalyst has adequate dehydration activity and good stability. It can co-exist with the Cu-based methanol synthesis catalyst without negatively affecting the latter catalyst's stability. This report documents the details of the development of this catalyst. These include initial leads, efforts in improving activity and stability, investigation and development of the best preparation parameters and procedures, mechanistic understanding and resulting preparation guidelines, and the accomplishments of this work.

  4. Plasma-enhanced atomic layer deposition of silicon dioxide films using plasma-activated triisopropylsilane as a precursor

    SciTech Connect

    Jeon, Ki-Moon; Shin, Jae-Su; Yun, Ju-Young; Jun Lee, Sang; Kang, Sang-Woo

    2014-05-15

    The plasma-enhanced atomic layer deposition (PEALD) process was developed as a growth technique of SiO{sub 2} thin films using a plasma-activated triisopropylsilane [TIPS, ((iPr){sub 3}SiH)] precursor. TIPS was activated by an argon plasma at the precursor injection stage of the process. Using the activated TIPS, it was possible to control the growth rate per cycle of the deposited films by adjusting the plasma ignition time. The PEALD technique allowed deposition of SiO{sub 2} films at temperatures as low as 50 °C without carbon impurities. In addition, films obtained with plasma ignition times of 3 s and 10 s had similar values of root-mean-square surface roughness. In order to evaluate the suitability of TIPS as a precursor for low-temperature deposition of SiO{sub 2} films, the vapor pressure of TIPS was measured. The thermal stability and the reactivity of the gas-phase TIPS with respect to water vapor were also investigated by analyzing the intensity changes of the C–H and Si–H peaks in the Fourier-transform infrared spectrum of TIPS.

  5. Oxyhydrochlorination catalyst

    DOEpatents

    Taylor, Charles E.; Noceti, Richard P.

    1992-01-01

    An improved catalyst and method for the oxyhydrochlorination of methane is disclosed. The catalyst includes a pyrogenic porous support on which is layered as active material, cobalt chloride in major proportion, and minor proportions of an alkali metal chloride and of a rare earth chloride. On contact of the catalyst with a gas flow of methane, HCl and oxygen, more than 60% of the methane is converted and of that converted more than 40% occurs as monochloromethane. Advantageously, the monochloromethane can be used to produce gasoline boiling range hydrocarbons with the recycle of HCl for further reaction. This catalyst is also of value for the production of formic acid as are analogous catalysts with lead, silver or nickel chlorides substituted for the cobalt chloride.

  6. New hydroprocessing catalysts prepared from molecular complexes

    SciTech Connect

    Ho, T.C.

    1994-12-31

    Current commercial hydroprocessing catalysts are transition metal sulfides (TMS) based on Group 8 and 11 metals. They are prepared by dispersing MoO{sub 3} and a promoter metal oxide, either CoO or NiO, on {gamma}-Al{sub 2}O{sub 3} or SiO{sub 2}-modified Al{sub 2}O{sub 3}. This is followed by sulfiding with a sulfur-bearing stream such as H{sub 2}S at high temperatures. The thus formed MoS{sub 2} crystallites are the backbone of the working catalysts. A potentially fruitful approach to new catalysts would be to molecularly incorporate promoter metals into the structure of MoS{sub 2} edge planes. As a first step, it would seem reasonable to exploit the use of heterometallic metal sulfur complexes as hydroprocessing catalyst precursors. The authors have developed several families of new catalysts along this line. In this paper the authors restrict themselves to the metal amine thiomolybdate-derived catalysts. Specifically, they give an overview of the performance of the bulk (unsupported) FeMo sulfide prepared from MAT. This low-surface-area catalyst shows a high HDN-to-HDS volumetric activity ratio and is also active for HDA. While most of the results are taken from their previous publications, some new results are reported here.

  7. Direct evidence of active surface reconstruction during oxidative dehydrogenation of propane over VMgO catalyst

    SciTech Connect

    Pantazidis, A.; Mirodatos, C.; Burrows, A.; Kiely, C.J.

    1998-07-25

    This paper presents a thorough investigation of an optimized VMgO catalyst (14 wt% V) for the oxidative dehydrogenation of propane, carried out in order to elucidate the nature and behavior of the active surface. The catalyst morphology and the surface composition are studied by means of HREM, XPS, UV-vis, XRD, and in-situ electrical conductivity techniques, as a function of the gaseous environments of the catalyst. The active surface is shown to be essentially a monolayer of amorphous VO{sub 4}{sup 3{minus}} units scattered over the magnesia as isolated and polymeric species. These surface vanadia units are found to stabilize an unusual polar (111) orientation of MgO up to temperatures of 800 C. A direct and outstanding evidence of a totally reversible phenomenon of order/disorder restructuration of this V overlayer is provided in conjunction with the redox state of the surface depending on the properties of the surrounding atmosphere (reductive or oxidative). These fast surface phenomena are assumed to determine the elementary steps of propane activation within the overall oxidative dehydrogenation of propane (ODHP) process.

  8. Redox-Active Nitroxide Radical Polymers: From Green Catalysts to Energy Storage Devices

    NASA Astrophysics Data System (ADS)

    Waskitoaji, Wihatmoko; Suga, Takeo; Nishide, Hiroyuki

    2009-09-01

    Robust but redox-active radical polymers bearing 2, 2, 6, 6-tetramethylpiperidin-N-oxy (TEMPO) were investigated as a metal-free, green mediator/catalyst for the oxidation of alcohol derivatives, and as a new electrode-active and charge-storage material. The TEMPO-mediated oxidation of the primary alcohol group of the natural cellulose improved the water-dispersivity of cellulose, and the polymer-supported catalysts or redox resins allow facile removal of catalysts from products by simple filtration. Other radical molecule (e.g. galvinoxyl) was also used as a mediator, which is coupled with the molecular oxygen. A reversible one-electron redox reaction of TEMPO allowed its application as an electrode-active material featuring high cyclability (>500 cycles), relatively high battery electrode capacity (100-135 mAh/g), and fast electrode kinetics, leading to the high power rate capability of the battery. The radical polymer-based electrodes also provided good processability and shape flexibility, which promised the paper-like and wearable energy-storage devices.

  9. Heterogeneous copper-silica catalyst from agricultural biomass and its catalytic activity

    NASA Astrophysics Data System (ADS)

    Andas, Jeyashelly; Adam, Farook; Rahman, Ismail Ab.

    2013-11-01

    A series of highly mesoporous copper catalysts (5-20 wt.%) supported on silica rice husk were synthesized via sol-gel route at room temperature. The FT-IR and 29Si MAS NMR spectroscopic studies revealed the successful substitution of copper into the silica matrix. Copper in the +2 oxidation state was evidenced from the DR/UV-vis and XPS analyses. Introduction of copper up to 10 wt.% (RH-10Cu) results in a progressive enhancement in the BET surface area. The activity of the copper catalysts was studied in the liquid-phase oxidation of phenol with H2O2 yielding catechol (CAT) and hydroquinone (HQ). Phenol conversion was influenced by various experimental conditions such as temperature, catalyst dosage, molar ratio of reactants, nature of solvent and percentage metal loading. Excellent activity was achieved when 10 wt.% copper was used and decreased with further increase in the copper loading. RH-10Cu could be regenerated several times without significant loss in the catalytic activity.

  10. Activity and selectivity of palladium catalysts during the liquid-phase hydrogenation of phenol. Influence of temperature and pressure

    SciTech Connect

    Gonzalez-Velasco, J.R.; Gonzalez-Marcos, M.P.; Arnaiz, S.; Gutierrez-Ortiz, J.I.; Gutierrez-Ortiz, M.A.

    1995-04-01

    Two series of highly dispersed palladium catalysts supported on alumina have been prepared by adsorption from solution, with palladium contents varying from 0.25 to 2.0 wt %. The first series was calcined at 773 K for 4 h in air, whereas the second series was just heated at 423 K for 1 h in nitrogen, before reduction. Complete dispersion of the metal has been found for the calcined catalysts, and metal dispersion was favored with low palladium contents for the noncalcined catalysts. The kinetic behavior of the catalysts has been analyzed for the liquid-phase hydrogenation of phenol in a stirred tank reactor, ensuring a chemically controlled regime for stirring speed above 750 rpm and catalyst particle below 0.08--0.16 mm in the studied conditions. Despite their higher metallic dispersion, the calcined catalysts presented lower activity than their corresponding noncalcined catalysts. The influence of hydrogen partial pressure on activity showed a reaction order of 2. The apparent activation energy resulted in 56.8 kJ/mol. Selectivity to cyclohexanone was found to be very high for all experiments. Some conclusions on the kinetic reaction rate equations and the apparent activation energies of phenol to cyclohexanone and cyclohexanone to cyclohexanol are given.

  11. Regeneration of field-spent activated carbon catalysts for low-temperature selective catalytic reduction of NOx with NH3

    SciTech Connect

    Jeon, Jong Ki; Kim, Hyeonjoo; Park, Young-Kwon; Peden, Charles HF; Kim, Do Heui

    2011-10-15

    In the process of producing liquid crystal displays (LCD), the emitted NOx is removed over an activated carbon catalyst by using selective catalytic reduction (SCR) with NH3 at low temperature. However, the catalyst rapidly deactivates primarily due to the deposition of boron discharged from the process onto the catalyst. Therefore, this study is aimed at developing an optimal regeneration process to remove boron from field-spent carbon catalysts. The spent carbon catalysts were regenerated by washing with a surfactant followed by drying and calcination. The physicochemical properties before and after the regeneration were investigated by using elemental analysis, TG/DTG (thermogravimetric/differential thermogravimetric) analysis, N2 adsorption-desorption and NH3 TPD (temperature programmed desorption). Spent carbon catalysts demonstrated a drastic decrease in DeNOx activity mainly due to heavy deposition of boron. Boron was accumulated to depths of about 50 {mu}m inside the granule surface of the activated carbons, as evidenced by cross-sectional SEM-EDX analysis. However, catalyst activity and surface area were significantly recovered by removing boron in the regeneration process, and the highest NOx conversions were obtained after washing with a non-ionic surfactant in H2O at 70 C, followed by treatment with N2 at 550 C.

  12. Design of a high activity and selectivity alcohol catalyst

    SciTech Connect

    Foley, H.C.; Mills, G.A.

    1992-02-07

    Results of the pyridine adsorption, studies on native and K-doped alumina provide fundamental grounding for the observed methanol dehydration activity of these samples. Both the reactor studies and the pyridine adsorption studies support the conclusion that the K-doped sample had reduced Lewis acidity. Moreover, we were able to measurably alter the acidity of the support surface by our ion exchange treatment. More significantly, when reactor results for transition-metal loaded samples are reconsidered in combination with their surface characteristics suggested by our pyridine adsorption studies, our hypothesis that Rh and Mo have ultimately titrated the support surface seems all the more convincing. Hence, in light of the pyridine adsorption results, the attenuation of a transition-metal based decomposition pathway for methanol on the metal-loaded samples-as seen in the reactor testing-is all the more reasonable.

  13. A nickel iron diselenide-derived efficient oxygen-evolution catalyst

    NASA Astrophysics Data System (ADS)

    Xu, Xiang; Song, Fang; Hu, Xile

    2016-08-01

    Efficient oxygen-evolution reaction catalysts are required for the cost-effective generation of solar fuels. Metal selenides have been reported as promising oxygen-evolution catalysts; however, their active forms are yet to be elucidated. Here we show that a representative selenide catalyst, nickel selenide, is entirely converted into nickel hydroxide under oxygen-evolution conditions. This result indicates that metal selenides are unstable during oxygen evolution, and the in situ generated metal oxides are responsible for their activity. This knowledge inspired us to synthesize nanostructured nickel iron diselenide, a hitherto unknown metal selenide, and to use it as a templating precursor to a highly active nickel iron oxide catalyst. This selenide-derived oxide catalyses oxygen evolution with an overpotential of only 195 mV for 10 mA cm-2. Our work underscores the importance of identifying the active species of oxygen-evolution catalysts, and demonstrates how such knowledge can be applied to develop better catalysts.

  14. Precursor nuclearity effects in supported vanadium oxides prepared by organometallic grafting.

    SciTech Connect

    Wegener, S. L.; Kim, H.; Marks, T. J.; Stair, P. C.

    2011-01-01

    Despite widespread importance in catalysis, the active and selective sites of supported vanadium oxide (VO{sub x}) catalysts are not well understood. Such catalysts are of great current interest because of their industrial significance and potential for selective oxidation processes. However, the fact that the nature of the active and selective sites is ambiguous hinders molecular level understanding of catalytic reactions and the development of new catalysts. Furthermore, complete structural elucidation requires isolation and characterization of specific vanadium oxide surface species, the preparation of which presents a significant synthetic challenge. In this study, we utilize the structural uniformity inherent in organometallic precursors for the preparation of supported vanadium oxide catalysts. The resulting catalysts are characterized by UV-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray absorption spectroscopy (XAS), UV-Raman spectroscopy, and H{sub 2}-temperature programmed reduction (H{sub 2}-TPR). Significant structural and reactivity differences are observed in catalysts prepared from different organometallic precursors, indicating that the chemical nature of surface vanadia can be influenced by the nuclearity of the precursor used for grafting.

  15. Can Ni phosphides become viable hydroprocessing catalysts?

    SciTech Connect

    Soled, S.; Miseo, S.; Baumgartner, J.; Guzman, J.; Bolin, T.; Meyer, R.

    2015-05-15

    We prepared higher surface area nickel phosphides than are normally found by reducing nickel phosphate. To do this, we hydrothermally synthesized Ni hydroxy phosphite precursors with low levels of molybdenum substitution. The molybdenum substitution increases the surface area of these precursors. During pretreatment in a sulfiding atmosphere (such as H2S/H2) dispersed islands of MoS2 segregate from the precursor and provide a pathway for H2 dissociation that allows reduction of the phosphite precursor to nickel phosphide at substantially lower temperatures than in the absence of MoS2. The results reported here show that to create nickel phosphides with comparable activity to conventional supported sulfide catalysts, one would have to synthesize the phosphide with surface areas exceeding 400 m2/g (i.e. with nanoparticles less than 30 Å in lateral dimension).

  16. Perlite as a potential support for nickel catalyst in the process of sunflower oil hydrogenation

    NASA Astrophysics Data System (ADS)

    Radonjić, V.; Krstić, J.; Lončarević, D.; Jovanović, D.; Vukelić, N.; Stanković, M.; Nikolova, D.; Gabrovska, M.

    2015-12-01

    Investigation was conducted in order to elucidate the possibility of using perlite as support for preparation of nickel based precursor catalyst, potentially applicable in vegetable oil hydrogenation process. On three differently prepared expanded perlite, nickel catalyst precursors with identical Ni/SiO2 = 1.1 and Ni/Mg = 10/1 ratios were synthesized by precipitation-deposition method. Different techniques, SEM micrography, He-pycnometry, calcimetry, Hg-porosimetry, N2-physisorption, H2-chemisorption and temperature programmed reduction, were used for characterization of obtained samples. Determining the precursor texture, morphology and reducibility shows a successfully deposited nickel phase on perlite support with promising properties for vegetable oil hydrogenation. Chosen precursor was reduced and passivated in paraffin oil and the obtained catalyst showed significant catalytic activity in the test of sunflower oil hydrogenation.

  17. Different Mechanisms Must Be Considered to Explain the Increase in Hippocampal Neural Precursor Cell Proliferation by Physical Activity

    PubMed Central

    Overall, Rupert W.; Walker, Tara L.; Fischer, Tim J.; Brandt, Moritz D.; Kempermann, Gerd

    2016-01-01

    The number of proliferating neural precursor cells in the adult hippocampus is strongly increased by physical activity. The mechanisms through which this behavioral stimulus induces cell proliferation, however, are not yet understood. In fact, even the mode of proliferation of the stem and progenitor cells is not exactly known. Evidence exists for several mechanisms including cell cycle shortening, reduced cell death and stem cell recruitment, but as yet no model can account for all observations. An appreciation of how the cells proliferate, however, is crucial to our ability to model the neurogenic process and predict its behavior in response to pro-neurogenic stimuli. In a recent study, we addressed modulation of the cell cycle length as one possible mode of regulation of precursor cell proliferation in running mice. Our results indicated that the observed increase in number of proliferating cells could not be explained through a shortening of the cell cycle. We must therefore consider other mechanisms by which physical activity leads to enhanced precursor cell proliferation. Here we review the evidence for and against several different hypotheses and discuss the implications for future research in the field. PMID:27536215

  18. Identifying the role of N-heteroatom location in the activity of metal catalysts for alcohol oxidation

    SciTech Connect

    Chan-Thaw, Carine E.; Veith, Gabriel M.; Villa, Alberto; Prati, Laura

    2015-04-02

    Here, this work focuses on understanding how the bonding of nitrogen heteroatoms contained on/in a activated carbon support influence the stability and reactivity of a supported Pd catalyst for the oxidation of alcohols in solution. The results show that simply adding N groups via solution chemistry is insufficient to improve catalytic properties. Instead a strongly bound N moiety is required to activate the catalyst and stabilize the metal particles.

  19. Studies on tetrahydrocannabinolic acid synthase that produces the acidic precursor of tetrahydrocannabinol, the pharmacologically active cannabinoid in marijuana.

    PubMed

    Taura, F

    2009-06-01

    Tetrahydrocannabinol (THC), the psychoactive component of marijuana, is now regarded as a promising medicine because this cannabinoid has been shown to exert a variety of therapeutic activities. It has been demonstrated that THC is generated from the acidic precursor, tetrahydrocannabinolic acid (THCA) by nonenzymatic decarboxylation, and that THCA is biosynthesized by THCA synthase, which catalyzes a unique biosynthetic reaction, the stereospecific oxidative cyclization of the geranyl group of the substrate cannabigerolic acid. Molecular characterization of THCA synthase has revealed its structural characteristics and reaction mechanism. THCA synthase is the first cannabinoid synthase to be studied and is potentially attractive target for various biotechnological applications as it produces the direct precursor of THC. This review describes the research history of this enzyme, i.e., purification, molecular cloning, biochemical characterization, and possible biotechnological application of THCA synthase. PMID:22495534

  20. The carburization of transition metal molybdates (MxMoO₄, M= Cu, Ni or Co) and the generation of highly active metal/carbide catalysts for CO₂ hydrogenation

    DOE PAGES

    Rodriguez, Jose A.; Xu, Wenqian; Ramirez, Pedro J.; Stachiola, Dario; Brito, Joaquin L.

    2015-05-06

    A new approach has been tested for the preparation of metal/Mo₂C catalysts using mixed-metal oxide molybdates as precursors. Synchrotron-based in situ time-resolved X-ray diffraction was used to study the reduction and carburization processes of Cu₃(MoO₄)₂(OH)₂, a-NiMoO₄ and CoMoO₄•nH₂O by thermal treatment under mixtures of hydrogen and methane. In all cases, the final product was β-Mo₂C and a metal phase (Cu, Ni, or Co), but the transition sequence varied with the different metals, and it could be related to the reduction potential of the Cu²⁺, Ni²⁺ and Co²⁺ cations inside each molybdate. The synthesized Cu/Mo₂C, Ni/Mo₂C and Co/Mo₂C catalysts were highlymore » active for the hydrogenation of CO₂. The metal/Mo₂C systems exhibited large variations in the selectivity towards methanol, methane and CnH₂n₊₂ (n > 2) hydrocarbons depending on the nature of the supported metal and its ability to cleave C-O bonds. Cu/Mo₂C displayed a high selectivity for CO and methanol production. Ni/Mo₂C and Co/Mo₂C were the most active catalysts for the activation and full decomposition of CO₂, showing high selectivity for the production of methane (Ni case) and CnH₂n₊₂ (n > 2) hydrocarbons (Co case).« less

  1. The carburization of transition metal molybdates (MxMoO₄, M= Cu, Ni or Co) and the generation of highly active metal/carbide catalysts for CO₂ hydrogenation

    SciTech Connect

    Rodriguez, Jose A.; Xu, Wenqian; Ramirez, Pedro J.; Stachiola, Dario; Brito, Joaquin L.

    2015-05-06

    A new approach has been tested for the preparation of metal/Mo₂C catalysts using mixed-metal oxide molybdates as precursors. Synchrotron-based in situ time-resolved X-ray diffraction was used to study the reduction and carburization processes of Cu₃(MoO₄)₂(OH)₂, a-NiMoO₄ and CoMoO₄•nH₂O by thermal treatment under mixtures of hydrogen and methane. In all cases, the final product was β-Mo₂C and a metal phase (Cu, Ni, or Co), but the transition sequence varied with the different metals, and it could be related to the reduction potential of the Cu²⁺, Ni²⁺ and Co²⁺ cations inside each molybdate. The synthesized Cu/Mo₂C, Ni/Mo₂C and Co/Mo₂C catalysts were highly active for the hydrogenation of CO₂. The metal/Mo₂C systems exhibited large variations in the selectivity towards methanol, methane and CnH₂n₊₂ (n > 2) hydrocarbons depending on the nature of the supported metal and its ability to cleave C-O bonds. Cu/Mo₂C displayed a high selectivity for CO and methanol production. Ni/Mo₂C and Co/Mo₂C were the most active catalysts for the activation and full decomposition of CO₂, showing high selectivity for the production of methane (Ni case) and CnH₂n₊₂ (n > 2) hydrocarbons (Co case).

  2. Highly active Pd-In/mesoporous alumina catalyst for nitrate reduction.

    PubMed

    Gao, Zhenwei; Zhang, Yonggang; Li, Deyi; Werth, Charles J; Zhang, Yalei; Zhou, Xuefei

    2015-04-01

    The catalytic reduction of nitrate is a promising technology for groundwater purification because it transforms nitrate into nitrogen and water. Recent studies have mainly focused on new catalysts with higher activities for the reduction of nitrate. Consequently, metal nanoparticles supported on mesoporous metal oxides have become a major research direction. However, the complex surface chemistry and porous structures of mesoporous metal oxides lead to a non-uniform distribution of metal nanoparticles, thereby resulting in a low catalytic efficiency. In this paper, a method for synthesizing the sustainable nitrate reduction catalyst Pd-In/Al2O3 with a dimensional structure is introduced. The TEM results indicated that Pd and In nanoparticles could efficiently disperse into the mesopores of the alumina. At room temperature in CO2-buffered water and under continuous H2 as the electron donor, the synthesized material (4.9 wt% Pd) was the most active at a Pd-In ratio of 4, with a first-order rate constant (k(obs) = 0.241 L min(-1) g(cata)(-1)) that was 1.3× higher than that of conventional Pd-In/Al2O3 (5 wt% Pd; 0.19 L min(-1) g(cata)(-1)). The Pd-In/mesoporous alumina is a promising catalyst for improving the catalytic reduction of nitrate. PMID:25600582

  3. Conversion of isoamyl alcohol over acid catalysts: Reaction dependence on nature of active centers

    SciTech Connect

    Babu, G.P.; Murthy, R.S.; Krishnan, V.

    1997-02-01

    Acid catalysts are known to catalyze the dehydration of alcohols. In addition some oxide catalysts with basic properties have also been shown to play an important role in such dehydration reactions. The dehydration of aliphatic alcohols to olefins has been studied in detail using alumina silica-alumina and zeolite catalysts. The olefin products further undergo isomerization in presence of acidic sites. The reaction of isoamyl alcohol on catalytic surfaces has not been investigated in greater detail. The dehydration of isoamyl alcohol is of considerable interest in fine chemicals. Isoamyl alcohol may also undergo dehydrogenation as observed in the case of n-butanol. The scope of the present work is to identify the nature of the active sites selective for dehydration and dehydrogenation of isoamyl alcohol and to modify the active sites to promote isomerization of dehydrated products. Four catalytic surfaces on which the acidic strength can be varied, as well as selectively suppressed, are chosen for this study. 17 refs., 1 fig., 3 tabs.

  4. Synthesis, characterization, and catalytic activity in Suzuki coupling and catalase-like reactions of new chitosan supported Pd catalyst.

