Surface impregnation combustion method to prepare nanostructured metallic catalysts without further reduction: As-burnt Cu-ZnO/SiO ₂ catalyst for low-temperature methanol synthesis

Nanostructured metallic catalysts (Cu/ZnO and Cu-ZnO/SiO ₂) 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/SiO ₂ 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 SiO ₂ 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 CO ₂ 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/SiO ₂ catalyst was closely related to Cu ⁰ 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 N ₂O chemisorption techniques.