Does the active surface area determine the activity of silica supported nickel catalysts in CO2 methanation reaction?

Two series of silica supported catalysts with comparable nickel contents varying from 2.5 to 20 wt% were prepared by wet impregnation method in the absence and presence of citric acid in the impregnation solution. Temperature-programmed reduction, X-ray diffraction and electron microscopy studies indicated changes of reducibility of nickel oxide species in the corresponding catalysts and formation of nickel nanoparticles of different size and morphology. A gradual increase in the performance of catalysts in the CO₂ methanation reaction was observed with increasing Ni loading. The application of a modified impregnation method led to a reduction in the size of the nickel crystallites, which increased the active surface area of the catalysts, improving their activity and selectivity towards methane at low temperatures, as well as their stability at high temperatures. It was shown that the high active surface area of silica-supported nickel catalysts, due to the presence of small crystallites, is a key factor in increasing their activity, pointing out that other catalyst properties may also play an important role. Hydrogen temperature-programmed desorption and in-situ DRIFTS adsorption/desorption of CO, CO₂ and CO₂ hydrogenation reaction studies indicated that modification of the method of catalyst synthesis led to changes in the surface properties of the catalysts, affecting the way CO₂ and H₂ activation and the transformation of resulted intermediate species to the final reaction products