Studies of metal-support interactions with "real" and "inverted" model systems: reactions of CO and small hydrocarbons with hydrogen on noble metals in contact with oxides

Two types of model catalysts are compared: thin film catalysts consisting o f polyhedral noble metal nanocrystals (Rh and Pt) supported by reducible an d non-reducible oxides, and their inverted pendants, submonolayers of titan ia and vanadia deposited under UHV conditions on the respective metal surfa ces (Pd and Rh(111) and Rh (polycrystalline)). The structure and compositio n of the inverse catalysts were examined in situ by LEED and AES and the na noparticles were characterized by HRTEM. The activity of thin film and inve rse catalysts was studied in a series of reactions, such as the ring openin g of methylcyclopentane and methylcyclobutane, the dissociation of CO and t he CO methanation. Reaction conditions comprise atmospheric pressure but al so molecular beam experiments. The reaction rates are related to the oxidat ion state of the supporting oxide, to the free metal surface area and to th e number of sites at the interface between metal and support.