    PubMed

    Baran, Talat; Inanan, Tülden; Menteş, Ayfer

    2016-07-10

    The aim of this study is to analyze the synthesis of a new chitosan supported Pd catalyst and examination of its catalytic activity in: Pd catalyst was synthesized using chitosan as a biomaterial and characterized with FTIR, TG/DTG, XRD, (1)H NMR, (13)C NMR, SEM-EDAX, ICP-OES, Uv-vis spectroscopies, and magnetic moment, along with molar conductivity analysis. Biomaterial supported Pd catalyst indicated high activity and long life time as well as excellent turnover number (TON) and turnover frequency (TOF) values in Suzuki reaction. Biomaterial supported Pd catalyst catalyzed H2O2 decomposition reaction with considerable high activity using comparatively small loading catalyst (10mg). Redox potential of biomaterial supported Pd catalyst was still high without negligible loss (13% decrease) after 10 cycles in reusability tests. As a consequence, eco-friendly biomaterial supported Pd catalyst has superior properties such as high thermal stability, long life time, easy removal from reaction mixture and durability to air, moisture and high temperature. PMID:27106147

  5. Synthesis, characterization, and catalytic activity in Suzuki coupling and catalase-like reactions of new chitosan supported Pd catalyst.

    PubMed

    Baran, Talat; Inanan, Tülden; Menteş, Ayfer

    2016-07-10

    The aim of this study is to analyze the synthesis of a new chitosan supported Pd catalyst and examination of its catalytic activity in: Pd catalyst was synthesized using chitosan as a biomaterial and characterized with FTIR, TG/DTG, XRD, (1)H NMR, (13)C NMR, SEM-EDAX, ICP-OES, Uv-vis spectroscopies, and magnetic moment, along with molar conductivity analysis. Biomaterial supported Pd catalyst indicated high activity and long life time as well as excellent turnover number (TON) and turnover frequency (TOF) values in Suzuki reaction. Biomaterial supported Pd catalyst catalyzed H2O2 decomposition reaction with considerable high activity using comparatively small loading catalyst (10mg). Redox potential of biomaterial supported Pd catalyst was still high without negligible loss (13% decrease) after 10 cycles in reusability tests. As a consequence, eco-friendly biomaterial supported Pd catalyst has superior properties such as high thermal stability, long life time, easy removal from reaction mixture and durability to air, moisture and high temperature.

  6. Thermodynamic explanation of the universal correlation between oxygen evolution activity and corrosion of oxide catalysts

    NASA Astrophysics Data System (ADS)

    Binninger, Tobias; Mohamed, Rhiyaad; Waltar, Kay; Fabbri, Emiliana; Levecque, Pieter; Kötz, Rüdiger; Schmidt, Thomas J.

    2015-07-01

    In recent years, the oxygen evolution reaction (OER) has attracted increased research interest due to its crucial role in electrochemical energy conversion devices for renewable energy applications. The vast majority of OER catalyst materials investigated are metal oxides of various compositions. The experimental results obtained on such materials strongly suggest the existence of a fundamental and universal correlation between the oxygen evolution activity and the corrosion of metal oxides. This corrosion manifests itself in structural changes and/or dissolution of the material. We prove from basic thermodynamic considerations that any metal oxide must become unstable under oxygen evolution conditions irrespective of the pH value. The reason is the thermodynamic instability of the oxygen anion in the metal oxide lattice. Our findings explain many of the experimentally observed corrosion phenomena on different metal oxide OER catalysts.

  7. Thermodynamic explanation of the universal correlation between oxygen evolution activity and corrosion of oxide catalysts

    PubMed Central

    Binninger, Tobias; Mohamed, Rhiyaad; Waltar, Kay; Fabbri, Emiliana; Levecque, Pieter; Kötz, Rüdiger; Schmidt, Thomas J.

    2015-01-01

    In recent years, the oxygen evolution reaction (OER) has attracted increased research interest due to its crucial role in electrochemical energy conversion devices for renewable energy applications. The vast majority of OER catalyst materials investigated are metal oxides of various compositions. The experimental results obtained on such materials strongly suggest the existence of a fundamental and universal correlation between the oxygen evolution activity and the corrosion of metal oxides. This corrosion manifests itself in structural changes and/or dissolution of the material. We prove from basic thermodynamic considerations that any metal oxide must become unstable under oxygen evolution conditions irrespective of the pH value. The reason is the thermodynamic instability of the oxygen anion in the metal oxide lattice. Our findings explain many of the experimentally observed corrosion phenomena on different metal oxide OER catalysts. PMID:26178185

  8. A general method for multimetallic platinum alloy nanowires as highly active and stable oxygen reduction catalysts

    SciTech Connect

    Bu, Lingzheng; Ding, Jiabao; Yao, Jianlin; Huang, Xiaoqing; Guo, Shaojun; Zhang, Xu; Lu, Gang; Su, Dong; Zhu, Xing; Guo, Jun

    2015-10-13

    The production of inorganic nanoparticles (NPs) with precise control over structures has always been a central target in various fields of chemistry and physics because the properties of NPs can be desirably manipulated by their structure.[1-4] There has been an intense search for high-performance noble metal NP catalysts particular for Pt.[5-9] Precious platinum (Pt) NPs are active catalysts for various heterogeneous reactions and show particularly superior performance in both the anodic oxidation reaction and the cathodic ORR in the fuel cells, but their rare content and high cost largely impede the practical application.[10-12] A potential strategy to address this tremendous challenge is alloying Pt NPs with the transition metals (TM).[13-16]

  9. A general method for multimetallic platinum alloy nanowires as highly active and stable oxygen reduction catalysts

    DOE PAGES

    Bu, Lingzheng; Ding, Jiabao; Yao, Jianlin; Huang, Xiaoqing; Guo, Shaojun; Zhang, Xu; Lu, Gang; Su, Dong; Zhu, Xing; Guo, Jun

    2015-10-13

    The production of inorganic nanoparticles (NPs) with precise control over structures has always been a central target in various fields of chemistry and physics because the properties of NPs can be desirably manipulated by their structure.[1-4] There has been an intense search for high-performance noble metal NP catalysts particular for Pt.[5-9] Precious platinum (Pt) NPs are active catalysts for various heterogeneous reactions and show particularly superior performance in both the anodic oxidation reaction and the cathodic ORR in the fuel cells, but their rare content and high cost largely impede the practical application.[10-12] A potential strategy to address this tremendousmore » challenge is alloying Pt NPs with the transition metals (TM).[13-16]« less

  10. Highly Active and Stable MgAl2O4 Supported Rh and Ir Catalysts for Methane Steam Reforming: A Combined Experimental and Theoretical Study

    SciTech Connect

    Mei, Donghai; Glezakou, Vassiliki Alexandra; Lebarbier, Vanessa MC; Kovarik, Libor; Wan, Haiying; Albrecht, Karl O.; Gerber, Mark A.; Rousseau, Roger J.; Dagle, Robert A.

    2014-07-01

    In this work we present a combined experimental and theoretical investigation of stable MgAl2O4 spinel-supported Rh and Ir catalysts for the steam methane reforming (SMR) reaction. Firstly, catalytic performance for a series of noble metal catalysts supported on MgAl2O4 spinel was evaluated for SMR at 600-850°C. Turnover rate at 850°C follows the order: Pd > Pt > Ir > Rh > Ru > Ni. However, Rh and Ir were found to have the best combination of activity and stability for methane steam reforming in the presence of simulated biomass-derived syngas. It was found that highly dispersed ~2 nm Rh and ~1 nm Ir clusters were formed on the MgAl2O4 spinel support. Scanning Transition Electron Microscopy (STEM) images show that excellent dispersion was maintained even under challenging high temperature conditions (e.g. at 850°C in the presence of steam) while Ir and Rh catalysts supported on Al2O3 were observed to sinter at increased rates under the same conditions. These observations were further confirmed by ab initio molecular dynamics (AIMD) simulations which find that ~1 nm Rh and Ir particles (50-atom cluster) bind strongly to the MgAl2O4 surfaces via a redox process leading to a strong metal-support interaction, thus helping anchor the metal clusters and reduce the tendency to sinter. Density functional theory (DFT) calculations suggest that these supported smaller Rh and Ir particles have a lower work function than larger more bulk-like ones, which enables them to activate both water and methane more effectively than larger particles, yet have a minimal influence on the relative stability of coke precursors. In addition, theoretical mechanistic studies were used to probe the relationship between structure and reactivity. Consistent with the experimental observations, our theoretical modeling results also suggest that the small spinel-supported Ir particle catalyst is more active than the counterpart of Rh catalyst for SMR. This work was financially supported by the

  11. Photoinduced Stepwise Oxidative Activation of a Chromophore–Catalyst Assembly on TiO2

    SciTech Connect

    Song, Wenjing; Glasson, Christopher R. K.; Luo, Hanlin; Hanson, Kenneth G.; Brennaman, Kyle M.; Concepcion, Javier J.; Meyer, Thomas J.

    2011-07-08

    To probe light-induced redox equivalent separation and accumulation, we prepared ruthenium polypyridyl molecular assembly [(dcb)2Ru(bpy-Mebim2py)Ru(bpy)(OH2)]4+ (RuaII–RubII–OH2) with Rua as light-harvesting chromophore and Rub as water oxidation catalyst (dcb = 4,4'-dicarboxylic acid-2,2'-bipyridine; bpy-Mebim2py = 2,2'-(4-methyl-[2,2':4',4''-terpyridine]-2'',6''-diyl)bis(1-methyl-1H-benzo[d]imidazole); bpy = 2,2'-bipyridine). When bound to TiO2 in nanoparticle films, it undergoes MLCT excitation, electron injection, and oxidation of the remote -RubII–OH2 site to give TiO2(e–)–RuaII–RubIII–OH23+ as a redox-separated transient. The oxidized assembly, TiO2–RuaII–RubIII–OH23+, similarly undergoes excitation and electron injection to give TiO2(e–)–RuaII–RubIV=O2+, with RubIV=O2+ a known water oxidation catalyst precursor. Injection efficiencies for both forms of the assembly are lower than those for [Ru(bpy)2(4,4'-(PO3H2)2bpy)]2+ bound to TiO2 (TiO2–Ru2+), whereas the rates of back electron transfer, TiO2(e–) → RubIII–OH23+ and TiO2(e–) → RubIV=O2+, are significantly decreased compared with TiO2(e–) → Ru3+ back electron transfer.

  12. Carrier effects of active carbon for methanol carbonylation with supported transition metal catalysts

    SciTech Connect

    Fujimoto, K.; Omata, K.; Yagita, H.

    1996-10-01

    Transition metals such as nickel or noble metals showed excellent catalytic activities for the vapor phase carbonylation of methanol to acetic acid. Reaction proceeded via the carbonylation of methanol to methyl acetate and its successive carbonylation to acetic acid anhydride followed by the hydrolysis. Under slightly pressurized conditions and at around 250{degrees}C methanol was completely carbonylated to acetic acid with the selectivity of 97% or higher. Also, other group 8 metals including noble metals showed excellent catalytic activity only when they were supported on active carbon, whose activity, ordered by strength of metal-halogen bonding showed a volcano-shape relationship with the peak at Rh. The role of active carbon as the active carrier was clarified by kinetics and catalyst characterization which showed that active carbon promoted the reductive elimination of intermediate for acetic acid formation by donating electron from carbon to nickel species.

  13. Influence of the precursor metamorphism degree on preparation of nitrogen-enriched activated carbons by ammoxidation and chemical activation of coals

    SciTech Connect

    Piotr Nowicki; Robert Pietrzak; Helena Wachowska

    2009-04-15

    The paper presents results of a study on obtaining N-enriched active carbons from four hard coals with different degree of metamorphism. The starting materials were carbonized, activated with KOH, and ammoxidized by a mixture of ammonia and air at the ratio 1:3 at 300 and 350{sup o}C, at each stage of the active carbon production. The efficiency of ammoxidation was found to depend on the degree of metamorphism of the precursor, the stage of processing at which ammoxidation is performed, and the temperature of this process. Ammoxidation of the active carbon led to a decrease in their surface area and pore volume, whereas that performed both at the stage of the precursor and the carbonizate brought improvement of textural parameters of the active carbons obtained. The sequence of the carbonization, activation, and ammoxidation processes had a significant effect on the acid-base character of the active carbon samples obtained. The majority of the active carbons modified at the stage of precursor and carbonizate showed considerable prevalence of surface acidic groups, whereas the samples ammoxidized after activation showed an intermediate acidic-basic character of the surface. 25 refs., 4 figs., 9 tabs.

  14. The contrasting catalytic efficiency and cancer cell antiproliferative activity of stereoselective organoruthenium transfer hydrogenation catalysts.

    PubMed

    Fu, Ying; Sanchez-Cano, Carlos; Soni, Rina; Romero-Canelon, Isolda; Hearn, Jessica M; Liu, Zhe; Wills, Martin; Sadler, Peter J

    2016-05-28

    The rapidly growing area of catalytic ruthenium chemistry has provided new complexes with potential as organometallic anticancer agents with novel mechanisms of action. Here we report the anticancer activity of four neutral organometallic Ru(II) arene N-tosyl-1,2-diphenylethane-1,2-diamine (TsDPEN) tethered transfer hydrogenation catalysts. The enantiomers (R,R)-[Ru(η(6)-C6H5(CH2)3-TsDPEN-N-Me)Cl] (8) and (S,S)-[Ru(η(6)-C6H5(CH2)3-TsDPEN-N-Me)Cl] (8a) exhibited higher potency than cisplatin against A2780 human ovarian cancer cells. When the N-methyl was replaced by N-H, i.e. to give (R,R)-[Ru(η(6)-Ph(CH2)3-TsDPEN-NH)Cl] (7) and (S,S)-[Ru(η(6)-Ph(CH2)3-TsDPEN-NH)Cl] (7a), respectively, anticancer activity decreased >5-fold. Their antiproliferative activity appears to be linked to their ability to accumulate in cells, and their mechanism of action might involve inhibition of tubulin polymerisation. This appears to be the first report of the potent anticancer activity of tethered Ru(II) arene complexes, and the structure-activity relationship suggests that the N-methyl substituents are important for potency. In the National Cancer Institute 60-cancer-cell-line screen, complexes 8 and 8a exhibited higher activity than cisplatin towards a broad range of cancer cell lines. Intriguingly, in contrast to their potent anticancer properties, complexes 8/8a are poor catalysts for asymmetric transfer hydrogenation, whereas complexes 7/7a are effective asymmetric hydrogenation catalysts. PMID:27109147

  15. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, April--June 1993

    SciTech Connect

    Song, Chunshan; Parfitt, D.P.; Schobert, H.H.

    1993-08-01

    The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular precursors, that can be used in low concentrations (activity for efficient hydroliquefaction of coals under temperature-programmed conditions. Several heterometallic complexes consisting of two transition metals, Mo and Co, and sulfur in a single molecule were synthesized and tested as precursors of bimetallic dispersed catalysts for liquefaction of a Montana subbituminous coal (DECS-9) at the loading level of 0.5 wt% Mo on dmmf coal. It was found that the structure of the precursors, in particular the ligands to the metal species, affect the activity of the resulting catalyst significantly. Among the M-M` type precursors tested, Mo-Co thiocubane, Mo{sub 2}Co{sub 2}S{sub 4}(Cp){sub 2}(CO){sub 2} [Cp = cyclopentadiene], designated as MoCo-TC2, produced in-situ the best catalyst The performance of the Mo-Co bimetallic catalyst was further enhanced by using temperature programmed (TPL) conditions consisting of a low temperature soaking at 200{degrees}C, programmed heat-up to 400 or 425{degrees}C followed by a 30 minutes hold. The pro ed heat-up serves as an in-situ activation of catalyst and coal pretreatment, which contributes to more effective hydrogenation of reactive fragments at high temperature.

  16. Preparation and characterization of nanosized gold catalysts supported on Co3O4 and their activities for CO oxidation.

    PubMed

    Kim, Ki-Joong; Song, Jae-Koon; Shin, Seong-Soo; Kang, Sang-Jun; Chung, Min-Chul; Jung, Sang-Chul; Jeong, Woon-Jo; Ahn, Ho-Geun

    2011-02-01

    Gold catalysts supported on Co3O4 were prepared by co-precipitation (CP), deposition-precipitation (DP), and impregnation (IMP) methods. The Au/Co3O4 catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) to understand the different activities for CO oxidation with different preparation methods. Gold particles below 5 nm supported on Co3O4 by DP method were found to be more exposed to the surface than those by CP and IMP methods, and this catalyst was highly active and stable in CO oxidation. Finally, catalytic activity of Au/Co3O4 catalyst for CO oxidation was strongly dependent on the gold particle size. PMID:21456247

  17. Catalytic Y-tailed amphiphilic homopolymers - aqueous nanoreactors for high activity, low loading SCS pincer catalysts.

    PubMed

    Patterson, Joseph P; Cotanda, Pepa; Kelley, Elizabeth G; Moughton, Adam O; Lu, Annhelen; Epps, Thomas H; O'Reilly, Rachel K

    2013-01-01

    A new amphiphilic homopolymer bearing an SCS pincer palladium complex has been synthesized by reversible addition fragmentation chain transfer polymerization. The amphiphile has been shown to form spherical and worm-like micelles in water by cryogenic transmission electron microscopy and small angle neutron scattering. Segregation of reactive components within the palladium containing core results in increased catalytic activity of the pincer compound compared to small molecule analogues. This allows carbon-carbon bond forming reactions to be performed in water with reduced catalyst loadings and enhanced activity.

  18. Counting Active Sites on Titanium Oxide-Silica Catalysts for Hydrogen Peroxide Activation through In Situ Poisoning with Phenylphosphonic Acid

    SciTech Connect

    Eaton, Todd R.; Boston, Andrew M.; Thompson, Anthony B.; Gray, Kimberly A.; Notestein, Justin M.

    2015-06-04

    Quantifying specific active sites in supported catalysts improves our understanding and assists in rational design. Supported oxides can undergo significant structural changes as surface densities increase from site-isolated cations to monolayers and crystallites, which changes the number of kinetically relevant sites. Herein, TiOx domains are titrated on TiOx–SiO2 selectively with phenylphosphonic acid (PPA). An ex situ method quantifies all fluid-accessible TiOx, whereas an in situ titration during cis-cyclooctene epoxidation provides previously unavailable values for the number of tetrahedral Ti sites on which H2O2 activation occurs. We use this method to determine the active site densities of 22 different catalysts with different synthesis methods, loadings, and characteristic spectra and find a single intrinsic turnover frequency for cis-cyclooctene epoxidation of (40±7) h-1. This simple method gives molecular-level insight into catalyst structure that is otherwise hidden when bulk techniques are used.

  19. Ozone-biological activated carbon integrated treatment for removal of precursors of halogenated nitrogenous disinfection by-products.

    PubMed

    Chu, Wenhai; Gao, Naiyun; Yin, Daqiang; Deng, Yang; Templeton, Michael R

    2012-03-01

    Pilot-scale tests were performed to reduce the formation of several nitrogenous and carbonaceous disinfection by-products (DBPs) with an integrated ozone and biological activated carbon (O(3)-BAC) treatment process following conventional water treatment processes (coagulation-sedimentation-filtration). Relative to the conventional processes alone, O(3)-BAC significantly improved the removal of turbidity, dissolved organic carbon, UV(254), NH(4)(+) and dissolved organic nitrogen from 98-99%, 58-72%, 31-53%, 16-93% and 35-74%, respectively, and enhanced the removal efficiency of the precursors for the measured DBPs. The conventional process was almost ineffective in removing the precursors of trichloronitromethane (TCNM) and dichloroacetamide (DCAcAm). Ozonation could not substantially reduce the formation of DCAcAm, and actually increased the formation potential of TCNM; it chemically altered the molecular structures of the precursors and increased the biodegradability of N-containing organic compounds. Consequently, the subsequent BAC filtration substantially reduced the formation of the both TCNM and DCAcAm, thus highlighting a synergistic effect of O(3) and BAC. Additionally, O(3)-BAC was effective at controlling the formation of the total organic halogen, which can be considered as an indicator of the formation of unidentified DBPs.

  20. Quaternary PtMnCuX/C (X = Fe, Co, Ni, and Sn) and PtMnMoX/C (X = Fe, Co, Ni, Cu and Sn) alloys catalysts: Synthesis, characterization and activity towards ethanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Ammam, Malika; Easton, E. Bradley

    2012-10-01

    In this account, two series of quaternary PtMnCuX/C (X = Fe, Co, Ni, and Sn) and PtMnMoX/C (X = Fe, Co, Ni, Cu and Sn) alloys catalysts have been synthesized and characterized by ICP, XRD, XPS, TEM and cyclic voltammetry. XRD spectra of each series illustrated that PtMnCuX/C (X = Fe, Co and Ni) and PtMnMoX/C (X = Fe, Co, Ni and Cu) alloys have been formed without significant free Mn, Cu, Mo or X co-catalysts. For PtMnCuSn/C and PtMnMoSn/C, in addition to alloy formation, significant free Sn-oxides are present in each catalyst. Cyclic voltammetry and chronoamperometry revealed that all quaternary showed superior electrocatalytic activity towards ethanol oxidation compared to the ternary precursor. Also, shift of the onset potential of ethanol oxidation towards less positive values were also recorded with the quaternary alloys, demonstrating a facilitated oxidation with the quaternary alloys compared to ternary alloy precursor. The magnitude of the gain in potential depend on the alloy composition and PtMnMoSn/C was found to be the best of all synthetized quaternary alloys with an onset potential of ethanol oxidation of only 0.059 V vs. Ag/AgCl.

  1. Collaboration between primitive cell membranes and soluble catalysts

    PubMed Central

    Adamala, Katarzyna P.; Engelhart, Aaron E.; Szostak, Jack W.

    2016-01-01

    One widely held model of early life suggests primitive cells consisted of simple RNA-based catalysts within lipid compartments. One possible selective advantage conferred by an encapsulated catalyst is stabilization of the compartment, resulting from catalyst-promoted synthesis of key membrane components. Here we show model protocell vesicles containing an encapsulated enzyme that promotes the synthesis of simple fatty acid derivatives become stabilized to Mg2+, which is required for ribozyme activity and RNA synthesis. Thus, protocells capable of such catalytic transformations would have enjoyed a selective advantage over other protocells in high Mg2+ environments. The synthetic transformation requires both the catalyst and vesicles that solubilize the water-insoluble precursor lipid. We suggest that similar modified lipids could have played a key role in early life, and that primitive lipid membranes and encapsulated catalysts, such as ribozymes, may have acted in conjunction with each other, enabling otherwise-impossible chemical transformations within primordial cells. PMID:26996603

  2. Collaboration between primitive cell membranes and soluble catalysts.

    PubMed

    Adamala, Katarzyna P; Engelhart, Aaron E; Szostak, Jack W

    2016-01-01

    One widely held model of early life suggests primitive cells consisted of simple RNA-based catalysts within lipid compartments. One possible selective advantage conferred by an encapsulated catalyst is stabilization of the compartment, resulting from catalyst-promoted synthesis of key membrane components. Here we show model protocell vesicles containing an encapsulated enzyme that promotes the synthesis of simple fatty acid derivatives become stabilized to Mg(2+), which is required for ribozyme activity and RNA synthesis. Thus, protocells capable of such catalytic transformations would have enjoyed a selective advantage over other protocells in high Mg(2+) environments. The synthetic transformation requires both the catalyst and vesicles that solubilize the water-insoluble precursor lipid. We suggest that similar modified lipids could have played a key role in early life, and that primitive lipid membranes and encapsulated catalysts, such as ribozymes, may have acted in conjunction with each other, enabling otherwise-impossible chemical transformations within primordial cells. PMID:26996603

  3. Active Hydrogenation Catalyst with a Structured, Peptide-Based Outer-Coordination Sphere

    SciTech Connect

    Jain, Avijita; Buchko, Garry W.; Reback, Matthew L.; O'Hagan, Molly J.; Ginovska-Pangovska, Bojana; Linehan, John C.; Shaw, Wendy J.

