Abstract:

A series of Cu-ZnO-ZrO₂ catalysts were prepared by the sol-gel method using copper, zinc, zirconium nitrate and different amounts of citric acid as raw materials. XRD, TG-DTA, H₂-TPR, CO₂-TPD, FTIR, and BET were used to characterize the physicochemical properties of the xerogel and the catalysts, and the catalytic activity of the catalysts for the hydrogenation of CO₂ to methanol was evaluated. The effect of the coordination of Cu²⁺, Zn²⁺, Zr⁴⁺ with citric acid on the performance of the catalysts during the gelation was studied. The results showed that changing the amount of citric acid could regulate the coordination mode of Cu²⁺, Zn²⁺, Zr⁴⁺ with carboxylic acid. Cu²⁺ and Zn²⁺ with strong coordination ability can participate in the construction of three-dimensional network during the formation of gel, whereas Zr⁴⁺ was dissociated from the three-dimensional network, so the grain sizes of the active components of CuO, ZnO and ZrO₂ in the catalyst can be regulated accordingly. When the molar amount of citric acid was 1.5 times of that of metal ions, the active components of CuO, ZnO and ZrO₂ in the catalyst had compatible grain sizes, resulting in good catalytic performance for the hydrogenation of CO₂ to methanol.

Key words: sol-gel, citric acid, carbon dioxide, catalyst, methanol, hydrogenation

摘要：

采用溶胶-凝胶法以铜、锌、锆硝酸盐和柠檬酸为原料，改变柠檬酸用量，制备出一系列Cu-ZnO-ZrO₂催化剂。通过X射线衍射仪（XRD）、热重分析仪（TG-DTG-DTA）、H₂程序升温还原（H₂-TPR）、CO₂程序升温脱附（CO₂-TPD）、红外光谱仪（FTIR）及BET比表面积等表征手段对干凝胶及催化剂理化性能进行测试，并在催化反应活性评价装置上对催化剂的CO₂加氢合成甲醇反应活性进行评价，研究凝胶过程中Cu²⁺、Zn²⁺、Zr⁴⁺与柠檬酸结合方式对催化剂性能的影响。结果表明：改变柠檬酸用量可调控Cu²⁺、Zn²⁺、Zr⁴⁺与羧酸的配位方式，配位能力较强的Cu²⁺、Zn²⁺在凝胶制备过程中参与三维网络的构筑，而配位能力相对较弱的Zr⁴⁺游离于三维网络之外，从而差异化地调控催化剂中活性组分CuO、ZnO、ZrO₂晶粒尺寸大小。当柠檬酸的摩尔量为金属离子摩尔量的1.5倍时，催化剂中的活性成分CuO、ZnO、ZrO₂晶粒尺寸相互匹配，表现出较好的CO₂加氢合成甲醇催化性能。

关键词: 溶胶-凝胶, 柠檬酸, 二氧化碳, 催化剂, 甲醇, 加氢