The influence of metal oxides on the activity and selectivity of transition metal catalysts

The catalytic activity and selectivity of transition metals are known to be affected by metal oxides deposited on their surface. Such deposits can result from the transfer of portions of the support during catalyst preparation or be introduced intentionally. The structure and composition of both monolayer and multilayer deposits of metal oxides on Ph and Pt are discussed and the effects of oxide composition and coverage on the rate of CO and CO2 hydrogenation are examined. It is shown that the effectiveness of an oxide correlates with its Lewis acidity, and that the later property can be described by the Pauling electronegativity of the cations in the oxide. The effects of oxide deposits on other reactions are also reviewed.