    2012-10-05

    The synthesis, catalytic activity, and structural features of a rhodium-based hydrogenation catalyst containing a phosphine ligand coupled to a 14-residue peptide are reported. Both CD and NMR spectroscopy show that the peptide adopts a helical structure in 1:1:1 TFE/MeCN/H2O that is maintained when the peptide is attached to the ligand and when the ligand is attached to the metal complex. The metal complex hydrogenates aqueous solutions of 3-butenol to 1-butanol at 360 ± 50 turnovers/Rh/h at 294 K. This peptide- based catalyst represents a starting point for developing and characterizing a peptide-based outer-coordination sphere that can be used to introduce enzyme-like features into molecular catalysts. This work was funded by the US DOE Basic Energy Sciences, Chemical Sciences, Geoscience and Biosciences Division (AJ, JCL and WJS), the Office of Science Early Career Research Program through the Office of Basic Energy Sciences (GWB, MLR and WJS). Part of the research was conducted at the W.R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by U.S. Department of Energy’s Office of Biolog-ical and Environmental Research (BER) program located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for the U.S. Department of Energy.

  4. CO2 copolymers from epoxides: catalyst activity, product selectivity, and stereochemistry control.

    PubMed

    Lu, Xiao-Bing; Ren, Wei-Min; Wu, Guang-Peng

    2012-10-16

    The use of carbon dioxide as a carbon source for the synthesis of organic chemicals can contribute to a more sustainable chemical industry. Because CO(2) is such a thermodynamically stable molecule, few effective catalysts are available to facilitate this transformation. Currently, the major industrial processes that convert CO(2) into viable products generate urea and hydroxybenzoic acid. One of the most promising new technologies for the use of this abundant, inexpensive, and nontoxic renewable resource is the alternating copolymerization of CO(2) and epoxides to provide biodegradable polycarbonates, which are highly valuable polymeric materials. Because this process often generates byproducts, such as polyether or ether linkages randomly dispersed within the polycarbonate chains and/or the more thermodynamically stable cyclic carbonates, the choice of catalyst is critical for selectively obtaining the expected product. In this Account, we outline our efforts to develop highly active Co(III)-based catalysts for the selective production of polycarbonates from the alternating copolymerization of CO(2) with epoxides. Binary systems consisting of simple (salen)Co(III)X and a nucleophilic cocatalyst exhibited high activity under mild conditions even at 0.1 MPa CO(2) pressure and afforded copolymers with >99% carbonate linkages and a high regiochemical control (∼95% head-to-tail content). Discrete, one-component (salen)Co(III)X complexes bearing an appended quaternary ammonium salt or sterically hindered Lewis base showed excellent activity in the selectively alternating copolymerization of CO(2) with both aliphatic epoxides and cyclohexene oxide at high temperatures with low catalyst loading and/or low pressures of CO(2). Binary or one-component catalysts based on unsymmetric multichiral Co(III) complexes facilitated the efficient enantioselective copolymerization of CO(2) with epoxides, providing aliphatic polycarbonates with >99% head-to-tail content. These

  5. A simple synthesis method of sulfur-free Fe-N-C catalyst witih high ORR activity

    SciTech Connect

    Ding, Zhongfen; Johnston, Christina M; Zelenay, Piotr

    2010-01-01

    To try to deconvolute which factors affect the activity and durability of metal-nitrogen-carbon (M-N-C) type non-precious catalysts for oxygen reduction reaction (ORR), M-N-C catalysts based on ion chloride, polyaniline (PANI) and Ketjen Black carbon support were synthesized using different synthetic conditions. The catalysts were characterized electrochemically and tested as cathodes for Hydrogen fuel cells. PANI is usually chemically oxidative polymerized using ammonium persulfate (APS) as oxidant. To eliminate sulfur in the synthesized catalysts, a simple synthesis method using ion chloride as oxidant for aniline polymerization was developed. Two different aniline polymerization conditions led to very different product morphologies. Synthesized at low initial proton concentration, the final product was composed of dense micrometer sized particles. A decomposable salt was found to be able to prohibit PANI cross linking during the drying and annealing process and thus led to porous product. The porous catalyst has much higher ORR activity than the dense product due to more accessible active sites. Synthesized at high proton concentration, the catalyst appeared to be porous. The decomposable salt treatment did not make too much improvement in the porous structure and electrochemical activity. However, fuel cell testing using air as cathode feeder indicates that the salt treatment improves mass transfer in the cathode layer. Catalyst synthesized using this simple method has performance comparable to our state-of-the art catalyst synthesized in a much more complicated procedure. The factor that sulfur sources are completely eliminated in the synthesis suggests that sulfur is not necessary for the ORR catalysis activity.

  6. Identifying active functionalities on few-layered graphene catalysts for oxidative dehydrogenation of isobutane.

    PubMed

    Dathar, Gopi Krishna Phani; Tsai, Yu-Tung; Gierszal, Kamil; Xu, Ye; Liang, Chengdu; Rondinone, Adam J; Overbury, Steven H; Schwartz, Viviane

    2014-02-01

    The general consensus in the studies of nanostructured carbon catalysts for oxidative dehydrogenation (ODH) of alkanes to olefins is that the oxygen functionalities generated during synthesis and reaction are responsible for the catalytic activity of these nanostructured carbons. Identification of the highly active oxygen functionalities would enable engineering of nanocarbons for ODH of alkanes. Few-layered graphenes were used as model catalysts in experiments to synthesize reduced graphene oxide samples with varying oxygen concentrations, to characterize oxygen functionalities, and to measure the activation energies for ODH of isobutane. Periodic density functional theory calculations were performed on graphene nanoribbon models with a variety of oxygen functionalities at the edges to calculate their thermal stability and to model reaction mechanisms for ODH of isobutane. Comparing measured and calculated thermal stability and activation energies leads to the conclusion that dicarbonyls at the zigzag edges and quinones at armchair edges are appropriately balanced for high activity, relative to other model functionalities considered herein. In the ODH of isobutane, both dehydrogenation and regeneration of catalytic sites are relevant at the dicarbonyls, whereas regeneration is facile compared with dehydrogenation at quinones. The catalytic mechanism involves weakly adsorbed isobutane reducing functional oxygen and leaving as isobutene, and O2 in the feed, weakly adsorbed on the hydrogenated functionality, reacting with that hydrogen and regenerating the catalytic sites.

  7. The influence of carbon support porosity on the activity of PtRu/Sibunit anode catalysts for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Rao, V.; Simonov, P. A.; Savinova, E. R.; Plaksin, G. V.; Cherepanova, S. V.; Kryukova, G. N.; Stimming, U.

    In this paper we analyse the promises of homemade carbon materials of Sibunit family prepared through pyrolysis of natural gases on carbon black surfaces as supports for the anode catalysts of direct methanol fuel cells. Specific surface area ( SBET) of the support is varied in the wide range from 6 to 415 m 2 g -1 and the implications on the electrocatalytic activity are scrutinized. Sibunit supported PtRu (1:1) catalysts are prepared via chemical route and the preparation conditions are adjusted in such a way that the particle size is constant within ±1 nm in order to separate the influence of support on the (i) catalyst preparation and (ii) fuel cell performance. Comparison of the metal surface area measured by gas phase CO chemisorption and electrochemical CO stripping indicates close to 100% utilisation of nanoparticle surfaces for catalysts supported on low (22-72 m 2 g -1) surface area Sibunit carbons. Mass activity and specific activity of PtRu anode catalysts change dramatically with SBET of the support, increasing with the decrease of the latter. 10%PtRu catalyst supported on Sibunit with specific surface area of 72 m 2 g -1 shows mass specific activity exceeding that of commercial 20%PtRu/Vulcan XC-72 by nearly a factor of 3.

  8. Active Site Dependent Reaction Mechanism over Ru/CeO2 Catalyst toward CO2 Methanation.

    PubMed

    Wang, Fei; He, Shan; Chen, Hao; Wang, Bin; Zheng, Lirong; Wei, Min; Evans, David G; Duan, Xue

    2016-05-18

    Oxygen vacancy on the surface of metal oxides is one of the most important defects which acts as the reactive site in a variety of catalytic reactions. In this work, operando spectroscopy methodology was employed to study the CO2 methanation reaction catalyzed by Ru/CeO2 (with oxygen vacancy in CeO2) and Ru/α-Al2O3 (without oxygen vacancy), respectively, so as to give a thorough understanding on active site dependent reaction mechanism. In Ru/CeO2 catalyst, operando XANES, IR, and Raman were used to reveal the generation process of Ce(3+), surface hydroxyl, and oxygen vacancy as well as their structural evolvements under practical reaction conditions. The steady-state isotope transient kinetic analysis (SSITKA)-type in situ DRIFT infrared spectroscopy undoubtedly substantiates that CO2 methanation undergoes formate route over Ru/CeO2 catalyst, and the formate dissociation to methanol catalyzed by oxygen vacancy is the rate-determining step. In contrast, CO2 methanation undergoes CO route over Ru surface in Ru/α-Al2O3 with the absence of oxygen vacancy, demonstrating active site dependent catalytic mechanism toward CO2 methanation. In addition, the catalytic activity evaluation and the oscillating reaction over Ru/CeO2 catalyst further prove that the oxygen vacancy catalyzes the rate-determining step with a much lower activation temperature compared with Ru surface in Ru/α-Al2O3 (125 vs 250 °C). PMID:27135417

  9. Catalyst dispersion and activity under conditions of temperature- staged liquefaction. Technical progress report, July--September 1991

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1992-02-01

    The general objectives of this research are (1) to investigate the use of highly dispersed catalysts for the pretreatment of coal by mild hydrogenation, (2) to identify the active forms of catalysts under reaction conditions and (3) to clarify the mechanisms of catalysis. The ultimate objective is to ascertain if mild catalytic hydrogenation resulting in very limited or no coal solubilization is an advantageous pretreatment for the transformation of coal into transportable fuels. The experimental program will focus upon the development of effective methods of impregnating coal with catalysts, evaluating the conditions under which the catalysts are most active and establishing the relative impact of improved impregnation on conversion and product distributions obtained from coal hydrogenation.

  10. Catalyst dispersion and activity under conditions of temperature-staged liquefaction. Technical progress report, October--December 1991

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1992-02-01

    The general objectives of this research are (1) to investigate the use of highly dispersed catalysts for the pretreatment of coal by mild hydrogenation, (2) to identify the active forms of the catalysts under reaction conditions and (3) to clarify the mechanisms of catalysis. The ultimate objective is to ascertain if mild catalytic hydrogenation resulting in very limited or no coal solubilization is an advantageous pretreatment for the transformation of coal into transportable fuels. The experimental program will focus upon the development of effective methods of impregnating coal with catalysts, evaluating the conditions under which the catalysts are most active and establishing the relative impact of improved impregnation on conversion and product distributions obtained from coal hydrogenation.

  11. In-line localized monitoring of catalyst activity in selective catalytic NO.sub.x reduction systems

    DOEpatents

    Muzio, Lawrence J.; Smith, Randall A.

    2009-12-22

    Localized catalyst activity in an SCR unit for controlling emissions from a boiler, power plant, or any facility that generates NO.sub.x-containing flue gases is monitored by one or more modules that operate on-line without disrupting the normal operation of the facility. Each module is positioned over a designated lateral area of one of the catalyst beds in the SCR unit, and supplies ammonia, urea, or other suitable reductant to the catalyst in the designated area at a rate that produces an excess of the reductant over NO.sub.x on a molar basis through the designated area. Sampling probes upstream and downstream of the designated area draw samples of the gas stream for NO.sub.x analysis, and the catalyst activity is determined from the difference in NO.sub.x levels between the two probes.

  12. Glycosphingolipid synthesis inhibitor represses cytokine-induced activation of the Ras-MAPK pathway in embryonic neural precursor cells.

    PubMed

    Yanagisawa, Makoto; Nakamura, Kazuo; Taga, Tetsuya

    2005-09-01

    Neuronal and glial cells in the central nervous system are generated from common neural precursor cells during development. To evaluate the functions of glycosphingolipids (GSLs) in neural precursor cells, neuroepithelial cells (NECs) were prepared from mouse embryos (E14.5), and the effects of an inhibitor of glucosylceramide synthesis, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), on NECs was investigated. In PDMP-treated NECs, the expression of GD3, a major ganglioside of NECs, disappeared. We found that basic fibroblast growth factor (bFGF)-induced proliferation and extracellular signal-regulated kinase (ERK) activation were repressed in PDMP-treated NECs. Leukemia inhibitory factor (LIF)-induced ERK activation was also abolished in PDMP-treated NECs, suggesting that PDMP specifically represses the Ras-MAPK pathway. bFGF-induced activation of the Ras-MAPK pathway in NECs is dependent on GSL-enriched microdomains, lipid rafts. The organization of lipid rafts and the distribution of Ras and Grb2-SOS in the microdomains were not affected. However, Ras activation was repressed in PDMP-treated NECs. In PDMP-treated NECs, some neuronal genes were up-regulated and glial genes were down-regulated. These results suggest that GSLs might be involved in the proliferation, survival, signal transduction and differentiation of NECs.

  13. Trimetallic Au/Pt/Rh Nanoparticles as Highly Active Catalysts for Aerobic Glucose Oxidation

    NASA Astrophysics Data System (ADS)

    Zhang, Haijun; Cao, Yingnan; Lu, Lilin; Cheng, Zhong; Zhang, Shaowei

    2015-02-01

    This paper reports the findings of an investigation of the correlations between the catalytic activity for aerobic glucose oxidation and the composition of Au/Pt/Rh trimetallic nanoparticles (TNPs) with average diameters of less than 2.0 nm prepared by rapid injection of NaBH4. The prepared TNPs were characterized by UV-Vis, TEM, and HR-TEM. The catalytic activity of the alloy-structured TNPs for aerobic glucose oxidation is several times higher than that of Au monometallic nanoparticles with nearly the same particle size. The catalytic activities of the TNP catalysts were dependent not only on the composition, but also on the electronic structure. The high catalytic activities of the Au/Pt/Rh TNPs can be ascribed to the formed negative-charged Au atoms due to electron donation of Rh neighboring atoms acting as catalytically active sites for aerobic glucose oxidation.

  14. Remarkable enhancement of O₂ activation on yttrium-stabilized zirconia surface in a dual catalyst bed.

    PubMed

    Richard, Mélissandre; Can, Fabien; Duprez, Daniel; Gil, Sonia; Giroir-Fendler, Anne; Bion, Nicolas

    2014-10-13

    Yttrium-stabilized zirconia (YSZ) has been extensively studied as an electrolyte material for solid oxide fuel cells (SOFC) but its performance in heterogeneous catalysis is also the object of a growing number of publications. In both applications, oxygen activation on the YSZ surface remains the step that hinders utilization at moderate temperature. It was demonstrated by oxygen isotope exchange that a dual catalyst bed system consisting of two successive LaMnO3 and YSZ beds without intimate contact drastically enhances oxygen activation on the YSZ surface at 698 K. It can be concluded that LaMnO3 activates the triplet ground-state of molecular oxygen into a low-lying singlet state, thereby facilitating the activation of the O2 molecule on the YSZ oxygen vacancy sites. This phenomenon is shown to improve the catalytic activity of the LaMnO3-Pd/YSZ system for the partial oxidation of methane.

  15. Synthesis of a novel multi N-halamines siloxane precursor and its antimicrobial activity on cotton

    NASA Astrophysics Data System (ADS)

    Wu, Lin; Xu, Yan; Cai, Lu; Zang, Xiong; Li, Zhanxiong

    2014-09-01

    A novel N-halamine siloxane antibacterial precursor N-(3-triethoxysilylpropyl)-N‧- (N″‧-heptylcarbamido-N″-ethyl)-butanediamide (TSHCEB) was synthesized and characterized in this study. The compound was then tethered to the surface of cotton fabrics through covalent ether linkages, followed by exposure to dilute sodium hypochlorite solutions to confer the cotton fabrics antibacterial property. The chemical structure of the monomer was confirmed by FTIR, 1H NMR and MS, and the surface of the treated cotton fabrics was characterized by FTIR, TGA, SEM, and XPS analysis. The antimicrobial cotton materials were then challenged with Gram-negative Escherichia coli O157:H7 (ATCC 43895) and Gram-positive Staphylococcus aureus (ATCC 6538). Results showed that it provided excellent antimicrobial properties against E. coli O157:H7 and S. aureus via direct contacting for 2-15 min. The controlled release of diverse chlorines was proved by inhibition zone. The chlorine bonded to the coating was stable under standard washing test and routine storage, stability toward UVA irradiation was also investigated, and the lost chlorine could be regenerated by rechlorination. The new N-halamine antibacterial precursor can provide superior antibacterial property within a short contact time.

  16. Facile synthesis and enhanced visible light photocatalytic activity of N and Zr co-doped TiO2 nanostructures from nanotubular titanic acid precursors.

    PubMed

    Zhang, Min; Yu, Xinluan; Lu, Dandan; Yang, Jianjun

    2013-01-01

    Zr/N co-doped TiO2 nanostructures were successfully synthesized using nanotubular titanic acid (NTA) as precursors by a facile wet chemical route and subsequent calcination. These Zr/N-doped TiO2 nanostructures made by NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO2 nanoparticles. Impacts of Zr/N co-doping on the morphologies, optical properties, and photocatalytic activities of the NTA precursor-based TiO2 were thoroughly investigated. The origin of the enhanced visible light photocatalytic activity is discussed in detail.

  17. Facile synthesis and enhanced visible light photocatalytic activity of N and Zr co-doped TiO2 nanostructures from nanotubular titanic acid precursors

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Yu, Xinluan; Lu, Dandan; Yang, Jianjun

    2013-12-01

    Zr/N co-doped TiO2 nanostructures were successfully synthesized using nanotubular titanic acid (NTA) as precursors by a facile wet chemical route and subsequent calcination. These Zr/N-doped TiO2 nanostructures made by NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO2 nanoparticles. Impacts of Zr/N co-doping on the morphologies, optical properties, and photocatalytic activities of the NTA precursor-based TiO2 were thoroughly investigated. The origin of the enhanced visible light photocatalytic activity is discussed in detail.

  18. Amorphous molybdenum sulfides as hydrogen evolution catalysts.

    PubMed

    Morales-Guio, Carlos G; Hu, Xile

    2014-08-19

    Providing energy for a population projected to reach 9 billion people within the middle of this century is one of the most pressing societal issues. Burning fossil fuels at a rate and scale that satisfy our near-term demand will irreversibly damage the living environment. Among the various sources of alternative and CO2-emission-free energies, the sun is the only source that is capable of providing enough energy for the whole world. Sunlight energy, however, is intermittent and requires an efficient storage mechanism. Sunlight-driven water splitting to make hydrogen is widely considered as one of the most attractive methods for solar energy storage. Water splitting needs a hydrogen evolution catalyst to accelerate the rate of hydrogen production and to lower the energy loss in this process. Precious metals such as Pt are superior catalysts, but they are too expensive and scarce for large-scale applications. In this Account, we summarize our recent research on the preparation, characterization, and application of amorphous molybdenum sulfide catalysts for the hydrogen evolution reaction. The catalysts can be synthesized by electrochemical deposition under ambient conditions from readily available and inexpensive precursors. The catalytic activity is among the highest for nonprecious catalysts. For example, at a loading of 0.2 mg/cm(2), the optimal catalyst delivers a current density of 10 mA/cm(2) at an overpotential of 160 mV. The growth mechanism of the electrochemically deposited film catalysts was revealed by an electrochemical quartz microcrystal balance study. While different electrochemical deposition methods produce films with different initial compositions, the active catalysts are the same and are identified as a "MoS(2+x)" species. The activity of the film catalysts can be further promoted by divalent Fe, Co, and Ni ions, and the origins of the promotional effects have been probed. Highly active amorphous molybdenum sulfide particles can also be prepared

  19. Preparation and evaluation of novel hydrous metal oxide (HMO)-supported noble metal catalysts

    SciTech Connect

    Gardner, T.J.; McLaughlin, L.I.; Evans, L.R.; Datye, A.K.

    1998-04-01

    Hydrous Metal Oxides (HMOs) are chemically synthesized materials that, because of their high cation exchange capacity, possess a unique ability to allow the preparation of highly dispersed supported-metal catalyst precursors with high metal loadings. This study evaluates high weight loading Rh/HMO catalysts with a wide range of HMO support compositions, including hydrous titanium oxide (HTO), silica-doped hydrous titanium oxide (HTO:Si), hydrous zirconium oxide (HZO), and silica-doped hydrous zirconium oxide (HZO:Si), against conventional oxide-supported Rh catalysts with similar weight loadings and support chemistries. Catalyst activity measurements for a structure-sensitive model reaction (n-butane hydrogenolysis) as a function of catalyst activation conditions show superior activity and stability for the ZrO{sub 2}, HZO, and HZO:Si supports, although all of the Rh/HMO catalysts have high ethane selectivity indicative of high Rh dispersion. For the TiO{sub 2}-, HTO-, and HTO:Si supported Rh catalysts, a significant loss of both catalyst activity and Rh dispersion is observed at more aggressive activation conditions, consistent with TiO{sub x} migration associated with SMSI phenomena. Of all the Rh/HMO catalysts, the Rh/HZO:Si catalysts appear to offer the best tradeoff in terms of high Rh dispersion, high activity, and high selectivity.

  20. Comparison of the Activity and the Stability in CO Oxidation of Au-Cu Catalysts Supported on TiO2 in Anatase or Rutile Phase.

    PubMed

    Zanella, Rodolfo; Bokhimi, Xim; Maturano, Viridiana; Morales, Antonio

    2015-09-01

    Au-Cu catalysts supported on anatase or rutile phases were prepared by deposition-precipitation method. The titania polymorph used as the support determined the catalytic behavior. For the Au-Cu/rutile catalysts, the metallic phase had smaller dimensions than for the Au-Cu/anatase catalysts. The catalysts supported on anatase, however, were more active and stable than those supported on rutile. A systematic study of the catalytic activity for CO oxidation as a function of the temperature of activation and the aging time was performed. The catalytic properties were correlated with the properties of the catalysts analyzed with X-ray powder diffraction, refinement of the crystalline structures with the Rietveld method, and transmission electron microscopy. When the support was anatase, a pretreatment at 400 degrees C in air led to the most active catalysts, whereas when the support was rutile, a pretreatment between 200 and 300 degrees C in air led to the most active catalysts; activation under hydrogen generated less active catalysts. The Au-Cu catalysts activated in air were more active for the oxidation of CO than the respective monometallic gold catalysts, indicating a promoting effect between gold and copper to catalyze this reaction.

  1. The Influence of the Anionic Counter-Ion on the Activity of Ammonium Substituted Hoveyda-Type Olefin Metathesis Catalysts in Aqueous Media

    NASA Astrophysics Data System (ADS)

    Gułajski, Łukasz; Grela, Karol

    Polar olefin metathesis catalysts, bearing an ammonium group are presented. The electron withdrawing ammonium group not only activates the catalysts electronically, but at the same time makes the catalysts more hydrophilic. Catalysts can be therefore efficiently used not only in traditional media, such as methylene chloride and toluene, but also in technical-grade alcohols, alcohol— water mixtures and in neat water. Finally, in this overview the influence of the anionic counter-ion on the activity of ammonium substituted Hoveyda-type olefin metathesis catalysts in aqueous media is presented.

