LOW-TEMPERATURE OXIDATION OF LIGHT-HYDROCARBONS OVER SILICA-SUPPORTED NOBLE-METAL CATALYSTS

A steady state oxidation of a natural gas (NG)( 95.2 % methane, 1.2 % ethane, 0.7 % propane, 2.1 % nitrogen with traces of butane and carbon dioxide) over Pd/SiO2 and Pt/SiO2 catalysts was run in a temperature range of 553-773 K with a NG to oxygen ratio equal to 9:1 in a flow rector. Water and carbon dioxide were found to be the only products of oxidation at temperatures below 613 K over Pt/SiO2 and below 668 K over Pd/SiO2. Above these temperatures hydrogen and carbon monoxides appeared in the products of oxidation. The temperature dependence of the selectivity toward hydrogen for both catalysts is discussed. The interaction of methane pulses with the surface of the preoxidized Pd/SiO2 catalysts at temperature of 543 K was also investigated. The formation of enhanced amounts of CH3 and CH2 species on the oxide surfaces with adsorbed oxygen as well as on oxide surface with deficit of oxygen in the lattice was found. The formation of the enhanced amount of carbon monoxide at the surface of oxide with moderate amount of adsorbed oxygen is considered as a result of the formation and then dehydrogenation of the methoxy species, CH2O, on O- ions.