Rhodium-doped iron oxides promoted by sodium for highly selective hydrogenation of CO 2 to ethanol and C 2+hydrocarbons

Hydrogenation of CO 2 to produce high-value C 2 + products has gained great interest, but catalyst design for highly selective ethanol still remains a challenge. Herein, bifunctional catalysts of iron oxide promoted with rhodium and sodium, Na-Rh-FeO x and Rh-FeO x-Na, were prepared by using simple methods of incipient wetness impregnation (IWI) and coprecipitation. The former catalyst prepared via IWI, Na-Rh-FeO x , is remarkably efficient for the hydrogenation of CO 2 to ethanol with high selectivity of 91 % at 200 degrees C in the liquid fraction. The latter catalyst synthesized solely through the coprecipitation in a sodium-containing medium, Rh-FeOx-Na, displayed the synergy effect to perform a better CO 2 conversion of 23 % at 200 degrees C. Characterization of catalysts via XRD, XPS, N 2 physisorption, CO 2-TPD, and gas pulse-chemisorption reveals that different preparation methods influenced the dispersion of sodium particles. This property, in turn, impacts the ratio of hydrogenactivating sites to CO-adsorption sites, directly related to the balance between dissociative- and nondissociative CO* intermediates, which is crucial for ethanol formation. Adding alkali metal facilitates the formation of iron carbide Fe 5 C 2 , known to be active for C - C propagation. Integrating Na-Rh-FeO x with ZSM-5 support further increased ethanol selectivity up to 97 % in liquid phase and 90 % in gas phase. By selecting a proper route for introducing alkali metals and combining with supports, the catalyst properties can be effectively tailored, thereby regulating the catalytic activity and selectivity.