Platinum Metals Review - Volume 47, Issue 1, 2003

The basic principles of semiconductor photochemistry, particularly using titania as a semiconductor photocatalyst, are discussed. When a platinum group metal or its oxide is deposited onto the surface of a sensitised semiconductor the overall efficiency of the reactions it takes part in are often improved, especially when the deposits are used as hydrogen and oxygen catalysts, respectively. Methods of depositing metal or metal oxide are examined, and a particular focus is given to a photodeposition process that uses a sacrificial electron donor. Platinum group metal and platinum group metal oxide coated semiconductor photocatalysts are prominent in heterogeneous systems that are capable of the photoreduction, oxidation and cleavage of water. There is a recent renaissance in work on water-splitting semiconductor-sensitised photosystems, but there are continued concerns over their irreproducibility, longevity and photosynthetic nature.

Some palladium carbonyl clusters containing the palladium in the (+1) formal oxidation state, and derivatives of these clusters investigated in our laboratories are examined in this paper. In particular, letranuclear carbonyl carboxylates of palladium are discussed as a model of key intermediates in various processes, including CO oxidation by a palladium catalyst with molecular oxygen as the oxidant. A second type of cluster, a palladium cationic cluster which contains N-donor ligands acts as a catalyst precursor for processes such as exhaust gas purification. A third type of palladium carbonyl cluster includes bimetallic compounds which catalyse new reactions, such as the low-temperature dehydration of alcohols.