Optimizing CO2 methanation: effect of surface basicity and active phase reducibility on Ni-based catalysts

Abstract

CO₂ methanation presents an intriguing avenue for utilizing carbon dioxide and generating methane as synthetic natural gas. This study delves into the innovative synthesis of MgO–Al₂O₃ mixed oxide support, a Co-active phase, and either Sr or Ce promoters to enhance the performance of Ni-based catalysts in CO₂ methanation. The primary objective is to identify the optimal ratio of Mg to Al for supporting 5 wt% Ni, followed by assessing the synergistic utilization of Co and Ni, along with different promoters, on the most promising support. Despite exhibiting comparable textural and basic characteristics, the increase of Mg content in Al₂O₃ introduces a delay in NiO reduction by promoting the formation of a NiO–MgO solid solution. The Ni₅/Mg₆₃Al₃₇ catalyst presents the highest CO₂ conversion of 92% and CH₄ yield of 82% at 400 °C. This catalytic activity surpasses that of Co₅/Mg₆₃Al₃₇ and Ni_2.5Co_2.5/Mg₆₃Al₃₇, mainly due to easier reduction of the monometallic Ni-based sample. Examining the impact of promoters on Ni_2.5Co_2.5/Mg₆₃Al₃₇ catalyst reveals the advantageous influence of Ce in terms of facilitative reduction and improved basicity. However, the promoting effect of Sr remains less discernible, potentially due to the already increased basicity resulting from the utilization of the MgO–Al₂O₃ support.