Hydrogenaton on Metal Surfaces:Why are Nanoparticles More Active than Single Crystals?

摘要

Hydrogenation of unsaturated hydrocarbons occurs efficiently on noble-metal catalysts,such as platinum,rhodium,and palladium.~[1] The reaction mechanism first proposed by Horiuti and Polanyi~[2]in 1934 proceeds by a) hydrogen dissociation on the metal surface,b) alkene adsorption,c) subsequent hydrogen addition to alkene and,finally,d) desorption of the product (alkane).Real hydrogenation catalysts represent very complex systms for studying reaction mechanisms at the molecular level.Therefore,model systems with a reduced complexity have been invoked ranging from single crystals to metal particls deposited on oxide films.~[3-8] The conclusions regawrding reaction mechanism and structural sensitivity are often based upon experiments on single metal crystals.~[3] In particulawr,hydrogenation of alkenes has been shown to be structure insensitive.