Abstract: A series of zirconia catalysts supported on Si-MCM-41 and Al-doped MCM-41 (Si/Al = 50) mesoporous molecular sieves, silica, γ-Al₂O₃, 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 γ-Al₂O₃, and 5%ZrO₂/MgO had no acidity because of the strong interaction between zirconia and MgO.

Key words: support effect, Meerwein-Ponndorf-Verley reduction, zirconia, MCM-41 mesoporous molecular sieve, benzaldehyde