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Gold Catalysts (gold + catalyst)
Kinds of Gold Catalysts Selected AbstractsMagnetically Separable Gold Catalyst for the Aerobic Oxidation of AminesCHEMCATCHEM, Issue 1 2009Linda Aschwanden Abstract A magnetically separable, recyclable gold catalyst consisting of gold nanoparticles supported on intimately mixed superparamagnetic ceria/iron oxide has been prepared by simple addition of the preformed mixed oxide support and the gold precursor, Au(OAc)3, to the reaction mixture of the aerobic oxidation of amines. The catalyst was characterized by means of X-ray diffraction (XRD), N2 adsorption, superconducting quantum-interference device (SQUID) measurements, time-of-flight secondary ion mass spectrometry (TOF-SIMS), scanning transmission electron microscopy (STEM), and scanning electron microscopy with an energy-dispersive X-ray spectrometer (SEM-EDAX). Catalytic tests with various amines showed high selectivity to the corresponding imines (87,100,%), and good separation efficiency and recyclability of the catalyst. [source] ChemInform Abstract: Selective Oxidation of Glycerol to Glyceric Acid Using a Gold Catalyst in Aqueous Sodium Hydroxide.CHEMINFORM, Issue 30 2002Silvio Carrettin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Fluorous Phosphine-Assisted Recycling of Gold Catalysts for Hydrosilylation of AldehydesMOLECULAR INFORMATICS, Issue 8-9 2006Diána Lantos Abstract The facile recycling of gold hydrosilylation catalyst was achieved by using fluorous phosphine-modified gold complexes and/or nanoparticles. [source] Highly Active Iron Oxide Supported Gold Catalysts for CO Oxidation: How Small Must the Gold Nanoparticles Be?,ANGEWANDTE CHEMIE, Issue 33 2010Yong Liu Gold? Ja! , Aber in welcher Form? Die im Titel bezeichneten Katalysatoren wurden nach einem Kolloidabscheidungsverfahren erhalten. Rastertransmissionselektronenmikroskopie-Untersuchungen belegen, dass das Vorliegen von Doppelschichten aus etwa 0.5,nm großen Goldclustern nicht zwingend für eine hohe katalytische Aktivität erforderlich ist (siehe Bild). [source] Selective Oxidation of Glycerol under Acidic Conditions Using Gold Catalysts,ANGEWANDTE CHEMIE, Issue 26 2010Alberto Villa Dr. Base? Wozu? PtAu-Nanopartikel auf H-Mordenit-Trägern vermitteln hoch aktiv und selektiv die Oxidation von Glycerin unter sauren Bedingungen, was die direkte Bildung der freien Säuren ermöglicht (siehe Bild). Anders als bei PtAu-Nanopartikeln auf Aktivkohle bedingt hier die hohe Selektivität für C3 -Verbindungen eine minimale H2O2 -Bildung. [source] ChemInform Abstract: Heterogeneous Gold Catalysts for Efficient Access to Functionalized Lactones.CHEMINFORM, Issue 7 2009Florentina Neatu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Preparation and Catalytic Properties of Nanosized Gold CatalystsCHEMINFORM, Issue 26 2006Yu-Wen Chen Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Heterogeneous Gold Catalysts for Efficient Access to Functionalized LactonesCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2008Florentina Nea Abstract A novel class of heterogeneous gold catalysts supported on zeolite beta-NH4+ was prepared by the deposition,precipitation method. This new class of catalyst showed interesting catalytic activities for the intramolecular cycloisomerization of ,-acetylenic carboxylic acids leading to functionalized ,-alkylidene ,-butyrolactones. Analysis of the supported gold species with in situ X-ray photoelectron spectroscopy (in situ XPS) suggests that cationic Au (possibly AuIII) can play an important role in such reactions. The high discrepancy in catalyst stability in favor of the Au supported on the zeolite system over bulk Au2O3 is explained by 1),the size of the particles and 2),the reversibility of the redox deactivating process (AuIII,AuI) in the presence of oxygen for the supported system. The efficiency of this system allowed reaction under mild heterogeneous conditions. The potential for catalyst recycling was also highlighted. [source] New Generation of Gold Catalysts: Nanoporous Foams and Tubes,Is Unsupported Gold Catalytically Active?CHEMPHYSCHEM, Issue 13 2007Masatake Haruta Prof. Dr. Gold fever: Gold turns out to be catalytically very active, provided that either one or two of the three conditions shown in the graphic are fulfilled. In CO oxidation at room temperature even unsupported gold is active in the presence of alkaline water. The active states of gold in the gold catalysts reported so far can be classified into four groups: bulk gold, nanoparticles, clusters or thin layers with