A catalyst made by the introduction of copper ions and cobalt ions into a Y-type zeolite to produce a CuCoY zeolite improves the reduction of NOx in exhaust from a lean burn engine, such as a diesel engine. A dual bed selective reduction reactor in the exhaust stream comprising a first bed of BaY or of Ag/alumina and a second bed of CuCoY is particularly effective in reduction of NOx. In one embodiment, the exhaust stream is suitably treated with an oxidant, such as ozone, and a reductant, such as a diesel hydrocarbon or oxygenated diesel hydrocarbon, before the exhaust passes in contact with the dual bed catalyst.