  2. Electro-catalytic activity of Ni–Co-based catalysts for oxygen evolution reaction

    SciTech Connect

    Ju, Hua; Li, Zhihu; Xu, Yanhui

    2015-04-15

    Graphical abstract: The electro-catalytic activity of different electro-catalysts with a porous electrode structure was compared considering the real electrode area that was evaluated by cyclic measurement. - Highlights: • Ni–Co-based electro-catalysts for OER have been studied and compared. • The real electrode area is calculated and used for assessing the electro-catalysts. • Exchange current and reaction rate constant are estimated. • Ni is more useful for OER reaction than Co. - Abstract: In the present work, Ni–Co-based electrocatalysts (Ni/Co = 0:6, 1:5, 2:4, 3:3, 4:2, 5:1 and 6:0) have been studied for oxygen evolution reaction. The phase structure has been analyzed by X-ray diffraction technique. Based on the XRD and SEM results, it is believed that the synthesized products are poorly crystallized. To exclude the disturbance of electrode preparation technology on the evaluation of electro-catalytic activity, the real electrode surface area is calculated based on the cyclic voltammetry data, assumed that the specific surface capacitance is 60 μF cm{sup −2} for metal oxide electrode. The real electrode area data are used to calculate the current density. The reaction rate constant of OER at different electrodes is also estimated based on basic reaction kinetic equations. It is found that the exchange current is 0.05–0.47 mA cm{sup −2} (the real surface area), and the reaction rate constant has an order of magnitude of 10{sup −7}–10{sup −6} cm s{sup −1}. The influence of the electrode potential on OER rate has been also studied by electrochemical impedance spectroscopy (EIS) technique. Our investigation has shown that the nickel element has more contribution than the cobalt; the nickel oxide has the best electro-catalytic activity toward OER.

  3. Tin-containing zeolites are highly active catalysts for the isomerization of glucose in water

    SciTech Connect

    Moliner, Manuel; Roman-Leshkov, Yuriy; Davis, Mark E.

    2010-04-06

    The isomerization of glucose into fructose is a large-scale reaction for the production of high-fructose corn syrup (HFCS; reaction performed by enzyme catalysts) and recently is being considered as an intermediate step in the possible route of biomass to fuels and chemicals. Here, it is shown that a large-pore zeolite that contains tin (Sn-Beta) is able to isomerize glucose to fructose in aqueous media with high activity and selectivity. Specifically, a 10% (wt/wt) glucose solution containing a catalytic amount of Sn-Beta (1:50 Sn:glucose molar ratio) gives product yields of approximately 46% (wt/wt) glucose, 31% (wt/wt) fructose, and 9% (wt/wt) mannose after 30 min and 12 min of reaction at 383 K and 413 K, respectively. This reactivity is achieved also when a 45 wt% glucose solution is used. The properties of the large-pore zeolite greatly influence the reaction behavior because the reaction does not proceed with a medium-pore zeolite, and the isomerization activity is considerably lower when the metal centers are incorporated in ordered mesoporous silica (MCM-41). The Sn-Beta catalyst can be used for multiple cycles, and the reaction stops when the solid is removed, clearly indicating that the catalysis is occurring heterogeneously. Most importantly, the Sn-Beta catalyst is able to perform the isomerization reaction in highly acidic, aqueous environments with equivalent activity and product distribution as in media without added acid. This enables Sn-Beta to couple isomerizations with other acid-catalyzed reactions, including hydrolysis/isomerization or isomerization/dehydration reaction sequences [starch to fructose and glucose to 5-hydroxymethylfurfural (HMF) demonstrated here].

  4. Crystal structures of Ziegler-Natta catalyst supports.

    PubMed

    Malizia, Federica; Fait, Anna; Cruciani, Giuseppe

    2011-12-01

    The crystal structures of three MgCl(2)·nEtOH complexes with n=1.5, 2.8, and 3.3 have been fully determined. Such complexes are the fundamental precursors for Ziegler-Natta polymerization catalysts used to produce polyolefins on a multimillion-ton scale worldwide. The ab initio structure solution showed that the structure of MgCl(2)·nEtOH complexes with n=1.5 and 2.8 are based on ribbons of metal-centered octahedra, whereas for n=3.3 this chainlike arrangement breaks into a threadlike structure of isolated octahedra linked by hydrogen bonds. A clear correlation between catalyst performance and the crystal structure of precursors has been found, and reveals the fundamental role of the latter in determining catalyst properties. The direct knowledge of building blocks in the precursor structures will help to develop more accurate models for activated catalysts. These models will not require the arbitrary and oversimplified assumption of locating the catalyst active sites on selected cut surfaces of the α-MgCl(2) crystal lattice. PMID:22052708

  5. Improvement of activated carbons as oxygen reduction catalysts in neutral solutions by ammonia gas treatment and their performance in microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Watson, Valerie J.; Nieto Delgado, Cesar; Logan, Bruce E.

    2013-11-01

    Commercially available activated carbon (AC) powders from different precursor materials (peat, coconut shell, coal, and hardwood) were treated with ammonia gas at 700 °C to improve their performance as oxygen reduction catalysts in neutral pH solutions used in microbial fuel cells (MFCs). The ammonia treated ACs exhibited better catalytic performance in rotating ring-disk electrode tests than their untreated precursors, with the bituminous based AC most improved, with an onset potential of Eonset = 0.12 V (untreated, Eonset = 0.08 V) and n = 3.9 electrons transferred in oxygen reduction (untreated, n = 3.6), and the hardwood based AC (treated, Eonset = 0.03 V, n = 3.3; untreated, Eonset = -0.04 V, n = 3.0). Ammonia treatment decreased oxygen content by 29-58%, increased nitrogen content to 1.8 atomic %, and increased the basicity of the bituminous, peat, and hardwood ACs. The treated coal based AC cathodes had higher maximum power densities in MFCs (2450 ± 40 mW m-2) than the other AC cathodes or a Pt/C cathode (2100 ± 1 mW m-2). These results show that reduced oxygen abundance and increased nitrogen functionalities on the AC surface can increase catalytic performance for oxygen reduction in neutral media.

  6. Lattice-Strain Control of Exceptional Activity in Dealloyed Core-Shell Fuel Cell Catalysts

    SciTech Connect

    Strasser, Peter

    2011-08-19

    We present a combined experimental and theoretical approach to demonstrate how lattice strain can be used to continuously tune the catalytic activity of the oxygen reduction reaction (ORR) on bimetallic nanoparticles that have been dealloyed. The sluggish kinetics of the ORR is a key barrier to the adaptation of fuel cells and currently limits their widespread use. Dealloyed Pt-Cu bimetallic nanoparticles, however, have been shown to exhibit uniquely high reactivity for this reaction. We first present evidence for the formation of a core-shell structure during dealloying, which involves removal of Cu from the surface and subsurface of the precursor nanoparticles. We then show that the resulting Pt-rich surface shell exhibits compressive strain that depends on the composition of the precursor alloy. We next demonstrate the existence of a downward shift of the Pt d-band, resulting in weakening of the bond strength of intermediate oxygenated species due to strain. Finally, we combine synthesis, strain, and catalytic reactivity in an experimental/theoretical reactivity-strain relationship which provides guidelines for the rational design of strained oxygen reduction electrocatalysts. The stoichiometry of the precursor, together with the dealloying conditions, provides experimental control over the resulting surface strain and thereby allows continuous tuning of the surface electrocatalytic reactivity - a concept that can be generalized to other catalytic reactions.

  7. Gold nanoparticles-graphene hybrids as active catalysts for Suzuki reaction

    SciTech Connect

    Li, Yang; Fan, Xiaobin; Qi, Junjie; Ji, Junyi; Wang, Shulan; Zhang, Guoliang; Zhang, Fengbao

    2010-10-15

    Graphene was successfully modified with gold nanoparticles in a facile route by reducing chloroauric acid in the presence of sodium dodecyl sulfate, which is used as both a surfactant and reducing agent. The gold nanoparticles-graphene hybrids were characterized by high-resolution transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction and energy X-ray spectroscopy. We demonstrate for the first time that the gold nanoparticles-graphene hybrids can act as efficient catalysts for the Suzuki reaction in water under aerobic conditions. The catalytic activity of gold nanoparticles-graphene hybrids was influenced by the size of the gold nanoparticles.

  8. Diarylrhodates as promising active catalysts for the arylation of vinyl ethers with Grignard reagents.

    PubMed

    Iwasaki, Takanori; Miyata, Yoshinori; Akimoto, Ryo; Fujii, Yuuki; Kuniyasu, Hitoshi; Kambe, Nobuaki

    2014-07-01

    Anionic diarylrhodium complexes, generated by reacting [RhCl(cod)]2 with 2 equiv of aryl Grignard reagents, were found to be effective active catalysts in cross-coupling reactions of vinyl ethers with aryl Grignard reagents, giving rise to the production of vinyl arenes. In this catalytic system, vinyl-O bonds were preferably cleaved over Ar-O or Ar-Br bonds. A lithium rhodate complex was isolated, and its crystal structure was determined by X-ray crystallography. PMID:24957673

  9. Low temperature catalysts for methanol production

    DOEpatents

    Sapienza, R.S.; Slegeir, W.A.; O'Hare, T.E.; Mahajan, D.

    1986-10-28

    A catalyst and process useful at low temperatures (below about 160 C) and preferably in the range 80--120 C used in the production of methanol from carbon monoxide and hydrogen are disclosed. The catalyst is used in slurry form and comprises a complex reducing agent derived from the component structure NaH--RONa-M(OAc)[sub 2] where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1-6 carbon atoms. This catalyst is preferably used alone but is also effective in combination with a metal carbonyl of a group VI (Mo, Cr, W) metal. The preferred catalyst precursor is NiC (where M = Ni and R = tertiary amyl). Mo(CO)[sub 6] is the preferred metal carbonyl if such component is used. The catalyst is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

  10. Low temperature catalysts for methanol production

    DOEpatents

    Sapienza, Richard S.; Slegeir, William A.; O'Hare, Thomas E.; Mahajan, Devinder

    1986-01-01

    A catalyst and process useful at low temperatures (below about 160.degree. C.) and preferably in the range 80.degree.-120.degree. C. used in the production of methanol from carbon monoxide and hydrogen is disclosed. The catalyst is used in slurry form and comprises a complex reducing agent derived from the component structure NaH--RONa--M(OAc).sub.2 where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1-6 carbon atoms. This catalyst is preferably used alone but is also effective in combination with a metal carbonyl of a group VI (Mo, Cr, W) metal. The preferred catalyst precursor is Nic (where M=Ni and R=tertiary amyl). Mo(CO).sub.6 is the preferred metal carbonyl if such component is used. The catalyst is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

  11. Low temperature catalysts for methanol production

    DOEpatents

    Sapienza, R.S.; Slegeir, W.A.; O'Hare, T.E.; Mahajan, D.

    1985-03-12

    A catalyst and process useful at low temperatures (below about 160/sup 0/C) and preferably in the range 80 to 120/sup 0/C used in the production of methanol from carbon monoxide and hydrogen is disclosed. The catalyst is used in slurry form and comprises a complex reducing agent derived from the component structure NaH-RONa-M(OAc)/sub 2/ where M is selected from the group consisting of Ni, Pd, and Co and R is a lower alkyl group containing 1 to 6 carbon atoms. This catalyst is preferably used alone but is also effective in combination with a metal carbonyl of a group VI (Mo, Cr, W) metal. The preferred catalyst precursor is Nic (where M = Ni and R = tertiary amyl). Mo(CO)/sub 6/ is the preferred metal carbonyl if such component is used. The catalyst is subjected to a conditioning or activating step under temperature and pressure, similar to the parameters given above, to afford the active catalyst.

  12. Osteoclast precursors in murine bone marrow express CD27 and are impeded in osteoclast development by CD70 on activated immune cells.

    PubMed

    Xiao, Yanling; Song, Ji-Ying; de Vries, Teun J; Fatmawati, Christien; Parreira, Diana B; Langenbach, Geerling E J; Babala, Nikolina; Nolte, Martijn A; Everts, Vincent; Borst, Jannie

    2013-07-23

    Osteoclasts (OCs) are bone-resorbing cells that are formed from hematopoietic precursors. OCs ordinarily maintain bone homeostasis, but they can also cause major pathology in autoimmune and inflammatory diseases. Under homeostatic conditions, receptor activator of nuclear factor kappa-B (RANK) ligand on osteoblasts drives OC differentiation by interaction with its receptor RANK on OC precursors. During chronic immune activation, RANK ligand on activated immune cells likewise drives pathogenic OC differentiation. We here report that the related TNF family member CD70 and its receptor CD27 can also mediate cross-talk between immune cells and OC precursors. We identified CD27 on a rare population (0.3%) of B220(-)c-Kit(+)CD115(+)CD11b(low) cells in the mouse bone marrow (BM) that are highly enriched for osteoclastogenic potential. We dissected this population into CD27(high) common precursors of OC, dendritic cells (DCs) and macrophages and CD27(low/neg) downstream precursors that could differentiate into OC and macrophages, but not DC. In a recombinant mouse model of chronic immune activation, sustained CD27/CD70 interactions caused an accumulation of OC precursors and a reduction in OC activity. These events were due to a CD27/CD70-dependent inhibition of OC differentiation from the OC precursors by BM-infiltrating, CD70(+)-activated immune cells. DC numbers in BM and spleen were increased, suggesting a skewing of the OC precursors toward DC differentiation. The impediment in OC differentiation culminated in a high trabecular bone mass pathology. Mice additionally presented anemia, leukopenia, and splenomegaly. Thus, under conditions of constitutive CD70 expression reflecting chronic immune activation, the CD27/CD70 system inhibits OC differentiation and favors DC differentiation.

  13. Lattice-Strain Control of the Activity in Dealloyed Core-Shell Fuel Cell Catalysts

    SciTech Connect

    Strasser, P.; Koh, Shirlaine; Anniyev, Toyli; Greeley, Jeff; More, Karren Leslie; Yu, Chengfei; Liu, Zengcai; Kaya, Sarpa; Nordlund, Dennis; Ogasawara, Hirohito; Toney, Michael F.; Anders, Nilsson

    2010-01-01

    Electrocatalysis will play a key role in future energy conversion and storage technologies, such as water electrolysers, fuel cells and metal-air batteries. Molecular interactions between chemical reactants and the catalytic surface control the activity and efficiency, and hence need to be optimized; however, generalized experimental strategies to do so are scarce. Here we show how lattice strain can be used experimentally to tune the catalytic activity of dealloyed bimetallic nanoparticles for the oxygen-reduction reaction, a key barrier to the application of fuel cells and metal-air batteries. We demonstrate the core-shell structure of the catalyst and clarify the mechanistic origin of its activity. The platinum-rich shell exhibits compressive strain, which results in a shift of the electronic band structure of platinum and weakening chemisorption of oxygenated species. We combine synthesis, measurements and an understanding of strain from theory to generate a reactivity-strain relationship that provides guidelines for tuning electrocatalytic activity.

  14. Proximate and Ultimate Analyses of Bagasse, Sorghum and Millet Straws as Precursors for Active Carbons

    NASA Astrophysics Data System (ADS)

    Lori, J. A.; Lawal, A. O.; Ekanem, E. J.

    This study reports the proximate and ultimate characteristics of bagasse, sorghum and millet straws in relation to their suitability for producing highly porous carbon. The results of ad hoc samples indicated, that particle size has a decisive influence on the proximate characteristics of bagasse, sorghum and millet straws. The effects of particle size on weight loss characteristics; rates of dehydration and de-volatilization of the carbon precursors were used to assess particle sizes that may be appropriate for carbonization. Particle sizes of 425-1180 µm are thus, suggested to be the most desirable, for the production of good quality porous carbon. This range of particles of bagasse, sorghum and millet straws were associated with diminishing ash contents. However, the optimum particle size of the cellulosic materials that is expected to yield highly porous carbon with minimum ash contents is 1180 µm.

  15. Sunlight-driven copper-catalyst activation applied to photolatent click chemistry.

    PubMed

    Beniazza, Rédouane; Lambert, Romain; Harmand, Lydie; Molton, Florian; Duboc, Carole; Denisov, Sergey; Jonusauskas, Gedeminas; McClenaghan, Nathan D; Lastécouères, Dominique; Vincent, Jean-Marc

    2014-10-01

    The synthesis, full characterization, photoreduction properties, and catalytic activity for the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction of a copper(II)-DMEDA (N,N'-dimethylethylendiamine) complex is reported. Spectroscopic studies (UV/Vis, EPR) demonstrated that under daylight illumination highly effective copper(II) to copper(I) reduction occurs in this complex. These findings are in agreement with a high photoreduction quantum yield value of 0.22 in MeOH, and a value approaching unity as determined in THF. The reduction process, which can also be conducted by irradiation at 365 nm by using a standard TLC (thin layer chromatography) lamp, is ascribed to a highly efficient photoinduced electron transfer (PET) process mediated by the benzophenone photosensitizer present in the carboxylate counterion. Having deaerated the reaction mixture, the photogenerated copper(I) species proved to be highly active for the CuAAC reaction, demonstrated by reactions conducted with low catalyst loading (0.5 mol %) on a range of clickable protected and non-protected mono- and disaccharides. Once initiated, the reaction can be stopped at any time on introducing air into the reaction medium. Deoxygenation followed by irradiation restores the activity, making the copper(II)-DMEDA complex a switchable catalyst of practical value. PMID:25171758

  16. Improved coal liquefaction using carbon-supported hydrogenation catalysts: Quarterly report for the period 1 January-31 March 1986

    SciTech Connect

    Scaroni, A.W.; Derbyshire, F.J.; Solar, J.M.; Abotsi, G.M.K.; Spears, R.

    1986-03-01

    Catalysts have been prepared by the impregnation of different porous carbons with molybdenum-containing precursor compounds using the incipient wetness technique. Two precursors were investigated; a solution of ammonium heptamolybdate (or, in some cases, ammoniumtetrathiomolybdate) in 90% H/sub 2/O/10% EtOH; a solution of molybdenumtricarbonyltriacetonitrile in acetonitrile. The fresh catalysts were characterized by x-ray photoelectron spectroscopy. The activities of the sulfided catalysts were measured for thiophene hydrodesulfurization in a continuous flow, atmospheric pressure reactor. The principal findings are that: (1) for a given support and at similar loading, the organometallic precursor confers a much higher activity than the ammonium salt precursors. The increase in lined-out activity can be higher by as much as a factor of 1.6 and (2) with catalysts prepared from molybdenumtricarbonyltriacetonitrile, the highest thiophene conversions were obtained with a high surface area active carbon. However, when (based upon a number of assumptions) the catalysts are compared at similar dispersions and corrected for surface area differences, the most active catalyst was found to be that prepared upon a graphitic support. 3 refs., 1 fig., 4 tabs.

  17. Surface state and catalytic activity and selectivity of nickel catalysts in hydrogenation reactions--3. Electronic and catalytic properties of nickel catalysts. [Butylene oxides

    SciTech Connect

    Okamoto, Y.; Nitta, Y.; Imanaka, T.; Teranishi, S.

    1980-08-01

    A relationship between a parameter ..delta.. q and the ESCA chemical shift was derived from available extended Hueckel calculation results and ESCA data for nickel boride and nickel phosphide. The ..delta.. q parameter described the change in electron density at the nickel metal that occurred due to the electron transfer between nickel and the other element. The ..delta.. q parameters were estimated for Rayney nickel and Urushibara nickel, which contained aluminum and zinc alloy components, respectively, from product ratios and rate ratios measured for cyclohexene and cyclooctene hydrogenation on these catalysts. The ..delta.. q parameter correlated the increase in specific activities with increasing electron density in the hydrogenation of styrene, the increase in poisoning coefficient for carbon disulfide and triphenylphosphine with increasing electron density in the hydrogenation of styrene, and the selectivity for n-butyl alcohol in the hydrogenation of 1,2-butylene oxide on various nickel catalysts.

  18. Synchronizing Substrate Activation Rates in Multicomponent Reactions with Metal-Organic Framework Catalysts.

    PubMed

    Aguirre-Díaz, Lina María; Iglesias, Marta; Snejko, Natalia; Gutiérrez-Puebla, Enrique; Monge, M Ángeles

    2016-05-01

    A study on the influence of the cation coordination number, number of Lewis acid centers, concurrent existence of Lewis base sites, and structure topology on the catalytic activity of six new indium MOFs, has been carried out for multicomponent reactions (MCRs). The new indium polymeric frameworks, namely [In8 (OH)6 (popha)6 (H2 O)4 ]⋅3 H2 O (InPF-16), [In(popha)(2,2'-bipy)]⋅3 H2 O (InPF-17), [In3 (OH)3 (popha)2 (4,4'-bipy)]⋅4 H2 O (InPF-18), [In2 (popha)2 (4,4'-bipy)2 ]⋅3 H2 O (InPF-19), [In(OH)(Hpopha)]⋅0.5 (1,7-phen) (InPF-20), and [In(popha)(1,10-phen)]⋅4 H2 O (InPF-21) (InPF=indium polymeric framework, H3 popha=5-(4-carboxy-2-nitrophenoxy)isophthalic acid, phen=phenanthroline, bipy=bipyridine), have been hydrothermally obtained by using both conventional heating (CH) and microwave (MW) procedures. These indium frameworks show efficient Lewis acid behavior for the solvent-free cyanosilylation of carbonyl compounds, the one pot Passerini 3-component (P-3CR) and the Ugi 4-component (U-4CR) reactions. In addition, InPF-17 was found to be a highly reactive, recyclable, and environmentally benign catalyst, which allows the efficient synthesis of α-aminoacyl amides. The relationship between the Lewis base/acid active site and the catalytic performance is explained by the 2D seven-coordinated indium framework of the catalyst InPF-17. This study is an attempt to highlight the main structural and synthetic factors that have to be taken into account when planning a new, effective MOF-based heterogeneous catalyst for multicomponent reactions.

  19. Platinum-Promoted Ga/Al2O3 as Highly Active, Selective, and Stable Catalyst for the Dehydrogenation of Propane**

    PubMed Central

    Sattler, Jesper J H B; Gonzalez-Jimenez, Ines D; Luo, Lin; Stears, Brien A; Malek, Andrzej; Barton, David G; Kilos, Beata A; Kaminsky, Mark P; Verhoeven, Tiny W G M; Koers, Eline J; Baldus, Marc; Weckhuysen, Bert M

    2014-01-01

    A novel catalyst material for the selective dehydrogenation of propane is presented. The catalyst consists of 1000 ppm Pt, 3 wt % Ga, and 0.25 wt % K supported on alumina. We observed a synergy between Ga and Pt, resulting in a highly active and stable catalyst. Additionally, we propose a bifunctional active phase, in which coordinately unsaturated Ga3+ species are the active species and where Pt functions as a promoter. PMID:24989975

  20. Hierarchical Pd-Sn Alloy Nanosheet Dendrites: An Economical and Highly Active Catalyst for Ethanol Electrooxidation

    PubMed Central

    Ding, Liang-Xin; Wang, An-Liang; Ou, Yan-Nan; Li, Qi; Guo, Rui; Zhao, Wen-Xia; Tong, Ye-Xiang; Li, Gao-Ren

    2013-01-01

    Hierarchical alloy nanosheet dendrites (ANSDs) are highly favorable for superior catalytic performance and efficient utilization of catalyst because of the special characteristics of alloys, nanosheets, and dendritic nanostructures. In this paper, we demonstrate for the first time a facile and efficient electrodeposition approach for the controllable synthesis of Pd-Sn ANSDs with high surface area. These synthesized Pd-Sn ANSDs exhibit high electrocatalytic activity and superior long-term cycle stability toward ethanol oxidation in alkaline media. The enhanced electrocataytic activity of Pd-Sn ANSDs may be attributed to Pd-Sn alloys, nanosheet dendrite induced promotional effect, large number of active sites on dendrite surface, large surface area, and good electrical contact with the base electrode. Because of the simple implement and high flexibility, the proposed approach can be considered as a general and powerful strategy to synthesize the alloy electrocatalysts with high surface areas and open dendritic nanostructures. PMID:23383368

  1. Stabilizing a Platinum1 Single-Atom Catalyst on Supported Phosphomolybdic Acid without Compromising Hydrogenation Activity.

    PubMed

    Zhang, Bin; Asakura, Hiroyuki; Zhang, Jia; Zhang, Jiaguang; De, Sudipta; Yan, Ning

    2016-07-11

    In coordination chemistry, catalytically active metal complexes in a zero- or low-valent state often adopt four-coordinate square-planar or tetrahedral geometry. By applying this principle, we have developed a stable Pt1 single-atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)-modified active carbon. This was achieved by anchoring Pt on the four-fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square-planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities.

