Effect of Rh loading on the selectivity to methanol and ethanol in the hydrogenation of CO₂ over the Rh/CeO₂ catalyst

The capture and hydrogenation of CO₂ into high-value chemicals such as alcohols is one of the important ways to reduce CO₂ emission and achieve carbon resource recycling. In this work, the catalytic performance of Rh/CeO₂ catalyst in the CO₂ hydrogenation was investigated; with the help of various characterization methods including XRD, Raman, H₂-TPR, CO₂-TPD, CO-DRIFTS and XPS, the influence of Rh loading (0.1%–2.0%) on the catalytic activity of Rh/CeO₂ and product selectivity in the CO₂ hydrogenation was revealed. The results indicate that for the hydrogenation of CO₂ at 250 ℃ and 3.0 MPa over the Rh/CeO₂ catalysts, ethanol is the major product at a low Rh loading of 0.1%. With the increase of Rh loading, the conversion of CO₂ increases, but accompanied by a decrease in the selectivity to ethanol; when the Rh loading reaches 2.0%, the main product turns to be methanol. It seems that the difference of various Rh/CeO₂ catalysts with different Rh loadings in the product selectivity for the CO₂ hydrogenation is ascribed to their difference in the structural and electronic properties of Rh; atomically dispersed Rh⁺ species favor the stabilization of CO* and its subsequent C–C coupling with CH₃* to form ethanol, whereas metallic Rh clusters facilitate the hydrogenation of CO* to produce methanol.