Methanation of Carbon Dioxide on Skeletal Nickel Catalysts with Magnesium Fluoride Scaffolds

Abstract A new class of skeleton nickel catalysts with high activity and selectivity in the CO 2 methanation reaction has been developed, where magnesium fluoride plays a structure‐forming component. The precursor for the skeleton catalyst is a binary magnesium–nickel fluoride solid solution (MgF 2 –NiF 2 ), synthesized using the precipitation method from magnesium nitrate, nickel nitrate, and ammonium fluoride. Upon reduction at 500 °C in a hydrogen atmosphere, only nickel fluoride is reduced, while magnesium fluoride maintains its structure unchanged, forming the structural framework for nickel nanoparticles. The catalyst achieves a specific surface area of up to 87.2 m 2 g −1 and a nickel metal surface area of up to 3.06 m 2 g −1 . The most active catalyst, containing 73.1 wt.% Ni can convert 73% of CO 2 to methane, with a selectivity of nearly 98% and a carbon balance of 0.98 at 400 °C, under high GHSV = 20,000 h −1 . Among the factors contributing to the high catalytic activity, the metallic surface area measured by hydrogen chemisorption, the content of metallic nickel, and the amount of hydroxyl groups were identified. A strong correlation with catalytic activity was also observed for the surface composition of the catalysts determined by XPS, including: (1) total nickel content, (2) metallic nickel content, (3) oxygen content, and (4) the atomic Ni/Mg ratio. Surprisingly, no correlation was found between the activity and the surface basicity of the catalysts as measured by the CO 2 ‐TPD method.