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 prese nce of oxygen over sol-gel alumina supported indium, gallium, cobalt a nd tin catalysts. The support alumina prepared by a sol-gel method had high surface area and accordingly active alumina sites for the reacti on. Particularly indium/alumina showed a high activity to reduce NO pr eferably by propene, propane and ethene but also by alcohols in the ab sence and the presence of water vapor, The activities of alumina suppo rted cobalt, silver and tin catalysts were increased when calcinating the catalysts at 800 degrees C instead of 600 degrees C. In the case o f gallium/alumina, NO2 has higher reactivity than NO to nitrogen when propene was used as a reductant, proving the significance of the oxida tion step of NO to NO2. The step of NO oxidation was promoted by prepa ring a physical mixture of 5 wt% Mn3O4 with indium/alumina or gallium/ alumina. The NO conversion to nitrogen was increased from 58 to 84% wi th the manganese oxide promotion over indium/alumina in the presence o f water. The reaction mechanistic differences between the alumina supp orted catalysts and Cu/ZSM-5 were also discussed. (C) 1998 Elsevier Sc ience B.V.