PARTIAL OXIDATION OF METHANE TO CARBON-MONOXIDE AND HYDROGEN WITH MOLECULAR-OXYGEN AND NITROUS-OXIDE OVER HYDROXYAPATITE CATALYSTS

Hydroxyapatites catalyze the partial oxidation of methane to carbon monoxide and hydrogen with molecular oxygen at a reaction temperature as low as 600-degrees-C. The predominant reactions can be stoichiometrically represented as CH4 + O2 - CO2 + 2H-2 and CH4 + O2 --> CO + H-2 + H2O. The former reaction is mainly catalyzed over stoichiometric apatite and the latter proceeds over the nonstoichiometric form. With oxygen as oxidant the H2/CO, ratios produced are strongly dependent on the Ca/P ratio in the hydroxyapatite, while with nitrous oxide little or no hydrogen is formed. With nitrous oxide as oxidant the active species on the hydroxyapatite are apparently capable of extracting hydrogen from methane, while in the presence of oxygen the active sites appear to interact directly with the carbon atoms. Rate data and infrared spectra of the apatite samples suggest that new sites, which are formed from P2O74- present in nonstoichiometric apatite, are responsible for the selective formation of carbon monoxide. (C) 1994 Academic Press, Inc.