Application of bimetallic Ru-Cu/TiO2 catalysts in efficient CO2 methanation

• Cu incorporation promotes low-temperature activity in Ru/TiO 2 catalysts. • Ru–Cu bimetallic catalysts achieve 86% CO 2 conversion at 350 °C. • Ru–Cu interaction improves metal dispersion, reducibility, and acidity. • Ru–Cu mixed nanoparticles favor enhanced CO 2 adsorption. • A reaction mechanism involving formate and carbonyl intermediates was identified. Exploring efficient monometallic or bimetallic supported catalysts to improve CO 2 methanation at low temperatures is an important topic in the field of heterogeneous catalysis. In the current research, bimetallic Ru-Cu/TiO 2 catalysts were prepared using the co-deposition-precipitation with urea method. Augmenting the ruthenium content from 0.5 to 1.5 wt% boosted the CO 2 conversion and improved the reducibility of the catalysts. Optimal metal loadings were found to be 2.0% copper and 1.5% ruthenium, and the synergistic interaction between Ru and Cu in the bimetallic catalysts was confirmed for CO 2 methanation. The Ru, Cu and Ru-Cu catalysts were characterized by X-ray diffraction, BET specific surface area, STEM-EDS microscopy, H 2 /TPR, CO adsorption DRIFTS, CO oxidation DRIFTS (as a model reaction to observe adsorbed species and reaction intermediates on the Ru, Cu and Ru-Cu catalyst surface), methanation followed by DRIFTS, as well as XPS. The outcomes revealed the strong interaction between Ru and Cu on the TiO 2 anatase support, which led to modified metal dispersion when both metals were present. Indeed, the heterogenous charge distribution in the bimetallic structure leads to cooperative nucleophilic and Lewis-acidic sites for CO 2 adsorption and bond activation. Additionally, hydrogen spillover in Ru-Cu/TiO 2 was observed, which improved CO 2 methanation and adsorption capacity. As for the Ru-Cu/TiO 2 catalyst, catalytic evaluation confirmed its significantly enhanced activity, selectivity, and stability with respect to the corresponding monometallic Ru and Cu catalysts. XPS and in-situ DRIFTS analyses indicated that metallic Ru 0 and Cu 0 were the most active species. Furthermore, the bimetallic catalyst demonstrated good reusability, maintaining its activity over repeated reaction cycles.