Nanofabrication of model catalysts and simulations of their reaction kinetics

Nanofabrication of Pt particles on SiO2, with particle sizes and separation s down to similar to 20 nm, and mon complex structures consisting of Pt par ticles deposited on top of CeO2 islands, have been made by electron beam li thography and lift-off techniques. Under catalytic reaction conditions (non flammable mixture of H-2 + O-2 in Ar at 1000 K, 1 atm) the originally depos ited, disk-shaped, and polycrystalline particles, transform to three-dimens ional crystalline particles. This restructuring is attributed to the surfac tant role of oxygen (promoting Pt mobility), and the nonwetting of late tra nsition metals on oxides. The exothermic H-2 + O-2 reaction is a possible a dditional driving force. The catalytic kinetics on 3D crystalline particles with well-defined facet planes were explored by Monte Carlo simulations. T he latter demonstrate that the catalytic kinetics on nm sized, crystalline particles may be absolutely unique and nonpredictable from single-crystal s tudies, primarily due to the diffusive mass transport between differently o riented facets on the particles. (C) 1999 American Vacuum Society. [S0734-2 101(99)03801-4].