Full Text for Volume 47 Number 1 (January 2003)

Among items appearing in this issue are the following:

The basic principles of the semiconductor-sensitised photochemistry of water, mainly using titania as the semiconductor photocatalyst, are discussed by Professor Andrew Mills and Soo-Keun Lee of the University of Strathclyde, Scotland. Depositing a platinum group metal or oxide onto the titania surface can often improve the overall efficiency of the photoreactions. Various methods of depositing the platinum metal or oxide are examined, with particular attention being given to a photodeposition process that uses a sacrificial electron donor to mop up the electrons produced in the photoreaction. Semiconductor photocatalysts coated with a platinum metal or oxide are prominent in heterogeneous systems involved in the photoreduction, photooxidation and photocleavage of water. There has been renewed interest recently in this photochemistry but concerns remain over reproducibility, longevity and the nature of the photoreactions.

The European Technical Director of Johnson Matthey Catalytic Systems Division, Martyn V. Twigg, comments on advances in emissions control technology discussed at the 2002 World Congress of the Society of Automotive Engineers (SAE) in Detroit. He describes the continuing progress being made by various companies concerned in the control of exhaust gas pollutant emissions, especially key trends in catalyst emissions control systems that depend upon platinum group metal catalysts.

The Catalyst Life Cycle conference, held at the University of Bath, U.K., in September, 2002, is reviewed by Stephen Poulston and Stephen Pollington of the Johnson Matthey Technology Centre. They report on the talks given at this biannual meeting on platinum metals catalyst deactivation/regeneration and on such diverse areas as large scale industrial reactions, automotive catalysis, fuel cells and fine chemical synthesis.

Palladium carbonyl clusters, where the palladium is in the (+1) formal oxidation state, and derivatives of these clusters are examined by Tatiana A. Stromnova of N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow. Tetranuclear 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.

F. A. Lewis, formerly of Queen’s University, Belfast, Nothern Ireland, has been involved in research on hydrogen diffusion in palladium and palladium alloys for many years. Here, with colleagues, he comments on the interpretation of some ‘uphill effects’ of the hydrogen diffusion coefficient in Pd₇₇Ag₂₃ alloy membranes that can occur due to Gorsky Effect and lattice strain gradient factors.

Donald S. Cameron reviews the first of a new series of biannual European fuel cell conferences entitled "Fuel Cells - Science and Technology 2002" which was held in Amsterdam, in September, 2002. These conferences are to be alternated with the Grove Symposium, giving a balance between the scientific and commercial aspects of the technology. The conference theme: ‘Scientific Advances in Fuel Cell Systems’, was chosen to focus on the scientific challenges posed by the introduction of these novel power generators.

Three short items are typical of the vast range of platinum group metals research that is being undertaken worldwide.

One item reports work by researchers at the University of St. Andrews, Scotland, who successfully used a new ligand, a diphenylphosphine functionalised polyhedral oligomeric silsesquioxane (POSS) dendrimer (with 16 or 48 diphenylphosphine end groups), for the rhodium-catalysed hydroformylation of oct-1-ene. Unexpectedly high regioselectivity to the linear aldehyde (86%) was obtained with a POSS dendritic ligand (with five atoms between the P atoms, and C-Si linkage).

Researchers at the University of Tokyo have developed an efficient heterogeneous ruthenium/alumina catalyst that can oxidise alcohols with 1 atm of oxygen or air, without additives. The catalyst has high activity for oxidising activated and non-activated alcohols, with selectivity of over 97%. Even less reactive primary alcohols (1-octanol and 1-decanol) could be oxidised. The catalyst system is reusable.

The temperature dependence of the light-switching effect in the ruthenium complex, [Ru(bpy)₂dppz]²⁺, has been researched by scientists at the University of North Carolina, Chapel Hill, U.S.A. Excited-state lifetime measurements taken in protic and aprotic solvents suggest that the light-switch effect is a competition between energetic factors (for darkness) and entropic factors (for light) and is not due to a state reversal. The dppz ligand has phz-like and bpy-like states, with the phz being associated with the dark state and the bpy being associated with the bright state.

The issue also contains a selection of abstracts based on recently published patent and scientific literature and ends with another of David Grove’s ‘Final Analysis’ items. Here, David describes how an additive can change the activity of a catalyst and how industrial catalysts become deactivated. He includes some measures that can be taken to improve catalyst performance.

Platinum Metals Review is available on the internet from the publications section of the Platinum Today site or from the host site Ingenta Select.

Susan V. Ashton
Editor

Anyone with an active interest in the platinum group metals and their uses who does not have ready access to a copy of Platinum Metals Review and who may benefit from reading it, is invited to request a specimen copy from:

The Editor, Johnson Matthey PLC, Orchard Road, Royston, Hertfordshire SG8 5HE, United Kingdom; Fax +44 (0) 1763 256359; Email jmpmr@matthey.com