Lean methane oxidation over Co3O4/Ce0.75Zr0.25 catalysts at low-temperature: Synergetic effect of catalysis and electric field

Electric field was introduced for ultra-lean methane oxidation over a series of Co3O4/Ce0.75Zr0.25 catalysts. Catalytic activities were significantly promoted by the electric field. It was found that the catalyst with 25% of Co loading showed the highest catalytic activity at 9 mA of electric currency, and the light-off temperature (T50) was as low as 240 °C. The effect of the electric field over the catalysts was examined from the structural and surface point of view (XRD, XRS, BET, H2-TPR). The obtained results demonstrated that the electric field facilitated the release of oxygen from lattice by promoting the reduction of Ce4+ to Ce3+, therefore reinforced the formation of Co3O4 on catalyst surface. Moreover, tetrahedral Co2+ in the Co3O4 spinel were oxidized to Co3+. Besides, electric field enhanced the reducing capacity of the Co3O4 with the newly formed tetrahedral Co3+ easily reduced at low-temperature conditions. The FTIR results revealed that the active sites of methane chemisorption located respectively at tetrahedral Co3+ with active O species from lattice in the electric field, and octahedral Co3+ with pre-adsorbed gaseous O2 formed at relatively higher-temperature in conventional catalytic process. The following dehydrogenation and oxidation processes were accelerated in the electric field with fast conversion rates of intermediates, namely methyl and formates species. Based on experimental results and comprehensive analysis, the mechanism of catalytic oxidation of methane over Co3O4/Ce0.75Zr0.25 catalysts with the assistance of electric field was proposed.