Synergistic Effect of Anion Modification and Precursor Regulation: Achieving Bidirectional Transformation of C1 Products in CO2 Hydrogenation

Exploring the development of catalytic CO2 hydrogenation systems with the high selectivity of a specific target product is fascinating, but it also faces enormous challenges. Here, we report the synergistic effect of anion modification and precursor regulation to achieve bidirectional transformation of CO2 hydrogenation products from CH4 to CO and CO to CH4. The Ru/TiO2(O) catalyst prepared from the RuO2 precursor exhibited high CH4 selectivity in a CO2 hydrogenation reaction, while the Ru/TiO2(O) catalysts modified with Cl–, NO3–, and SO42– achieved complete product transformation from CH4 to CO. However, the Ru/TiO2(Cl) catalyst prepared from RuCl3 precursor tends to generate CO products in CO2 hydrogenation reactions and exhibits high CH4 selectivity after modification with OH– and CO32–. The successful synthesis of different anion-modified Ru/TiO2 catalysts has been confirmed by various characterization techniques such as ion chromatography, XRD, TEM, etc. The XPS characterization and DFT calculations results indicate that the modification of different anions has a strong interaction with the Ru metal on the Ru/TiO2 catalyst surfaces, effectively regulating the electronic properties of the Ru metal. Pulse adsorption experiments and H2 molecule dissociation simulations have demonstrated that anions affect the adsorption and dissociation properties of catalysts for H2, thus ultimately affecting the hydrogenation efficiency of CO2. In situ DRIFTS confirmed that CO2 follows different hydrogenation and desorption processes catalyzed by the Ru/TiO2 catalysts modified with different anions. The characterization of CO-TPD and CO-DRIFTS demonstrated that the anions regulate the adsorption properties of CO intermediates on the catalyst surface, which is the fundamental reason for the change of the CO2 hydrogenation products. Our work confirms the feasibility of anion modification and precursor regulation strategies in regulating CO2 hydrogenation selectivity, and we believe this work will provide a new direction for further understanding the influence of the catalyst surface structure on hydrogenation and the design of highly selective catalysts.