(67b) Theoretical Insights Into Catalytic Conversion Methane and Light Alkanes Over

The catalytic conversion of natural gas as well as other light alkanes into energy, liquid fuels and chemicals via reforming, partial oxidation and combustion processes occur through similar elementary C-H and O₂ bond activation steps which differ only in the nature of the active sites and the local surface coverage of oxygen under operating conditions. The prevailing chemistry is ultimately controlled by the reaction conditions which set the chemical potential and reactivity of oxygen on the surface and the makeup of the active sites as well as by particle size effects.  Experimental results for the partial oxidation of methane over supported metal clusters reveal the presence of at least four different kinetic regimes which can be described by unique rate expressions that result for methane over the bare, low oxygen-covered, high-covered, and fully-covered metal surfaces.  First-principle density functional theoretical calculations and kinetic Monte Carlo simulation are used here to elucidate the elementary C-H and O₂ activation steps at different surface sites and to establish the influence of surface coverage on the activity to form CO and CO₂ over different transition metal surfaces. The results are used to understand the diverse experimental kinetic regimes in methane partial oxidation, the influence of the metal, as well as particle size effects.   The results are naturally extended to the conversion of light alkane as well as C₁ and C₂ oxygenates over different transition metal and oxide surfaces.  Light alkanes show unique sensitivity of selectivity to changes in particle size.