Abstract: Impure gas streams containing contaminating amounts of NO.sub.x, e.g., automotive exhaust fumes and industrial waste gases, are purified by contacting same, in the presence of ammonia, at an elevated temperature, with a catalyst composition which comprises an inorganic oxide support substrate having a catalytically effective amount of a metal oxide active phase deposited thereon, such support substrate comprising at least one alumina, aluminate, titanium dioxide and/or zirconium dioxide and such catalytically active phase comprising at least one vanadium oxide and/or molybdenum oxide and/or tungsten oxide, the surface of the support substrate being chemically bonded to the metals V and/or Mo and/or W and the catalyst being devoid of V.sub.2 O.sub.3 and/or MoO.sub.3 and/or WO.sub.3 crystalline phases, and thereby selectively reducing such NO.sub.x values while minimizing the formation of N.sub.2 O.

Abstract: Impure gas streams containing contaminating amounts of NO.sub.x, e.g., automotive exhaust fumes and industrial waste gases, are purified by contacting same, in the presence of ammonia, at an elevated temperature, with a catalyst composition which comprises an inorganic oxide support substrate having a catalytically effective amount of a metal oxide active phase deposited thereon, such support substrate comprising at least one alumina, aluminate, titanium dioxide and/or zirconium dioxide and such catalytically active phase comprising at least one vanadium oxide and/or molybdenum oxide and/or tungsten oxide, the surface of the support substrate being chemically bonded to the metals V and/or Mo and/or W and the catalyst being devoid of V.sub.2 O.sub.3 and/or MoO.sub.3 and/or WO.sub.3 crystalline phases, and thereby selectively reducing such NO.sub.x values while minimizing the formation of N.sub.2 O.