Nanofabrication of model catalysts and simulations of their reaction kinetics

Abstract

Nanofabrication of Pt particles on SiO 2 , with particle sizes and separations down to ∼20 nm , and more complex structures consisting of Pt particles deposited on top of CeO 2 islands, have been made by electron beamlithography and lift-off techniques. Under catalyticreaction conditions (nonflammable mixture of H 2 +O 2 in Ar at 1000 K, 1 atm) the originally deposited, disk-shaped, and polycrystalline particles, transform to three-dimensional crystalline particles. This restructuring is attributed to the surfactant role of oxygen (promoting Pt mobility), and the nonwetting of late transition metals on oxides. The exothermic H 2 +O 2 reaction is a possible additional driving force. The catalytic kinetics on 3D crystalline particles with well-defined facet planes were explored by Monte Carlo simulations. The latter demonstrate that the catalytic kinetics on nm sized, crystalline particles may be absolutely unique and nonpredictable from single-crystal studies, primarily due to the diffusive mass transport between differently oriented facets on the particles.