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

Macroporous catalysts often exhibit excellent mass and heat transfer properties, which can reduce pressure drop and mitigate hot spot formation during the reaction process. Addressing the issues of the active component sintering due to the strong exothermicity of CO₂ methanation and the demand for operation at high space velocities, in this work, a nickel-based catalyst with high surface area and large pore size and pore volume was prepared by in-situ growth of NiMgAl layered double hydroxide (NiMgAl-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 investigated. The results demonstrate that the catalyst phase composition can be controlled by adjusting the calcination temperature, while the reduction degree of Ni is regulated by altering the reduction temperature, which are effective in inhibiting the sintering of Ni, increasing the number of active Ni⁰ sites, and then enhancing the catalytic activity of Ni-MgO/Al₂O₃. By conducting the calcination of NiMgAl-LDH precursor at 400 °C and subsequent reduction at 650 °C, the resulted Ni-MgO/Al₂O₃ catalyst shows the highest active Ni surface area and exhibits the highest CO₂ conversion and CH₄ selectivity in the CO₂ methanation, suggesting that the surface area of metal nickel is a crucial factor for the catalytic performance of Ni-MgO/Al₂O₃. Furthermore, the Ni-MgO/Al₂O₃ catalyst performs well at a high space velocity of WHSV = 80000 mL/(g·h) and a good stability at 550 °C, where the CO₂ conversion and CH₄ selectivity keep at 54% and 79%, respectively.