Enhanced activity of In and Ga-supported sol-gel alumina catalysts for NO reduction by hydrocarbons in lean conditions

Nitrogen monoxide was reduced efficiently by hydrocarbons in the presence of oxygen over sol-gel alumina supported indium, gallium, cobalt and tin catalysts. The support alumina prepared by a sol-gel method had high surface area and accordingly active alumina sites for the reaction. Particularly indium/alumina showed a high activity to reduce NO preferably by propene, propane and ethene but also by alcohols in the absence and the presence of water vapor, The activities of alumina supported cobalt, silver and tin catalysts were increased when calcinating the catalysts at 800 degrees C instead of 600 degrees C. In the case of gallium/alumina, NO(2) has higher reactivity than NO to nitrogen when propene was used as a reductant, proving the significance of the oxidation step of NO to NO(2). The step of NO oxidation was promoted by preparing a physical mixture of 5 wt% Mn(3)O(4) with indium/alumina or gallium/alumina. The NO conversion to nitrogen was increased from 58 to 84% with the manganese oxide promotion over indium/alumina in the presence of water. The reaction mechanistic differences between the alumina supported catalysts and Cu/ZSM-5 were also discussed. (C) 1998 Elsevier Science B.V.