Surface impregnation combustion method to prepare nanostructured metallic catalysts without further reduction: As-burnt Cu–ZnO/SiO2 catalyst for low-temperature methanol synthesis

Nanostructured metallic catalysts (Cu/ZnO and Cu–ZnO/SiO2) were prepared by sol–gel auto-combustion method and a novel surface impregnation combustion method in the argon atmosphere, using metal nitrates and citric acid. The X-ray diffraction patterns revealed that all the xerogels were converted into Cu/ZnO or Cu–ZnO/SiO2 catalysts directly without further reduction. Cu crystallite size in the as-burnt catalyst which was prepared by surface impregnation combustion method was limited to only 7 nm, because the support SiO2 could disperse Cu–ZnO, adsorb heat and promote heat diffusion, leading to the combustion process significantly mild and smooth. The activity of the as-burnt catalysts was investigated for low-temperature methanol synthesis from syngas containing CO2 using 2-butanol as a promoter at 443 K and 5.0 MPa for 4 h. The activity of the as-burnt Cu/ZnO and Cu–ZnO/SiO2 catalyst was closely related to Cu0 surface areas and the Cu crystallite sizes. The effects of different preparation methods on the properties of catalysts were studied by XRD, TG–DTA, FT-IR, Raman spectrum, SEM, BET and N2O chemisorption techniques.