A C1 mechanism for methane oxidation on platinum

Platinum-catalyzed methane oxidation processes have significant potential in pollutant emission control and chemical synthesis. Detailed models, including elementary gas and catalyst phase chemistry and multicomponent transport, have been developed in the literature. However, the catalyst-phase chemical reaction mechanisms have a number of drawbacks. In this study, we apply a multistep methodology to construct a Cl surface reaction mechanism for methane oxidation on platinum. First, a comprehensive set of elementary Cl reaction steps is laid down, followed by calculation of thermodynamically consistent, species-coverage-dependent activation energies and heats of reaction. Next, order-of-magnitude estimates of the preexponentials are obtained from transition state theory and simulations are conducted using this reaction mechanism to obtain predictions of targeted experiments. Reaction path analysis and sensitivity analysis are subsequently employed to identify the important steps for each experiment and refine the preexponentials of these reactions. Finally, this mechanism is validated by comparison with other sets of experiments. Ignition and extinction temperatures, fuel conversion, selectivity to syngas, and laser-induced fluorescence signals from OH radicals, under various operating conditions, are predicted well by the mechanism. It is found that the dominant pathway for the surface dissociation of methane changes with operating conditions from oxygen-assisted prior to ignition to pyrolytic at high temperatures and for fuel-rich mixtures. A coupling between the carbon and hydrogen subsets of the reaction mechanism is identified through analysis of the hydroxyl mole fraction at high temperatures. Overall, this surface reaction mechanism overcomes many limitations of previous work and is capable of capturing the physics of methane oxidation on platinum over a wide range of operating conditions. (C) 2003 Elsevier Science (USA). All rights reserved.