Catalytic Synergy: Mesoporous Silica and Ruthenium-Structure-Activity Relationships in CO2 Methanation and Toluene Hydrogenation.

The rational design of supported ruthenium catalysts for sustainable energy applications requires precise control over metal nanoparticle size, dispersion, and metal-support interactions. This study investigates the influence of mesoporous silica support topology-SBA-15 (2D hexagonal, cylindrical pores), SBA-12 (3D hexagonal structure), and SBA-3 (2D hexagonal)-on the structure and catalytic performance of 1 wt% ruthenium catalysts in CO2 methanation and gas-phase toluene hydrogenation. Comprehensive characterization by nitrogen physisorption, low- and high-angle X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), CO chemisorption, and transmission electron microscopy (TEM) revealed that support pore architecture dictates ruthenium particle size (1.2 nm for Ru/SBA-15, 2.8 nm for Ru/SBA-3, 4.3 nm for Ru/SBA-12) and dispersion (80%, 35%, 23%, respectively) through geometric confinement effects. Catalytic testing demonstrated contrasting structure-activity relationships: CO2 methanation exhibited strong structure sensitivity with turnover frequency (TOF) increasing with particle size (Pearson's r = 0.96), favoring Ru/SBA-3 and Ru/SBA-12 with near-optimal 3-4 nm particles, while toluene hydrogenation showed weaker structure sensitivity, with Ru/SBA-12 achieving the highest TOF owing to its larger particle size and higher crystallinity. These findings underscore the critical importance of tailoring mesoporous support topology to match reaction-specific structure sensitivity, providing fundamental insights for the design of bifunctional catalysts for hydrogenation reactions.