Low‐Content Ru Catalysts for Efficient CO2 Methanation

A series of low-content Ru-based catalysts supported on Al2O3, TiO2, CeO2, MgO, and ZrO2 were synthesized via incipient wetness impregnation and evaluated for CO2 methanation. Among them, Ru/TiO2 exhibited the highest activity in terms of turnover frequency (TOF = 3.35 s−1) and selectivity toward CH4 (> 95%). To elucidate the underlying reaction mechanism, operando Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analyses were performed, revealing the presence of key surface intermediates. Based on these observations, several power-law and Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic models were formulated and fitted to experimental data. A detailed comparison of different mechanistic hypotheses was conducted, highlighting the role of CO2 dissociation and stepwise hydrogenation pathways. A two active site model that considers CO2 adsorption on the basic sites of the support and the continuation of the reaction by hydrogen spillover from Ru nanoparticles provided the best agreement with experimental results. Overall, the combination of catalytic testing, operando spectroscopy, and kinetic modeling offers a comprehensive understanding of the CO2 methanation pathway over Ru/TiO2 and provides a reliable basis for catalyst comparison and reactor design to effectively manage thermal issues.