Enhanced methane combustion over monoclinic single-site Mn-containing nanosized MFI zeolite catalyst

Abstract

Our study addresses a critical challenge in the development of thermally stable, selective, and efficient catalysts for lean methane (CH₄) combustion. This reaction is of paramount importance for environmental remediation, particularly in mitigating methane, a potent greenhouse gas from both industrial and natural sources, as well as for applications in clean energy technologies. Incorporating transition metals into nanosized zeolite frameworks offers synergistic benefits, including enhanced thermal stability and active Lewis acid sites. In this study, manganese (Mn) was directly incorporated into a pure silica MFI zeolite (MnFI) to generate active sites for catalytic lean methane (CH₄) combustion. Structural characterization revealed that Mn incorporation altered the order in MnFI zeolite, highlighting the monoclinic P2₁/n character. This modification was accompanied by a reduction in silanol site density, indicating successful framework integration of Mn. High-angle annular-dark field scanning transmission electron microscopy (HAADF-STEM) visualized the isolated Mn atoms within the zeolite framework. The synergy between the Mn sites and the monoclinic structure enhanced the thermal stability and introduced active Lewis acid sites in sample MnFI. Catalytically, the MnFI zeolite outperformed a reference Mn-containing sample prepared by incipient wetness impregnation, achieving higher CH₄ conversion under lean conditions. Notably, MnFI maintained a stable CH₄ conversion of 65.1% at 590 °C over 120 hours without deactivation, demonstrating excellent long-term performance and structural integrity under reaction conditions. No H₂ or CO byproducts were detected in the flue gas, suggesting the suppression of side reactions, such as CH₄ reforming or the water-gas shift, by MnFI.