Catalytic combustion of low-concentration methane over transition metal oxides supported on open cell foams

Abstract

Methane is a potent greenhouse gas, and mitigating its substantial emissions, primarily from coal mines with low concentrations, is among the most effective strategies to slow global warming. Catalytic combustion using transition metal oxides is increasingly pivotal in addressing this issue; however, the low-temperature activity of these catalysts limits their widespread application. In this study, we aimed to develop highly active and cost-effective catalysts for large-scale combustion of low-concentration methane. To this end, a series of transition metal oxides (Cr₂O₃, Mn₂O₃, Fe₂O₃, Co₃O₄, NiO, and CuO) supported on open cell foams were synthesized, and their catalytic performance for methane combustion at 1 vol% CH₄ was assessed in a fixed-bed reactor. Comprehensive characterization was conducted using XRD, SEM-EDS, XPS, H₂-TPR, and O₂-TPD techniques to elucidate the underlying mechanisms of CH₄ catalytic combustion. Results demonstrated that the structured catalysts exhibited exceptional activity and thermal stability. Among them, NiO showed the highest activity, followed by Fe₂O₃ and Co₃O₄ with similar activity, and then Mn₂O₃, CuO, and Cr₂O₃ showing progressively lower reactivities. Complete CH₄ conversion was achieved over NiO at approximately 500 °C, comparable to certain noble metal catalysts. The superior catalytic activity was attributed to the abundant reactive oxygen species, originating from chemically adsorbed oxygen and surface lattice oxygen transformations. Additionally, the rich oxygen vacancies facilitated CH₄ dissociation and enhanced activity. This study provides an effective framework for advancing catalyst design to improve methane oxidation efficiency, thereby enhancing the practical management and utilization of low-concentration methane emissions from coal mining activities.