Preparation And Catalysis Property Of Core-shell And Layeral CuO-ZnO-Al₂O₃/Zeolite

Carbon dioxide is one of the main greenhouse gases. The reasonable recycling of carbon dioxide can effectively achieve a virtuous circle, which can not only alleviate the energy crisis, but also reduce the greenhouse effect. So the study is significant for energy-saving and environmental protection.Methanol synthesis by carbon dioxide hydrogenation and methanol dehydration to dimethyl ether (DME) are complicated chemical processes. In this paper, progress of methanol synthesis by carbon dioxide hydrogenation was reviewed. The active center models and catalytic mechanisms of methanol catalysts were discussed. The industrial production and application of DME were introduced. Preparation of DME catalysts and their influencing factors were analyzed. Based on the review, the following works were mainly carried out.Hard carbon with perfect spherical morphology was prepared by a hydrothermal synthesis method. Various metal salts were dispersed together with carbon spheres in water to make metal ions incorporate into carbon sphere hydrophilic shell. The removal of carbon via calcination yields multiple metal oxide composite nanoparticles. NaZSM-5@CuO-ZnO-Al2O3core-shell catalyst was prepared hydrothermally by CuO-ZnO-Al2O3composite nanoparticles as the core and NaZSM-5as the shell. It was characterized by XRD, SEM, EDS, BET and thermal analysis. The experimental results showed that the core-shell catalyst exhibited higher catalytic activity for the hydrogenation of CO2to dimethyl ether. Under reaction conditions of the pressure of3.0MPa, space velocity (SV) of1800mL·gcat-1·h-1, CO2/H2volume ratio of1:3, and temperature of270℃, the conversion of CO2reaches48.3%, with a dimethyl ether yield and selectivity of23.4%and48.5%, respectively.Expanded graphite as the carrier, layered catalyst of CuO-ZnO-Al2O3was prepared by ultrasonic method. It was characterized by the methods of XRD, TG-DTA, SEM and BET. Mechanically mixing Layered CuO-ZnO-Al2O3with HZSM-5can obtain composite catalyst of CuO-ZnO-Al2O3/HZSM-5. Composite catalyst of CuO-ZnO-Al2O3/HZSM-5for the synthesis of dimethyl ether from hydrogenation of CO2was studied in the fixed-bed reactor and the catalytic activity were investigated under the reaction conditions that temperature at265℃, space velocity (SV) at1800mL·gcat-1·h-1, volume ratio of CO2/H2at1:3, pressure at3.0MPa, CuO-ZnO-Al2O3/HZSM-5=2/1, w(CuO/ZnO)=2:1and the amount of expanded graphite is5%. The result shows that the conversion of CO2can be reached to45.43%, with a dimethyl ether selectivity and yield of37.81%and17.18%, respectively.