EFFECTS OF ACID OR BASE ADDITIVES ON THE CATALYTIC COMBUSTION ACTIVITY OF CHROMIUM AND COBALT OXIDES

The effects of acid and base additives on the catalytic combustion activity of chromium and cobalt oxides supported on gamma-alumina were investigated. Two methods, physical mixing and coimpregnation, were used for the addition of additives in the catalysts. The combustion of carbon monoxide and ethane was carried out in a fixed-bed differential reactor. The physical properties of catalysts were characterized by temperature-programmed reduction, UV-vis diffuse reflectance, X-ray powder diffraction, and temperature-programmed desorption of ammonia. It is concluded that the cobalt phase is present primarily as CoAl2O4, but the reducibility and the catalytic oxidation activity of chromium oxide is strongly affected by the presence of this cobalt aluminate. Investigations on carbon monoxide oxidation indicate that the addition of a base additive to the chromium and cobalt oxides catalyst can enhance the carbon monoxide oxidation, but that acid additives decrease oxidation. On the other hand, the study of ethane combustion indicates that the addition of a base additive to the catalyst can reduce the ethane conversion, although the selectivity of carbon dioxide is increased up to 100%. Moreover, addition of an acid additive to the catalyst can enhance the ethane conversion; however, the selectivity for carbon dioxide is reduced.