Now utilising more than one third of the Western World’s demand for platinum, it is interesting to recall that the use of platinum metals catalysts to control the emissions from gasoline fuelled, spark ignition engines has only arisen in the last twenty years. A concise account of the major technical and scientific advances made during this time has recently been given by Kathleen C. Taylor, of the General Motors Research Laboratories (Chemtech ., 1990, 20, (9), 551-555).

Initially the control of carbon monoxide and gaseous hydrocarbons was achieved by the use of platinum and palladium. After 1981 more stringent standards were introduced, including a new requirement to decrease nitrogen oxides emissions. The approach adopted was to oxidise the first two components while simultaneously reducing the latter. Including rhodium in the catalyst formulation enables this to be achieved. Cerium oxide additions also improve the performance of these “three-way” catalysts, while engine controls ensure that the air-to-fuel ratio is maintained at the stoichiometric composition, where platinum-rhodium catalysts promote the conversion of the three major pollutants simultaneously.

Further work is still required, for example, to improve catalyst activity under cold-start conditions and tolerance of high temperatures. The development of catalytic converters has already contributed to significantly lower vehicle emissions and improved air quality, and to our knowledge of platinum metals catalysis.