柠檬酸盐凝胶法制备纳米CuO-ZnO-ZrO_2的工艺分析及CO_2加氢制甲醇的性能

采用柠檬酸盐凝胶法制备出纳米CuO-ZnO-ZrO_2(CZZ)催化剂,应用XPS、BET、XRD、H_2-TPR、H_2-TPD、CO_2-TPD和TG-DTA等检测手段对催化剂及前驱体的结构进行表征。研究了湿凝胶干燥时间和柠檬酸用量对催化剂结构的影响,并与燃烧法制得的催化剂进行对比,考察了不同催化剂CO_2加氢制甲醇的性能。研究表明,延长湿凝胶干燥时间可有效防止催化剂焙烧时发生喷溅,有利于催化剂中各组分的分散,提高催化剂对H_2和CO_2的吸附能力;112℃干燥48h制得的催化剂(CZZ-48h)BET比表面积为43.5m~2/g,高于燃烧法;柠檬酸用量等于化学计量比时催化剂的性能最佳,在240℃、2.6MPa、空速为3600h-1、H_2/CO_2(体积比)为3的条件下甲醇时空收率达109.4g/(kg·h);柠檬酸过量会影响催化剂组分的分散度,并造成分解残留覆盖催化剂表面活性位而不利于CO_2加氢反应。

Preparation of nanometer CuO-ZnO-ZrO2 catalysts through citrate-gel process and their catalytic properties for methanol synthesis from CO2

CuO-ZnO-ZrO₂(CZZ) nanocatalysts were successfully prepared by citrate-gel method. The catalysts and their precursors were characterized by X-ray photoelectron spectroscopy (XPS), N₂ adsorption specific surface area measurement (BET), X-ray diffraction (XRD), H₂-temperature-programmed reduction (H₂-TPR), H₂ and CO₂-temperature-programmed desorption (H₂ and CO₂-TPD) and thermogravimetric analysis (TG-DTA). Drying time of the wet gel and the dosage of citric acid were systematicly studied, while combustion method was also conducted with the comparison of those obtained catalysts. Results show that, prolonged drying process can effectively prevent particle spattering during calcination, benefit the dispersion of different components in the catalyst, and improve the adsorption ability of catalyst for H₂ and CO₂. Sample CZZ-48h, which was dried at 112℃, 48h, maintained a much higher BET specific surface area than that prepared by combustion method. The CuO-ZnO-ZrO₂ catalyst, in which 100% of stoichiometric amount of citric acid was added, exhibited an optimum catalytic behavior with a space-time-yield of methanol 109.4g·h^-1·kg^-1 under the condition of 240℃, 2.6 MPa, 3600h^-1, H₂/CO₂=3. The detriment of the catalytic performance excessive amounts of citric acid is ascribed to decline dispersion of the catalyst component, and decomposition residual covering on the surface active species of the catalyst.