Selective reduction of NO with propene over Ga2O3-Al2O3: Effect of sol-gelmethod on the catalytic performance

The effect of the preparation method on the activity of Ga2O3-Al2O3 for the selective reduction of NO with propene was investigated. Ga2O3-Al2O3 prepa red by the sol-gel method (Ga2O3-Al2O3(S)) exhibited excellent activity for NO reduction, compared with Al2O3, Ga2O3, and impregnated Ga2O3/Al2O3 (Ga2 O3/ Al2O3(I)). XRD measurements of Ga2O3-Al2O3(S) indicated that a part of the Al3+ ions in Al2O3 are substituted by Ga3+ ions, resulting in the forma tion of a composite oxide, [GaxAl(1-x)](2)O-3 (x < 1). On the other hand, G a2O3 particles and Al2O3 particles were found to be present separately for Ga2O3/Al2O3(I) The high catalytic activity of Ga2O3-Al2O3(S) was accounted for by the high surface area and the nature of the [GaxAl(1-x)](2)O-3 (x < 1) composite oxide, which was formed uniformly by the present sol-gel metho d. The comparison of the reactivity between NO and NO2 suggested the partic ipation of NO2 in NO reduction. The kinetic order for NO reduction was foun d to be 0.3 with respect to propene and 0.7 with respect to oxygen on both Ga2O3/Al2O3(I) and Ga2O3-Al2O3(S). However, a significant difference in the reaction order with respect to NO was observed between Ga2O3/Al2O3(I) and Ga2O3-Al2O3(S), 0.4 order on the former catalyst, and zero order on the lat ter one, indicating the presence of strongly adsorbed NOx species on the ca talyst surface. On the basis of these results, a reaction mechanism was pro posed in which the NOx adspecies formed through NO oxidation is reduced to nitrogen via organic intermediates containing nitrogen and oxygen. (C) 2000 Academic Press.