Catalytic Methane Oxidation at Low Temperatures Using Ozone

Abstract

Methane oxidation using ozone at low temperatures (< 673 K) was studied both in the gas phase and with catalysts. Gas phase reactions were significant even at low temperatures, however, catalysts could improve the reactivity both under oxygen-rich and oxygen-deficient conditions. MgO was found to be active for the conversion of methane to CO and CO2 at oxygen-rich conditions, while Li/MgO catalyst promoted the production of formaldehyde at oxygen-deficient conditions. A selectivity to HCHO over 90% was achieved with a 4% methane conversion at 650 K on a Li/MgO catalyst, while no detectable conversion of methane was observed using oxygen as the oxidant. Methane oxidation to form formaldehyde was found to occur at the same temperature range when ozone decomposition happened, which suggested that the active oxygen species for methane oxidation were formed by ozone decomposition. Values of the ratio of converted CH4/converted O3 above unity clearly indicated the involvement of a chain reaction mechanism.