In situ growth of nickel based catalysts on the surface of macroporous Al₂O₃ for CO₂ methanation

Macroporous catalysts exhibit excellent mass and heat transfer properties, thereby reducing pressure drop and mitigating hot spot formation during the reaction process. Addressing the issue of sintering of the active component on the catalyst due to the strong exothermicity of CO₂ methanation and the demand for reactions to operate at high space velocities, this study for the first time utilized macroporous Al₂O₃ for CO₂ methanation reactions. A catalyst comprising a high surface area, large pore size, and high pore volume was prepared by in-situ growth of layered double hydroxide (LDH) precursors on the surface of macroporous Al₂O₃. The effects of calcination temperature, reduction temperature, and space velocity on the catalyst structure and reaction performance were studied. The phase composition of the catalyst is controlled by adjusting the calcination temperature, the reduction degree of Ni is regulated and the sintering of Ni is avoided by controlling the reduction temperature , and the number of active sites of Ni⁰ in the reduced catalyst is increased, thus the activity of the catalyst is improved. The results demonstrate that after calcination of the NiMgAl-LDH precursor at 400 ℃ and reduction at 650 ℃, the resulted Ni-MgO/Al₂O₃ showed the highest Ni activity-specific surface area, which is the best catalyst with highest CO₂ conversion and CH₄ selectivity, indicating that increasing the surface area of metal nickel is crucial for the catalytic performance. Furthermore, the material maintained high catalytic performance at WHSV = 80000 mL/(g·h), indicating its suitability for high space velocity operations. Additionally, at a test temperature of 550 ℃, the catalyst exhibited excellent stability, with CO₂ conversion and CH₄ selectivity respectively remaining at 54% and 79%.