Catalytic oxidation of methane over PdO in wire microcalorimetry

A two-dimensional model of a weakly buoyant flow over a horizontal wire with surface reaction was developed, using a literature mechanism, to simulate the heat release rate of the catalytic oxidation of methane (2 vol.% in air) over a Pd wire with a porous 1-2 mu m PdO surface layer, acquired by wire microcalorimetry over the temperature range of 600-770 K. The experimental and simulation results demonstrate that the catalytic oxidation is characterized by a low-temperature, reaction-controlled regime in which the internal pore surface is totally accessible to the reactions, and a high-temperature regime in which finite-rate pore diffusion also affects the overall heat release rate. Furthermore, the controlling reactions are identified to be the oxidative adsorption of methane, desorption of oxygen, and adsorption of oxygen, with the former two being facilitating and the last retarding. The reaction mechanism was modified using the response surface methodology and the experimental data in the low-temperature reaction-controlled regime, yielding satisfactory prediction of the global activation energy and identification of the role of oxygen coverage in the transition of the global activation energy.