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 act ivity of chromium and cobalt oxides supported on gamma-alumina were in vestigated. Two methods, physical mixing and coimpregnation, were used for the addition of additives in the catalysts. The combustion of car bon monoxide and ethane was carried out in a fixed-bed differential re actor. The physical properties of catalysts were characterized by temp erature-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 t he reducibility and the catalytic oxidation activity of chromium oxide is strongly affected by the presence of this cobalt aluminate. Invest igations on carbon monoxide oxidation indicate that the addition of a base additive to the chromium and cobalt oxides catalyst can enhance t he carbon monoxide oxidation, but that acid additives decrease oxidati on. On the other hand, the study of ethane combustion indicates that t he addition of a base additive to the catalyst can reduce the ethane c onversion, although the selectivity of carbon dioxide is increased up to 100%. Moreover, addition of an acid additive to the catalyst can en hance the ethane conversion; however, the selectivity for carbon dioxi de is reduced.