苯乙酮氢转移反应中ZrO2/MCM-41和ZrO2/AC的催化性能对比

采用浸渍法制备了分别以活性炭(AC)和全硅MCM-41介孔分子筛负载的ZrO2催化剂,并对其进行了XRD、氮气吸附-脱附、X射线光电子能谱、差热-热重分析和吡啶吸附原位红外光谱等表征,考察了其在以异丙醇为氢源还原苯乙酮为α-苯乙醇的Meerwein-Ponndorf-Verley(MPV)反应中的催化活性,并与水合ZrO2进行对比.研究了载体对催化剂活性的影响.结果表明,ZrO2经MCM-41负载后,与载体发生强相互作用,可能形成Si—O—Zr键,ZrO2在载体表面呈高分散的无定形态,Zr—OH数目显著增加,L酸性增强,并形成B酸中心,使催化剂活性显著高于水合ZrO2;ZrO2负载在AC上后,与载体未发生强相互作用,ZrO2在载体表面未呈高分散状态,增加的Zr—OH数目相对较少,L酸性较弱,未形成B酸中心,催化活性未明显增加,但在较高焙烧温度(400～600℃)下,其仍能保持稳定的催化活性,这可归因于ZrO2/AC中AC孔道疏通及AC石墨层对苯乙酮上苯环的吸附作用,使活性位附近的反应底物浓度显著增大.

Comparison of ZrO2/MCM-41 and ZrO2/AC Catalysts in Hydrogen Transfer Reaction of Acetophenone

Zirconia(ZrO2) was supported on active carbon(AC) or siliceous MCM-41 mesoporous materials(ZrO2/MCM-41) respectively through the impregnation method,At the same time,these samples were cha-racterized by XRD,N2 adsorption-desorption,XPS,TG-DSC and FTIR spectra of adsorbed pyridine methods. Their catalytic activities in the Meerwein-Ponndorf-Verley(MPV) reduction of acetophenone with α-propanol as a hydrogen donor were investigated,and compared to that of hydrous zirconia to study the support effect on their catalytic activities.The results showed that catalytic activity was significantly improved upon loading zirconia on MCM-41 support,due to the formation of Si-O-Zr bond between zirconia and MCM-41 supported,which resulted in the formation of highly dispersed amorphous zirconia in the catalyst,consequently a marked increase of the amount of the Zr-OH group,the strengthening of Lewis acidity and an appearance of Brnsted acid sites.In contrast to ZrO2/MCM-41,no obvious increase of catalytic activity was observed after loading zirconia on AC support owing to the weak interaction between zirconia and AC support,which resulted in the lower dispersion of zirconia on AC support,consequently a less increase of number of Zr-OH groups and weak Lewis acidity.However,ZrO2/AC calcined at higher temperature(400-600 ℃) still retained steady activity,which may be due to the dredging of pores in AC during the calcination,and the increase of concentration of acetophenone near the active sites via the π-π electron interaction between the benzene ring in the acetophenone and graphite layer of AC support.