Sodium Promoted FeZn@SiO 2 -C Catalysts for Sustainable Production of Low Olefins by CO 2 Hydrogenation.

A prepared FeZnNa@SiO₂-C catalyst with graphitized carbon (C)-modified mesoporous SiO₂ supports metal nanoparticles with the sol–gel method. The effect of adding metal Na and Zn promoters as a dispersion on the CO₂ hydrogenation to low olefins was systematically studied. The results showed that Zn–Na, as a combination, could promote the absorption of CO₂ and improved the conversion rate of CO₂. Na as an alkaline substance can improve the absorption of more acidic CO₂, which could increase the conversion rate of CO₂ to 59.03%. Meanwhile, the addition of secondary metal Zn to Fe-based catalysts to form a surface alloy could alter the adsorption of CO₂ and the activation of C-O bonds, inhibit the subsequent hydrogenation of olefins to paraffins, and facilitate the reduction of Fe₂O₃ and the formation of active Fe₅C₂ species. The formation of active Fe₅C₂ species was found in TEM and XRD, and the selectivity of the target product was 41.07%. The deep hydrogenation of olefins was inhibited, and the space–time yield (STY) of low olefins was raised again by inhibiting their deep hydrogenations, up to 0.0436. However, the corresponding STY did not increase infinitely with the increase of Na doping, and higher catalytic performance for CO₂ hydrogenation could be exhibited when the Na doping reached 6.4%. Compared with Fe@SiO₂-C catalyst, Na- and Zn-promoted Fe-based catalysts, prepared by the modified sol-gel method, can be used directly for highly efficient CO₂ hydrogenation to low olefins and thus has a more promising application prospect in the future. [ABSTRACT FROM AUTHOR]