Cation-doping tuned flower-like Co-based spinel structure for methane combustion: Structure-effect and reaction pathway confirmation

Flower-like structure Co-based spinel oxide, composed of porous nanosheets, were synthesized using a hydrothermal method and applied to methane combustion. The physical and chemical properties of the ACo₂O₄ (A = Co, Ni, Mn, Fe, Mg) catalysts was discussed and the impact of incorporating different +2 and +3 metal ions into the Co₃O₄ spinel octahedral position on its structure and catalytic performance for methane combustion was explored. Results from activity evaluations revealed that the NiCo₂O₄ catalyst displayed superior performance, achieving a remarkable methane conversion of 90 % at 441 °C and space velocity of 20000 mL/(g·h). This was attributed to the introduction of +2 cations into the Co³⁺ sites, which greatly distorted the ordered structure of Co₃O₄ and formed an inverse spinel structure. It facilitated lattice distortion of spinel and the fracture of Co-O bond, which was beneficial to the formation of oxygen vacancies (Ov). More Ov heightened the mobility of lattice oxygen species, thereby improving the activity of methane oxidation at high temperature. The unique flower-like structure, resembling a lotus, endowed the NiCo₂O₄ catalyst with excellent water resistance and long-term stability. This work introduced a novel approach to designing and preparing non-noble metal catalysts with high efficiency, elevated temperature resistance and water resistance, demonstrating significant potential in the realm of industrial application.