AN INVESTIGATION ON THE REACTION-MECHANISM FOR THE PARTIAL OXIDATION OF METHANE TO SYNTHESIS GAS OVER PLATINUM

The partial oxidation of methane to synthesis gas has been investigate d by admitting pulses of pure methane, pure oxygen and mixtures of met hane and oxygen to platinum sponge at temperatures ranging from 973 to 1073 K. On reduced platinum the decomposition of methane results in t he formation of surface carbon and hydrogen. No deposition of carbon o ccurs during the interaction of methane with a partly oxidised catalys t. Oxygen is present in three different forms under the conditions stu died: platinum oxide, dissolved oxygen and chemisorbed oxygen species. Carbon monoxide and hydrogen are produced directly from methane via o xygen present as. platinum oxide. Activation of methane involving diss olved oxygen provides a parallel route to carbon dioxide and water. Bo th platinum oxide and chemisorbed oxygen species are involved in the o xidation of carbon monoxide and hydrogen. In the presence of both meth ane and dioxygen at a stoichiometric feed ratio the dominant pathways are the direct formation of CO and H-2 followed by their consecutive o xidation. A Mars-van Krevelen redox cycle is postulated for the partia l oxidation of methane: the oxidation of methane is accompanied by the reduction of platinum oxide, which is reoxidised by incorporation of dioxygen into the catalyst.