Selective Hydrogenation of CO2 to Ethanol over Sodium-Modified Rhodium Nanoparticles Embedded in Zeolite Silicalite-1

Catalytic transformation of CO2 into chemicals in large demand such as ethanol has attracted much research attention under the background of establishing carbon-neutral societies. Supported Rh catalysts are promising candidates for the hydrogenation of CO2 to ethanol but suffer from low ethanol productivity and poor catalyst stability. Here, we report that zeolite silicalite-1 embedded Na-promoted Rh nanoparticles (Na-Rh@S-1) demonstrate high productivity and stability for CO2 hydrogenation to ethanol. The ethanol selectivity of 24% was attained at a CO2 conversion of 10%, and the space-time yield of ethanol reached 72 mmol gRh–1 h–1, which outperformed most of the Rh-based catalysts reported to date. While a reference catalyst prepared by impregnation underwent deactivation, the Na-Rh@S-1 catalyst was stable for at least for 100 h owing to the confinement effect. The Na+ modifier played crucial roles in enhancing the CO2 conversion and ethanol selectivity by suppressing methane formation. The characterizations suggest that the presence of Na+ enables the coexistence of Rh0 and Rh+ and enhances CO2 adsorption, thus boosting ethanol formation. A comparative study between CO and CO2 hydrogenation reveals that the Na-Rh@S-1 catalyst is significantly more active and selective toward CO2 hydrogenation to ethanol.