Surface reaction mechanism development for platinum-catalyzed oxidation of methane

Previously published mechanisms for methane oxidation on platinum have focused on fuel-lean or fuel-rich conditions and were often limited to a narrow range of operating conditions. A new C1 reaction mechanism for methane oxidation on Pt is presented, consisting of 31 reversible, elementary, thermodynamically consistent steps. Preexponential factors are estimated using transition state theory, and activation energies are calculated using the semiempirical bond order conservation (BOC) technique. Recently optimized reaction subsets for hydrogen and carbon monoxide oxidation on platinum are also used. The effect of adsorbate-adsorbate interactions on the activation energies of the surface reactions is also included through the BOC framework. Using this mechanism, ignition-extinction for fuel-lean and fuel-rich mixtures is studied. Reaction path and sensitivity analyses are carried out to capture the underlying physics in methane oxidation on Pt. For example, it is found for the first time that the dominant path for methane decomposition changes from oxygen and hydroxyl assisted, prior to ignition, to pyrolytic at high temperatures and for relatively fuel-rich mixtures. Finally, comparison of model predictions to experimental conversion and selectivity data for fuel-rich mixtures and laser-induced fluorescence data for fuel-lean mixtures is presented, showing good performance of the new mechanism. Overall; this mechanism captures the underlying physics of methane oxidation on Pt and overcomes most of the limitations of previously published mechanisms.