Low-Temperature Methane Catalytic Combustion on a New Pt-Based Catalyst Confined in a MnO₂/Al₂O₃ Carrier

In this study, a hierarchically confined Pt/MnO₂-meso-Al₂O₃ catalyst with 0.5 wt% Pt loading was synthesized via a precipitation method using MnO₂ as a promoter and mesoporous Al₂O₃ (m-Al₂O₃) as a support, and its methane catalytic combustion performance and structure-activity relationship were systematically investigated. The results demonstrate that the 0.5 wt% Pt-loaded Pt-MnO₂/m-Al₂O₃ catalyst achieved 90% methane conversion at 236 °C. The enhanced performance is attributed to three synergistic mechanisms: (1) Pt doping induced lattice contraction in MnO₂ (XRD revealed a 0.03 Å reduction in the (001) interplanar spacing), which facilitated the formation of Mn³⁺-oxygen vacancy pairs (XPS indicated a Mn³⁺- content of 79.87%); (2) the MnPt₃O₆ interfacial structure (HAADF-STEM confirmed lattice spacings of 0.21 nm) accelerated oxygen species cycling, with the 0.5 wt% Pt-loaded catalyst for lattice oxygen desorption capacity (O₂-TPD) increasing by 54% compared to undoped samples; (3) the mesoporous m-Al₂O₃ carrier provided effective confinement, achieving a high specific surface area (27.6 m²/g) and sub-nanometer Pt dispersion (particle size < 2 nm). Under conditions of 1000 ppm CH₄ and a space velocity of 30,000 h^-1, the catalyst maintained a methane conversion rate of 98.2 ± 0.5% during continuous operation for 300 h. Post-cycling characterization revealed a stable crystalline structure (XRD full width at half maximum of 0.35° ± 0.02°) and grain size (15.5 ± 0.5 nm), confirming its robustness for industrial applications. This study provides theoretical and experimental foundations for the rational design of highly efficient catalysts for low-concentration methane elimination. For comparison, a Co-doped catalyst (1.0 wt% Co-MnO₂/Al₂O₃) was also prepared, which exhibited significantly lower activity (T₉₀ = 251 °C), underscoring the unique role of Pt in the confined architecture. This study provides theoretical and experimental foundations for the rational design of highly efficient catalysts for low-concentration methane elimination.