HYDROGENATION OF NORBORNADIENE ON SUPPORTED METAL-CATALYSTS - EVIDENCE FOR A NOVEL MECHANISM OF HYDROGEN ACTIVATION

Norbornadiene hydrogenates on Cu and Au dispersed on basic supports such as MgO to give significant yields of nortricyclene in addition to norbornene and norbornane, whereas only the latter products are found using Pt on the same supports as catalysts. This novel finding is evidence for a mechanism where surface olefin-metal complexes and not the metal atoms per se are directly involved in activating molecular hydrogen. Dissociation of H-2 is then a step which occurs simultaneously with the addition of the first H atom to the adsorbed olefin and is not a prior independent event, as is thought to be the case in conventional mechanisms. The new mechanism helps to explain why metals with low or negligible capacity for hydrogen chemisorption, e.g. Pt/TiO2 after high temperature reduction, are still very effective hydrogenation catalysts.