Supported gold catalysts for the total oxidation of alkanes and carbon monoxide

Gold catalysts on oxide supports prepared by coprecipitation (CoOx, MnOx, CuO, Fe2O3 and CeO2), deposition-precipitation (TiO2) and impregnation (CoOx and MnOx) have been characterised and tested for the total oxidation of methane, ethane and propane, and the catalytic activity was contrasted with their performance for oxidation of CO at ambient temperature. Many of the oxides selected as supports are active alkane activation catalysts at high temperature (e.g. MnOx and CoOx). The addition of gold to these active materials for the alkane combustion leads to a marked increase in the catalytic activity in all cases investigated. All the supports were active for the oxidation of alkanes but the addition of gold leads to a decrease in the temperature at which oxidation is first observed. The most effective catalyst for alkane oxidation was Au/CoOx which was found to retain constant high activity for a 48 h test period, and the highest activity catalysts were prepared by coprecipitation rather than impregnation. Interestingly, no correlation between alkane oxidation and CO oxidation was apparent in these studies indicating that different mechanisms of oxygen activation and/or different active sites are involved. This is discussed in terms of recent observations concerning selective versus total oxidation with gold catalysts.