specific sizes, and cations. [source] Pulsed Vapor-Liquid-Solid Growth of Antimony Selenide and Antimony Sulfide NanowiresADVANCED MATERIALS, Issue 31 2009Ren Bin Yang Antimony sulfide and antimony selenide nanowires are prepared in an original pulsed vapor-liquid-solid growth mode. The molecular precursors are not mixed together in the gas phase; therefore the chemical reaction forming the solid only occurs in the gold catalyst. The material is stoichiometric and highly crystalline. Wires consisting of Sb2S3 and Sb2Se3 segments can be obtained with the same process. [source] Routes to Grow Well-Aligned Arrays of ZnSe Nanowires and Nanorods,ADVANCED MATERIALS, Issue 11 2005X. Zhang Well-aligned ZnSe nanowires and nanorods can be grown on ZnSe epilayers on different GaAs substrates, with and without catalyst, by metal,organic chemical vapor deposition. Gold particles affect the number density, growth direction, and the morphology of the resulting nanostructures. In the absence of the gold catalyst, hexagonal nanorods grow along the <111> directions (see Figure). Growth defects on the epilayers may be the nucleation sites of the nanorods. [source] Heterogeneous Gold-Catalysed Synthesis of PhenolsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10-11 2006Silvio Carrettin Abstract Nanoparticles of gold supported on nanocrystalline CeO2 catalyse the isomerisation of ,-alkynylfurans to phenols. Initial leaching of gold was observed, which could be minimised by calcining. Subsequent runs showed that once all soluble species had leached, the surface-bound, cationic gold species is still active and can reach turnover numbers of up to 391. This is the first time that a heterogeneous gold catalyst showed activity in the gold-catalysed phenol synthesis. [source] ChemInform Abstract: Gold-Catalyzed Domino Reactions Consisting of Regio- and Stereoselective 1,2-Alkyl Migration.CHEMINFORM, Issue 43 2010Wenbo Li Abstract A cationic gold(I)-catalyzed domino reaction involving highly regio- and stereoselective 1,2-alkyl migration and heterocyclization or oxygen transfer is developed, in which the product selectivity is controlled by the counteranion of the gold catalyst. [source] Au-Catalyzed Tandem Cyclization/[1,2]-Alkyl Migration Reaction of Epoxy Alkynes: Synthesis of SpiropyranonesCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2008Xing-Zhong Shu Dr. Abstract A novel gold-catalyzed tandem cyclization/[1,2]-alkyl migration process of epoxy alkynes to spiropyranones has been discovered. From this process, the construction of adjacent multiple stereocenters with a new quaternary carbon atom is achieved. The gold-catalyzed domino process is stereospecific with respect to the migrating carbon atom. A type of unusual CC bond cleavage of epoxide systems has also been discovered, which can lead to the formation of two Z,alkenes and a carbonyl functional group in one step with excellent stereoselectivity. Furthermore, this efficient domino process could be achieved in the presence of the simplest and least expensive gold catalyst [NaAuCl4],2,H2O with a low catalyst loading. [source] Water Compatible Gold(III)-Catalysed Synthesis of Unsymmetrical Ethers from AlcoholsCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2008Abstract An efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols catalysed by the simplest and least expensive gold catalyst, NaAuCl4, is described for the first time. The procedure enables the etherification of benzylic and tertiary alcohols with moderate to good yields under mild conditions with low catalyst loading. Symmetrical ethers, the usual side products in the etherification of alcohols, were not detected in this case. The formation of the racemic ether from a chiral benzyl alcohol suggests the intermediacy of a carbocation, which has not previously been postulated for gold-catalysed reactions involving alcohols. [source] Increasing the Number of Oxygen Vacancies on TiO2 by Doping with Iron Increases the Activity of Supported Gold for CO OxidationCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2007Silvio Carrettin Dr. Abstract The addition of iron to high-area TiO2 (Degussa P25, a mixture of anatase and rutile) increases the number of oxygen defect sites that react with O2 to form peroxide and superoxide species. In the presence of gold nanoclusters on the TiO2 surface, the superoxide species become highly reactive, and the activity of the supported gold catalyst for CO oxidation is approximately twice that of the most active comparable catalysts described in the literature. Images of the catalyst obtained