La-promoted Ru/ZrO2 catalysts: Insights about catalytic performance and active site for CO2 methanation

The establishment of a carbon-neutral society is one of humanity's top priorities. However, the inertness of CO 2 imposes a barrier for its transformation to distinct added-value products at appreciable reaction rates. Therefore, catalysts with improved properties must be developed. Herein, 0.4 wt% Ru catalysts supported on ZrO 2 and La promoted ZrO 2 with different La loadings were prepared by wet impregnation and systematically investigated for CO 2 methanation. Catalytic testing showed that La incorporation enhanced activity, with 0.4Ru/1.5La-ZrO 2 achieving the highest CH 4 formation rate, while maintaining 100% CH 4 selectivity and stable conversion over 72 h. The structural and surface properties of the catalysts were examined by ex-situ techniques (BET, CO 2 -TPD, H 2 -TPR, XPS). Complementary in-situ studies provided mechanistic insights. EPR showed that La stabilized Ru 3+ species that were gradually reduced into active Ru 0 /Ru + clusters during reaction. In-situ DRIFTS analysis revealed adsorbed CO on Ru sites as the main reaction intermediate, with formates and carbonates acted as spectator species, and demonstrated that 1.5 wt% La optimized intermediate coverage, whereas higher La loadings diminished CO adsorption and surface-accessible Ru. The combined ex-situ and in-situ characterization demonstrated that tuning La loading is important to balance basicity and metal-support interactions, offering clear design strategy for efficient and stable Ru-based CO 2 methanation catalysts.