Complete combustion of methane over indium tin oxides catalysts.

Indium tin oxide (ITO) catalysts with different In/Sn ratios have been prepared by the co-precipitation method. The catalysts were evaluated for methane combustion at different temperatures (673-873 K) with a space velocity of 30 000 h(-1). The results showed that methane could be completely oxidized at 873 K with ITO catalysts. Doping an appropriate amount of tin into In2O3 could greatly improve its activity, while the performances of Indium-doped tin oxides were worse than that of SnO2. A significant improvement of the activity was obtained on the catalyst In8Sn2, which contains 80 wt. % of indium oxide and 20 wt. % of tin oxide. Crystal defection and the amount of oxygen vacancy caused by doping were the main factors that would affect catalytic activity of ITO catalysts. The catalytic activity is strongly inhibited by the presence of a large amount of water vapor at the entire temperature range, while only the activity at low temperature (under 823 K) decreased in the presence of sulfur dioxide. By doping Sn into In2O3, its tolerance to SO2 could be enhanced due to the higher resistance of SnO2.