Design of supported metal/metal oxide catalysts for low-temperature ethanol production by CO2 hydrogenation

Abstract

The selective hydrogenation of CO₂ to multi-carbon oxygenates remains a key challenge in heterogeneous catalysis. In this work, a series of M¹–M²O_x/TiO₂ catalysts (M¹ = Ru, Rh, Ir, Pd, Pt; M² = V, Cr, Mo, W) were systematically screened for low-temperature CO₂ hydrogenation to ethanol, and the C₂ (ethanol) selectivity was identified as a critical descriptor that serves as a proxy for the intrinsic C–C coupling capacity and preserves the performance ranking at matched CO₂ conversion. Among them, the MoO_x/Rh/TiO₂ catalyst (Rh loading = 1.0 wt%, Mo/Rh molar ratio = 1.0), prepared by the sequential impregnation method, exhibited superior C–C coupling performance, achieving 4.5 % ethanol selectivity and 10.6 % total C₂ selectivity at 180 °C and 4 MPa. Mechanistic studies based on contact time variation revealed that CO serves as a key intermediate, with longer residence times favoring C–C bond formation. Structural characterizations (TPD, DRIFTS, TEM, XRD) indicated that MoO_x enhances surface basicity and modifies the electronic state of Rh, leading to the coexistence of Rh⁰ and Rh⁺ species. This bifunctional surface facilitates both CO₂ activation and ethanol formation. These findings highlight the critical role of Rh–MoO_x interfacial synergy in enabling selective ethanol production from CO₂ under mild conditions, providing insights for the design of efficient catalysts for C₂ oxygenate production.