Study Of Bifunctional Catalyst For The Synthesis Of Dimethyl Ether From Biomass-derived Gas

The synthesis of dimethyl ether ?DME? from biomass-derived gas was catalyzed by the bifunctional catalyst composed of CuO-ZnO-Al₂O₃ and HZSM-5. The effects of content of promoter Li and different additives ?Ce, Y, Ga, Zr? on the catalytic performance of the CuO-ZnO-Al₂O₃/HZSM-5 catalyst for the synthesis of DME were studied. Furthermore, the effect of preparation methods on the catalytic performance of the CuO-ZnO-Al₂O₃-ZrO₂/HZSM-5 catalyst was investugated. The prepared catalysts were evaluated by pressurized fixed bed reactor, and characterized by XRD, N2 low temperature adsorption, N2O chemical adsorption, SEM, XPS and H₂-TPR. The main results achieved are as follows:1. Effect of Li₂O content on performance of CuO-ZnO-Al₂O₃-Li₂O?x?/HZSM-5 catalystA series of CuO-ZnO-Al₂O₃-Li₂O mixed oxides were prepared by a traditional co-precipitation method, and the effect of Li₂O content on the performance of CuO-ZnO-Al₂O₃-Li₂O?x?/HZSM-5 catalyst was investigated. The results show that the addition of an appropriate amount of Li can promote the dispersion of the active components in the catalyst and increase the Cu surface area, thereby increasing the conversion of CO.Under the conditions of H₂/CO/CO₂=2:2:1,P=3.0 MPa,T=250 0C,WHSV=2400 mL h-1·9cat-1,the CO conversion and DME selectivity of 61.1% and 63.4% were obtained on the CZAL-0.5/HZSM-5 catalyst. In addition, the addition of Li can also effectively prevent the growth of Cu crystals, thereby enhancing the long-term stability of the composite catalyst.2. Effect of the additives ?Ce, Y, Ga, Zr? on the performance of CuO-ZnO-Al₂O₃/HZSM-5 catalystThe effects of the addition of Ce, Y, Ga and Zr on the performance of CuO-ZnO-Al₂O₃/HZSM-5 catalyst were investigated. The results show that the different kinds of additives have different effects on the performance of the catalyst. The addition of the promoter Zr can promote the dispersion of the active component Cu in the catalyst, and improve the Cu surface area, thus improving the conversion of CO and the yield of DME. In addition, the addition of Zr can also improve the stability of the composite catalyst.3. Effect of preparation methods on the performance of the CuO-ZnO-Al₂O₃-ZrO₂/HZSM-5 catalystIn order to explore the effect of the preparation methods on the performance of the catalyst,CuO-ZnO-Al₂O₃-ZrO₂ were prepared by traditional co-precipittion with Na2CO3 as pricipitant,oxalate co-precipitation,solid state reaction and combustion methods. The results show that the catalytic activity of the CuO-ZnO-Al₂O₃-ZrO₂ prepared by traditional co-precipittion method mixed with HZSM-5 is the best due to the smallest Cu particles and the largest surface area of metallic copper.