Preparation of nanometer CuO-ZnO-ZrO₂ catalysts through citrate-gel process and their catalytic properties for methanol synthesis from CO₂

CuO-ZnO-ZrO₂(CZZ) nanocatalysts were successfully prepared by citrate-gel method. The catalysts and their precursors were characterized by X-ray photoelectron spectroscopy (XPS), N₂ adsorption specific surface area measurement (BET), X-ray diffraction (XRD), H₂-temperature-programmed reduction (H₂-TPR), H₂ and CO₂-temperature-programmed desorption (H₂ and CO₂-TPD) and thermogravimetric analysis (TG-DTA). Drying time of the wet gel and the dosage of citric acid were systematicly studied, while combustion method was also conducted with the comparison of those obtained catalysts. Results show that, prolonged drying process can effectively prevent particle spattering during calcination, benefit the dispersion of different components in the catalyst, and improve the adsorption ability of catalyst for H₂ and CO₂. Sample CZZ-48h, which was dried at 112℃, 48h, maintained a much higher BET specific surface area than that prepared by combustion method. The CuO-ZnO-ZrO₂ catalyst, in which 100% of stoichiometric amount of citric acid was added, exhibited an optimum catalytic behavior with a space-time-yield of methanol 109.4g·h^-1·kg^-1 under the condition of 240℃, 2.6 MPa, 3600h^-1, H₂/CO₂=3. The detriment of the catalytic performance excessive amounts of citric acid is ascribed to decline dispersion of the catalyst component, and decomposition residual covering on the surface active species of the catalyst.