Nitrate Combustion Methods to Prepare Highly Active Cu/ZnO Catalysts for Low-Temperature Methanol Synthesis: Comparative Behaviors of Citric Acid in Air or Argon Atmosphere

Abstract A citric acid-assisted solid-state method is developed to prepare highly active Cu/ZnO catalysts in different atmospheres (air and argon). The entire catalyst preparation process is accomplished with inexpensive raw materials. It is environmentally friendly in that no water is used and no waste water is produced during the entire process. These as-prepared catalysts are investigated in low-temperature methanol synthesis with CO2-containing syngas. The properties of these catalysts are systematically studied by thermogravimetry differential thermal analysis, X-ray diffraction, Fourier transform-infrared spectroscopy, Raman spectroscopy, temperature-programmed reduction, Brunauer–Emmett–Teller, and N2O chemisorption techniques. The activity and methanol selectivity of Cu/ZnO catalysts are closely related to the metallic Cu0 surface areas and Cu crystalline sizes. Compared with traditional solid-state or sol–gel autocombustion methods, the catalysts prepared by this citric acid-assisted solid-state method exhibit much higher activity and methanol selectivity.