Spinel powders with additions of Zn2+, Ni2+, Mn2+ and Fe2+ cations into Ga2O3-Al2O3 were synthesized by a co-precipitation method from a mixed solution of nitrate salts in the presence of aqueous ammonia. Effective reduction of NO to N-2 using hydrocarbon in the presence of a high concentration of O-2 can be accomplished using spinel-type catalysts. Among the catalysts tested, 30 mol% ZnO-containing Ga2O3-Al2O3 with a pure spinel phase structure exhibited the highest catalytic activity for NO reduction. The addition of ZnO further enhanced the activity of Ga2O3-Al2O3 over a wide temperature region. The high activity of ZnO-Ga2O3-Al2O3 was attributed to the spinel-type structure and could be qualitatively correlated with acid-base centers. Combined effect of H2O vapor and SO2 on ZnO-Ga2O3-Al2O3 catalyst for the reduction of NO by C2H4 at 500 degreesC was also studied. (C) 2004 Elsevier B.V. All rights reserved.