Enhanced light olefin production from CO2 over potassium promoted Fe-Co bimetallic ZrO2 supported catalysts

Over 1300 tons of carbon dioxide (CO2) is emitted into the earth's atmosphere every second, threatening to breach the limiting global temperature increase of 1.5 degrees C set under the Paris Agreement. It is considered as sustainable feedstock that ensures season-wide availability for producing oxygenates and olefins. Likewise, CO2 hydrogenation to lower olefins was performed using bimetallic Fe-Co catalysts, processed in situ in a fixed-bed catalytic microreactor at 280-380 degrees C and a pressure of 0.5-3 MPa. A MOF framework (UIO-66) was used to fabricate ZrO2 NPs. In addition, a series of potassium-promoted Fe-Co bimetallic catalysts over the ZrO2 NPs were prepared, characterised and studied for the hydrogenation of carbon dioxide to light olefins. With increasing K content, the selectivity of C2-C4 increased under all operating conditions. The spent catalyst exhibits the bimodal size distribution of Fe3C, Fe2O3 and Fe degrees after a modified Fischer-Tropsch synthesis (M-FTS) reaction. The XANES data shows that the energy of the Fe K-edge and the Zr K-edge are shifted in a positive direction compared to the respective foil, indicating the presence of oxides in the fresh catalyst. Under the optimised reaction conditions, the H2-pretreated K promoted Fe-Co catalyst (K5Co3Fe10/ZrO2) showed remarkably low methanation with an olefin (C2-C4) selectivity of 38 %. In addition, the catalyst exhibits excellent stability and activity, providing nearly constant CO2 conversion and selectivity of (C2- C4=) lower olefins, CO and paraffin over the 100 h time-onstream.