  2. Composite catalyst surfaces: Effect of inert and active heterogeneities on pattern formation

    SciTech Connect

    Baer, M.; Bangia, A.K.; Kevrekidis, I.G.; Haas, G.; Rotermund, H.H.; Ertl, G.

    1996-12-05

    Spatiotemporal dynamics in reaction-diffusion systems can be altered through the properties (reactivity, diffusivity) of the medium in which they occur. We construct active heterogeneous media (composite catalytic surfaces with inert as well as active illusions) using microelectronics fabrication techniques and study the spatiotemporal dynamics of heterogeneous catalytic reactions on these catalysts. In parallel, we perform simulations as well as numerical stability and bifurcation analysis of these patterns using mechanistic models. At the limit of large heterogeneity `grain size` (compared to the wavelength of spontaneously arising structures) the interaction patterns with inert or active boundaries dominates (e.g., pinning, transmission, and boundary breakup of spirals, interaction of pulses with corners, `pacemaker` effects). At the opposite limit of very small or very finely distributed heterogeneity, effective behavior is observed (slight modulation of pulses, nearly uniform oscillations, effective spirals). Some representative studies of transitions between the two limits are presented. 48 refs., 11 figs.

  3. Selenium-ligated palladium(II) complexes as highly active catalysts for carbon-carbon coupling reactions: the Heck reaction.

    PubMed

    Yao, Qingwei; Kinney, Elizabeth P; Zheng, Chong

    2004-08-19

    Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation. PMID:15330667

  4. Selenium-ligated palladium(II) complexes as highly active catalysts for carbon-carbon coupling reactions: the Heck reaction.

    PubMed

    Yao, Qingwei; Kinney, Elizabeth P; Zheng, Chong

    2004-08-19

    Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation.

  5. Method for dispersing catalyst onto particulate material and product thereof

    DOEpatents

    Utz, Bruce R.; Cugini, Anthony V.

    1992-01-01

    A method for dispersing finely divided catalyst precursors onto the surface of coal or other particulate material includes the steps of forming a wet paste mixture of the particulate material and a liquid solution containing a dissolved transition metal salt, for instance a solution of ferric nitrate. The wet paste mixture is in a state of incipient wetness with all of this solution adsorbed onto the surfaces of the particulate material without the presence of free moisture. On adding a precipitating agent such as ammonia, a catalyst precursor such as hydrated iron oxide is deposited on the surfaces of the coal. The catalyst is activated by converting it to the sulfide form for the hydrogenation or direct liquefaction of the coal.

  6. Active sites and mechanisms for H2O2 decomposition over Pd catalysts

    PubMed Central

    Plauck, Anthony; Stangland, Eric E.; Dumesic, James A.; Mavrikakis, Manos

    2016-01-01

    A combination of periodic, self-consistent density functional theory (DFT-GGA-PW91) calculations, reaction kinetics experiments on a SiO2-supported Pd catalyst, and mean-field microkinetic modeling are used to probe key aspects of H2O2 decomposition on Pd in the absence of cofeeding H2. We conclude that both Pd(111) and OH-partially covered Pd(100) surfaces represent the nature of the active site for H2O2 decomposition on the supported Pd catalyst reasonably well. Furthermore, all reaction flux in the closed catalytic cycle is predicted to flow through an O–O bond scission step in either H2O2 or OOH, followed by rapid H-transfer steps to produce the H2O and O2 products. The barrier for O–O bond scission is sensitive to Pd surface structure and is concluded to be the central parameter governing H2O2 decomposition activity. PMID:27006504

  7. Antimicrobial activities of silver used as a polymerization catalyst for a wound-healing matrix

    PubMed Central

    Babu, Ranjith; Zhang, Jianying; Beckman, Eric J.; Virji, Mohammed; Pasculle, William A.; Wells, Alan

    2007-01-01

    Wound healing is a complex and orchestrated process that re-establishes the barrier and other functions of the skin. While wound healing proceeds apace in healthy individual, bacterial overgrowth and infection disrupts this process with significant morbidity and mortality. As such, any artificial matrix to promote wound healing must also control infecting microbes. We had earlier developed a two-part space-conforming gel backbone based on polyethyleneglycol (PEG) or lactose, which used ionic silver as the catalyst for gelation. As silver is widely used as an in vitro antimicrobial, use of silver as a catalyst for gelation provided the opportunity to assess its function as an anti-microbial agent in the gels. We found that these gels show bacteriostatic and bactericidal activity for a range of Gram-negative and Gram-positive organisms, including aerobic as well as anaerobic bacteria. This activity lasted for days, as silver leached out of the formed gels over a day in the manner of second-order decay. Importantly the gels did not limit either cell growth or viability, though cell migration was affected. Adding collagen I fragments to the gels corrected this effect on cell migration. We also found that the PEG gel did not interfere with hemostasis. These observations provide the basis for use of the gel backbones for incorporation of anesthetic agents and factors that promote wound repair. In conclusion, silver ions can serve dual functions of catalyzing gelation and providing anti-microbial properties to a biocompatible polymer. PMID:16635526

  8. Isoselenazolones as catalysts for the activation of bromine: bromolactonization of alkenoic acids and oxidation of alcohols.

    PubMed

    Balkrishna, Shah Jaimin; Prasad, Ch Durga; Panini, Piyush; Detty, Michael R; Chopra, Deepak; Kumar, Sangit

    2012-11-01

    Isoselenazolones were synthesized by a copper-catalyzed Se-N bond forming reaction between 2-halobenzamides and selenium powder. The catalytic activity of the various isoselenazolones was studied in the bromolactonization of pent-4-enoic acid. Isoselenazolone 9 was studied as a catalyst in several reactions: the bromolactonization of a series of alkenoic acids with bromine or N-bromosuccinimide (NBS) in the presence of potassium carbonate as base, the bromoesterification of a series of alkenes using NBS and a variety of carboxylic acids, and the oxidation of secondary alcohols to ketones using bromine as an oxidizing reagent. Mechanistic details of the isoselenazolone-catalyzed bromination reaction were revealed by (77)Se NMR spectroscopic and ES-MS studies. The oxidative addition of bromine to the isoselenazolone gives the isoselenazolone(IV) dibromide, which could be responsible for the activation of bromine under the reaction conditions. Steric effects from an N-phenylethyl group on the amide of the isoselenazolone and electron-withdrawing fluoro substituents on the benzo fused-ring of the isoselenazolone appear to enhance the stability of the isoselenazolone as a catalyst for the bromination reaction. PMID:23046286

  9. Surface characterization and dehydrocyclization activity of Pt/KL catalysts prepared by different methods

    NASA Astrophysics Data System (ADS)

    Arcoya, Adolfo; Seoane, Xosé Lois; Grau, Javier Mario

    2003-01-01

    Three Pt/KL-zeolite catalysts containing 1 wt.% of metal were prepared by different procedures: CI-1 and CI-2 by wetness impregnation of the zeolite with aqueous solutions of Pt(NH 3) 4(OH) 2 and Pt(NH 3) 4(NO 3) 2, respectively, and CE-3 by ion exchange with a Pt(NH 3) 4(OH) 2 solution. These samples were successively calcined at 573 K and reduced at 773 K. An additional sample, CE-3-n, was obtained from CE-3 by ion-exchange with KNO 3. The catalysts were characterized by H 2-O 2 titration, TPD of NH 3, XRD, CO-FTIR and XPS and tested in the dehydrocyclization of n-heptane to toluene at 723 K, 100 kPa, WHSV=3.4 h -1 and H 2/ nC 7=7.3 mol mol -1 in a fixed bed tubular reactor. Characterization results show that Pt dispersion for the ion exchanged samples is higher than for the impregnated ones and CE-3 is the more acidic catalyst. FTIR measurements indicate that the highest population of electron reach platinum species (Pt δ- ) is found in CE-3-n, while CE-3 exhibits the highest concentration of electron deficient platinum species (Pt δ+ ). The order of dehydrocyclization activity, CE-3-n>CI-2>CI-1>CE-3, roughly correlates with that of the intensity of the FTIR bands attributed to Pt δ- . The low selectivity toward toluene of CE-3 is attributed to the protons generated during the reduction of Pt 2+ exchanged.

  10. Ruthenium carbenes supported on mesoporous silicas as highly active and selective hybrid catalysts for olefin metathesis reactions under continuous flow.

    PubMed

    Bru, Miriam; Dehn, Richard; Teles, J Henrique; Deuerlein, Stephan; Danz, Manuel; Müller, Imke B; Limbach, Michael

    2013-08-26

    In the search for a highly active and selective heterogenized metathesis catalyst, we systematically varied the pore geometry and size of various silica-based mesoporous (i.e., MCM-41, MCM-48, and SBA-15) and microporous (ZSM-5 and MWW) versus macroporous materials (D11-10 and Aerosil 200), besides other process parameters (temperature, dilution, and mean residence time). The activity and, especially, selectivity of such "linker-free" supports for ruthenium metathesis catalysts were evaluated in the cyclodimerization of cis-cyclooctene to form 1,9-cyclohexadecadiene, a valuable intermediate in the flavor and fragrance industry. The optimized material showed not only exceptionally high selectivity to the valuable product, but also turned out to be a truly heterogeneous catalyst with superior activity relative to the unsupported homogeneous complex. PMID:23852995

  11. Ruthenium carbenes supported on mesoporous silicas as highly active and selective hybrid catalysts for olefin metathesis reactions under continuous flow.

    PubMed

    Bru, Miriam; Dehn, Richard; Teles, J Henrique; Deuerlein, Stephan; Danz, Manuel; Müller, Imke B; Limbach, Michael

    2013-08-26

    In the search for a highly active and selective heterogenized metathesis catalyst, we systematically varied the pore geometry and size of various silica-based mesoporous (i.e., MCM-41, MCM-48, and SBA-15) and microporous (ZSM-5 and MWW) versus macroporous materials (D11-10 and Aerosil 200), besides other process parameters (temperature, dilution, and mean residence time). The activity and, especially, selectivity of such "linker-free" supports for ruthenium metathesis catalysts were evaluated in the cyclodimerization of cis-cyclooctene to form 1,9-cyclohexadecadiene, a valuable intermediate in the flavor and fragrance industry. The optimized material showed not only exceptionally high selectivity to the valuable product, but also turned out to be a truly heterogeneous catalyst with superior activity relative to the unsupported homogeneous complex.

  12. Cationic Silica-Supported N-Heterocyclic Carbene Tungsten Oxo Alkylidene Sites: Highly Active and Stable Catalysts for Olefin Metathesis.

    PubMed

    Pucino, Margherita; Mougel, Victor; Schowner, Roman; Fedorov, Alexey; Buchmeiser, Michael R; Copéret, Christophe

    2016-03-18

    Designing supported alkene metathesis catalysts with high activity and stability is still a challenge, despite significant advances in the last years. Described herein is the combination of strong σ-donating N-heterocyclic carbene ligands with weak σ-donating surface silanolates and cationic tungsten sites leading to highly active and stable alkene metathesis catalysts. These well-defined silica-supported catalysts, [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(OTf)] and [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(+) ][B(Ar(F) )4 (-) ] [IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene, B(Ar(F) )4 =B(3,5-(CF3 )2 C6 H3 )4 ] catalyze alkene metathesis, and the cationic species display unprecedented activity for a broad range of substrates, especially for terminal olefins with turnover numbers above 1.2 million for propene.

  13. Cationic Silica-Supported N-Heterocyclic Carbene Tungsten Oxo Alkylidene Sites: Highly Active and Stable Catalysts for Olefin Metathesis.

    PubMed

    Pucino, Margherita; Mougel, Victor; Schowner, Roman; Fedorov, Alexey; Buchmeiser, Michael R; Copéret, Christophe

    2016-03-18

    Designing supported alkene metathesis catalysts with high activity and stability is still a challenge, despite significant advances in the last years. Described herein is the combination of strong σ-donating N-heterocyclic carbene ligands with weak σ-donating surface silanolates and cationic tungsten sites leading to highly active and stable alkene metathesis catalysts. These well-defined silica-supported catalysts, [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(OTf)] and [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(+) ][B(Ar(F) )4 (-) ] [IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene, B(Ar(F) )4 =B(3,5-(CF3 )2 C6 H3 )4 ] catalyze alkene metathesis, and the cationic species display unprecedented activity for a broad range of substrates, especially for terminal olefins with turnover numbers above 1.2 million for propene. PMID:26928967

  14. Dinuclear thiazolylidene copper complex as highly active catalyst for azid-alkyne cycloadditions.

    PubMed

    Schöffler, Anne L; Makarem, Ata; Rominger, Frank; Straub, Bernd F

    2016-01-01

    A dinuclear N-heterocyclic carbene (NHC) copper complex efficiently catalyzes azide-alkyne cycloaddition (CuAAC) "click" reactions. The ancillary ligand comprises two 4,5-dimethyl-1,3-thiazol-2-ylidene units and an ethylene linker. The three-step preparation of the complex from commercially available starting compounds is more straightforward and cost-efficient than that of the previously described 1,2,4-triazol-5-ylidene derivatives. Kinetic experiments revealed its high catalytic CuAAC activity in organic solvents at room temperature. The activity increases upon addition of acetic acid, particularly for more acidic alkyne substrates. The modular catalyst design renders possible the exchange of N-heterocyclic carbene, linker, sacrificial ligand, and counter ion. PMID:27559407

  15. Understanding Iron-based catalysts with efficient Oxygen reduction activity from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Hafiz, Hasnain; Barbiellini, B.; Jia, Q.; Tylus, U.; Strickland, K.; Bansil, A.; Mukerjee, S.

    2015-03-01

    Catalysts based on Fe/N/C clusters can support the oxygen-reduction reaction (ORR) without the use of expensive metals such as platinum. These systems can also prevent some poisonous species to block the active sites from the reactant. We have performed spin-polarized calculations on various Fe/N/C fragments using the Vienna Ab initio Simulation Package (VASP) code. Some results are compared to similar calculations obtained with the Gaussian code. We investigate the partial density of states (PDOS) of the 3d orbitals near the Fermi level and calculate the binding energies of several ligands. Correlations of the binding energies with the 3d electronic PDOS's are used to propose electronic descriptors of the ORR associated with the 3d states of Fe. We also suggest a structural model for the most active site with a ferrous ion (Fe2+) in the high spin state or the so-called Doublet 3 (D3).

  16. Nonactivated and Activated Biochar Derived from Bananas as Alternative Cathode Catalyst in Microbial Fuel Cells

    PubMed Central

    Yuan, Haoran; Deng, Lifang; Qi, Yujie; Kobayashi, Noriyuki; Tang, Jiahuan

    2014-01-01

    Nonactivated and activated biochars have been successfully prepared by bananas at different thermotreatment temperatures. The activated biochar generated at 900°C (Biochar-act900) exhibited improved oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performances in alkaline media, in terms of the onset potential and generated current density. Rotating disk electron result shows that the average of 2.65 electrons per oxygen molecule was transferred during ORR of Biochar-act900. The highest power density of 528.2 mW/m2 and the maximum stable voltage of 0.47 V were obtained by employing Biochar-act900 as cathode catalyst, which is comparable to the Pt/C cathode. Owning to these advantages, it is expected that the banana-derived biochar cathode can find application in microbial fuel cell systems. PMID:25243229

  17. Nonactivated and activated biochar derived from bananas as alternative cathode catalyst in microbial fuel cells.

    PubMed

    Yuan, Haoran; Deng, Lifang; Qi, Yujie; Kobayashi, Noriyuki; Tang, Jiahuan

    2014-01-01

    Nonactivated and activated biochars have been successfully prepared by bananas at different thermotreatment temperatures. The activated biochar generated at 900°C (Biochar-act900) exhibited improved oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performances in alkaline media, in terms of the onset potential and generated current density. Rotating disk electron result shows that the average of 2.65 electrons per oxygen molecule was transferred during ORR of Biochar-act900. The highest power density of 528.2 mW/m(2) and the maximum stable voltage of 0.47 V were obtained by employing Biochar-act900 as cathode catalyst, which is comparable to the Pt/C cathode. Owning to these advantages, it is expected that the banana-derived biochar cathode can find application in microbial fuel cell systems.

  18. Methane-induced Activation Mechanism of Fused Ferric Oxide-Alumina Catalysts during Methane Decomposition.

    PubMed

    Reddy Enakonda, Linga; Zhou, Lu; Saih, Youssef; Ould-Chikh, Samy; Lopatin, Sergei; Gary, Daniel; Del-Gallo, Pascal; Basset, Jean-Marie

    2016-08-01

    Activation of Fe2 O3 -Al2 O3 with CH4 (instead of H2 ) is a meaningful method to achieve catalytic methane decomposition (CMD). This reaction of CMD is more economic and simple against commercial methane steam reforming (MSR) as it produces COx -free H2 . In this study, for the first time, structure changes of the catalyst were screened during CH4 reduction with time on stream. The aim was to optimize the pretreatment conditions through understanding the activation mechanism. Based on results from various characterization techniques, reduction of Fe2 O3 by CH4 proceeds in three steps: Fe2 O3 →Fe3 O4 →FeO→Fe0. Once Fe0 is formed, it decomposes CH4 with formation of Fe3 C, which is the crucial initiation step in the CMD process to initiate formation of multiwall carbon nanotubes. PMID:27345621

  19. Dinuclear thiazolylidene copper complex as highly active catalyst for azid–alkyne cycloadditions

    PubMed Central

    Schöffler, Anne L; Makarem, Ata; Rominger, Frank

    2016-01-01

    Summary A dinuclear N-heterocyclic carbene (NHC) copper complex efficiently catalyzes azide–alkyne cycloaddition (CuAAC) “click” reactions. The ancillary ligand comprises two 4,5-dimethyl-1,3-thiazol-2-ylidene units and an ethylene linker. The three-step preparation of the complex from commercially available starting compounds is more straightforward and cost-efficient than that of the previously described 1,2,4-triazol-5-ylidene derivatives. Kinetic experiments revealed its high catalytic CuAAC activity in organic solvents at room temperature. The activity increases upon addition of acetic acid, particularly for more acidic alkyne substrates. The modular catalyst design renders possible the exchange of N-heterocyclic carbene, linker, sacrificial ligand, and counter ion. PMID:27559407

  20. Role of Surface Cobalt Silicate in Single-Walled Carbon Nanotube Synthesis from Silica-Supported Cobalt Catalysts

    SciTech Connect

    Li, N.; Wang, X; Derrouiche, S; Haller, G; Pfefferle, L

    2010-01-01

    A silica-supported cobalt catalyst has been developed via incipient wetness impregnation for high-yield synthesis of single-walled carbon nanotubes (SWNTs). Co/SiO{sub 2}-impregnated catalysts have not been observed to be efficient for SWNT synthesis. Using an appropriately chosen precursor, we show that effective catalysts can be obtained for SWNT synthesis with yields up to 75 wt %. Detailed characterization indicates that the active sites for SWNT synthesis are small cobalt particles resulting from the reduction of a highly dispersed surface cobalt silicate species. The SWNTs produced by this catalyst are of high quality and easy to purify, and the process is simple and scalable.

  1. Role of surface cobalt silicate in single-walled carbon nanotube synthesis from silica-supported cobalt catalysts.

    PubMed

    Li, Nan; Wang, Xiaoming; Derrouiche, Salim; Haller, Gary L; Pfefferle, Lisa D

    2010-03-23

    A silica-supported cobalt catalyst has been developed via incipient wetness impregnation for high-yield synthesis of single-walled carbon nanotubes (SWNTs). Co/SiO2-impregnated catalysts have not been observed to be efficient for SWNT synthesis. Using an appropriately chosen precursor, we show that effective catalysts can be obtained for SWNT synthesis with yields up to 75 wt %. Detailed characterization indicates that the active sites for SWNT synthesis are small cobalt particles resulting from the reduction of a highly dispersed surface cobalt silicate species. The SWNTs produced by this catalyst are of high quality and easy to purify, and the process is simple and scalable. PMID:20201563

  2. Pt-Co Bimetallic Catalyst Supported on Single Walled Carbon Nanotube: XAS and Aqueous Phase Reforming Activity Studies

    SciTech Connect

    Wang, X.; Li, N; Pfefferle, L; Haller, G

    2009-01-01

    We have developed a simple method to create a catalyst with atomically dispersed Pt on top of Co nanoparticles on single walled carbon nanotubes (SWNT) supports by sequential impregnation of Pt(II) and Co(II) solutions following by hydrogen reduction. The aqueous phase reforming activity is much higher than for Pt monometallic catalysts on SWNT supports prepared by several methods, either pre-reduced in hydrogen or in the liquid phase. The high selectivity of the monometallic catalysts is maintained for the bimetallic systems. The Extended X-ray Absorption Fine Structure (EXAFS) results at the Pt LIII edge show no observable Pt-Pt bond. Only Pt-Co bonds were observed, indicating high dispersion of Pt. The enhanced activity comes from two sources: the high dispersion of Pt and the effect of the Co as co-catalyst or modifier. This contribution demonstrates the possibility to further engineer bimetallic catalysts to improve the aqueous phase reforming activity, especially to retain good selectivity at high conversion.

  3. Enhancing low-temperature activity and durability of Pd-based diesel oxidation catalysts using ZrO2 supports

    DOE PAGES

    Kim, Mi -Young; Kyriakidou, Eleni A.; Choi, Jae -Soon; Toops, Todd J.; Binder, Andrew J.; Thomas, Cyril; Schwartz, Viviane; Chen, Jihua; Hensley, Dale K.; Parks, II, James E.

    2016-01-18

    In this study, we investigated the impact of ZrO2 on the performance of palladium-based oxidation catalysts with respect to low-temperature activity, hydrothermal stability, and sulfur tolerance. Pd supported on ZrO2 and SiO2 were synthesized for a comparative study. Additionally, in an attempt to maximize the ZrO2 surface area and improve sulfur tolerance, a Pd support with ZrO2-dispersed onto SiO2 was studied. The physicochemical properties of the catalysts were examined using ICP, N2 sorption, XRD, SEM, TEM, and NH3-, CO2-, and NOx-TPD. The activity of the Pd catalysts were measured from 60 to 600 °C in a flow of 4000 ppmmore » CO, 500 ppm NO, 1000 ppm C3H6, 4% O2, 5% H2O, and Ar balance. The Pd catalysts were evaluated in fresh, sulfated, and hydrothermally aged states. Overall, the ZrO2-containing catalysts showed considerably higher CO and C3H6 oxidation activity than Pd/SiO2 under the reaction conditions studied.« less

  4. Highly active PtAu alloy nanoparticle catalysts for the reduction of 4-nitrophenol.

    PubMed

    Zhang, Jianming; Chen, Guozhu; Guay, Daniel; Chaker, Mohamed; Ma, Dongling

    2014-02-21

    To enhance the catalytic activity of gold nanoparticles (AuNPs) for the hydrogenation of nitro-aromatic chemicals, Pt was introduced into AuNPs to form "bare" PtAu alloy NPs using a physical approach, pulsed laser ablation in liquid (PLAL), on single metal-mixture targets. These PLAL-NPs are deemed to favor catalysis due to the absence of any surfactant molecules on their unique "bare and clean" surface. The PLAL-NPs were facilely assembled onto CeO2 nanotubes (NTs) by simply mixing them without conducting any surface functionalization, representing another advantage of these NPs. Their catalytic activity was assessed in 4-nitrophenol (4-NP) hydrogenation. The reaction catalyzed by alloy-NP/CeO2-NT catalysts demonstrates a remarkably higher reaction rate in comparison with that catalyzed by pure Au and Pt NPs, and other similar Au and Pt containing catalysts reported recently. A "volcano-like" catalytic activity dependence of the alloy NPs on their chemical composition suggests a strong synergistic effect between Au and Pt in the 4-NP reduction, far beyond the simple sum of their individual contributions. It leads to the significantly enhanced catalytic activity of Pt30Au70 and Pt50Au50 alloy NPs, outperforming not only each single constituent, but also their physical mixtures and most recently reported AuNP based nanocatalysts. The favorable d-band center shift of Pt after alloying, and co-operative actions between Pt clusters and nearby Au (or mixed PtAu) sites were proposed as possible mechanisms to explain such a strong synergistic effect on catalysis.

