Nanofabrication of model catalysts and simulations of their reaction kinetics

Nanofabrication of Pt particles on SiO2, with particle sizes and separations down to ∼20 nm, and more complex structures consisting of Pt particles deposited on top of CeO2 islands, have been made by electron beam lithography and lift-off techniques. Under catalytic reaction conditions (nonflammable mixture of H2+O2 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 H2+O2 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.