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Silver Cluster (silver + cluster)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Direct Dehydrogenative Amide Synthesis from Alcohols and Amines Catalyzed by ,-Alumina Supported Silver Cluster

CHEMISTRY - A EUROPEAN JOURNAL, Issue 39 2009
Ken-ichi Shimizu Dr.
Silver clusters immobilized on ,-Al2O3 catalyze direct amide synthesis from alcohols and amines in the presence of catalytic amount of weak base (Cs2CO3). The reaction proceeds by cooperation of the coordinatively unsaturated silver site, as well as acid and base sites of the oxide support (see scheme). [source]

Oxidant-Free Dehydrogenation of Alcohols Heterogeneously Catalyzed by Cooperation of Silver Clusters and Acid,Base Sites on Alumina

CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2009
Ken-ichi Shimizu Dr.
Abstract Trifunctional green catalysis: In-depth characterization shows that oxidant-free selective oxidation of alcohols by silver nanoparticles on ,-Al2O3, as a new heterogeneous catalyst, proceeds through cooperation of silver, acid, and base sites (see figure). A ,-alumina-supported silver cluster catalyst,Ag/Al2O3,has been shown to act as an efficient heterogeneous catalyst for oxidant-free alcohol dehydrogenation to carbonyl compounds at 373,K. The catalyst shows higher activity than conventional heterogeneous catalysts based on platinum group metals (PGMs) and can be recycled. A systematic study on the influence of the particle size and oxidation state of silver species, combined with characterization by Ag,K-edge XAFS (X-ray absorption fine structure) has established that silver clusters of sizes below 1,nm are responsible for the higher specific rate. The reaction mechanism has been investigated by kinetic studies (Hammett correlation, kinetic isotope effect) and by in situ FTIR (kinetic isotope effect for hydride elimination reaction from surface alkoxide species), and the following mechanism is proposed: 1),reaction between the alcohol and a basic OH group on the alumina to yield alkoxide on alumina and an adsorbed water molecule, 2),CH activation of the alkoxide species by the silver cluster to form a silver hydride species and a carbonyl compound, and 3),H2 desorption promoted by an acid site in the alumina. The proposed mechanism provides fundamental reasons for the higher activities of silver clusters on acid,base bifunctional support (Al2O3) than on basic (MgO and CeO2) and acidic to neutral (SiO2) ones. This example demonstrates that catalysts analogous to those based on of platinum group metals can be designed with use of a less expensive d10 element,silver,through optimization of metal particle size and the acid,base natures of inorganic supports. [source]

Direct Dehydrogenative Amide Synthesis from Alcohols and Amines Catalyzed by ,-Alumina Supported Silver Cluster

CHEMISTRY - A EUROPEAN JOURNAL, Issue 39 2009
Ken-ichi Shimizu Dr.
Silver clusters immobilized on ,-Al2O3 catalyze direct amide synthesis from alcohols and amines in the presence of catalytic amount of weak base (Cs2CO3). The reaction proceeds by cooperation of the coordinatively unsaturated silver site, as well as acid and base sites of the oxide support (see scheme). [source]

Surface-enhanced Raman scattering and density functional theory studies of bis(4-aminophenyl)sulfone,

JOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2010
Guillermo Diaz-Fleming
Abstract Raman and surface-enhanced Raman scattering (SERS) spectra of dapsone by using colloidal silver nanoparticles have been recorded. Density functional theory was used for the optimization of ground state geometries and simulation of the vibrational spectrum of this molecule. The SERS spectrum with a large silver cluster as a model metallic surface was simulated for the first time. Taking into account the experimental and calculated Raman as well as the SERS normal modes and the corresponding assignments, along with the modeling of the free dapsone and the one in the presence of the colloidal silver nanoparticles, the importance of the sulfone group on the SERS effect in dapsone was inferred. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Oxidant-Free Dehydrogenation of Alcohols Heterogeneously Catalyzed by Cooperation of Silver Clusters and Acid,Base Sites on Alumina

CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2009
Ken-ichi Shimizu Dr.
Abstract Trifunctional green catalysis: In-depth characterization shows that oxidant-free selective oxidation of alcohols by silver nanoparticles on ,-Al2O3, as a new heterogeneous catalyst, proceeds through cooperation of silver, acid, and base sites (see figure). A ,-alumina-supported silver cluster catalyst,Ag/Al2O3,has been shown to act as an efficient heterogeneous catalyst for oxidant-free alcohol dehydrogenation to carbonyl compounds at 373,K. The catalyst shows higher activity than conventional heterogeneous catalysts based on platinum group metals (PGMs) and can be recycled. A systematic study on the influence of the particle size and oxidation state of silver species, combined with characterization by Ag,K-edge XAFS (X-ray absorption fine structure) has established that silver clusters of sizes below 1,nm are responsible for the higher specific rate. The reaction mechanism has been investigated by kinetic studies (Hammett correlation, kinetic isotope effect) and by in situ FTIR (kinetic isotope effect for hydride elimination reaction from surface alkoxide species), and the following mechanism is proposed: 1),reaction between the alcohol and a basic OH group on the alumina to yield alkoxide on alumina and an adsorbed water molecule, 2),CH activation of the alkoxide species by the silver cluster to form a silver hydride species and a carbonyl compound, and 3),H2 desorption promoted by an acid site in the alumina. The proposed mechanism provides fundamental reasons for the higher activities of silver clusters on acid,base bifunctional support (Al2O3) than on basic (MgO and CeO2) and acidic to neutral (SiO2) ones. This example demonstrates that catalysts analogous to those based on of platinum group metals can be designed with use of a less expensive d10 element,silver,through optimization of metal particle size and the acid,base natures of inorganic supports. [source]