NO.sub.x in an exhaust gas stream is oxidized in a first stage oxidation catalyst thereby forming NO.sub.2. In a subsequent stage, the NO.sub.2 is directed to a lean NO.sub.x trap whereat NO.sub.2 is reduced to N.sub.2. Hydrocarbon fuel is controllably injected into the gaseous stream at a position upstream of the lean NO.sub.x trap. Carbon is oxidized in a carbon trap positioned downstream from the lean NO.sub.x trap.
Magdi K. Khair; Charles T. Hare