Catalytic combustion of carbon by alkali metal carbonates supported on perovskite-type oxide

Catalytic activity of alkali metal carbonates was studied for the combustion of activated carbon grains at 673-773 K by supporting the carbonates on carbon, alumina, and a perovskite-type oxide (La0.8Sr0.2Cr0.5Mn0.45Pt0.05O3, LSCMP). Catalytic activity of V2O5/gamma-Al2O3 as a typical. transition metal oxide catalyst was also measured for comparison. Potassium carbonate supported on the carbon exhibited the largest initial rate of the combustion among the catalysts at 723 K, while the achieved conversion within 3 h increased almost proportional to the ratio of alkali metal to carbon. V2O5 gamma-Al2O3 also showed linear increase 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, indicating a very large catalytic turnover number while the initial activity was comparable to that of the same salts on carbon. However, the carbonate supported on gamma-Al2O3 and LSCMP alone showed very limited activity, The carbonate supported on LSCMP showed higher activity than carbonates supported on carbon at 673 K. The alkali carbonate seems to be active at lower temperatures on LSCMP. The activities of other alkali 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 active species on the support in the catalytic combustion. The unique roles of LSCMP are deduced.