Preparation of mesoporous titanosilicate molecular sieves with a cage type 3D porous structure for cyclohexene epoxidation

Abstract

We report on the preparation of mesoporous titanosilicate with a 3D porous structure and Fm3m symmetry using Pluronic F127 as structure directing agent and titanium isopropoxide as a titanium source. The amount of titanium in the silica framework of the materials is controlled by a simple adjustment of the molar water to hydrochloric acid (nH2O/nHCl) ratio. The materials with different nSi/nTi ratios are also prepared by varying the amount of titanium source in the synthesis gel at an optimized nH2O/nHCl of 463. The structural order, the textural parameters, morphology, the nature and co-ordination of Ti species, and the amount of Ti content in the samples are analyzed by various techniques including X-ray diffraction (XRD), N2 adsorption, high resolution scanning electron microscopy (HRSEM), UV–vis diffused reflectance spectroscopy (UV–vis DRS), and inductively coupled plasma emission spectroscopy (ICP), respectively. All the materials prepared with various nSi/nTi ratios exhibit well-ordered porous structure and possess high BET surface areas (673–941m2g−1) and large pore volumes (0.46–0.71cm3g−1). The pore diameter of the samples also increases with increasing the Ti content in the samples. UV–vis results confirm that most of the Ti atoms are in the tetrahedral co-ordination. Finally, the materials are subjected to cyclohexene epoxidation using TBHP/H2O2 as oxidant and acetonitrile as solvent in order to investigate their catalytic activity. Ti-KIT-5 samples display a high catalytic activity with TBHP as oxidant and remain inactive when H2O2 was used. The amount of Ti plays a crucial role in controlling the catalytic activity of the samples. Of the catalysts studied, Ti-KIT-5(5) where the number in the parenthesis indicates the Si/Ti ratio shows the best activity, affording a high conversion to cyclohexene. Among the catalysts studied, Ti-KIT-5-5 exhibited better catalytic activity with respect to reaction time, reaction temperature, conversion and epoxide selectivity.