Surface reaction kinetics of methane oxidation over PdO

Abstract

A two-site mean field extended microkinetic model was developed based on DFT data to investigate the methane oxidation reaction over PdO(1 0 1) for environmental applications at atmospheric to moderate pressures, fuel-lean and low-temperature model exhaust gas conditions. The mechanism includes various carbonaceous pathways for methane oxidation together with lattice oxygen vacancy formation via Mars-van-Krevelen steps. The mechanism was compared with catalytic light-off curves (573–823 K) on a Pd/Al2O3 coated on monolith for CH4/O2/H2O/N2 mixtures with 1000 ppm CH4, 10 vol% O2 at varying H2O feed concentration (0–12 vol%) and pressure (1–4 bar). The mechanism was demonstrated to quantitatively reproduce experimental light-off curves for dry and wet feeds and capture the water inhibition phenomena, when catalyst deactivation and/or particle size dependent kinetic effects are taken into account. A degree of rate control analysis reveals dissociative CH4 adsorption via hydrogen abstraction over Pdcus-Ocus site-pairs as the major rate controlling step during light-off. Supplementary in situ DRIFTS investigations analyzed for dry and wet reactive gas-mixtures containing different types of C1-fuels, namely methane, methanol and formic acid were conducted to identify surface species during catalytic methane oxidation and hydroxide formation.