by scanning transmission electron microscopy combined with spectra of the catalyst measured in the working state (Raman, extended X-ray absorption fine structure, and X-ray absorption near-edge structure) indicate strong interactions of gold with the support and the presence of iron near the interfaces between the gold clusters and the TiO2 support. The high activity of the catalysts is attributed to the presence of defects in these sites that activate oxygen. [source] Gold Catalysis: Alkylideneoxazolines and -oxazoles from Intramolecular Hydroamination of an Alkyne by a TrichloroacetimidateEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2006A. Stephen K. Hashmi Abstract Several propargylic trichloroacetimidates have been prepared and their reactions with gold catalysts studied. Only with the propargyl and the 1-methylpropargyl substituent was a selective cyclization observed; with gold(III) chloride in acetonitrile only the product of a fast hydroamination to 4-methylene-4,5-dihydrooxazoles was obtained, in chloroform the slower subsequent aromatization could not be prevented which delivered the oxazoles after long reaction times. Up to 3333 turnovers could be reached. With gold(I) catalysts in chloroform or dichloromethane selective hydroamination to 4-methylene-4,5-dihydrooxazoles without subsequent aromatization was exclusively observed. The gold(I) catalysts also allowed chemoselective cycloisomerization of N -propargylcarboxamides to 5-methylene-4,5-dihydrooxazoles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Organocatalyzed Conjugate Addition of Carbonyl Compounds to Nitrodienes/Nitroenynes and Synthetic ApplicationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2010Sébastien Belot Abstract The purpose of this study is to point out the synthetic utility of a new class of Michael acceptors (nitrodienes and nitroenynes). The highly enantioselective organocatalytic Michael addition of carbonyl compounds to these functionalized nitroolefins has been carried out in the presence of (S)-diphenylprolinol silyl ether to achieve some interesting building blocks in high selectivities. The adducts thus obtained can be easily converted by taking advantage of the corresponding unsaturated carbon-carbon bond. In presence of the double bond, metathesis or electrophilic activation could be carried out whereas in the presence of the triple bond electrophilic activation could be conducted. We thus focused on a gold-catalyzed cyclization of the bis-homopropargylic alcohol to afford the corresponding substituted tetrahydrofuran. Then, we also demonstrated that organic and gold catalysts were compatible in a one-pot process. Indeed, we developed a one-pot enantioselective organocatalytic Michael addition to a nitroenyne followed by a gold-catalyzed acetalization/cyclization to achieve tetrahydrofuranyl ethers in high diastereo- and enantioselectivities with excellent yields. [source] Synthesis and photoluminescence properties of silicon nanowires treated by high-pressure water vapor annealingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2007B. Salhi Abstract This paper reports on silicon nanowires (SiNWs) growth on porous silicon (PS) template using vapor-liquid-solid (VLS) technique and the effect of high-pressure water vapor annealing (HWA) on their optical properties. Gold nanoparticles (Au NPs) with average mean diameter of 50 and 20 nm were used as catalysts. The SiNWs were obtained by thermal decomposition of silane gas (SiH4) at high temperature (540 °C) catalyzed by the Au NPs. The resulting nanostructures display comparable diameter to the initial gold catalysts and are few microns long without a preferential growth direction. We have next examined the optical properties of the 20 nm diameter SiNWs. As-prepared SiNWs display a weak photoluminescence (PL), which is related to the recombination emissions from defect centers. High-pressure water vapor annealing (HWA) at 260 °C and 2.6 MPa of the SiNWs led to an increase of the PL by a factor 10 without significant changes in the emission band. TEM analysis of the HWA-treated SiNWs showed a crystalline silicon core surrounded by an amorphous oxide layer. