A highly loaded Ni@SiO2 core–shell catalyst for CO methanation

The specific catalytic activity of a supported metal catalyst increases with an increase in the number of active sites per mass of catalyst, which can be accomplished by increasing the metal content and/or decreasing the particle size of the metal. However, this leads to sintering of metal particles during the reaction, especially in highly exothermic reactions such as CO methanation. In this study, we prepared different SiO2-supported Ni catalysts by wet impregnation and sol–gel methods, and applied them to CO methanation. The prepared catalysts were characterized with N2 physisorption, X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), temperature-programmed reduction with H2 (H2-TPR), and transmission electron microscopy (TEM). Some problems associated with the wet impregnation method, such as sintering of Ni and the inability to load the silica with large amounts of Ni, were avoided by using the sol–gel method, in which size-controlled NiO was first synthesized using a polymer stabilizing agent, and then coated with a mesoporous silica shell through a polymerization approach. The prepared 55 wt% [email protected]2 catalyst exhibited the co-presence of Ni nanoparticles (mean size = 8.0 ± 4.4 nm) and nanorods (mean length = 15.5 ± 13 nm, mean width = 8.1 ± 4.4 nm). This catalyst was far superior for CO methanation than the conventional 33 wt% Ni/SiO2 catalyst prepared by wet impregnation, in which the Ni particle size was 24.5 nm. The 55 wt% [email protected]2 catalyst also exhibited excellent catalytic performance for selective CO methanation in the presence of an excessive amount of CO2.