Importance of metal intimacy in tuning CO2 hydrogenation selectivity over Cu-exchanged TiO2 supported Rh catalysts via enhanced CO intermediate interaction

Abstract

It is crucial to regulate the metal intimacy in bimetallic catalysts for tuning the product selectivity in CO₂ hydrogenation. In this study, we developed a Rh/Cu–TiO₂ catalyst using a Cu ion-exchange strategy to construct the Cu–TiO₂ support with highly dispersed Cu species, thereby enhancing the intimacy between Rh and Cu. HRTEM confirmed that the ion-exchange method achieved exceptional Cu dispersion (2.67 ± 0.83 nm nanoparticles) and improved the intimacy between Rh and Cu species. The catalytic CO₂ hydrogenation performance of the Rh/Cu–TiO₂ catalyst was systematically examined and compared with a conventional co-impregnated RhCu/TiO₂ catalyst. Interestingly, activity evaluation results demonstrated that the improved Rh–Cu intimacy in the Rh/Cu–TiO₂ catalyst can promote the adsorption of *CO intermediates as well as their further hydrogenation into CH₄ or coupling with CH_x species to produce ethanol. Accordingly, Rh_0.25/Cu–TiO₂ exhibited the best ethanol STY (558.4 mg_ethanol g_Rh⁻¹ h⁻¹), representing a 1.9-fold enhancement versus the co-impregnated RhCu/TiO₂ catalyst (284.4 mg_ethanol g_Rh⁻¹ h⁻¹). Through comprehensive characterization techniques, including H₂-TPR, CO-TPD, XPS, CO-DRIFTS, and in situ DRIFTS, we demonstrate that the enhanced Rh–Cu intimacy and its effective regulation of the surface electronic structure can (i) strengthen the adsorption and dissociation capacity of *CO on Rh⁰ sites as well as the hydrogenation activity on Cu⁰ sites, (ii) promote the dissociative hydrogenation of partial *CO species to form *CH_x intermediates, and (iii) thereby facilitate both methane formation and efficient C–C coupling between *CH_x and adjacent *CO species to produce ethanol. Our findings underscore that regulating the intimacy of active sites is essential for designing highly efficient catalysts to modulate product selectivity in CO₂ hydrogenation, particularly toward ethanol synthesis.