Size- and support-dependency in the catalysis of gold

5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

With petrol prices on the rise, biofuels are big news these days. For applications in the transportation sector, perhaps the best known liquid biofuel is biomass-derived ethanol. But ethanol has its limitations: it is highly volatile, absorbs water and has a low energy density. A team from the University of Wisconsin-Madison has developed a two-step catalytic process that can convert fructose into a potentially better liquid biofuel, 2,5-dimethylfuran (DMF). This has 40%-higher energy density and a higher boiling point than ethanol, and is not water soluble. Fructose can be made directly from biomass or from glucose and although there's some work needed before DMF production can be made commercially viable, this new catalytic process looks promising. Diminishing fossil fuel reserves and growing concerns about global warming indicate that sustainable sources of energy are needed in the near future. For fuels to be useful in the transportation sector, they must have specific physical properties that allow for efficient distribution, storage and combustion; these properties are currently fulfilled by non-renewable petroleum-derived liquid fuels. Ethanol, the only renewable liquid fuel currently produced in large quantities, suffers from several limitations, including low energy density, high volatility, and contamination by the absorption of water from the atmosphere. Here we present a catalytic strategy for the production of 2,5-dimethylfuran from fructose (a carbohydrate obtained directly from biomass or by the isomerization of glucose) for use as a liquid transportation fuel. Compared to ethanol, 2,5-dimethylfuran has a higher energy density (by 40 per cent), a higher boiling point (by 20 K), and is not soluble in water. This catalytic strategy creates a route for transforming abundant renewable biomass resources1,2 into a liquid fuel suitable for the transportation sector, and may diminish our reliance on petroleum.

Production of dimethylfuran for liquid fuels from biomass-derived carbohydrates

2.5. Stabilization of IL Emulsions by Nanoparticles 2623 3. Hydrogenations in ILs 2623 3.1. Hydrogenation on IL-Stabilized Nanoparticles 2623 3.1.1. Hydrogenation of 1,3-Butadiene 2623 3.1.2. Hydrogenation of Alkenes and Arenes 2624 3.1.3. Hydrogenation of Ketones 2624 3.2. Homogeneous Catalytic Hydrogenation in ILs 2624 3.3. Hydrogenation of Functionalized ILs 2625 3.3.1. Selective Hydrogenation of Polymers 2625 3.4. Asymmetric Hydrogenations 2626 3.4.1. Enantioselective Hydrogenation 2626 3.5. Role of the ILs Purity in Hydrogenation Reactions 2628

Catalysis in ionic liquids

The authors review the development of extended x-ray absorption fine structure (EXAFS) within the last decade. Advances in experimental techniques have been largely stimulated by the availability of synchrotron radiation. The theory of EXAFS has also matured to the point where quantitative comparison with experiments can be made. The authors review in some detail the analysis of EXAFS data, starting from the treatment of raw data to the extraction of distances and amplitude information, and they also discuss selected examples of applications of EXAFS chosen to illustrate both the strength and limitations of EXAFS as a structural tool.

Extended x-ray absorption fine structure—its strengths and limitations as a structural tool

We report spectra isolating the LIII x‐ray absorption threshold resonance of the elements iridium, platinum, and gold in the pure metallic state and in a variety of compounds. When normalized spectra obtained on the metals are subtracted from those obtained on the compounds, the resulting difference spectra are related to differences in the electronic structure of the absorber atom in the two types of environment. The change in area of a threshold resonance line obtained from such a difference spectrum can be related to the ionicity of the bonds of the absorber atom in its compounds. Measurements on supported platinum and iridium catalysts provide information on electronic changes in the metal due to the small size of the metal clusters or to interaction with the support material. Information on electronic changes due to interaction of the catalysts with gas molecules may also be obtained.

Effect of chemical environment on magnitude of x‐ray absorption resonance at LIII edges. Studies on metallic elements, compounds, and catalysts

Catalysis over Supported Metals. V. The Effect of Crystallite Size on the Catalytic Activity of Nickel

Nature of ruthenium-copper catalysts

Extended x‐ray absorption fine structure (EXAFS) studies were made in a series of highly dispersed metal catalysts to obtain structural information on the metal clusters present. Clusters of osmium, iridium, and platinum dispersed on silica or alumina were investigated. The metal clusters in the catalysts constituted 1.0 wt.% of the total mass. Chemisorption measurements indicated that the metal dispersions approached unity, where dispersion is defined as the ratio of surface metal atoms to total metal atoms in the clusters. When EXAFS data on the metal clusters are compared with data on the corresponding bulk metals, the lower average coordination number of the metal atoms in a cluster is evident. The decrease in coordination number is accompanied by an increase in the root mean square deviation of interatomic distance about the equilibrium value.

Extended x-ray absorption fine structure (EXAFS) of dispersed metal catalysts

A study was made of the extended x‐ray absorption fine structure (EXAFS) associated with the K absorption edges of ruthenium and copper in a silica supported ruthenium–copper catalyst containing 1.0 wt.% ruthenium and 0.63 wt.% copper (1:1 atomic ratio of ruthenium to copper). Previous chemisorption and catalysis studies indicated a strong interaction between the ruthenium and copper in the catalyst, and led to the suggestion that the catalyst consisted of bimetallic clusters of ruthenium and copper dispersed on the silica. The EXAFS data of this investigation provide information on the structure of the ruthenium–copper clusters. The ruthenium in the bimetallic clusters appears to be very similar to the ruthenium in a silica supported ruthenium reference catalyst, in that the ruthenium atoms are coordinated predominantly to other ruthenium atoms and only to a minor extent to copper atoms. By contrast, the copper atoms in the clusters have nearest neighbors which are more nearly equally distributed among c...

John H. Sinfelt

Papers

Effect of chemical environment on magnitude of x‐ray absorption resonance at LIII edges. Studies on metallic elements, compounds, and catalysts

Catalysis over Supported Metals. V. The Effect of Crystallite Size on the Catalytic Activity of Nickel

Nature of ruthenium-copper catalysts

Extended x-ray absorption fine structure (EXAFS) of dispersed metal catalysts

Structure of bimetallic clusters. Extended x-ray absorption fine structure (EXAFS) studies of Ru--Cu clusters