Promoting effect of Fe modification on the direct synthesis of dimethyl carbonate from CO2 and methanol over Fe–Ce binary oxide

Abstract

Direct synthesis of dimethyl carbonate (DMC) using CO₂ and methanol as raw materials is an environmentally friendly and promising route for recycling carbon sources from exhaust gases. Herein, well-constructed CeO₂-based nanoparticle catalysts promoted by various Fe contents were synthesized via a facile co-precipitation method and demonstrated to be highly effective for direct DMC synthesis. The uniform doping of iron species in ceria lattice resulted in the formation of more surface oxygen vacancies, and thereby more coordinatively unsaturated surface metal cations and lattice oxygen anions were generated, which served as the Lewis acidic–basic sites required for the reaction. Based on in situ DRIFTS results, it was deduced that the oxygen vacancies played a crucial role in activating CO₂ to reactive bidentate carbonates and the formation of active terminal methoxy intermediates was also enhanced by Fe incorporation. Consequently, a maximum DMC yield of 3.84 mmol g⁻¹ h⁻¹ was obtained on Fe_0.04Ce_0.96O_x under relatively mild reaction conditions of 130 °C and 3.0 MPa. Additionally, in the tandem reaction system using 2-cyanopyridine (2-CP) as a dehydrating agent, the catalytic activity for 2-CP hydration was found to be closely associated with the total basicity of the catalysts, and in turn a higher hydration rate was more conducive to the DMC synthesis through enhancing in situ water removal efficiency. As expected, the present work provides in-depth insights into the structure–performance relationship of Fe-modified ceria-based catalysts for direct DMC synthesis from CO₂ and methanol and offers meaningful guidance for the advancement of highly efficient catalysts.