Deactivation Mechanism, Countermeasures, and Enhanced CH₄ Oxidation Performance of Nickel/Cobalt Oxides

Nickel/cobalt oxides (Ni x Co 3− x O 4 ) are enticing candidates for replacing noble metal catalysts in low‐temperature methane complete oxidation. Poor thermal stability is the main drawback of these kinds of materials. Understanding the relationships among the morphology, composition, activity, and thermal stability of Ni x Co 3− x O 4 is crucial to develop robust Ni x Co 3− x O 4 for CH 4 oxidation. Herein, a series of hierarchical Ni x Co 3− x O 4 ( x = 0.1, 0.5, or 1) are synthesized by a hydrothermal method followed by thermal treatment at various temperatures for lean methane combustion. The results show that the decrease in surface area, surface Ni 3+ + Co 3+ amount, and defective oxygen amount are the main reasons for the performance degradation of Ni x Co 3− x O 4 after an elevated temperature treatment (500 and 800 °C). Proper decrease in the Ni/Co ratio, that is, Ni 0.5 Co 2.5 O 4 , slows down the thermal deactivation of NiCo 2 O 4 . Hierarchically structured Ni 0.5 Co 2.5 O 4 shows high CH 4 oxidation activity with a 90% CH 4 conversion temperature of 380 °C and a satisfied long‐term (>50 h) CH 4 combustion stability even after thermal treatment at 500 °C. These results demonstrate that simultaneous consideration of morphology manipulation and Ni/Co ratio optimization is an effective strategy for designing robust nickel/cobalt oxides for catalytic methane combustion.