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

Abstract

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 °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 °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° 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-on-stream.