  5. Subnanometer platinum clusters highly active and selective catalysts for the oxidative dehydrogenation of propane.

    SciTech Connect

    Vajda, S; Pellin, M. J.; Greeley, J. P.; Marshall, C. L.; Curtiss, L. A.; Ballentine, G. A.; Elam, J. W.; Catillon-Mucherie, S.; Redfern, P. C.; Mehmood, F.; Zapol, P.; Yale Univ.

    2009-03-01

    Small clusters are known to possess reactivity not observed in their bulk analogues, which can make them attractive for catalysis. Their distinct catalytic properties are often hypothesized to result from the large fraction of under-coordinated surface atoms. Here, we show that size-preselected Pt{sub 8-10} clusters stabilized on high-surface-area supports are 40-100 times more active for the oxidative dehydrogenation of propane than previously studied platinum and vanadia catalysts, while at the same time maintaining high selectivity towards formation of propylene over by-products. Quantum chemical calculations indicate that under-coordination of the Pt atoms in the clusters is responsible for the surprisingly high reactivity compared with extended surfaces. We anticipate that these results will form the basis for development of a new class of catalysts by providing a route to bond-specific chemistry, ranging from energy-efficient and environmentally friendly synthesis strategies to the replacement of petrochemical feedstocks by abundant small alkanes.

  6. Factors affecting activated carbon-based catalysts for selective hydrogen sulfide oxidation

    SciTech Connect

    Li, Huixing; Monnell, J.D.; Alvin, M.A.; Vidic, R.D.

    2008-09-01

    The primary product of coal gasification processes is synthesis gas (syngas), a mixture of CO, H2, CO2, H2O and a number of minor components. Among the most significant minor components in syngas is hydrogen sulfide (H2S). In addition to its adverse environmental impact, H2S poisons the catalysts and hydrogen purification membranes, and causes severe corrosion in gas turbines. Technologies that can remove H2S from syngas and related process streams are, therefore, of considerable practical interest. To meet this need, we work towards understanding the mechanism by which prospective H2S catalysts perform in simulated fuel gas conditions. Specifically, we show that for low-temperature gas clean-up (~1408C) using activated carbon fibers and water plays a significant role in H2S binding and helps to prolong the lifetime of the material. Basic surface functional groups were found to be imperative for significant conversion of H2S to daughter compounds, whereas metal oxides (La and Ce) did little to enhance this catalysis. We show that although thermal regeneration of the material is possible, the regenerated material has a substantially lower catalytic and sorption capacity.

  7. Regional brain cytochrome oxidase activity in beta-amyloid precursor protein transgenic mice with the Swedish mutation.

    PubMed

    Strazielle, C; Sturchler-Pierrat, C; Staufenbiel, M; Lalonde, R

    2003-01-01

    Cytochrome oxidase activity was examined in a transgenic mouse model of Alzheimer's disease with overexpression of the 751 amino acid isoform of beta-amyloid precursor protein with the Swedish mutation under control of the murine thy-1 promoter. The neuritic plaques, abundantly localized in the hippocampus and anterior neocortical areas, showed a core devoid of enzymatic activity surrounded by higher cytochrome oxidase activity at the sites of the dystrophic neurites and activated glial cells. Quantitative measures, taken only in the healthy-appearing regional areas without neuritic plaques, were higher in numerous limbic and non-limbic regions of transgenic mice in comparison with controls. Enzymatic activity was higher in the dentate gyrus and CA2-CA3 region of the hippocampus, the anterior cingulate and primary visual cortex, two olfactory structures, the ventral part of the neostriatum, the parafascicularis nucleus of the thalamus, and the subthalamic nucleus. Brainstem regions anatomically related with altered forebrain regions were more heavily labeled as well, including the substantia nigra, the periaqueductal gray, the superior colliculus, the medial raphe, the locus coeruleus and the adjacent parabrachial nucleus, as well as the pontine nuclei, red nucleus, and trigeminal motor nucleus. Functional brain organization is discussed in the context of Alzheimer's disease. Although hypometabolism is generally observed in this pathology, the increased cytochrome oxidase activity obtained in these transgenic mice can be the result of a functional compensation on the surviving neurons, or of an early mitochondrial alteration related to increased oxidative damage. PMID:12732258

  8. Selectivity, activity, and metal-support interactions of Rh bimetallic catalysts. Progress report, 15 November 1981-15 August 1982

    SciTech Connect

    Haller, G L

    1982-08-01

    We report on a detailed investigation of the effect of TiO/sub 2/ support on Rh-Ag interaction as exhibited in catalytic activity. The temporal evolution of activity over Rh-Ag/TiO/sub 2/ for ethane hydrogenolysis and hydrogen chemisorption as a function of temperature, Ag to Rh ratio, the Rh particle size, Rh loading, and ambient gas were studied. Preliminary extended x-ray absorption fine structure (EXAFS) analysis of Rh/TiO/sub 2/ catalysts indicate that 100% exposed (dispersed) catalyst prepared by ion exchange may be atomically dispersed after low temperature reduction. 7 figures, 1 table.

  9. Aryl-palladium-NHC complex: efficient phosphine-free catalyst precursors for the carbonylation of aryl iodides with amines or alkynes.

    PubMed

    Zhang, Chunyan; Liu, Jianhua; Xia, Chungu

    2014-12-21

    A series of aryl-palladium-NHC compounds was prepared according to the reported methods and their catalytic activity in the carbonylation of aryl iodides to synthesize α-keto amides and alkynones was examined. These practical aryl-palladium-NHC complexes have shown highly efficient catalyzed carbonylation and Sonogashira carbonylation reactions, with high turnover number in synthesis of α-keto amides (TON = 4300) and in synthesis of alkynones (TON = 980).

  10. Activated Carbon Catalysts for the Production of Hydrogen for the Sulfur-Iodine Thermochemical Water Splitting Cycle

    SciTech Connect

    Lucia M. Petkovic; Daniel M. Ginosar; Harry W. Rollins; Kyle C Burch; Cristina Deiana; Hugo S. Silva; Maria F. Sardella; Dolly Granados

    2009-05-01

    Seven activated carbon catalysts obtained from a variety of raw material sources and preparation methods were examined for their catalytic activity to decompose hydroiodic acid (HI) to produce hydrogen; a key reaction in the sulfur-iodine (S-I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. Within the group of ligno-cellulosic steam-activated carbon catalysts, activity increased with surface area. However, both a mineral-based steam-activated carbon and a ligno-cellulosic chemically-activated carbon displayed activities lower than expected based on their higher surface areas. In general, ash content was detrimental to catalytic activity while total acid sites, as determined by Bohem’s titrations, seemed to favor higher catalytic activity within the group of steam-activated carbons. These results suggest, one more time, that activated carbon raw materials and preparation methods may have played a significant role in the development of surface characteristics that eventually dictated catalyst activity and stability as well.

  11. Tyrosine phosphorylation is a mandatory proximal step in radiation-induced activation of the protein kinase C signaling pathway in human B-lymphocyte precursors.

    PubMed Central

    Uckun, F M; Schieven, G L; Tuel-Ahlgren, L M; Dibirdik, I; Myers, D E; Ledbetter, J A; Song, C W

    1993-01-01

    Ionizing radiation triggers a signal in human B-lymphocyte precursors that is intimately linked to an active protein-tyrosine kinase regulatory pathway. We show that in B-lymphocyte precursors, irradiation with gamma-rays leads to (i) stimulation of phosphatidylinositol turnover; (ii) downstream activation by covalent modification of multiple serine-specific protein kinases, including protein kinase C; and (iii) activation of nuclear factor kappa B. All of the radiation-induced signals were effectively prevented by the protein-tyrosine kinase inhibitors genistein and herbimycin A. Thus, tyrosine phosphorylation is an important and perhaps mandatory proximal step in the activation of the protein kinase C signaling cascade in human B-lymphocyte precursors. Our report expands current knowledge of the radiation-induced signaling cascade by clarifying the chronological sequence of biochemical events that follow irradiation. Images PMID:8419931

  12. Controlled leaching with prolonged activity for Co-LDH supported catalyst during treatment of organic dyes using bicarbonate activation of hydrogen peroxide.

    PubMed

    Jawad, Ali; Li, Yibing; Lu, Xiaoyan; Chen, Zhuqi; Liu, Weidong; Yin, Guochuan

    2015-05-30

    The effluents from industries are commonly non-biodegradable and produce various hazardous intermediate products by chemical reactions that have direct impact on environment. In the present investigation, a series of Co-Mg/AL ternary LDH catalysts with fixed Mg/Al ratio were prepared by co-precipitation method. The effect of Co on the activity of the catalyst was monitored on the degradation of methylene blue (MB) as model compound at batch level using bicarbonate activation of H2O2 (BAP) system. On bench level, the best CoMgAl-4 catalyst can completely decolorize both methylene blue (MB) and methylene orange (MO) in short time, while in fixed bed, the catalyst was found stable for over 300 h with nearly 100% decolorization and excellent chemical oxygen demand (COD) removal. No leaching of Co was detected for the entire fixed experiment which may be accounted for long life stability and good activity of the catalyst. The ternary LDH catalysts were characterized by AES, XRD, FTIR, BET, and SEM for its compositional, phase structure, optical properties, textural, and surface morphology respectively. The XRD analysis confirmed characteristic pattern of hydrotalcite like structures without impurity phases. The formation of superoxide and hydroxyl radical as ROS was proposed with CoMgAl-4 by radical's scavengers.

  13. Gasification characteristics of an activated carbon catalyst during the decomposition of hazardous waste material in supercritical water

    SciTech Connect

    Matsumura, Yukihiko; Nuessle, F.W.; Antal, M.J. Jr.

    1996-12-31

    Recently, carbonaceous materials including activated carbon were proven to be effective catalysts for hazardous waste gasification in supercritical water. Using coconut shell activated carbon catalyst, complete decomposition of industrial organic wastes including methanol and acetic acid was achieved. During this process, the total mass of the activated carbon catalyst changes by two competing processes: a decrease in weight via gasification of the carbon by supercritical water, or an increase in weight by deposition of carbonaceous materials generated by incomplete gasification of the biomass feedstocks. The deposition of carbonaceous materials does not occur when complete gasification is realized. Gasification of the activated carbon in supercritical water is often favored, resulting in changes in the quality and quantity of the catalyst. To thoroughly understand the hazardous waste decomposition process, a more complete understanding of the behavior of activated carbon in pure supercritical water is needed. The gasification rate of carbon by water vapor at subcritical pressures was studied in relation to coal gasification and generating activated carbon.

  14. Electron donor properties of claus catalysts--1. Influence of NaOH on the catalytic activity of silica gel

    SciTech Connect

    Dudzik, Z.; George, Z.M.

    1980-05-01

    ESR spectroscopy showed that SO/sub 2/ adsorbed on silica gel impregnated with NaOH formed the SO/sub 2//sup -/ anion radical. With increasing NaOH concentration, the SO/sub 2/ adsorption and the activity for the reaction of H/sub 2/S with SO/sub 2/ (Claus reaction) went through a maximum at 1.0-1.4% NaOH. The SO/sub 2/ anion radical apparently formed by electron transfer from the catalyst surface and was a reaction intermediate which reacted rapidly with H/sub 2/S. The NaOH catalyst had similar stability and activity as commercial alumina catalyst in five-day tests under Claus conditions.

  15. Gasification characteristics of an activated carbon catalyst during the decomposition of hazardous waste materials in supercritical water

    SciTech Connect

    Matsumura, Yukihiko; Nuessle, F.W.; Antal, M.J. Jr.

    1996-10-01

    Recently, carbonaceous materials were proved to be effective catalysts for hazardous waste decomposition in supercritical water. Gasification of the carbonaceous catalyst itself is also expected, however, under supercritical conditions. Thus, it is essential to determine the gasification rate of the carbonaceous materials during this process to determine the active lifetime of the catalysts. For this purpose, the gasification characteristics of granular coconut shell activated carbon in supercritical water alone (600-650{degrees}C, 25.5-34.5 MPa) were investigated. The gasification rate at subatmospheric pressure agreed well with the gasification rate at supercritical conditions, indicating the same reaction mechanism. Methane generation under these conditions is via pyrolysis, and thus is not affected by the water pressure. An iodine number increase of 25% was observed as a result of the supercritical water gasification.

  16. XAFS study on structure-activity correlations of α-Co(OH)2 nanosheets water oxidation catalysts

    NASA Astrophysics Data System (ADS)

    Huang, Junheng; Liu, Qinghua; Yao, Tao; Pan, Zhiyun; Wei, Shiqiang

    2016-05-01

    Understanding the structure-activity of the metal hydroxide materials is critical to the design of an efficient oxygen evolution reaction (OER) catalyst for water oxidation. A challenge is to identify and collect surface active site relative to bulk. Here, we have prepared an ultrathin α-Co(OH)2 nanosheet with large exposed surface Co sites as an high-efficiency O2 evolution catalyst. Using XAFS technique, we have investigated the oxidation state and local structural evolutions of the α-Co(OH)2 nanosheets catalyst. A coordination-miss Co sites (CoO6-x) with oxidation state of +3.3 on the nanosheet surface is revealed after the OER procedure, indicating the in situ formation of y-CoOOH nanosheet is a key factor leading to an enhanced water oxidation performance.

  17. Novel activating JAK2 mutation in a patient with Down syndrome and B-cell precursor acute lymphoblastic leukemia.

    PubMed

    Malinge, Sebastien; Ben-Abdelali, Raouf; Settegrana, Catherine; Radford-Weiss, Isabelle; Debre, Marianne; Beldjord, Kheira; Macintyre, Elizabeth A; Villeval, Jean-Luc; Vainchenker, William; Berger, Roland; Bernard, Olivier A; Delabesse, Eric; Penard-Lacronique, Virginie

    2007-03-01

    Activation of tyrosine kinase genes is a frequent event in human hematologic malignancies. Because gene activation could be associated with gene dysregulation, we attempted to screen for activating gene mutation based on high-level gene expression. We focused our study on the Janus kinase 2 (JAK2) gene in 90 cases of acute leukemia. This strategy led to the identification of a novel JAK2-acquired mutation in a patient with Down syndrome (DS) with B-cell precursor acute lymphoblastic leukemia (BCP-ALL). This mutation involves a 5-amino acid deletion within the JH2 pseudokinase domain (JAK2DeltaIREED). Expression of JAK2DeltaIREED in Ba/F3 cells induced constitutive activation of the JAK-STAT pathway and growth factor-independent cell proliferation. These results highlight the JAK2 pseudokinase domain as an oncogenic hot spot and indicate that activation of the JAK-STAT pathway may contribute to lymphoid malignancies and hematologic disorders observed in children with DS.

  18. Comparison of equilibria and kinetics of high surface area activated carbon produced from different precursors and by different chemical treatments

    SciTech Connect

    Ahmadpour, A.; King, B.A.; Do, D.D.

    1998-04-01

    Activated carbons prepared by chemical activation of coal and macadamia nutshell precursors with KOH and ZnCl{sub 2} have been studied in terms of their equilibrium and dynamic characteristics. These characteristics were then related to the micropore properties: surface area, volume, and half-width. Volumetric techniques were used for equilibria characterization and an FT-IR batch adsorber for dynamics. Carbons activated by KOH resulted in a more microporous structure, while those activated by zinc chloride were more mesoporous. High surface area samples were further studied in terms of their methane adsorption uptake. It was found that nutshell-derived activated carbons have a higher adsorption capacity per unit mass than those derived from coal; however, this was offset by lower particle density (mass/volume). High-pressure (2 GPa) pelletization of the carbons used for dynamic testing had a detrimental effect on capacity, presumably from pore collapse. Dynamic characteristics were found to be rather similar between the samples, with those treated with KOH displaying slower adsorption time scales.

  19. Vaticaffinol, a resveratrol tetramer, exerts more preferable immunosuppressive activity than its precursor in vitro and in vivo through multiple aspects against activated T lymphocytes

    SciTech Connect

    Feng, Li-Li; Wu, Xue-Feng; Liu, Hai-Liang; Guo, Wen-Jie; Luo, Qiong; Tao, Fei-Fei; Ge, Hui-Ming; Shen, Yan; Tan, Ren-Xiang; Xu, Qiang Sun, Yang

    2013-03-01

    In the present study, we aimed to investigate the immunosuppressive activity of vaticaffinol, a resveratrol tetramer isolated from Vatica mangachapoi, on T lymphocytes both in vitro and in vivo, and further explored its potential molecular mechanism. Resveratrol had a wide spectrum of healthy beneficial effects with multiple targets. Interestingly, its tetramer, vaticaffinol, exerted more intensive immunosuppressive activity than resveratrol. Vaticaffinol significantly inhibited T cells proliferation activated by concanavalin A (Con A) or anti-CD3 plus anti-CD28 in a dose- and time-dependent manner. It also induced Con A-activated T cells undergoing apoptosis through mitochondrial pathway. Moreover, this compound prevented cells from entering S phase and G2/M phase during T cells activation. In addition, vaticaffinol inhibited ERK and AKT signaling pathways in Con A-activated T cells. Furthermore, vaticaffinol significantly ameliorated ear swelling in a mouse model of picryl chloride-induced ear contact dermatitis in vivo. In most of the aforementioned experiments, however, resveratrol had only slight effects on the inhibition of T lymphocytes compared with vaticaffinol. Taken together, our findings suggest that vaticaffinol exerts more preferable immunosuppressive activity than its precursor resveratrol both in vitro and in vivo by affecting multiple targets against activated T cells. - Graphical abstract: Vaticaffinol, a resveratrol tetramer isolated from Vatica mangachapoi, exerts more intensive immunosuppressive activity than its precursor resveratrol does in vitro and in vivo. Its mechanism may involve multiple effects against activated T cells: regulation of signalings involved in cell proliferation, G0/G1 arrest of T cells, as well as an apoptosis induction in activated effector T cells. Highlights: ► Vaticaffinol, a resveratrol tetramer, exerts more potent activity than its precursor. ► It inhibited T cells proliferation and prevented them from entering

  20. Activation of SIRT3 by the NAD⁺ precursor nicotinamide riboside protects from noise-induced hearing loss.

    PubMed

    Brown, Kevin D; Maqsood, Sadia; Huang, Jing-Yi; Pan, Yong; Harkcom, William; Li, Wei; Sauve, Anthony; Verdin, Eric; Jaffrey, Samie R

    2014-12-01

    Intense noise exposure causes hearing loss by inducing degeneration of spiral ganglia neurites that innervate cochlear hair cells. Nicotinamide adenine dinucleotide (NAD(+)) exhibits axon-protective effects in cultured neurons; however, its ability to block degeneration in vivo has been difficult to establish due to its poor cell permeability and serum instability. Here, we describe a strategy to increase cochlear NAD(+) levels in mice by administering nicotinamide riboside (NR), a recently described NAD(+) precursor. We find that administration of NR, even after noise exposure, prevents noise-induced hearing loss (NIHL) and spiral ganglia neurite degeneration. These effects are mediated by the NAD(+)-dependent mitochondrial sirtuin, SIRT3, since SIRT3-overexpressing mice are resistant to NIHL and SIRT3 deletion abrogates the protective effects of NR and expression of NAD(+) biosynthetic enzymes. These findings reveal that administration of NR activates a NAD(+)-SIRT3 pathway that reduces neurite degeneration caused by noise exposure.

  1. Activation of SIRT3 by the NAD⁺ precursor nicotinamide riboside protects from noise-induced hearing loss.

    PubMed

    Brown, Kevin D; Maqsood, Sadia; Huang, Jing-Yi; Pan, Yong; Harkcom, William; Li, Wei; Sauve, Anthony; Verdin, Eric; Jaffrey, Samie R

    2014-12-01

    Intense noise exposure causes hearing loss by inducing degeneration of spiral ganglia neurites that innervate cochlear hair cells. Nicotinamide adenine dinucleotide (NAD(+)) exhibits axon-protective effects in cultured neurons; however, its ability to block degeneration in vivo has been difficult to establish due to its poor cell permeability and serum instability. Here, we describe a strategy to increase cochlear NAD(+) levels in mice by administering nicotinamide riboside (NR), a recently described NAD(+) precursor. We find that administration of NR, even after noise exposure, prevents noise-induced hearing loss (NIHL) and spiral ganglia neurite degeneration. These effects are mediated by the NAD(+)-dependent mitochondrial sirtuin, SIRT3, since SIRT3-overexpressing mice are resistant to NIHL and SIRT3 deletion abrogates the protective effects of NR and expression of NAD(+) biosynthetic enzymes. These findings reveal that administration of NR activates a NAD(+)-SIRT3 pathway that reduces neurite degeneration caused by noise exposure. PMID:25470550

  2. Heterobimetallic Metal–Organic Framework as a Precursor to Prepare a Nickel/Nanoporous Carbon Composite Catalyst for 4-Nitrophenol Reduction

    SciTech Connect

    Yang, Ying; Zhang, Ying; Sun, Cheng Jun; Li, Xinsong; Zhang, Wen; Ma, Xiaohui; Ren, Yang; Zhang, Xin

    2014-11-01

    Nickel/nanoporous carbon (Ni/NPC) composites are facilely prepared by direct pyrolysis of nonporous heterobimetallic zinc-nickel-terephthalate frameworks (Zn1-xNixMOF, x approximate to 0-1, MOF= metal-organic framework) at 1223 K in situ. Tailoring the Ni/Zn ratio creates densely populated and small Ni nanocrystals (Ni NCs) while maintaining sufficient porosity and surface area in the final product, which exhibits the largest activity factor (9.2 s(-1)g(-1)) and excellent stability toward 4-nitrophenol reduction.

  3. Preliminary results from screening tests of commercial catalysts with potential use in gas turbine combustors. I - Furnace studies of catalyst activity

    NASA Technical Reports Server (NTRS)

    Anderson, D. N.

    1976-01-01

    Thirty commercially produced monolith and pellet catalysts were tested as part of a screening process to select catalysts suitable for use in a gas turbine combustor. The catalysts were contained in a 1.8 centimeter diameter quartz tube and heated to temperatures varying between 300 and 1200 K while a mixture of propane and air passed through the bed at space velocities of 44,000 to 70,000 per hour. The amount of propane oxidized was measured as a function of catalyst temperature. Of the samples tested, the most effective catalysts proved to be noble metal catalysts on monolith substrates.

  4. Preliminary results from screening tests of commercial catalysts with potential use in gas turbine combustors. Part 1: Furnace studies of catalyst activity

    NASA Technical Reports Server (NTRS)

    Anderson, D. N.

    1976-01-01

    Thirty commercially produced monolith and pellet catalysts were tested as part of a screening process to select catalysts suitable for use in a gas turbine combustor. The catalysts were contained in a 1.8 centimeter diameter quartz tube and heated to temperatures varying between 300 and 1,200 K while a mixture of propane and air passed through the bed at space velocities of 44,000 to 70,000/hour. The amount of propane oxidized was measured as a function of catalyst temperature. Of the samples tested, the most effective catalysts proved to be noble metal catalysts on monolith substrates.

