Modification Of CuO-ZnO-ZrO₂/SAPO-34 And Its Catalysis Properties On CO₂ Hydrogenation To Light Olefins

CO₂ is the most wide carbon resources of the natural world and the major member of greenhouse gas. The problem of the utilizing of carbon dioxide has caused concern among the fields of chemical industry and environmental protection. It is a hot topic of chemical utilizing CO₂ as a carbon resource. Light olefins are the most important raw materials in chemical industry and play a big role in the development of human society at now and in the future. In recent years, with the rapid development of industry, the demands of ethylene and propylene have been increased rapidly. However, the major method of preparing light olefins is cracking naphtha, there is no doubt that it will bring pressure to our lean oil country. One of the effective ways to remit the pressure of oil resources excessive consumption and ecological environment pollution is transforming the CO₂ to light olefins. Therefore, in this dissertation, the the modification of CuO-ZnO-ZrO₂ and SAPO-34 by rare earth metals and SiO₂ and bifunctional catalysts prepared by mechanically mixing were studied. Its application in the hydrogenation of carbon dioxide to light olefins was investigated.1. Y₂O₃, La₂O₃ and CeO₂ modified CuO-ZnO-ZrO₂ were prepared by co-precipitation method. The samples were characterized by the methods of XRD, SEM, TEM, BET, TPR and TG. Rare earth metals modified CuO-ZnO-ZrO₂ have good dispersion and higher specific surface area. The activity of bifunctional catalysts prepared by mechanical mixing of modified CuO-ZnO-ZrO₂ with SAPO-34 for the hydrogenation of carbon dioxide to light olefins was investigated. Under the conditions of reaction temperature at 400 ?, pressure at 3.0 MPa,space velocity?SV? of 1800 1/h, CO₂/H₂?molar ratio? of 1:3, mass ratio of Ce-CuO-ZnO-ZrO₂/SAPO-34 to 1:1 and the quality of bifunctional catalyst of 1.0g, the conversion of CO₂ could reach to 54.6%, with a light olefins selectivity and yield of 51.1% and 27.9%, respectively.2. Y, La and Ce modified SAPO-34?Me-SAPO-34,where Me = Y, La and Ce? were prepared by the hydrothermal method, respectively. The samples were characterized by the methods of XRD, SEM, FT-IR, BET, NH3-TPD and TG. The results show that rare earths are added into SAPO-34 framework. They have higher specific surface area and smaller particles size, as well as the changes in the pore diameter and acidity. Bifunctional catalysts of CuO-ZnO-ZrO₂/Me-SAPO-34 were prepared by mechanically mixing Me-SAPO-34 with CuO-ZnO-ZrO₂ in the weight ratio of 1:1. Its catalytic activity for carbon dioxide hydrogenation to light olefins was investigated. Under the conditions of reaction temperature at 400 ?, pressure at 3.0 MPa,space velocity?SV? of 1800 1/h,CO₂/H₂?molar ratio? of 1:3 and bifunctional catalyst mass of 1.0 g, CuO-ZnO-ZrO₂/La-SAPO-34 exhibits good catalytic activity, in which the conversion of CO₂ could reach to 49.7% with a light olefins selectivity and yield of 54.5% and 27.1%, respectively.3. SiO₂-doped CuO-ZnO-ZrO₂ was prepared by co-precipitation method. The samples were characterized by the methods of XRD, BET, SEM, TEM, TPR and TG. SiO₂-doped CuO-ZnO-ZrO₂ has higher specific surface area, better dispersion and higher thermal stability. The activity of bifunctional catalysts prepared by mechanical mixing of 8%SiO₂-CuO-ZnO-ZrO₂ with SAPO-34 for the hydrogenation of carbon dioxide to light olefins was investigated on a fixed-bed reactor. Under the conditions of reaction temperature at 420 ?, pressure at 3.0 MPa,space velocity?SV? of 1800 1/h, CO₂/H₂?molar ratio? of 1:3, mass ratio of 8%SiO₂-CuO-ZnO-ZrO₂ to SAPO-34 of 1:1 and the quality of bifunctional catalyst of 1.0 g, the conversion of CO₂ could reach to 53.9%, with a light olefins selectivity and yield of 52.9% and 28.5%, respectively.