Surface-Bonded Precursor Determines Particle Size Effects for Alkene Hydrogenation on Palladium

摘要

Reactions of linear alkenes with metal surfaces have been previously studied on model catalyst systems with varying degrees of complexity, from single crystals to metal particles deposited on well-ordered oxide films.[1]-[15] Based on these studies, the majority of which were conducted with ethene, it has been suggested that alkene hydrogenation is structure insensitive. This means that the reaction only depends on the number of metal atoms on the surface and is independent of the crystallographic orientation of the particle facets and particle size. These size effects are difficult to study in real catalytic systems because the mean particle size and distribution cannot be controlled accurately. Herein, we report the particle size effects on alkene reactivity (ethene and trans-2-pentene) using well-defined Pd/Al_2O_3 model catalysts, where the particle size can be varied in a controllable manner.