ZrO_2/MCM-41催化的苯乙酮氢转移反应

Hydrogen-Transfer Reaction of Acetophenone over ZrO_2/MCM-41

通过浸渍法分别制备了硅胶(SiO2)、全硅MCM-41介孔分子筛负载ZrO2催化剂,考察其在以异丙醇为氢源,苯乙酮的氢转移反应中的催化性能,并与纯ZrO2进行对比,同时对各催化剂进行XRD、N2吸附-脱附、XPS、吡啶原位吸附红外等表征分析。结果表明:与纯ZrO2相比,负载型催化剂活性明显增加,归因于ZrO2与载体发生强相互作用,形成Si-O-Zr键,使催化剂表面的Zr-OH数目显著增加,出现B酸中心,且L酸中心强度增强。ZrO2/MCM-41的催化活性优于ZrO2/SiO2,可归因为前者中ZrO2的分散程度较高。ZrO2/MCM-41的最佳ZrO2负载量为5%(wt);最佳反应时间8 h;最佳异丙醇和苯乙酮摩尔比为10:1。苯乙酮含吸电子取代基后转化率升高,而含供电子取代基后转化率降低。5%ZrO2/MCM-41的催化活性随重复使用次数增加而逐渐降低。

The catalysts of zirconia supported on silica gel and siliceous MCM-41 mesoporous materials, respectively, were prepared by the impregnation method. Their catalytic activities in the Meerwein-Ponndorf-Vefley （MPV） reduction of acetophenone with ct-propanol as hydrogen donor were investigated, and compared to that of using hydrous zirconia as catalyst. At the same time, these samples were characterized by XRD, N2 adsorption-desorption, XPS, FT-IR spectra of adsorbed pyridine methods, respectively. The results show that loading zirconia on MCM-41 or silica gel can significantly improved its catalytic activity. The results show that the catalytic activity can be significantly improved by loading Zirconia on MCM-41 or silica gel, which causes the occurance of the strong interaction between Zirconia and supports, results in the formation of Si-O-Zr bonds and consequently causes a marked increase of the amount of the Zr-OH group on the catatyst surface, the appearance of Bronzed acid sites and the strengthening of Lewis acidity. ZrO2/MCM-41 shows better catalytic activity than ZrO2/SiO2 due to the highly dispersion of ZrO2 on MCM-41. The best loading amount of ZrO2 in ZrO2/MCM-41 is 5%（wt）. The reaction can be essentially completed after 8 h. The best mole ratio of 2-propanol to acetophenone is 10：1. Compared with acetophenone, the conversion of acetophenone with electron-withdrawing group linked to the aromatic ring is higher, while the conversion of acetophenone with electron-releasing group linked to aromatic ring is lower. When the 5%ZrOa/MCM-41 was reused, gradually dropping catalytic activity was observed.