A catalyst system for the reduction of NO.sub.x is disclosed. One embodiment of the catalyst system is based on a catalyst in a first zone, including a catalyst support, gallium, and at least one promoting metal; and a catalyst in the second zone following the first zone. The second-zone catalyst includes a second catalyst support and a zeolite material. The catalyst system further includes a gas stream comprising an organic reductant, such as a hydrocarbon material or a compound containing oxygen or nitrogen. A method for reducing NO.sub.x, utilizing the catalyst system, is also described.