  5. Redox properties and VOC oxidation activity of Cu catalysts supported on Ce₁-xSmxOδ mixed oxides.

    PubMed

    Konsolakis, Michalis; Carabineiro, Sónia A C; Tavares, Pedro B; Figueiredo, José L

    2013-10-15

    A series of Cu catalysts supported on Ce1-xSmxOδ mixed oxides with different molar contents (x=0, 0.25, 0.5, 0.75 and 1), was prepared by wet impregnation and evaluated for volatile organic compounds (VOC) abatement, employing ethyl acetate as model molecule. An extensive characterization study was undertaken in order to correlate the morphological, structural and surface properties of catalysts with their oxidation activity. The optimum performance was obtained with Cu/CeO2 catalyst, which offers complete conversion of ethyl acetate into CO2 at temperatures as low as 260°C. The catalytic performance of Cu/Ce1-xSmxOδ was interpreted on the basis of characterization studies, showing that incorporation of samarium in ceria has a detrimental effect on the textural characteristics and reducibility of catalysts. Moreover, high Sm/Ce atomic ratios (from 1 to 3) resulted in a more reduced copper species, compared to CeO2-rich supports, suggesting the inability of these species to take part in the redox mechanism of VOC abatement. Sm/Ce surface atomic ratios are always much higher than the nominal ratios indicating an impoverishment of catalyst surface in cerium oxide, which is detrimental for VOC activity. PMID:23995554

  6. Fe3-xCuxO4 as highly active heterogeneous Fenton-like catalysts toward elemental mercury removal.

    PubMed

    Zhou, Changsong; Sun, Lushi; Zhang, Anchao; Wu, Xiaofeng; Ma, Chuan; Su, Sheng; Hu, Song; Xiang, Jun

    2015-04-01

    A series of novel spinel Fe3-xCuxO4 (0active heterogeneous Fenton-like catalysts to remove elemental mercury (Hg0) from the simulated flue gases. Inductively coupled plasma-Atomic emission spectrometry (ICP-AES), X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area, and X-ray photoelectron spectrometer (XPS) were used to characterize the catalysts. The catalysts were confirmed the presence of the redox pairs Fesurf2+/Fesurf3+ and Cusurf+/Cusurf2+ on the surface of the cubic structure. The performance of heterogeneous Fenton-like reactions for Hg0 removal was evaluated in a lab-scale bubbling reactor at the solution temperature of 50°C. The systematic studies on the effects of different catalysts, H2O2 concentration and solution pH values on Hg0 removal efficiencies were performed. The recycling of the Fe3-xCuxO4 catalysts in Fenton-like solution is stable and Hg0 removal efficiency remain above 90% after 3 cycles. The active hydroxyl radical (OH) generated during heterogeneous Fenton-like reactions was confirmed through electron spin resonance (ESR) spin-trapping technique. The Hg0 removal mechanism has been discussed based on the experimental and analytical results. PMID:25655441

  7. Mint proteins are required for synaptic activity-dependent amyloid precursor protein (APP) trafficking and amyloid β generation.

    PubMed

    Sullivan, Sarah E; Dillon, Gregory M; Sullivan, Josefa M; Ho, Angela

    2014-05-30

    Aberrant amyloid β (Aβ) production plays a causal role in Alzheimer disease pathogenesis. A major cellular pathway for Aβ generation is the activity-dependent endocytosis and proteolytic cleavage of the amyloid precursor protein (APP). However, the molecules controlling activity-dependent APP trafficking in neurons are less defined. Mints are adaptor proteins that directly interact with the endocytic sorting motif of APP and are functionally important in regulating APP endocytosis and Aβ production. We analyzed neuronal cultures from control and Mint knockout neurons that were treated with either glutamate or tetrodotoxin to stimulate an increase or decrease in neuronal activity, respectively. We found that neuronal activation by glutamate increased APP endocytosis, followed by elevated APP insertion into the cell surface, stabilizing APP at the plasma membrane. Conversely, suppression of neuronal activity by tetrodotoxin decreased APP endocytosis and insertion. Interestingly, we found that activity-dependent APP trafficking and Aβ generation were blocked in Mint knockout neurons. We showed that wild-type Mint1 can rescue APP internalization and insertion in Mint knockout neurons. In addition, we found that Mint overexpression increased excitatory synaptic activity and that APP was internalized predominantly to endosomes associated with APP processing. We demonstrated that presenilin 1 (PS1) endocytosis requires interaction with the PDZ domains of Mint1 and that this interaction facilitates activity-dependent colocalization of APP and PS1. These findings demonstrate that Mints are necessary for activity-induced APP and PS1 trafficking and provide insight into the cellular fate of APP in endocytic pathways essential for Aβ production.

  8. Catalysts for the selective oxidation of hydrogen sulfide to sulfur

    DOEpatents

    Srinivas, Girish; Bai, Chuansheng

    2000-08-08

    This invention provides catalysts for the oxidation of hydrogen sulfide. In particular, the invention provides catalysts for the partial oxidation of hydrogen sulfide to elemental sulfur and water. The catalytically active component of the catalyst comprises a mixture of metal oxides containing titanium oxide and one or more metal oxides which can be selected from the group of metal oxides or mixtures of metal oxides of transition metals or lanthanide metals. Preferred metal oxides for combination with TiO.sub.2 in the catalysts of this invention include oxides of V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Tc, Ru, Rh, Hf, Ta, W, Au, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Catalysts which comprise a homogeneous mixture of titanium oxide and niobium (Nb) oxide are also provided. A preferred method for preparing the precursor homogenous mixture of metal hydroxides is by coprecipitation of titanium hydroxide with one or more other selected metal hydroxides. Catalysts of this invention have improved activity and/or selectivity for elemental sulfur production. Further improvements of activity and/or selectivity can be obtained by introducing relatively low amounts (up to about 5 mol %)of a promoter metal oxide (preferably of metals other than titanium and that of the selected second metal oxide) into the homogeneous metal/titanium oxide catalysts of this invention.

  9. Structural and mechanistic basis for the high activity of Fe–N–C catalysts toward oxygen reduction

    SciTech Connect

    Li, Jingkun; Ghoshal, Shraboni; Liang, Wentao; Sougrati, Moulay-Tahar; Jaouen, Frédéric; Halevi, Barr; McKinney, Samuel; McCool, Geoff; Ma, Chunrong; Yuan, Xianxia; Ma, Zi-Feng; Mukerjee, Sanjeev; Jia, Qingying

    2016-01-01

    The development of efficient non-platinum group metal (non-PGM) catalysts for oxygen reduction reaction (ORR) is of paramount importance for clean and sustainable energy storage and conversion devices. The major bottleneck in developing Fe–N–C materials as the leading non-PGM catalysts lies in the poor understanding of the nature of active sites and reaction mechanisms. Herein, we report a scalable metal organic framework-derived Fe–N–C catalyst with high ORR activity demonstrated in practical H2/air fuel cells, and an unprecedented turnover frequency (TOF) in acid in rotating disk electrode. By characterizing the catalyst under both ex situ and operando conditions using combined microscopic and spectroscopic techniques, we show that the structures of active sites under ex situ and working conditions are drastically different. Resultantly, the active site proposed here, a non-planar ferrous Fe–N4 moiety embedded in distorted carbon matrix characterized by a high Fe2+/3+ redox potential, is in contrast with those proposed hitherto derived from ex situ characterizations. This site reversibly switches to an in-plane ferric Fe–N4 moiety poisoned by oxygen adsorbates during the redox transition, with the population of active sites controlled by the Fe2+/3+ redox potential. The unprecedented TOF of the active site is correlated to its near-optimal Fe2+/3+ redox potential, and essentially originated from its favorable biomimetic dynamic nature that balances the site-blocking effect and O2 dissociation. The porous and disordered carbon matrix of the catalyst plays pivotal roles for its measured high ORR activity by hosting high population of reactant-accessible active sites.

  10. Effect of Mo on the active sites of VPO catalysts upon the selective oxidation of n-butane

    SciTech Connect

    Irusta, S.; Boix, A.; Pierini, B.; Caspani, C.; Petunchi, J.

    1999-10-25

    The effect of the addition of Mo to VPO formulations on the physiochemical and catalytic properties of VPO solids was studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Laser Raman spectroscopy (LRS), temperature-programmed reduction, and a flow reactor system. The addition of Mo to the oxides increases the activity and selectivity of the VPO catalysts. The promoting effect is a function of both the Mo loading and the way such cation was added to the VPO matrix. The best catalyst was obtained when 1% Mo was impregnated on the NOHPO{sub 4}-0.5H{sub 2}O phase. At 400 C 36% of molar yield to maleic anhydride was obtained in this catalyst against 12% of the unpromoted catalysts and only 3% of the solids where Mo was added during the phosphatation step. The impregnated 1% Mo catalyst achieved a molar yield of 50% after 700 h under reaction stream (equilibrated catalysts). (VO){sub 2}P{sub 2}O{sub 7} was the only phase detected by XRD and LRS in all the catalysts studied. They showed comparable BET surface areas and crystallinity after 400 h under reaction conditions. A local order distortion of the O{sub 3}-P-O-P-O{sub 3} structure was detected by LRS in the impregnated Mo VPO catalysts. After 400 h on stream, both promoted and unpromoted solids only showed V{sup IV} on the surface layer. The main effect on the addition of Mo by impregnation to VPO oxides was enhanced by the very strong Lewis acid sites and the liability of the oxygen of (VO){sub 2}P{sub 2}O{sub 7}. This suggests that the promoting effect is more electronic in nature than structural. Polymeric MO{sub 3} species were detected neither by TPR nor by LRS. All the promoted catalysts presented a surface molybdenum enrichment but whereas the coprecipitated Mo VPO solid only shows surface Mo{sup VI}, both Mo{sup VI} coexist in the impregnated catalyst.

  11. Periodic trends in the hydrodenitrogenation activity of carbon-supported transition metal sulfide catalysts

    SciTech Connect

    Eijsbouts, S.; De Beer, V.H.J.; Prins, R.

    1988-01-01

    Periodic trends of transition metals for the catalysis of reactions such as hydrogenation, hydrogenolysis, isomerization and hydrogen oxidation have been well studied. When activity versus position of the transition metal in the periodic table is plotted, quite often these trends are manifested in the form of so-called volcano-type curves. In the present study, the authors have chosen the HDN of quinoline at moderately high pressure as a model reaction, and they have used the same carbon-supported transition metal sulfide catalysts studied by Vissers et al. Results are shown for the following transition metals: V, Cr, Mn, Fe, Co, Ni, Mo, Ru, Rh, Pd, W, Re, Os, Ir, and Pt. 9 references.

  12. The active component of vanadium-molybdenum catalysts for the oxidation of acrolein to acrylic acid

    SciTech Connect

    Andrushkevich, T.V.; Kuznetsova, T.G.

    1986-12-01

    The catalytic properties of the vanadium-molybdenum oxide system were investigated in the oxidation of acrolein to acrylic acid. The active component of the catalyst is the compound VMo/sub 3/O/sub 11/, the maximum amount of which is observed at a content of 7-15 mole% V/sub 2/O/sub 4/. The compound VMo/sub 3/O/sub 11/ is formed in the thermodecomposition of silicomolybdovanadium heteropoly acids or isopoly compounds, reduced with respect to vanadium, and contains V/sup 4 +/ and Mo/sup 6 +/. The optimum treatment for the formation of this compound is treatment in the reaction mixture at 400 degrees C.

  13. Oxygen reduction at carbon supported ruthenium-selenium catalysts: Selenium as promoter and stabilizer of catalytic activity

    NASA Astrophysics Data System (ADS)

    Schulenburg, Hendrik; Hilgendorff, Marcus; Dorbandt, Iris; Radnik, Jörg; Bogdanoff, Peter; Fiechter, Sebastian; Bron, Michael; Tributsch, Helmut

    Carbon supported ruthenium-based catalysts (Ru/C) for the oxygen reduction in acid electrolytes were investigated. A treatment of Ru/C catalysts with selenious acid had a beneficial effect on catalytic activity but no influence on intrinsic kinetic properties, like Tafel slope and hydrogen peroxide generation. Reasons for the increased activity of RuSe x/C catalysts are discussed. Potential step measurements suggest that at potentials around 0.8 V (NHE) a selenium or selenium-oxygen species protects the catalyst from formation of inactive RuO 2-films. This protective effect leads to an enhanced activity of RuSe x/C compared to Ru/C. No evidence was found for a catalytically active stoichiometric selenium compound. The active phase may be described as a ruthenium suboxide RuO x (x < 2) layer integrated in a RuSe y phase or RuSe yO v (y < 2, v < 2) layer at the particle surface.

  14. Effect of the detonation nanodiamond surface on the catalytic activity of deposited nickel catalysts in the hydrogenation of acetylene

    NASA Astrophysics Data System (ADS)

    Tveritinova, E. A.; Kulakova, I. I.; Zhitnev, Yu. N.; Kharlanov, A. N.; Fionov, A. V.; Chen, W.; Buyanova, I.; Lunin, V. V.

    2013-07-01

    A comparative study is performed of the catalytic activity of nanosized nickel deposited on detonation synthesis nanodiamond (DND) and coal (CSUG) produced by burning sugar and crystalline quartz in the hydrogenation of acetylene. Nanosized nickel is obtained through the thermal decomposition of nickel formate under a dynamic vacuum. The catalysts are studied by means of scanning electron and transmission electron microscopy, X-ray fluorescence, IR-spectroscopy, X-ray diffraction, and pulse microcatalytic method. It is shown that Ni/DND is an active catalyst of acetylene hydrogenation, considerably surpassing Ni/quartz and Ni/CSUG. The apparent activation energy of the hydrogenation of acetylene is calculated, and the region of the reaction are determined for all catalysts. It is found that the influence of the structure and nature of a functional coating of nanodiamond on the catalytic activity of Ni/DND deposited catalyst in the hydrogenation of acetylene. The ability of Ni/DND to hold active hydrogen is detected.

  15. IL-4 inhibits osteoclast formation through a direct action on osteoclast precursors via peroxisome proliferator-activated receptor γ1

    PubMed Central

    Bendixen, Amy C.; Shevde, Nirupama K.; Dienger, Krista M.; Willson, Timothy M.; Funk, Colin D.; Pike, J. Wesley

    2001-01-01

    IL-4 is a pleiotropic immune cytokine secreted by activated TH2 cells that inhibits bone resorption both in vitro and in vivo. The cellular targets of IL-4 action as well as its intracellular mechanism of action remain to be determined. We show here that IL-4 inhibits receptor activator of NF-κB ligand-induced osteoclast differentiation through an action on osteoclast precursors that is independent of stromal cells. Interestingly, this inhibitory effect can be mimicked by both natural as well as synthetic peroxisome proliferator-activated receptor γ1 (PPARγ1) ligands and can be blocked by the irreversible PPARγ antagonist GW 9662. These findings suggest that the actions of IL-4 on osteoclast differentiation are mediated by PPARγ1, an interpretation strengthened by the observation that IL-4 can activate a PPARγ1-sensitive luciferase reporter gene in RAW264.7 cells. We also show that inhibitors of enzymes such as 12/15-lipoxygenase and the cyclooxygenases that produce known PPARγ1 ligands do not abrogate the IL-4 effect. These findings, together with the observation that bone marrow cells from 12/15-lipoxygenase-deficient mice retain sensitivity to IL-4, suggest that the cytokine may induce novel PPARγ1 ligands. Our results reveal that PPARγ1 plays an important role in the suppression of osteoclast formation by IL-4 and may explain the beneficial effects of the thiazolidinedione class of PPARγ1 ligands on bone loss in diabetic patients. PMID:11226258

  16. Stable and catalytically active iron porphyrin-based porous organic polymer: Activity as both a redox and Lewis acid catalyst

    PubMed Central

    Oveisi, Ali R.; Zhang, Kainan; Khorramabadi-zad, Ahmad; Farha, Omar K.; Hupp, Joseph T.

    2015-01-01

    A new porphyrin-based porous organic polymer (POP) with BET surface area ranging from 780 to 880 m2/g was synthesized in free-base form via the reaction of meso-tetrakis(pentafluorophenyl) porphyrin and a rigid trigonal building block, hexahydroxytriphenylene. The material was then metallated with Fe(III) imparting activity for Lewis acid catalysis (regioselective methanolysis ring-opening of styrene oxide), oxidative cyclization catalysis (conversion of bis(2-hydroxy-1-naphthyl)methanes to the corresponding spirodienone), and a tandem catalytic processes: an in situ oxidation-cyclic aminal formation-oxidation sequence, which selectively converts benzyl alcohol to 2-phenyl-quinazolin-4(3H)-one. Notably, the catalyst is readily recoverable and reusable, with little loss in catalytic activity. PMID:26177563

  17. An in-depth understanding of the bimetallic effects and coked carbon species on an active bimetallic Ni(Co)/Al2O3 dry reforming catalyst.

    PubMed

    Liao, Xin; Gerdts, Rihards; Parker, Stewart F; Chi, Lina; Zhao, Yongxiang; Hill, Martyn; Guo, Junqiu; Jones, Martin O; Jiang, Zheng

    2016-06-29

    Ni/Al2O3, Co/Al2O3 and bimetallic Ni(Co)/Al2O3 catalysts were prepared using an impregnation method and employed in CO2 dry reforming of methane under coking-favored conditions. The spent catalysts were carefully characterized using typical characterization technologies and inelastic neutron scattering spectroscopy. The bimetallic catalyst exhibited a superior activity and anti-coking performance compared to Ni/Al2O3, while the most resistant to coking behavior was Co/Al2O3. The enhanced activity of the Ni(Co)/Al2O3 bimetallic catalyst is attributed to the reduced particle size of metallic species and resistance to forming stable filamentous carbon. The overall carbon deposition on the spent bimetallic catalyst is comparable to that of the spent Ni/Al2O3 catalyst, whereas the carbon deposited on the bimetallic catalyst is mainly less-stable carbonaceous species as confirmed by SEM, TPO, Raman and INS characterization. This study provides an in depth understanding of alloy effects in catalysts, the chemical nature of coked carbon on spent Ni-based catalysts and, hopefully, inspires the creative design of a new bimetallic catalyst for dry reforming reactions. PMID:27326792

  18. An in-depth understanding of the bimetallic effects and coked carbon species on an active bimetallic Ni(Co)/Al2O3 dry reforming catalyst.

    PubMed

    Liao, Xin; Gerdts, Rihards; Parker, Stewart F; Chi, Lina; Zhao, Yongxiang; Hill, Martyn; Guo, Junqiu; Jones, Martin O; Jiang, Zheng

    2016-06-29

    Ni/Al2O3, Co/Al2O3 and bimetallic Ni(Co)/Al2O3 catalysts were prepared using an impregnation method and employed in CO2 dry reforming of methane under coking-favored conditions. The spent catalysts were carefully characterized using typical characterization technologies and inelastic neutron scattering spectroscopy. The bimetallic catalyst exhibited a superior activity and anti-coking performance compared to Ni/Al2O3, while the most resistant to coking behavior was Co/Al2O3. The enhanced activity of the Ni(Co)/Al2O3 bimetallic catalyst is attributed to the reduced particle size of metallic species and resistance to forming stable filamentous carbon. The overall carbon deposition on the spent bimetallic catalyst is comparable to that of the spent Ni/Al2O3 catalyst, whereas the carbon deposited on the bimetallic catalyst is mainly less-stable carbonaceous species as confirmed by SEM, TPO, Raman and INS characterization. This study provides an in depth understanding of alloy effects in catalysts, the chemical nature of coked carbon on spent Ni-based catalysts and, hopefully, inspires the creative design of a new bimetallic catalyst for dry reforming reactions.

  19. NEDD4 REGULATES PAX7 LEVELS PROMOTING ACTIVATION OF THE DIFFERENTIATION PROGRAM IN SKELETAL MUSCLE PRECURSORS

    PubMed Central

    Bustos, Francisco; de la Vega, Eduardo; Cabezas, Felipe; Thompson, James; Cornelison, DDW; Olwin, Bradley B.; Yates, John R.; Olguín, Hugo C.

    2015-01-01

    The transcription factor Pax7 regulates skeletal muscle stem cell (satellite cells) specification and maintenance through various mechanisms, including repressing the activity of the muscle regulatory factor MyoD. Hence, Pax7-to-MyoD protein ratios can determine maintenance of the committed-undifferentiated state or activation of the differentiation program. Pax7 expression decreases sharply in differentiating myoblasts but is maintained in cells (re)acquiring quiescence, yet the mechanisms regulating Pax7 levels based on differentiation status are not well understood. Here we show that Pax7 levels are directly regulated by the ubiquitin-ligase Nedd4. Our results indicate that Nedd4 is expressed in quiescent and activated satellite cells, that Nedd4 and Pax7 physically interact during early muscle differentiation – correlating with Pax7 ubiquitination and decline – and that Nedd4 loss of function prevented this effect. Furthermore, even transient nuclear accumulation of Nedd4 induced a drop in Pax7 levels and precocious muscle differentiation. Consequently, we propose that Nedd4 functions as a novel Pax7 regulator, which activity is temporally and spatially controlled to modulate the Pax7 protein levels and therefore satellite cell fate. PMID:26304770

  20. Global Cosmic Ray Intensity Changes, Solar Activity Variations and Geomagnetic Disturbances as North Atlantic Hurricane Precursors

    NASA Astrophysics Data System (ADS)

    Kavlakov, S. P.

    It was shown that specific changes of the sunspots (SS) number, cosmic ray (CR) intensity and geomagnetic activity indices AP and KP were statistically noticeable in the interval of 30 days before the appearance of a cyclonic rotational system over the North Atlantic, developing gradually in a major hurricane.

  1. Education for Liberation: A Precursor to Youth Activism for Social Justice

    ERIC Educational Resources Information Center

    Atkinson, Kristen N.

    2012-01-01

    This paper presents a participatory research approach to the study of youth activism within a community development and movement-building program. It employs participatory ethnography theory and methods to explore an innovative model of social change for social justice. Building on community youth development and transformative social work…

  2. Preparation of supported heterogeneous catalysts by pulse impregnation: Application to Ru[sub 3](CO)[sub 12]/2,2[prime]-bipyridine/SiO[sub 2] catalyst

    SciTech Connect

    Haukka, M.; Pakkanen, T.A. )

    1994-07-01

    In this paper, the authors introduce pulse impregnation, a method for preparing supported heterogeneous catalysts by successive impregnation cycles. Pulse impregnation is a method for preparing supported heterogeneous catalysts from the liquid phase. In the pulse-impregnation technique the catalyst surface is grown gradually in consecutive cycles, with each cycle consisting of separate deposition and activation steps. During the deposition step, the catalyst precursor or precursors are deposited onto the support from a suitable solvent. The actual chemically bonded catalyst phase is formed during the activation step (e.g., thermal activation). Pulse impregnation was tested in the separate deposition of 2,2[prime]-bipyridine and Ru[sub 3](CO)[sub 12] onto a silica support, and in the preparation of Ru[sub 3](CO)[sub 12]/2,2[prime]-bipyridine/SiO[sub 2] catalyst, in a column-type reactor system. Macroscopically uniform deposition was achieved with both 2,2[prime]-bipyridine and Ru[sub 3](CO)[sub 12]. Various solvent systems were used to control the amount of solute adsorbed during deposition. In the preparation of the Ru[sub 3](CO)[sub 12]/2,2[prime]-bipyridine/SiO[sub 2] catalyst, the ruthenium content increased nearly linearly with the number of preparation cycles. The effects of the preparation method on the catalyst activity was also tested in 1-hexane hydroformylation. 31 refs., 7 figs., 1 tab.

