Low Temperature Complete Combustion of Lean Methane over Cobalt-Nickel Mixed-Oxide Catalysts

Cobalt-nickel mixed oxides with different Co/Ni molar ratios were prepared by co-precipitation and used for the catalytic combustion of lean methane. The catalytic performances for methane combustion were evaluated at steady-state conditions at temperatures ranging from 250 to 500 degrees C, which were increased in step sizes of 25 degrees C. Among the catalysts, the cobalt-nickel mixed-oxide catalysts with an appropriate Co/Ni ratio exhibit a high catalytic performance for the lean methane combustion, with the catalyst having a Co/Ni molar ratio of 1:4 showing the highest catalytic activity (methane conversion reached 100% at 425 degrees C). On the basis of TEM and XRD results, the nanoparticles of the catalysts have a suitable interparticle spacing and more crystal defects. X-ray photoelectron spectroscopy (XPS) results reveal a high number of surface-active oxygen species and appropriate aliovalent cobalt ion numbers in the catalysts for high catalytic activity. All these effects contribute to the outstanding performance of these catalysts in the combustion of lean methane at low temperatures.