水热法制备Cu-ZnO纳米催化剂用于乙酸乙酯加氢

Hydrothermal preparation of Cu-ZnO catalyst for catalytic hydrogenation of ethyl acetate

摘要:

以六水硝酸锌、三水硝酸铜、尿素为原料，采用水热法制备了不同铜锌物质的量比n（n=1/4，3/7，2/3，1和3/2，对应铜摩尔分数分别为0.2，0.3，0.4，0.5和0.6）的Cu-ZnO催化剂，用SEM、XRD、H2-TPR、BET等方法对Cu-ZnO催化剂进行了结构表征。研究了铜摩尔分数对催化剂形貌及乙酸乙酯加氢反应的影响。结果表明，水热法制得的Cu-ZnO催化剂均为纳米片自组装成的开放型纳米花结构。当铜摩尔分数为0.4时，纳米片厚小于50nm，纳米花直径约10μm，乙酸乙酯转化率最高。铜摩尔分数过低或过高时加氢活性下降。表征发现，铜摩尔分数为0.4的催化剂中Cu与ZnO的结合强度适中，活性位分散均匀。考察了水热条件对催化性能的影响，在最优水热条件（130℃、10h）下合成的催化剂乙酸乙酯转化率达到94% 〔加氢反应条件为220℃、3MPa、氢气与乙酸乙酯物质的量比20、液时空速2.0g酯(g催化剂•h）〕。在催化剂稳定性（300h）测试中乙酸乙酯转化率保持在92%以上。

Abstract:

Cu-ZnO catalysts with different Cu-Zn molar ratios (n=1/4, 3/7, 2/3, 1 and 3/2, corresponding to copper mole fraction of 0.2, 0.3, 0.4, 0.5 and 0.6) were prepared by hydrothermal method using zinc nitrate hexahydrate, copper nitrate trihydrate and urea. The structure of Cu-ZnO catalysts was characterized by SEM, XRD, H2-TPR and BET. The effects of copper mole fraction on the morphology of catalyst and the hydrogenation of ethyl acetate were studied. The results show that the Cu-ZnO catalysts prepared by hydrothermal method are all self-assembled nanoflower structures. When the copper mole fraction is 0.4, the thickness of the nanosheet is less than 50 nm, the diameter of the nanoflower is about 10μm, and the conversion rate of ethyl acetate is the highest. When the mole fraction of copper is too high or too low, the activity decreases. It was found that the binding strength of Cu and ZnO was moderate and the active sites were well dispersed in the catalyst with copper mole fraction of 0.4. The effects of hydrothermal conditions on the catalytic performance were investigated. The conversion of ethyl acetate reached 94% under the optimal hydrothermal conditions〔hydrogenation reaction conditions: 220℃, 3Mpa, mass ratio of hydrogen to ethyl acetate: 20, space-time velocity of liquid: 2.0g ester (g catalyst•h)〕. The conversion of ethyl acetate remained above 92% in the stability test of catalyst (300h).