ZrCdOx/SAPO-18双功能催化剂催化CO2加氢合成低碳烯烃性能

采用并流共沉淀法制备了不同Zr/Cd原子比(n_Zr/n_Cd)的ZrCdO_x金属氧化物,并与水热法制备的不同硅铝比(n_{SiO_(2})/n_{Al_(2}O₃))的片状SAPO-18分子筛物理混合制得ZrCdO_x/SAPO-18双功能催化剂,研究了其催化CO₂加氢直接合成低碳烯烃性能。采用透射电子显微镜(TEM)、X射线衍射(XRD)、N2吸附-脱附、CO₂程序升温脱附(CO₂-TPD)、NH3程序升温脱附(NH3-TPD)和X射线光电子能谱(XPS)对催化剂进行了分析。与单一ZrO2相比,引入CdO使得ZrCdO_x比表面积下降,当n_Zr/n_Cd=8时制备的Zr8Cd1氧化物呈现出无定形小颗粒状,Zr与Cd之间较强的协同作用使得Zr Cd Ox氧化物产生了更多的氧空位,有利于CO₂的吸附活化。通过对Zr8Cd1金属氧化物与SAPO-18(硅铝比0.1)的质量比、工艺反应温度、压力和空速对催化性能影响的考察,获得了最佳反应条件。研究还发现,当SAPO-18的硅铝比从0.1降为0.01时,Br?nsted酸含量降低,产物中烯烃/烷烃物质的量之比从18.6提高至37.2,但副产物CO含量迅速增加,低碳烯烃时空收率明显下降。

Catalytic Performance for CO2 Hydrogenation to Light Olefins over ZrCdOx/SAPO-18 Bifunctional Catalyst

ZrCdO_xmetal oxides with various Zr/Cd atomic ratios (n_Zr/n_Cd) were prepared by parallel coprecipitation method, the sheet-like SAPO-18 zeolites with molar ratio of SiO₂ to Al₂O₃ (n_{SiO 2}/n _{Al 2 O3}) of 0.1 and 0.01 were hydrothermally synthesized. The metal oxide and SAPO-18 were physically mixed to prepare ZrCdO_x/SAPO-18 bifunctional catalyst, and to study the catalytic performance for CO₂ hydrogenation to light olefins. Transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption-desorption, temperature-programmed desorption of CO₂ (CO₂TPD), temperature programmed desorption of ammonia (NH₃-TPD) and X ray photoelectron spectroscopy (XPS) were applied to analyze the catalysts. Compared with the sole ZrO₂, the introduction of CdO decreased the BET (Brunauer Emmett Teller) surface area of ZrCdO_x. The Zr₈Cd₁ oxide prepared with n_Zr/n_Cd=8 exhibited the small amorphous particles, the strong synergetic effect between Zr and Cd led to the generation of more oxygen vacancies in ZrCdO_xoxide, which was beneficial to the adsorption and activation of CO₂. The effect of mass ratio of Zr₈Cd₁ oxide to SAPO-18 (n_{SiO 2}/n_Al2O3=0.1), and the reaction temperature, pressure and space velocity on catalytic performance were investigated, and the optimal reaction conditions were obtained. Moreover, it is also found that when the ratio of n _{SiO 2}/n _{Al 2 O3} decreased from 0.1 to 0.01, the content of Brønsted acid reduced, the molar ratio of olefins to paraffin increased from 18.6 to 37.2; however, the content of by-product CO increased rapidly, and the space-time yield of light olefins decreased remarkably.