Molecular studies of model surfaces of metals from single crystals to nanoparticles under catalytic reaction conditions. Evolution from prenatal and postmortem studies of catalysts.
ABSTRACT Molecular level studies of metal crystal and nanoparticle surfaces under catalytic reaction conditions at ambient pressures during turnover were made possible by the use of instruments developed at the University of California at Berkeley. Sum frequency generation vibrational spectroscopy (SFGVS), owing to its surface specificity and sensitivity, is able to identify the vibrational features of adsorbed monolayers of molecules. We identified reaction intermediates, different from reactants and products, under reaction conditions and for multipath reactions on metal single crystals and nanoparticles of varying size and shape. The high-pressure scanning tunneling microscope (HP-STM) revealed the dynamics of a catalytically active metallic surface by detecting the mobility of the adsorbed species during catalytic turnover. It also demonstrated the reversible and adsorbate-driven surface restructuring of platinum when exposed to molecules such as CO and ethylene. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) detected the reversible changes of surface composition in rhodium-palladium, platinum-palladium, and other bimetallic nanoparticles as the reactant atmosphere changed from oxidizing to reducing. It was found that metal nanoparticles of less than 2 nm in size are present in higher oxidation states, which alters and enhances their catalytic activity. The catalytic nanodiode (CND) confirmed that a catalytic reaction-induced current flow exists at oxide-metal interfaces, which correlates well with the reaction turnover.
- SourceAvailable from: Matjaž Kavčič[Show abstract] [Hide abstract]
ABSTRACT: Non-magnetic Pt catalysts, supported on carbon coated magnetic Co nanoparticles, changed catalytic performance in the presence of an external magnetic field. This behavior relates to an electronic change of Pt induced by a localized magnetic field, which modifies the CO adsorption geometry. In situ resonant inelastic X-ray scattering (RIXS) experiments and theory reveal the change of atop CO adsorption geometry on the Pt catalyst to bridged geometry under an external magnetic field. This observation opens the possibility of catalytic control by means of an external magnetic field.Nanoscale 07/2013; · 6.73 Impact Factor
Article: Concluding remarks.[Show abstract] [Hide abstract]
ABSTRACT: At the end of such a successful International Conference you would, I know, wish me to express our collective thanks for all the hard, patient work of the many people who have engineered this impressively smooth organisation. Priority must go to Christian Janot, Albert Wright and Bernt Maier who, between them have carried the load of formulating policy, arranging funding, deciding on administrative arrangements and selecting scientific committees and who will now start the difficult task of editing the Proceedings. The ILL has, of course, contributed enormously to the success of the meeting, not just in providing hospitality, financial assistance and a generous committment of personnel but through the encouragement offered by the past director Dr. B.E.F. Fender and the current director, Professor R. Haensel. Then there is the small army of people who have played a role 'behind-the-scenes' and who are mentioned below. To all these we extend our sincere thanks.Faraday Discussions 01/2013; 162:395-401. · 3.82 Impact Factor
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ABSTRACT: Mesoporous SiO(2), Al(2)O(3), TiO(2), Nb(2)O(5), and Ta(2)O(5) were synthesized through a soft-templating approach by a self-assembled framework of Pluronic P123 and utilized for the preparation of 3-dimensional catalysts as supports. Colloidal Pt nanoparticles with an average diameter of 1.9nm were incorporated into the mesoporous oxides by sonication-induced capillary inclusion. The Pt nanoparticles supported on mesoporous oxides were evaluated in the hydrogenation reaction of furfural (70torr furfural and 700torr H(2) with a balance of He) to study the effect of catalyst supports on selectivity. In the temperature ranges of 170-240°C, the major products of this reaction were furan, furfuryl alcohol, and 2-methyl furan through a main reaction pathway of either decarbonylation or carbonyl group hydrogenation. While Pt nanoparticles with the size ranges of 1.5-7.1 exhibited strong structure-dependent selectivity, various supports loaded with only 1.9nm Pt nanoparticles produced dominantly furan as a major product. Compared to the inert silica support, TiO(2) and Nb(2)O(5) facilitated an increase in the production of furfuryl alcohol via carbonyl group hydrogenation as a result of a charge transfer interaction between the Pt and the acidic surface of the oxides. The same trend was confirmed on 2-dimensional type catalysts, in which thin films of SiO(2), Al(2)O(3), TiO(2), Nb(2)O(5), and ZrO(2) were prepared as supports. When furfural hydrogenation was conducted (1torr furfural, 100torr H(2), and 659torr He) over Pt nanoparticle monolayers deposited on oxide substrates, only TiO(2) was shown to increase the production of furfuryl alcohol, while other oxides produced furan.Journal of Colloid and Interface Science 11/2012; · 3.55 Impact Factor