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

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 (673–941 m2 g−1) and large pore volumes (0.46–0.71 cm3 g−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.

Herein we report on the preparation and the catalytic activity of the Ti-KIT-5 materials with different Ti content in the epoxidation of the cyclohexene. The amount of the Ti in KIT-5 is finely controlled with a simple adjustment of the local H+ ion concentration in the synthesis mixture. The pore diameter, pore volume, and the specific surface area of the sample increase with increasing the loading of Ti in the silica framework. The prepared materials were tested in the liquid-phase epoxidation of cyclohexene and found that the catalyst is highly active, stable and purely heterogeneous.Figure optionsDownload as PowerPoint slideHighlights
► First report on the preparation of titanium substituted KIT-5.
► Controlling of the Co content in KIT-5 by tuning water to HCl ratio.
► Increase of the textural parameters of Ti-KIT-5 upon the addition of Ti.
► Showed higher activity and stability for epoxidation of cyclohexene.