Operando XAS and DFT Uncover Structure-Performance Relationships in Re/TiO ₂ for Selective CO ₂ Hydrogenation to Methanol

The conversion of CO₂ into value-added chemicals, such as methanol, offers a promising pathway toward a renewable energy future. However, a precise kinetic control and a highly selective catalyst are necessary to overcome the thermodynamic preference for CO₂ hydrogenation to methane. Rhenium-based catalysts, particularly Re/TiO₂, demonstrate high activity and selectivity for methanol under high-pressure conditions. For example, at 100 bar and 200 °C, a methanol selectivity of 97-99% was obtained. Catalysts with 1 wt % Re and 5 wt % Re/TiO₂ were used to study the effect of cluster sizes. At 250 °C, the 1 wt % catalyst achieves 97% selectivity at 23% conversion, whereas 5 wt % Re/TiO₂ achieves 74% selectivity at 40% conversion, corresponding to a drop in space-time yield from 65 to 16 g_CH₃OH·g_Re ^-1·h^-1, respectively. X-ray absorption spectroscopy provided insights into the structure of the active sites, while density functional theory calculations revealed the effects of cluster size on the energy barriers for H₂ activation, CH₃OH dissociation, and CH₃OH desorption, all of which directly influence conversion and selectivity. These results underscore the importance of balancing cluster size for optimal catalyst performance and provide insights into the design of efficient and selective catalysts for renewable methanol production.