Synergistic Effect of Alkali Na and K Promoter on Fe-Co-Cu-Al Catalysts for CO2 Hydrogenation to Light Hydrocarbons

Alkali metal K- and/or Na-promoted FeCoCuAl catalysts were synthesized by precipitation and impregnation, and their physicochemical and catalytic performance for CO2 hydrogenation to light hydrocarbons was also investigated in the present work. The results indicate that Na and/or K introduction leads to the formation of active phase metallic Fe and Fe-Co crystals in the order Na < K < K-Na. The simultaneous introduction of Na and K causes a synergistic effect on increasing the basicity and electron-rich property, promoting the formation of active sites Fe@Cu and Fe-Co@Cu with Cu0 as a crystal core. These effects are advantageous to H2 dissociative adsorption and CO2 activation, giving a high CO2 conversion with hydrogenation. Moreover, electron-rich Fe@Cu (110) and Fe-Co@Cu (200) provide active centers for further H2 dissociative adsorption and O-C-Fe intermediate formation after adsorption of CO produced by RWGS. It is beneficial for carbon chain growth in C2+ hydrocarbons, including olefins and alkanes. FeCoCuAl simultaneously modified by K-Na exhibits the highest CO2 conversion and C2+ selectivity of 52.87 mol% and 89.70 mol%, respectively.