Construction of Single-Cluster Rhodium Catalyst for Efficient CO2 Hydrogenation to Ethanol.

Abstract

Thermocatalytic conversion of carbon dioxide (CO2) into ethanol is a promising strategy for efficient utilization of CO2. However, it remains a grand challenge to achieve a high ethanol yield due to the difficulty in accurate control of CO2 activation and C-C coupling under thermocatalytic reaction conditions. Herein, a precise rhodium (Rh) single-cluster catalyst on carbon nitride support (RhSC/CN) was designed for CO2 hydrogenation to ethanol. The RhSC/CN catalyst, with an average Rh-Rh coordination number of 2.06, exhibits a record turnover frequency (TOFRh) of 595.2 h-1, a high ethanol selectivity of 95.3% and an ethanol yield of 17.5 mmol gcat -1 h-1 at 240 °C and 5.0 MPa (H2/CO2 = 3), surpassing previously reported Rh-based catalysts. Density functional theory calculations, in situ diffuse reflectance infrared Fourier transform spectroscopy, X-ray absorption spectroscopy and H2/D2 isotope exchange probing experiments altogether reveal the reaction mechanism, and show that the synergetic interaction between Rh-Rh and Rh-N sites boosts CO2 adsorption and asymmetric C-C coupling between CH3* and CO* to form CH3CO*, leading to a high ethanol selectivity. This discovery provides new insights into the design of single-cluster catalysts for simultaneously promoting CO2 reactivity and ethanol selectivity.