  3. Stabilizing and enhancing activity of Ag as a catalyst for oxygen redaction reaction on hydrogen fuel cell cathodes

    NASA Astrophysics Data System (ADS)

    Stolbov, Sergey; Alcantara Ortigoza, Marisol

    2013-03-01

    Progress in searching for cost-effective and highly active catalysts for the oxygen reduction reaction (ORR) on hydrogen fuel cell cathodes is hindered by the fact that only a few elements (expensive and scarce Pt, Ir, Au) do not dissolve in the reaction environment (acidic medium at the expected operating potential +0.8 to +1.0 V vs SHE). Yet, in this work, we explore silver as an active element for the ORR catalysts. Although the dissolution potential (DP) of elemental Ag is 0.8 V, we rely on our finding that binding of a metal monolayer (ML) to a reactive substrate can significantly increase its DP. Using our approach, we select Ag/Ru/W, Ag/Nb, and Ag/Ta as promising candidates for the ORR catalysts (where Ag and Ru are MLs). Our evaluation of DP within density functional theory (DFT) shows that, indeed, in the selected structures, DP of Ag significantly increases as compared to that of Ag(111) and, in the case of Ag/Nb, even exceeds that of Pt. The ORR free-energy diagrams calculated within DFT suggest that the above systems are more active toward ORR than Pt. We thus predict here three highly active and truly cost-effective ORR catalysts. This work was supported by NSF under Grant CBET-1249134

  4. Activity modulation of core and shell in nanozeolite@enzyme bi-functional catalyst for dynamic kinetic resolution.

    PubMed

    Li, Xiang; Yan, Yueer; Wang, Wanlu; Zhang, Yahong; Tang, Yi

    2015-01-15

    A core-shell nanozeolite@enzyme bi-functional catalyst is prepared by using nanozeolite β as acidic core and immobilized Candida antarctica lipase B (CALB) as enzyme shell for the purpose of dynamic kinetic resolution (DKR), and polydiallyldimethylammonium chloride (PDDA) is used as interlayer to compart core and shell. The activities of core and shell in bi-functional catalyst are modulated to achieve the matching between racemization and kinetic resolution (KR) rates in DKR, i.e., a slow racemization rate on core while a fast KR rate on shell. Nanozeolite β with intermediate SiO2/Al2O3 ratio provides proper acid amount for racemization step. A relatively thick layer of PDDA not only improves the activity of CALB by its coverage for surface acidic sites but also limits the accessibility and diffusion of substrate towards the acidic core. The CALB shell with larger immobilized amount and higher enzyme activity offers enhanced driving force of DKR process, leading to higher conversion, selectivity and yield. The preparation and activity modulation of core-shell catalyst provide an ideal method to improve the catalytic performance of bi-functional catalyst.

  5. Impact of carbon on the surface and activity of silica-carbon supported copper catalysts for reduction of nitrogen oxides

    NASA Astrophysics Data System (ADS)

    Spassova, I.; Stoeva, N.; Nickolov, R.; Atanasova, G.; Khristova, M.

    2016-04-01

    Composite catalysts, prepared by one or more active components supported on a support are of interest because of the possible interaction between the catalytic components and the support materials. The supports of combined hydrophilic-hydrophobic type may influence how these materials maintain an active phase and as a result a possible cooperation between active components and the support material could occur and affects the catalytic behavior. Silica-carbon nanocomposites were prepared by sol-gel, using different in specific surface areas and porous texture carbon materials. Catalysts were obtained after copper deposition on these composites. The nanocomposites and the catalysts were characterized by nitrogen adsorption, TG, XRD, TEM- HRTEM, H2-TPR, and XPS. The nature of the carbon predetermines the composite's texture. The IEPs of carbon materials and silica is a force of composites formation and determines the respective distribution of the silica and carbon components on the surface of the composites. Copper deposition over the investigated silica-carbon composites leads to formation of active phases in which copper is in different oxidation states. The reduction of NO with CO proceeds by different paths on different catalysts due to the textural differences of the composites, maintaining different surface composition and oxidation states of copper.

  6. Active low-valent niobium catalysts from NbCl5 and hydrosilanes for selective intermolecular cycloadditions.

    PubMed

    Satoh, Yasushi; Obora, Yasushi

    2011-10-21

    An active niobium catalyst was developed via a simple and nontoxic reduction method from NbCl(5)/hydrosilane and utilized for the selective [2 + 2 + 2] cycloaddition reaction of terminal alkynes and alkenes/α,ω-dienes, to give 1,3-cyclohexadiene derivatives in high yields with excellent chemo- and regioselectivity. PMID:21919436

  7. Combinatorial high-throughput screening for highly active Pd-Ir-Ce based ternary catalysts in electrochemical oxygen reduction reaction.

    PubMed

    Park, Sung Hyeon; Choi, Chang Hyuck; Koh, Jae Kang; Pak, Chanho; Jin, Seon-ah; Woo, Seong Ihl

    2013-11-11

    A combinatorial library having 66 different ternary compositions of Pd-Ir-Ce was prepared via the impregnation method to find the optimum ternary composition with the highest performance toward oxygen reduction reaction (ORR) in acid media. Its performance in ORR activity of the combinatorial array was evaluated through two different combinatorial high-throughput screening methods to gain validity: (1) multielectrode half-cell method and (2) optical screening method. From the combinatorial results, the spot at 79:12:9 for Pd-Ir-Ce (at. %) in the array showed the highest ORR activity. The electrochemical characterizations of the single catalyst demonstrates that the optimized Pd79Ir12Ce9/C catalyst shows 1.5 times the ORR activity compared to that of Pd/C catalyst at 0.85 V (vs. RHE). In the Pd-Ir-Ce based catalysts, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results reveal that Ir and Ce are present in the form of IrO2 and CeO2, respectively, and the electron configuration of Pd is effectively modified through the decoration with IrO2 and CeO2. From the results, we suggest that the electro-modification of Pd through strong metal-metal oxide interaction with IrO2-CeO2 was a reason for the enhanced ORR activity.

  8. Effects of plasmochemical treatments and cerium additions on the structural characteristics and activity of copper catalyst particles in isopropanol dehydrogenation

    NASA Astrophysics Data System (ADS)

    Platonov, E. A.; Lobanov, N. N.; Galimova, N. A.; Protasova, I. A.; Yagodovskii, V. D.

    2012-08-01

    The effect of the treatment of the 5 wt % Cu/SiO2 (I) and (5 wt % Cu + 0.5 wt % Ce)/SiO2 (II) catalysts with glow discharge plasma in O2, H2, and Ar on their structural characteristics was studied by X-ray phase analysis; the influence of cerium additions and plasmochemical treatments on the catalyst activity in isopropanol dehydrogenation was also investigated. Under the plasmochemical treatment, the diameters of Cu particles in catalyst I nearly doubled and microstresses in the metal particles also changed. Catalyst II was X-ray amorphous both before and after plasmochemical treatments. The activity of I after plasmochemical treatment increased because of the increase in the number of centers and changes in their composition. Growth of the activity of I compared with the activity of II was explained by the formation of new catalytic centers due to positive charging of the Ce+α adatom on the surface of the copper particle.

  9. Rhomboid Enhancer Activity Defines a Subset of Drosophila Neural Precursors Required for Proper Feeding, Growth and Viability.

    PubMed

    Gresser, Amy L; Gutzwiller, Lisa M; Gauck, Mackenzie K; Hartenstein, Volker; Cook, Tiffany A; Gebelein, Brian

    2015-01-01

    Organismal growth regulation requires the interaction of multiple metabolic, hormonal and neuronal pathways. While the molecular basis for many of these are well characterized, less is known about the developmental origins of growth regulatory structures and the mechanisms governing control of feeding and satiety. For these reasons, new tools and approaches are needed to link the specification and maturation of discrete cell populations with their subsequent regulatory roles. In this study, we characterize a rhomboid enhancer element that selectively labels four Drosophila embryonic neural precursors. These precursors give rise to the hypopharyngeal sensory organ of the peripheral nervous system and a subset of neurons in the deutocerebral region of the embryonic central nervous system. Post embryogenesis, the rhomboid enhancer is active in a subset of cells within the larval pharyngeal epithelium. Enhancer-targeted toxin expression alters the morphology of the sense organ and results in impaired larval growth, developmental delay, defective anterior spiracle eversion and lethality. Limiting the duration of toxin expression reveals differences in the critical periods for these effects. Embryonic expression causes developmental defects and partially penetrant pre-pupal lethality. Survivors of embryonic expression, however, ultimately become viable adults. In contrast, post-embryonic toxin expression results in fully penetrant lethality. To better define the larval growth defect, we used a variety of assays to demonstrate that toxin-targeted larvae are capable of locating, ingesting and clearing food and they exhibit normal food search behaviors. Strikingly, however, following food exposure these larvae show a rapid decrease in consumption suggesting a satiety-like phenomenon that correlates with the period of impaired larval growth. Together, these data suggest a critical role for these enhancer-defined lineages in regulating feeding, growth and viability.

  10. Activating Receptor NKG2D Targets RAE-1-Expressing Allogeneic Neural Precursor Cells in a Viral Model of Multiple Sclerosis

    PubMed Central

    Weinger, Jason G.; Plaisted, Warren C.; Maciejewski, Sonia M.; Lanier, Lewis L.; Walsh, Craig M.; Lane, Thomas E.

    2014-01-01

    Transplantation of major histocompatibility complex (MHC)-mismatched mouse neural precursor cells (NPCs) into mice persistently infected with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in rapid rejection that is mediated, in part, by T cells. However, the contribution of the innate immune response to allograft rejection in a model of viral-induced neurological disease has not been well defined. Herein, we demonstrate that the natural killer (NK) cell-expressing activating receptor NKG2D participates in transplanted allogeneic NPC rejection in mice persistently infected with JHMV. Cultured NPCs derived from C57BL/6 (H-2b) mice express the NKG2D ligand retinoic acid early precursor transcript (RAE)-1 but expression was dramatically reduced upon differentiation into either glia or neurons. RAE-1+ NPCs were susceptible to NK cell-mediated killing whereas RAE-1- cells were resistant to lysis. Transplantation of C57BL/6-derived NPCs into JHMV-infected BALB/c (H-2d) mice resulted in infiltration of NKG2D+CD49b+ NK cells and treatment with blocking antibody specific for NKG2D increased survival of allogeneic NPCs. Further, transplantation of differentiated RAE-1- allogeneic NPCs into JHMV-infected BALB/c mice resulted in enhanced survival, highlighting a role for the NKG2D:RAE-1 signaling axis in allograft rejection. We also demonstrate that transplantation of allogeneic NPCs into JHMV-infected mice resulted in infection of the transplanted cells suggesting that these cells may be targets for infection. Viral infection of cultured cells increased RAE-1 expression, resulting in enhanced NK cell-mediated killing through NKG2D recognition. Collectively, these results show that in a viral-induced demyelination model, NK cells contribute to rejection of allogeneic NPCs through an NKG2D signaling pathway. PMID:24898518

  11. Rhomboid Enhancer Activity Defines a Subset of Drosophila Neural Precursors Required for Proper Feeding, Growth and Viability.

    PubMed

    Gresser, Amy L; Gutzwiller, Lisa M; Gauck, Mackenzie K; Hartenstein, Volker; Cook, Tiffany A; Gebelein, Brian

    2015-01-01

    Organismal growth regulation requires the interaction of multiple metabolic, hormonal and neuronal pathways. While the molecular basis for many of these are well characterized, less is known about the developmental origins of growth regulatory structures and the mechanisms governing control of feeding and satiety. For these reasons, new tools and approaches are needed to link the specification and maturation of discrete cell populations with their subsequent regulatory roles. In this study, we characterize a rhomboid enhancer element that selectively labels four Drosophila embryonic neural precursors. These precursors give rise to the hypopharyngeal sensory organ of the peripheral nervous system and a subset of neurons in the deutocerebral region of the embryonic central nervous system. Post embryogenesis, the rhomboid enhancer is active in a subset of cells within the larval pharyngeal epithelium. Enhancer-targeted toxin expression alters the morphology of the sense organ and results in impaired larval growth, developmental delay, defective anterior spiracle eversion and lethality. Limiting the duration of toxin expression reveals differences in the critical periods for these effects. Embryonic expression causes developmental defects and partially penetrant pre-pupal lethality. Survivors of embryonic expression, however, ultimately become viable adults. In contrast, post-embryonic toxin expression results in fully penetrant lethality. To better define the larval growth defect, we used a variety of assays to demonstrate that toxin-targeted larvae are capable of locating, ingesting and clearing food and they exhibit normal food search behaviors. Strikingly, however, following food exposure these larvae show a rapid decrease in consumption suggesting a satiety-like phenomenon that correlates with the period of impaired larval growth. Together, these data suggest a critical role for these enhancer-defined lineages in regulating feeding, growth and viability. PMID

  12. PGM-free Fe-N-C catalysts for oxygen reduction reaction: Catalyst layer design

    NASA Astrophysics Data System (ADS)

    Stariha, Sarah; Artyushkova, Kateryna; Workman, Michael J.; Serov, Alexey; Mckinney, Sam; Halevi, Barr; Atanassov, Plamen

    2016-09-01

    This work studies the morphology of platinum group metal-free (PGM-free) iron-nitrogen-carbon (Fe-N-C) catalyst layers for the oxygen reduction reaction (ORR) and compares catalytic performance via polarization curves. Three different nitrogen-rich organic precursors are used to prepare the catalysts. Using scanning electron microscopy (SEM) and focused ion beam (FIB) tomography, the porosity, Euler number (pore connectivity), overall roughness, solid phase size and pore size are calculated for catalyst surfaces and volumes. Catalytic activity is determined using membrane electrode assembly (MEA) testing. It is found that the dominant factor in MEA performance is transport limitations. Through the 2D and 3D metrics it is concluded that pore connectivity has the biggest effect on transport performance.

  13. Exceptional methanol electro-oxidation activity by bimetallic concave and dendritic Pt-Cu nanocrystals catalysts

    NASA Astrophysics Data System (ADS)

    Wang, Ying-Xia; Zhou, Hui-Jing; Sun, Ping-Chuan; Chen, Tie-Hong

    2014-01-01

    PtCux (x = 1, 2 and 3) bimetallic nanocrystals with concave surface and dendritic morphology were prepared and used as electrocatalysts in methanol oxidation reaction (MOR) for polymer electrolyte membrane fuel cells. The bimetallic nanocrystals were synthesized via one-pot co-reduction of H2PtCl6 and Cu(acac)2 by oleylamine and polyvinyl pyrrolidone (PVP) in an autoclave at 180 °C. The concave dendritic bimetallic nanostructure consisted of a core rich in Cu and nanodendrites rich in Pt, which was formed via galvanic replacement of Cu by Pt. It was found that PVP played an important role in initiating, facilitating, and directing the replacement reaction. The electrochemical properties of the PtCux were characterized by cyclic voltammetry (CV) and chronoamperometry (CA). The concave dendritic PtCu2/C nanocrystals exhibited exceptionally high activity and strong poisoning resistance in MOR. At 0.75 V (vs. reversible hydrogen electrode, RHE) the mass activity and specific activity of PtCu2/C were 3.3 and 4.1 times higher than those of the commercial Pt/C catalysts, respectively. The enhanced catalytic activity could be attributed to the unique concave dendritic morphology of the bimetallic nanocrystals.

  14. A highly active and stable hydrogen evolution catalyst based on pyrite-structured cobalt phosphosulfide

    PubMed Central

    Liu, Wen; Hu, Enyuan; Jiang, Hong; Xiang, Yingjie; Weng, Zhe; Li, Min; Fan, Qi; Yu, Xiqian; Altman, Eric I.; Wang, Hailiang

    2016-01-01

    Rational design and controlled synthesis of hybrid structures comprising multiple components with distinctive functionalities are an intriguing and challenging approach to materials development for important energy applications like electrocatalytic hydrogen production, where there is a great need for cost effective, active and durable catalyst materials to replace the precious platinum. Here we report a structure design and sequential synthesis of a highly active and stable hydrogen evolution electrocatalyst material based on pyrite-structured cobalt phosphosulfide nanoparticles grown on carbon nanotubes. The three synthetic steps in turn render electrical conductivity, catalytic activity and stability to the material. The hybrid material exhibits superior activity for hydrogen evolution, achieving current densities of 10 mA cm−2 and 100 mA cm−2 at overpotentials of 48 mV and 109 mV, respectively. Phosphorus substitution is crucial for the chemical stability and catalytic durability of the material, the molecular origins of which are uncovered by X-ray absorption spectroscopy and computational simulation. PMID:26892437

  15. Activity and selectivity control by niobium for the preferential oxidation of co on pt supported catalysts

    SciTech Connect

    Guerrero, S.; Miller, J.T.; Wolf, E.E.

    2010-10-22

    The promotional effect of Nb on Pt supported on alumina or on niobia, was studied for the preferential oxidation of CO (PROX) in hydrogen. The results show a unique effect of Nb as a promoter to Pt. At low Nb loadings on Pt/alumina, the CO oxidation activity and selectivity are significantly increased. The CO selectivity is 100% at conversions up to about 60%. For Pt supported on Nb{sub 2}O{sub 5}, however, the CO oxidation activity is strongly suppressed with low CO conversion but high H{sub 2} oxidation activity. Pt on niobia, therefore, is poorly selective for the PROX reaction, but is an active hydrogen oxidation catalyst, resistant to CO poisoning. For Pt supported on highly loaded Nb-alumina or Nb{sub 2}O{sub 5}, XPS indicate an increase in the Pt and Nb oxidation states. These surface changes also correlate with changes in the DRIFTS spectra suggesting that CO is more weakly adsorbed on Pt/Nb{sub 2}O{sub 5} compared to Pt/Al{sub 2}O{sub 3}, or Pt/Nb-Al{sub 2}O{sub 3}.

  16. A highly active and stable hydrogen evolution catalyst based on pyrite-structured cobalt phosphosulfide

    NASA Astrophysics Data System (ADS)

    Liu, Wen; Hu, Enyuan; Jiang, Hong; Xiang, Yingjie; Weng, Zhe; Li, Min; Fan, Qi; Yu, Xiqian; Altman, Eric I.; Wang, Hailiang

    2016-02-01

    Rational design and controlled synthesis of hybrid structures comprising multiple components with distinctive functionalities are an intriguing and challenging approach to materials development for important energy applications like electrocatalytic hydrogen production, where there is a great need for cost effective, active and durable catalyst materials to replace the precious platinum. Here we report a structure design and sequential synthesis of a highly active and stable hydrogen evolution electrocatalyst material based on pyrite-structured cobalt phosphosulfide nanoparticles grown on carbon nanotubes. The three synthetic steps in turn render electrical conductivity, catalytic activity and stability to the material. The hybrid material exhibits superior activity for hydrogen evolution, achieving current densities of 10 mA cm-2 and 100 mA cm-2 at overpotentials of 48 mV and 109 mV, respectively. Phosphorus substitution is crucial for the chemical stability and catalytic durability of the material, the molecular origins of which are uncovered by X-ray absorption spectroscopy and computational simulation.

  17. A highly-active and stable hydrogen evolution catalyst based on pyrite-structured cobalt phosphosulfide

    DOE PAGES

    Liu, Wen; Hu, Enyuan; Jiang, Hong; Xiang, Yingjie; Weng, Zhe; Li, Min; Fan, Qi; Yu, Xiqian; Altman, Eric I.; Wang, Hailiang

    2016-02-19

    Rational design and controlled synthesis of hybrid structures comprising multiple components with distinctive functionalities are an intriguing and challenging approach to materials development for important energy applications like electrocatalytic hydrogen production, where there is a great need for cost effective, active and durable catalyst materials to replace the precious platinum. Here we report a structure design and sequential synthesis of a highly active and stable hydrogen evolution electrocatalyst material based on pyrite-structured cobalt phosphosulfide nanoparticles grown on carbon nanotubes. The three synthetic steps in turn render electrical conductivity, catalytic activity and stability to the material. The hybrid material exhibits superiormore » activity for hydrogen evolution, achieving current densities of 10 mA cm–2 and 100 mA cm–2 at overpotentials of 48 mV and 109 mV, respectively. Lastly, phosphorus substitution is crucial for the chemical stability and catalytic durability of the material, the molecular origins of which are uncovered by X-ray absorption spectroscopy and computational simulation.« less

  18. Specifically modified Env immunogens activate B-cell precursors of broadly neutralizing HIV-1 antibodies in transgenic mice

    PubMed Central

    McGuire, Andrew T.; Gray, Matthew D.; Dosenovic, Pia; Gitlin, Alexander D.; Freund, Natalia T.; Petersen, John; Correnti, Colin; Johnsen, William; Kegel, Robert; Stuart, Andrew B.; Glenn, Jolene; Seaman, Michael S.; Schief, William R.; Strong, Roland K.; Nussenzweig, Michel C.; Stamatatos, Leonidas

    2016-01-01

    VRC01-class broadly neutralizing HIV-1 antibodies protect animals from experimental infection and could contribute to an effective vaccine response. Their predicted germline forms (gl) bind Env inefficiently, which may explain why they are not elicited by HIV-1 Env-immunization. Here we show that an optimized Env immunogen can engage multiple glVRC01-class antibodies. Furthermore, this immunogen activates naive B cells expressing the human germline heavy chain of 3BNC60, paired with endogenous mouse light chains in vivo. To address whether it activates B cells expressing the fully humanized gl3BNC60 B-cell receptor (BCR), we immunized mice carrying both the heavy and light chains of gl3BNC60. B cells expressing this BCR display an autoreactive phenotype and fail to respond efficiently to soluble forms of the optimized immunogen, unless it is highly multimerized. Thus, specifically designed Env immunogens can activate naive B cells expressing human BCRs corresponding to precursors of broadly neutralizing HIV-1 antibodies even when the B cells display an autoreactive phenotype. PMID:26907590

  19. Specifically modified Env immunogens activate B-cell precursors of broadly neutralizing HIV-1 antibodies in transgenic mice.

    PubMed

    McGuire, Andrew T; Gray, Matthew D; Dosenovic, Pia; Gitlin, Alexander D; Freund, Natalia T; Petersen, John; Correnti, Colin; Johnsen, William; Kegel, Robert; Stuart, Andrew B; Glenn, Jolene; Seaman, Michael S; Schief, William R; Strong, Roland K; Nussenzweig, Michel C; Stamatatos, Leonidas

    2016-01-01

    VRC01-class broadly neutralizing HIV-1 antibodies protect animals from experimental infection and could contribute to an effective vaccine response. Their predicted germline forms (gl) bind Env inefficiently, which may explain why they are not elicited by HIV-1 Env-immunization. Here we show that an optimized Env immunogen can engage multiple glVRC01-class antibodies. Furthermore, this immunogen activates naive B cells expressing the human germline heavy chain of 3BNC60, paired with endogenous mouse light chains in vivo. To address whether it activates B cells expressing the fully humanized gl3BNC60 B-cell receptor (BCR), we immunized mice carrying both the heavy and light chains of gl3BNC60. B cells expressing this BCR display an autoreactive phenotype and fail to respond efficiently to soluble forms of the optimized immunogen, unless it is highly multimerized. Thus, specifically designed Env immunogens can activate naive B cells expressing human BCRs corresponding to precursors of broadly neutralizing HIV-1 antibodies even when the B cells display an autoreactive phenotype. PMID:26907590

  20. Cytoplasmic p53 and Activated Bax Regulate p53-dependent, Transcription-independent Neural Precursor Cell Apoptosis

    PubMed Central

    Geng, Ying; Walls, K.C.; Ghosh, Arindam P.; Akhtar, Rizwan S.; Klocke, Barbara J.; Roth, Kevin A.

    2010-01-01

    The prodeath effects of p53 are typically mediated via its transcriptional upregulation of proapoptotic Bcl-2 family members, including PUMA, Noxa, and/or Bax. We previously reported that staurosporine (STS), a broad-spectrum kinase inhibitor and prototypical apoptosis-inducing agent, produced p53-dependent, Bax-dependent, neural precursor cell (NPC) apoptosis, but that this effect occurred independently of new gene transcription and PUMA expression. To further characterize the mechanism by which p53 regulates NPC death, we used primary cerebellar NPCs derived from wild-type, p53-deficient, and Bax-deficient neonatal mice and the mouse cerebellar neural stem cell line, C17.2. We found that STS rapidly increased p53 cytoplasmic immunoreactivity in neuritic-like processes in C17.2 cells, which preceded Bax activation and caspase-3 cleavage. Confocal microscopy analysis of STS-treated cells revealed partial colocalization of p53 with the mitochondrial marker pyruvate dehydrogenase as well as with conformationally altered “activated” Bax, suggesting an interaction between these proapoptotic molecules in triggering apoptotic death. Nucleophosmin (NPM), a CRM1-dependent nuclear chaperone, also exhibited partial colocalization with both activated Bax and p53 following STS treatment. These observations suggest that cytoplasmic p53 can trigger transcription-independent NPC apoptosis through its potential interaction with NPM and activated Bax. (J Histochem Cytochem 58:265–275, 2010) PMID:19901272