CATALYTIC COMBUSTION OF CARBON BY ALKALI-METAL CARBONATES SUPPORTED ON PEROVSKITE-TYPE OXIDE

Catalytic activity of alkali metal carbonates was studied for the comb ustion of activated carbon grains at 673-773 K by supporting the carbo nates on carbon, alumina, and a perovskite-type oxide (La0.8Sr0.2Cr0.5 Mn0.45Pt0.05O3, LSCMP). Catalytic activity of V2O5/gamma-Al2O3 as a ty pical. transition metal oxide catalyst was also measured for compariso n. Potassium carbonate supported on the carbon exhibited the largest i nitial rate of the combustion among the catalysts at 723 K, while the achieved conversion within 3 h increased almost proportional to the ra tio of alkali metal to carbon. V2O5 gamma-Al2O3 also showed linear inc rease of achieved conversion with the amount of catalyst, although the slope was much smaller, indicating that the catalytic turnover number is limited. In contrast, the carbonate supported on LSCMP showed high conversion at an alkali metal to carbon ratio as low as 0.012, indica ting a very large catalytic turnover number while the initial activity was comparable to that of the same salts on carbon. However, the carb onate supported on gamma-Al2O3 and LSCMP alone showed very limited act ivity, The carbonate supported on LSCMP showed higher activity than ca rbonates supported on carbon at 673 K. The alkali carbonate seems to b e active at lower temperatures on LSCMP. The activities of other alkal i carbonates were also measured to examine the role of LSCMP support. Results are discussed from the view point of the reductive activation of the alkali metal salts, sublimation, trapping, and escape of the ac tive species on the support in the catalytic combustion. The unique ro les of LSCMP are deduced.