Support Effect in Meerwein-Ponndorf-Verley Reduction of Benzaldehyde over Supported Zirconia Catalysts

A series of zirconia catalysts supported on Si-MCM-41 and Al-doped MCM-41 (Si/Al = 50) mesoporous molecular sieves, silica, γAl2O3, and MgO were prepared by the wet impregnation method. The catalytic activities of these materials in the Meerwein-Ponndorf-Verley reduction (MPV) of benzaldehyde with 2-propanol as reducing agent were investigated, and compared to that of hydrous zirconia. The materials were characterized by X-ray diffraction, nitrogen adsorption-desorption, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy, and Fourier transform infrared and thermal desorption of pyridine. Loading zirconia on Si-MCM-41, Al-MCM-41, and SiO2 gave improved catalytic activity. This is attributed to a strong interaction of zirconia with the support to form Si–O–Zr bonds, which gave a significant increase in the amount of exposed Zr–OH groups and stronger Lewis acidity as well as an appearance of Brönsted acid sites. The activity of 5%ZrO2/Si-MCM-41 was the highest, followed by those of 5%ZrO2/Al-MCM-41 and 5%ZrO2/SiO2. However, 5%ZrO2/Al2O3 and 5%ZrO2/MgO gave very low catalytic activities. This is ascribed to that the acidities of 5%ZrO2/Al2O3 and the γ Al2O3 support were similar due to the weak interaction of zirconia with γAl2O3, and 5%ZrO2/MgO had no acidity because of the strong interaction between zirconia and MgO.

摘要采用浸渍法制备了 Si-MCM-41 和 Al-MCM-41 (Si/Al = 50) 介孔分子筛, SiO2, γ-Al2O3 及 MgO 等负载的 ZrO2 催化剂, 考察了其在以异丙醇为氢源苯甲醛 Meerwein-Ponndorf-Verley (MPV) 还原反应中的催化活性, 并与纯 ZrO2 的催化活性进行对比. 同时, 采用 X 射线衍射、N2 吸脱附法、X 射线光电子能谱、紫外-可见漫反射光谱和吡啶原位吸附红外光谱等手段表征了催化剂. 结果表明, ZrO2 负载于 Si-MCM-41, Al-MCM-41 和 SiO2 后, 催化活性明显提高, 这归因于 ZrO2 与载体间存在强相互作用形成 Zr−O−Si 键, 使催化剂表面 Zr−OH 数量显著增多, Lewis 酸中心强度增强, 并出现 Brönsted 酸中心, 三种催化剂的活性高低次序是 5%ZrO2/Si-MCM-41 > 5%ZrO2/Al-MCM-41 > 5%ZrO2/SiO2. 而 5%ZrO2/Al2O3 和 5%ZrO2/MgO 基本无催化活性, 可归因为 ZrO2 与 γ-Al2O3 的弱相互作用使 5%ZrO2/Al2O3 的酸性与γ-Al2O3 类似, ZrO2 与 MgO 的强相互作用使 5%ZrO2/MgO 基本无酸性.

Graphical abstractInteraction between zirconia and support plays an important role in the surface acidity of supported zirconia catalysts, which is in a good correlation with their catalytic activities in the Meerwein-Ponndorf-Verley reduction of benzaldehyde with 2-propanol.Figure optionsDownload full-size imageDownload as PowerPoint slide