Effect of Morphology on Catalytic Activity: Hydrocarbon Reforming Reactions on Platinum Crystal Surfaces.

摘要

During the last 50 years, one of the objectives of heterogeneous catalysis research has been to identify the surface atoms, the active sites, which catalyze each step in a reaction of interest. In general, the technique used is to vary the surface structure of the catalyst in a systematic way, and to observe the changes in activity and selectivity that may result. Three forms of metal catalysts have been used in these studies: Metal particles dispersed on porous supports, metal films and metal crystals. Crystals are used because their surface morphology can be determined with electron diffraction methods, and various structural features can be introduced in a controlled manner. In this work, five different faces of platinum single crystals were used to investigate the catalytic activity of three surface features: Flat, close-packed planes of metal atoms, edge atoms present at the termination of a flat plane, and corner atoms present at kinks, or zig-zags, in atomic steps. These may be thought of as models of atom groupings which may be present on metal particles in industrial catalysts. Several hydrocarbon-hydrogen reactions, representative of those that occur in commercial petroleum reforming processes, were studied.