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

Abstract

Nickel/cobalt oxides (NixCo3−xO4) 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 NixCo3−xO4 is crucial to develop robust NixCo3−xO4 for CH4 oxidation. Herein, a series of hierarchical NixCo3−xO4 (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 Ni3+ + Co3+ amount, and defective oxygen amount are the main reasons for the performance degradation of NixCo3−xO4 after an elevated temperature treatment (500 and 800 °C). Proper decrease in the Ni/Co ratio, that is, Ni0.5Co2.5O4, slows down the thermal deactivation of NiCo2O4. Hierarchically structured Ni0.5Co2.5O4 shows high CH4 oxidation activity with a 90% CH4 conversion temperature of 380 °C and a satisfied long‐term (>50 h) CH4 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.