Rh-Based Bimetallic Alloys: Unraveling the Synergistic Catalysis in CO2 Hydrogenation to Ethanol

The utilization of Rh-based catalysts in the direct production of ethanol from CO2 has been a subject of significant interest. However, to date, the precise active sites responsible for ethanol generation and the C–C coupling mechanism remain elusive. In this study, we present a Rh-based catalyst featuring nanoscale Rh–Fe alloy sites, which achieved an ethanol selectivity of 49.1% among all hydrocarbon and oxygenate products (CO excluded) under relatively mild reaction conditions (3.0 MPa, 200 °C, with a low metal loading of ≤1 wt %). The formation of ethanol proceeds via the HCOO* pathway with a CO insertion mechanism occurring at the alloy sites with a specific cluster size, where CH2* and CO* act as the crucial intermediates for C–C coupling. The electron interaction within the Rh–Fe alloy sites effectively reduces the energy barrier for the formation of the CH2CO* intermediate, thereby facilitating the production of ethanol. In contrast to the Rh–Fe alloy sites, the geminal-dicarbonyl binding configuration of CO* intermediates on Rh single sites favors the generation of byproducts such as methane and methanol, rather than ethanol. This research offers insights into the active sites and reaction mechanism of hydrogenation of CO2 to ethanol, thus enhancing the efficient utilization of Rh-based catalysts.