Defect engineered Co/NiO-MgO catalysts for efficient CO₂ methanation

In recent years, interest in CO₂ methanation has increased due to its ability to address climate change, store renewable energy, and promote sustainable development. This process converts CO₂ and H₂ into methane, a major component of CNG, providing a promising option for carbon recycling. However, its effectiveness and selectivity depend heavily on catalyst design and operating conditions. This study suggests that the performance of CO₂ methanation over NiO-MgO catalysts is influenced by the synthesis method as well as the cobalt incorporation. Fast vs. slow synthesis, along with Co incorporation by ionic substitution and wet impregnation, is likely to affect defect density, reducibility, CO₂ adsorption, and reaction intermediates. These factors can control overall catalytic activity. Comprehensive characterization was done to find the structural, morphological, and textural properties of the catalysts. Among all samples, the Co/NiO-MgO catalyst prepared through ionic substitution using the solution combustion method (CNM_IC) showed the highest performance. It achieved 72% CO₂ conversion and 96% CH₄ selectivity at 400 °C. This performance comes from its high concentration of oxygen vacancies (O_V/O_L = 3.83) and a high amount of medium-strength basic sites (58.31 µmol g^-1). In situ FTIR analysis showed that the reaction takes place through both CO and formate intermediates. Additionally, the CNM_IC catalyst showed great stability, maintaining high CO₂ conversion and CH₄ selectivity over 25 hours of continuous operation.