In–Co–Zn/C–N catalysts derived from ZIFs for selective hydrogenation of CO2 into methanol

Abstract

Recently, In₂O₃-based catalysts have shown great promise in methanol synthesis from CO₂ hydrogenation due to their high methanol selectivity. However, low CO₂ conversion restricts their application. Herein, we report In₂O₃ combined with zeolitic imidazolate framework (ZIF)-derived Co–Zn/C–N catalysts for the CO₂ hydrogenation reaction in a fixed-bed reactor. The catalysts were characterized by X-ray diffractometry, transmission electron microscopy, CO₂ and H₂ temperature desorption measurements, X-ray photoelectron spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. Compared to pure In₂O₃, In–Co–Zn/C–N-4 (PM) shows higher CO₂ conversion, with even higher methanol selectivity. A CO₂ conversion of 7.0% was achieved with a methanol selectivity over 77% and the space time yield (STY) of methanol was 3.3 mmol g_cat⁻¹ h⁻¹ under the conditions of H₂/CO₂ = 3 : 1, 2 MPa, 300 °C and GHSV = 6 L g_cat⁻¹ h⁻¹. The In–Co–Zn/C–N-4 (IMP) catalyst shows much lower methanol selectivity (46.6%) and stability due to the formation of Co₃InC_0.75. ZnO effectively weakens the interactions between Co and In, and the physically-mixed method further prevents the formation of Co₃InC_0.75. DRIFTS results were used to predict the possible methanol and CO production pathway through a formate intermediate for the In–Co–Zn/C–N catalyst.