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Various catalytic control strategies must be carefully considered in order to make substantial progress towards meeting che more stringent NOx and hydrocarbon emission standards being proposed for the 1990s. In the development of newer catalyst technologies, this paper discusses the effects of noble metal loadings, catalyst volumes, improved washcoat technologies, base metal promoters/stabilizers, and air/fuel ratio operation on catalyst performance. The effect of various vehicle systems on FTP modal catalyst performance determined the factors influencing NOx control over selected vehicles. The results of these studies indicate that improvements in catalyst technologies will need to be systematically coupled with improvements in system control technology to simultaneously optimize the total emission system to achieve the more stringent standards being proposed.