Molecular Dynamics Simulation of the Low-Temperature Partial Oxidation of CH4

Low-temperature partial oxidation of methane was investigated using reactive molecular dynamics (MD) and quantum mechanical (QM) methods. In particular, the ReaxFF hydrocarbon force field [Chenoweth, K.; et al. J. Phys. Chem. A 2008, 112, 1040] was employed to simulate a [20 CH4 + 10 O-2] model system at 500 degrees C. The chemical mechanism of the partial oxidation of methane was proposed on the basis of analysis of the computed trajectory of this model system. The partial oxidation of methane was observed to be initiated by the abstraction of hydrogen from CH4 by O-2 and the atomization of CH4 itself. Subsequent radical recombination between hydrogen atoms and the dehydrogenation of CH4 were the primary pathways by which H, was formed. In agreement with current models of low-temperature combustion, radicals including H3C-OO and H2C-OO were also observed during the MD simulation. The observed reaction mechanism was subsequently analyzed using QM methods. For instance, structural features of prominent radical species observed during the MD simulation were analyzed using density functional theory (DFT) and coupled-cluster (CCSD(T)) methods. Enthalpies of reaction of all observed chemical processes were calculated using DFT and the W1 composite method. Where possible, comparisons with experimental data were made.