Selective formation of light olefins from CO2 hydrogenation over Fe–Zn–K catalysts

• Fe–Zn–K catalysts were prepared by microwave-aided hydrothermal procedure followed by incipient wetness impregnation.
• Addition of zinc changed the reduction and surface adsorption behavior of the catalysts.
• The hydrocarbon distribution was greatly improved over Fe–Zn–K catalysts by zinc promotion.
• 53.58% of C2–C4 olefins in overall hydrocarbon products was obtained on 1Fe–1Zn–K catalyst from CO2 hydrogenation.

Fe–Zn–K catalysts were prepared in varied Fe/Zn molar ratios using microwave-aided hydrothermal procedure followed by K modification with impregnation method and applied to CO2 hydrogenation reaction via Fischer–Tropsch synthesis for the selective production of C2–C4 olefins. Results showed that the prepared catalysts had uniform particles within about 100 nm. Addition of zinc to iron matrix formed ZnFe2O4 spinel phase and ZnO phase, and caused increase of the surface areas, enhanced the interaction between iron and zinc and altered the reduction and CO2 adsorption behaviors. The catalysts displayed high activity for the CO2 conversion and significant improvement in the product distribution. The proper interactions between Fe and Zn proved to be advantageous to suppress the production of C5+ hydrocarbons and promote the production of C2–C4 olefin. At set reaction conditions of H2/CO2 of 3, GHSV of 1000 h−1, 320 °C, and 0.5 MPa, the 1Fe–1Zn–K catalyst with H2/CO reduction showed the best performance with the CO2 conversion of 51.03%. The selectivity of C2–C4 olefins in overall hydrocarbons and the ratio of olefin to paraffin in the C2–C4 fraction reached 53.58% and 6.86, respectively.

In this work, Fe–Zn–K catalysts were prepared by microwave-aided hydrothermal procedure and subsequent potassium promotion by incipient wetness impregnation. The homogeneous precipitation method had advantages in improving the particle uniformity and the dispersion of active components over traditional co-precipitation method. Results showed that the prepared catalysts had uniform particles. The catalyst samples displayed good activity and light olefin selectivity in CO2 hydrogenation. The addition of zinc has played an important role in tailoring CO2 hydrogenation activity and product distribution by modifying the structure and surface adsorption behavior of iron catalysts, and thus improving the product distribution and stability of the catalysts. It is proved that Zn promoted iron catalysts is favorable for CO2 hydrogenation to light olefins with high activity and stability.Figure optionsDownload as PowerPoint slide