In considering the typical experimental conditions used for studies of methane oxidation to oxygenates or hydrocarbons in the presence of catalysts, it is clear that a significant potential exists for the appearance of non-catalyzed, thermally activated gas-phase reactions of methane and oxygen. Experimentally, in a quartz reactor at 800 °C with a 3:1 methane-to-oxygen ratio and residence times of the order of 5-10 sec, significant conversion of methane (30%) to light hydrocarbons and COx with appreciable selectivity (25%) to C2+ components is observed due solely to these background reactions. In order to identify and describe the contribution of the gas phase processes during catalyzed reactions, a chemical kinetic model (HCT) developed at this Laboratory has been employed to describe these homogeneous gas phase reactions. Overall, the model predicts very well the trends and steady state results observed when tested against a series of experimental reactions comparing the effects of various reaction parameters such as residence time, temperature, and gas composition. The ability to accurately predict the magnitude of these background reactions should provide a means to begin to dissect the contributions of thermal gas phase chemistry from those of solely catalytic action.

New catalysts materials containing niobium and lanthanum have been synthesized. It is observe that niobium alone at high loading levels is an oxidation catalyst facilitating the production of carbon dioxide. This behavior is modified when lanthanum is incorporated into the catalyst material. In that case, improved selectivity to oxidative coupling products of methane is observed. These results appear to be a consequence of catalyst interaction with the existing background gas phase reactions.

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