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A series of zeolite based diesel catalysts has been examined on IDI and DI engines on engine test benches, and in the respective cars. These zeolites have been modified by hydrogen exchange, rare-earth metal exchange and transition metal doping. The features of the zeolite based diesel catalysts are a similar emission reduction of particulate matter, a lower hydrocarbon and carbon monoxide emission reduction, a significantly lower degree of sulphate formation at higher exhaust gas temperatures, compared to that of diesel catalysts containing noble metals, cost reduction by avoiding noble metal as the active component. Some typical emission changes, related to engine-out emissions, from stationary engine dynamometer tests are (in percent): Some typical relative emission changes from chassis dynamometer tests (FTP) are: The diesel exhaust reaction mechanism at the zeolite based catalysts is assumed to be a mixture of hydrocarbon cracking and oxidation.