Enhanced CO2 hydrogenation to methanol over Cu-ZnO-Al2O3 catalyst modified with zirconium: Experimental and theoretical insights

Abstract

For CO₂ hydrogenation to methanol, optimizing catalytic performance with long life and excellent activity remains one of the major challenges. In this paper, a series of Cu-ZnO-Al₂O₃ (CZA) catalysts modified with different amounts of Zr were prepared by the co-precipitation method. The effect of Zr promoter on the catalytic performance was explored by experiment combined with DFT calculation. The experimental results show that Cu-ZnO-Al₂O₃-Zr catalyst with a molar ratio of Cu/Zn/Al/Zr = 2:1:1:0.5 could improve the activity and stability of the catalyst, achieving a CO₂ conversion (25.1 %) and methanol selectivity (60.3 %) under condition of 260 ℃, 6 MPa and 6000 mL × g_cat^-1 × h⁻¹, which is higher than that of the commercial Cu-based catalyst (X_CO2 = 20.5 %, S_MeOH = 33 %). TEM and XRD characterizations show that Zr doping promotes the dispersion of Cu species by forming small Cu particles. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) investigation reveals that the CO₂ hydrogenation to methanol on Cu/ZnO/Al₂O₃-Zr0.5 catalyst follows the formate pathway. DFT calculation results show that the creation of ZrO_x/Cu₂O interfaces could significantly promote the adsorption of intermediates by reducing the reaction energy barrier of several elementary steps. This work has demonstrated the role of Zr doping in the catalytic improvement of Cu-based catalysts via experiments combination with theoretical calculation, providing new insights in the catalyst designing for CO₂ hydrogenation to methanol.