Superior catalytic combustion of methane over Pd supported on oxygen vacancy-rich NiAl2O4†

Catalytic combustion of methane is an effective solution to reducing the greenhouse gas emission from natural gas-fueled engines. However, existing methane combustion catalysts suffer from insufficient low-temperature activity and poor hydrothermal stability. In this study, we demonstrate that PdO nanoparticles supported on oxygen vacancy-rich NiAl₂O₄ spinel, prepared by a simple and affordable procedure, render a remarkable enhancement in catalytic methane combustion below 400 °C. The calcination temperature was used as a robust means to tune the concentration of oxygen vacancies in the NiAl₂O₄ spinel. The particle size of PdO can be effectively controlled by adjusting the temperature of the subsequent calcination of the Pd-loaded spinel catalyst. The optimized catalyst, Pd/NiAl₂O₄-900–550, i.e. NiAl₂O₄ calcined at 900 °C, impregnated with Pd, and subsequently calcined at 550 °C, achieved a T₅₀ as low as 325 °C, whilst exhibiting excellent stability. After continuous treatment in 10% H₂O at 750 °C for 10 h, T₅₀ remains at below 396 °C. The characterization of the catalyst before, after and in situ methane combustion confirms that the high oxygen vacancy concentration and stable PdO nanoparticles both contribute to its excellent activity and stability. The present study introduces a new paradigm for preparing cost-effective and scalable redox catalysts supported on NiAl₂O₄ spinel with rich and tunable oxygen vacancies.