溶胶凝胶法制备Cu-ZnO-ZrO2催化剂：pH对其性能的影响

Preparation of Cu-ZnO-ZrO2 Catalyst by Sol-gel Method: Effect of pH on Its Properties

摘要:

采用溶胶-凝胶法以硝酸盐、柠檬酸为原料，加入氨水调节溶液pH，制备出一系列Cu-ZnO-ZrO2催化剂。并通过粉末XRD、热重-差示扫描量热分析(TG-DSC)、N2吸附-脱附(BET)、氢气程序升温还原(H2-TPR)、CO2程序升温脱附(CO2-TPD)、SEM、TEM及傅里叶变换红外光谱(FTIR)对干凝胶及催化剂进行了理化性能测试，并在高温高压固定床反应器上进行催化剂活性评价。讨论了溶液pH对干凝胶结构及催化剂性能的影响。结果表明：pH为0.5制备得到的干凝胶中存在未配位的游离羧酸，同时又有部分羧酸通过羧基与金属离子进行了配位，而pH为4、6、8、10制备得到的干凝胶中不存在游离羧酸，羧酸均通过羧基与金属离子进行了配位。pH的改变调控着Cu2+、Zn2+、Zr4+与柠檬酸之间的配位能力，使得pH为6时制备得到的催化剂具有较大的比表面积以及铜分散度，比表面积为92.5 m2/g，铜分散度为18.63%，并表现出较好的CO2加氢合成甲醇催化性能 ，CO2转化率为24.7%，甲醇选择选择性为42.3%。

Abstract:

A series of Cu-ZnO-ZrO2 catalysts were prepared by sol-gel method using nitrate and citric acid as raw materials by adding ammonia water to adjust the pH value of the solution. XRD, thermal analysis (TG-DSC), N2 adsorption desorption (BET), H2 temperature programmed reduction (H2-TPR), CO2 temperature programmed desorption (CO2 -TPD), SEM,TEM and Fourier transform infrared (FTIR) spectroscopy were used to characterize the catalysts. The catalyst activity was evaluated in a high temperature and high pressure fixed bed reactor. The effect of pH of solution on the structure of dry gel and the performance of catalyst was discussed. The results showed that there was an uncoordinated free carboxylic acid in the dried gel prepared at pH 0.5, and some carboxylic acids were coordinated with metal ions through the carboxyl group. The free carboxylic acid was not present in the dried gel prepared at pH 4, 6, 8, and 10. The carboxylic acid was coordinated to the metal ion through the carboxyl group. The change of pH regulated the coordination ability between Cu2+, Zn2+, Zr4+ and citric acid. The catalyst prepared at pH 6 had a large specific surface area and copper dispersion, with a specific surface area of 92.5 m2/g and a copper dispersion of 18.63%, which exhibited better methanol synthesis by CO2 hydrogenation performance,Xco2=24.7%,SCH3OH=42.3%.