Promotional effect of Ti on mesoporous silica-supported Ru catalysts for CO2 methanation

Understanding the role of metal promoter in CO2 methanation is essential for advancing catalyst design and developing efficient methanation catalysts. Herein, a series of mesoporous Ti-promoted silica materials with different Ti-loadings was synthesized via the aerosol-assisted sol-gel process. These materials possess a spherical morphology with high specific surface area and homogeneous distribution of dispersed Ti species, even at Ti-loading as high as 16 mol%, thus allowing to investigate the role of Ti as a promoter in silica-supported Ru CO2 methanation catalysts. Keeping the Ru loading constant, higher Ti loadings (up to 12 mol%) lead to superior catalytic activity in CO2 methanation. At 300 C, the Ru-mass-normalized CO2 conversion rate of Ru/12%Ti-SiO2 catalyst is 2.3 times higher than that of unpromoted Ru/SiO2 catalyst. The improved activity correlates well with the smaller crystallite size of RuO2 nanoparticles, which translates to higher Ru dispersion after reductive treatment with H2. Overall, Ti helps stabilize Ru species and impedes crystal growth. With a Ti loading of 12 mol%, the crystallization of small anatase TiO2 is induced after RuO2 impregnation and during subsequent calcination, in turn forming the interfacial contact between Ru and TiO2 after H2 reduction. In-situ DRIFTS suggests that the promotion of CO2 activation and CO adsorption at these interfacial sites is responsible for the enhanced catalytic activity in Ti-promoted Ru-SiO2 methanation catalyst.