Facile solid-state synthesis of Cu-Zn-O catalysts for novel ethanol synthesis from dimethyl ether (DME) and syngas (CO + H_2)

摘要

The Cu_x-Zn_y, -O (Cu:Zn = x:y) mixed oxide catalysts with different Cu:Zn atomic ratio were prepared through a new solid-state reaction method. The physicochemical properties of these catalysts were characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), N_2 adsorption and H_2 temperature programmed reduction (H_2-TPR). The results showed that with the increase of the molar ratio of Cu:Zn, the crystallite sizes decreased at first and then increased. The smallest crystallite size was realized when the molar ratio of Cu:Zn was 4:6. At the same time, the largest surface area was also obtained at this molar ratio. The catalytic performances of Cu_x-Zn_y,-O mixed oxide to hydrogenation of methyl acetate were tested using flow-type fixed bed reactor. The conversion of the Cu_(0.4)-Zn_(0.6)-O catalyst to methyl acetate was 72.6%, higher than those of Cu_x-Zn_y-O catalysts with other molar ratios. The highest catalytic activity of the Cu_(0.4)-Zn_(0.6)-O catalyst was due to its smaller crystallite size, larger surface area and higher particles dispersion compared with the other samples. Furthermore, Cu_(0.4)-Zn_(0.6)-O catalyst was tested in dual-catalyst-bed reactor to synthesize ethanol from dimethyl ether (DME) and syngas (CO + H_2) with the coexisting zeolite catalyst. For comparison, the Cu-Zn-O catalyst prepared by the conventional co-precipitation method was also tested as a reference catalyst. The reaction results showed that the conversion of Cu_(0.4)-Zn_(0.6)-O catalyst to DME was higher than that of Cu-Zn-O catalyst. All in all, both the preparation method and the molar ratio of Cu-Zn are responsible for the catalytic activity of the prepared catalysts.