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Recent Advances in Asymmetric Gold CatalysisCHEMCATCHEM, Issue 6 2010Sujata Sengupta Au revoir: Recent years have seen explosive growth in the use of homogeneous gold catalysts, owing to their excellent chemoselectivity, high efficiency, and applicability under mild conditions. In this Minireview, recent progress regarding asymmetric gold catalysis is summarized with discussion focused on homogeneous Au catalysts promoting CC multiple bond activation toward the synthesis of enantiomerically enriched products. [source] Characterization of the Oxidation States of Supported Gold Species by IR Spectroscopy of Adsorbed COCHEMIE-INGENIEUR-TECHNIK (CIT), Issue 6 2007M. Mihaylov Dr. Abstract The use of IR spectroscopy of adsorbed CO for determination of gold speciation on supported gold catalysts is reviewed. Different ionic and metallic sites (Au3+, Au+, Au0, and Au,) can be differentiated on the basis of the frequency and stability of their surface carbonyl species formed after CO adsorption. In addition, the study of CO adsorption and reaction with other gases can provide unique information on the mechanisms of catalytic reactions with participation of CO. Finally, results from complementary techniques such as X-ray absorption spectroscopy, also useful for determination of gold oxidation state, are briefly considered. [source] Gold Catalysis: Tandem Reactions of Diyne,Diols and External Nucleophiles as an Easy Access to Tricyclic Cage-Like Structures,CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2010Stephen Abstract Different diyne,diols composed of two terminal homopropargylic alcohol groups were prepared by bi-directional synthesis. Subjection of the syn diastereomers to NAC,gold catalysts (NAC=nitrogen acyclic carbene) in the presence of external nucleophiles such as water or anilines provided substituted and highly rigid heterocyclic cages. The corresponding anti disastereomers polymerised. An intermediate of the reactions of the syn diastereomers could be isolated and even be characterised by crystal structure analysis. Overall, eight new bonds are formed in the reaction, which proceeds by a multistep sequence of highly selective hydroalkoxylations and hydrohydroxylation or hydroaminations. For furyl substituents and for internal alkynes competing reaction pathways could be identified. By the cross-coupling of a product with an iodoaryl substituent, the use of these cage compounds as geometrically defined linking groups by using orthogonal transition-metal-catalysed methodology, namely, gold and palladium catalysis, could be demonstrated. [source] Heterogeneous Gold Catalysts for Efficient Access to Functionalized LactonesCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2008Florentina Nea Abstract A novel class of heterogeneous gold catalysts supported on zeolite beta-NH4+ was prepared by the deposition,precipitation method. This new class of catalyst showed interesting catalytic activities for the intramolecular cycloisomerization of ,-acetylenic carboxylic acids leading to functionalized ,-alkylidene ,-butyrolactones. Analysis of the supported gold species with in situ X-ray photoelectron spectroscopy (in situ XPS) suggests that cationic Au (possibly AuIII) can play an important role in such reactions. The high discrepancy in catalyst stability in favor of the Au supported on the zeolite system over bulk Au2O3 is explained by 1),the size of the particles and 2),the reversibility of the redox deactivating process (AuIII,AuI) in the presence of oxygen for the supported system. The efficiency of this system allowed reaction under mild heterogeneous conditions. The potential for catalyst recycling was also highlighted. [source] New Generation of Gold Catalysts: Nanoporous Foams and Tubes,Is Unsupported Gold Catalytically Active?CHEMPHYSCHEM, Issue 13 2007Masatake Haruta Prof. Dr. Gold fever: Gold turns out to be catalytically very active, provided that either one or two of the three conditions shown in the graphic are fulfilled. In CO oxidation at room temperature even unsupported gold is active in the presence of alkaline water. The active states of gold in the gold catalysts reported so far can be classified into four groups: bulk gold, nanoparticles, clusters or thin layers with specific sizes, and cations. [source] Kinetic and DFT Studies on the Photoinduced Desorption of Sulfur from Gold Nanoparticles Loaded on Titanium DioxideCHEMPHYSCHEM, Issue 12 2005Tomokazu Kiyonaga Cleaning poisoned gold catalysts: Kinetic analysis of the photoinduced desorption of sulfur from gold nanoparticles loaded on TiO2 particles in water revealed that the rate constant increases with increasing pH. Photoelectrochemical measurements and DFT calculations led to the conclusion that this reaction results from an upward shift in the Fermi energy of gold nanoparticles by irradiation. The picture shows a high-resolution TEM image of an Au nanoparticle on TiO2. [source] | ||||||||||||||||||||||