Effect of Sulfate Modification on Structure Properties, Surface Acidity, and Transesterification Catalytic Performance of Titanium-Submitted Mesoporous Molecular Sieve

A series of sulfated titanium-submitted mesoporous molecular sieves denoted as S/Ti-MCM-41 were prepared by wet impregnation method with H2SO4 solution as promoter. The results of XRD, N-2 adsorption-desorption, NH3-TPD, FTIR of pyridine adsorption, and XPS analysis indicated that S/Ti-MCM-41 samples possess well-ordered hexagonal mesostructure, although the pore diameter and specific surface area shrunk with the increasing coverage of sulfur species. As a result of the electron inductive effect from the S=O bond of SO42-, Lewis acidity is intensified significantly and new Bronsted acid sites are generated from the activated hydroxyl groups. Bronsted acid sites are medium strength, while part of the Lewis acid sites are of weak strength and part of them are medium. The S/Ti-MCM-41 catalysts exhibited desirable activity for transesterification of dimethyl oxalate and phenol.