Catalytic Control of Nitrogen Oxide Emissions from Motor Vehicles

Abstract

Regulations requiring stricter control of nitrogen oxide (NOx) emissions from automobiles came into force in 1981 in the United States. This has necessitated the development of new catalyst systems that are capable of controlling NOx as well as hydrocarbon and carbon monoxide emissions from spark ignition engines. These devices are known as three-way catalysts, and the development of these catalysts is traced from the first major commercial use of NOx control catalysts, ie. those employed on stack gas clean-up on nitric acid plants. Current European and US legislation on automobile NOx emissions is summarised and the effect of engine fuelling on NOx production is discussed. Reaction mechanisms involved in three-way catalysts, catalyst composition, catalyst performance, products found, and the effect on fuel consumption are presented. Although catalytic clean-up devices are the best developed and most practical method of emission control currently available, an ideal solution would be to reduce NOx emissions at source. Novel catalytic methods available for this are discussed.