A Novel Strategy To Enhance Methane Combustion Performance and Stability of Flower-Like Al2O3–Supported Pd Catalysts by Modification with Co5Mn1Ox, LaCoO3, or Ce0.6Zr0.4O2

Abstract

The development of CH₄ combustion catalysts with good low-temperature activities and stability still faces a great challenge. In this work, flower-like alumina (NF-Al₂O₃), M/NF-Al₂O₃ (M = Co₅Mn₁O_x, LaCoO₃, and Ce_0.6Zr_0.4O₂ (CZO)), and Pd/M/NF-Al₂O₃ (Pd loading = 2.00, 2.07, and 1.93 wt %) catalysts were fabricated using the hydrothermal, incipient wetness impregnation, and NaBH₄ reduction methods, respectively. The Pd/M/NF-Al₂O₃ catalysts showed good catalytic activity for methane combustion, among which Pd/Co₅Mn₁O_x/NF-Al₂O₃ performed the best: The temperatures (T_50% and T_90%) at CH₄ conversions = 50 and 90% were 285 and 323 °C at a gas hourly space velocity of ca. 20,000 mL/(g h), respectively; the methane reaction rate at 280 °C was 50.1 μmol/(g_Pd s), and the turnover frequency (TOF_Pd) at 280 °C was 0.018 s^–1. In addition, the Pd/Co₅Mn₁O_x/NF-Al₂O₃ sample exhibited good water and sulfur dioxide resistance. The enhanced methane combustion performance of Pd/Co₅Mn₁O_x/NF-Al₂O₃ was mainly attributed to two factors: (i) the unique three-dimensional flower-like layered structure of NF-Al₂O₃ effectively promoted dispersion of the Pd species; and (ii) the introduction of Co₅Mn₁O_x stabilized the active Pd²⁺ species and provided the more reactive oxygen species. Methane combustion over Pd/Co₅Mn₁O_x/NF-Al₂O₃ might take place according to the pathway of gaseous methane → adsorbed methane → formate and carbonate → CO₂ and H₂O. This work provides valuable insight into the modification of the Pd/Al₂O₃ catalyst and a new idea for the design of high-performance methane combustion catalysts in the future.