Transition metal modified Ce-based catalysts for low concentration methane combustion in porous media burners

Abstract

Coal mine methane is typically emitted at low concentration, making self-sustaining combustion for methane abatement challenging. Herein, Ce-based catalysts doped with Mn, Fe, and Co were supported on open cell foams to couple dopant-regulated surface chemistry with porous-media heat recirculation for lean methane combustion. Combined characterizations and DFT calculations revealed that transition-metal dopants regulated the CeO2 surface chemistry by increasing Ce3+ concentration, promoting oxygen vacancy formation, and enhancing reactive oxygen mobility. Among the catalysts, the Co-doped sample exhibited the strongest redox promotion effect, extending the flammability limit to 0.38 and sustaining stable combustion at inlet velocities up to 0.127 m/s. More importantly, Ce-Co converted localized heat release into a broader and smoother axial temperature field with a moderated peak temperature of around 700 °C, thereby suppressing hotspots while maintaining high CH4 conversion, CO below 900 ppm, and single-digit NOx emissions. DFT calculations further revealed that dopant effects arise mainly from stabilizing dehydrogenated CHx* intermediates rather than strengthening molecular CH4 adsorption. Co doping gave the highest work function and strongest CH2* stabilization, with an adsorption energy of -275.32 kJ/mol. These findings identify the synergy among oxygen mobility, CHx* intermediate stabilization, and porous-media heat feedback as the key to stable and low-emission lean methane combustion.