Catalytic Properties of High-Density Monodispersive Metal Nanostructures
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Catalytic Properties of High-Density Monodispersive Metal Nanostructures Sergey A. Gurevich, Irina N. Yassievich, Vladimir M. Kozhevin, Denis A. Yavsin, Mihail A. Zabelin, Pavel A. Tret’yakov, Tat’yana N. Rostovshikova1, and Vladimir V. Smirnov1 A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, 26, Politekhnicheskaya, St. Petersburg, 194021, Russia 1 Chemistry Department, Moscow State University, Vorob'evy gory, Moscow, 119899, Russia ABSTRACT We report on ultra-high catalytic activity of high-density monodispersive Cu and Ni nanostructures fabricated by newly developed laser electrodispersion technique. In these structures the particle sizes are 5 nm for Cu and 2.5 nm for Ni (relative size dispersion is less than 20%). Due to fast cooling during particle formation Cu and Ni grains have amorphous structure. The catalytic activity of Cu-based structures were studied in chlorohydrocarbons transformations reactions, while Ni structures were tested in the reaction of 1-nonene hydrogenation. The measured catalytic activity vs. particle surface density dependencies exhibit a maximum corresponding to densely packed one-layer granulated films. About an order of magnitude increase in the catalytic activity is observed when increasing the dielectric permittivity of the reactant solution. It is suggested that the observed high catalytic activity is due to thermally activated interparticle electron tunneling, which results in the appearance of negatively and positively charged particles in densely packed granulated films. INTRODUCTION Besides the fundamental interest in understanding the phenomena at a solid surface a large part of activity is related to insight in chemical surface reactions and, in particular, in heterogeneous catalysis. Last years a new direction in heterogeneous catalysis become more and more important, i.e. the catalysis by nanostructured materials. Most of the nanostructured catalysts consist of the particles with the size ranging form hundreds down to several nanometers. In nanoparticles the number of surface atoms is comparable with that in the volume and the radius of surface curvature is extremely small. In general, it is precisely these factors that provide enhanced catalytic activity of nanostructures when compared to their bulk counterparts. A number of chemical reactions of practical meaning are best catalyzed by metals such as Сu, Pt, Pd, Ni, Fe, Сo, etc. The key factor offering the catalytic activity of a particular metal in the particular reaction is the appropriate change of reagent molecule energy levels in course the molecule approaches the surface. Constituting the major effect of chemisorption this energy level transformation guides the chemical reaction in the energy preferable way, which may be the only practical way attainable due to thermal activation. As for metallic nanoparticles the requirements for lowering the activation barriers provided by chemisorption remain in force. However, some additional factors come into play as well. Most important is that th
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