CATALYTIC CHEMISTRY OF SUPPORTED PALLADIUM FOR COMBUSTION OF METHANE

The high-temperature catalytic chemistry of supported palladium for methane oxidation has been studied. Palladium oxide supported on alumina decomposes in two distinct steps in air at one atmosphere. The first step occurs between 750 and 800-degrees-C and is believed to be a decomposition of palladium-oxygen species dispersed on bulk palladium metal designated (PdO(x)/Pd). The second decomposition is between 800 and 850-degrees-C and behaves like crystalline palladium oxide designated (PdO). To reform the oxide, the temperature must be decreased well below 650-degrees-C. Thus, there is a significant hysteresis between decomposition to palladium and re-formation of the oxide. Above 500-degrees-C, methane oxidation occurs readily when the catalyst contains PdO. However, when only palladium metal is present no oxygen adsorption occurs and no methane activity exists. One may conclude that the high temperature (> 500-degrees-C) activity of a supported palladium containing catalyst is due to the ability of palladium oxide to chemisorb oxygen. Palladium, as a metal, does not chemisorb oxygen above 650-degrees-C and thus, is completely inactive toward methane oxidation.