A sol–gel auto-combustion method to prepare Cu/ZnO catalysts for low-temperature methanol synthesis

Abstract

Metallic Cu/ZnO catalysts were prepared by a sol–gel auto-combustion method using metal nitrates and citric acid. The activity of the burnt catalysts was investigated for low-temperature methanol synthesis from CO₂-containing syngas using ethanol as solvent and a promoter. The activity and the methanol selectivity of the burnt Cu/ZnO catalysts were closely related to metallic Cu⁰ surface areas and Cu crystalline sizes, and were greatly influenced by the reaction temperature. The effects of M/CA mole ratios on the properties of the burnt catalysts and catalytic activity were systematically studied by Thermogravimetry, Differential Thermal Analysis, Fourier Transform-Infrared, Raman spectrum, X-Ray Diffraction, Scanning Electron Microscope-Energy Dispersive Spectroscopy, Temperature-Programmed Reduction, Brunauer–Emmett–Teller, and N₂O chemisorption techniques. The fierceness degree and the temperature of the whole catalyst preparation process were closely related to the balance between the combustion and the pyrolysis processes respectively. Upon continually increasing the citric acid content in the initial precursors, the combustion process became much milder, but excess citric acid in the chelated compound could lead to more violent amorphous carbon oxidation and much more severe pyrolysis of organic residues.