Synthesis, Characterization and Catalytic Performance of Ti-Containing Mesoporous Molecular Sieves Assembled from Titanosilicate Precursors

Abstract

Novel Ti-containing mesoporous materials with wormhole structure (Ti-WMS) can be assembled from preformed titanosilicate-1 precursors with long-chain alkylamines as structure directors. The obtained products were characterized by a series of techniques including powder X-ray diffraction, transmission electron microscopy, FT-infrared spectroscopy, UV−visible spectroscopy, N2 sorption, and hyperpolarized 129Xe NMR at variable temperature. The catalytic properties of the materials were investigated by oxidative desulfurization reactions. The results show that Ti-WMS, whose synthesis utilizes zeolite precursors as total or part of the silica and titanium sources, is a pure mesoporous phase. However, the prepared materials contain additional micropores except the uniform mesopores, which is confirmed by N2 sorption and 129Xe NMR. Infrared spectra indicate that there are zeolitic primary and secondary building units in the pore walls of Ti-WMS. UV−visible spectroscopy results confirm the existence of active Ti4+ species. Ti-WMS is very active in the oxidation of bulky sulfides such as benzothiophene, dibenzothiophene, and 4,6-dimethyl dibenzothiophene, with activities similar to Ti-HMS. However, in thiophene oxidation, which is not diffusion-limited, Ti-WMS exhibits much higher catalytic activity than Ti-HMS because of the presence of micropores and zeolite-like active sites.