A Novel Coprecipitation Path to a High-Performing Ni/MgO Catalyst for Carbon Dioxide Methanation.

Abstract

The novel crystalline bimetallic single-source precursor (Ni_1-xMg_x)₁₂(CO₃)₈(OH)₆O · y H₂O with x = 0-0.5 can be converted into a highly active Ni/MgO CO₂ methanation catalyst. All stages of preparation, namely, coprecipitation, crystallization, calcination, and reduction, as well as the spent catalysts have been comprehensively analyzed using powder X-ray diffraction, physisorption, transmission electron microscopy, and other techniques. The scalable synthesis allows attaining unusually high surface areas around 230 m² g^-1 for the calcined precatalyst Ni_1-xMg_xO. During reduction, this oxide solid solution separates into metallic Ni and Ni-depleted oxide to form the active catalyst with finely interdispersed nanoparticles of both components with a high porosity. A high methane production rate is observed in a CO₂/H₂ (1:4) feed at high space velocities of ≈150 Lh^-1 g^-1. This performance is competitive with an industrial methanation catalyst and depends strongly on the Ni:Mg ratio utilized in the synthesis. For an equimolar ratio, the new catalyst is found to be 4 times as active as the benchmark. Due to the nanoscaled microstructure, the novel material can stabilize very high Ni loadings (≤77 wt%) with only minor sintering effects at a reaction temperature of 240-280 °C. This material thus closes the gap between thermally unstable Raney-type and conventional lower loaded impregnated industrial catalysts.