Synthesis, characterization of high Ti-containing Ti-MCM-41 catalysts and their activity evaluation in oxidation of cyclohexene and epoxidation of higher olefins |
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Authors: | M Ramakrishna Prasad G Madhavi A Ramachander Rao S J Kulkarni K V Raghavan |
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Affiliation: | (1) Indian Institute of Chemical Technology, Hyderabad, 500 007, India |
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Abstract: | A series of titanium rich isomorphous substituted Ti MCM-41 and HMS materials have been synthesized with different Si/Ti ratios.
The highest amount of Ti incorporated in synthesis gel is in TiMCM-41 (Si/Ti = 10). Whereas for TiHMS catalysts, Ti is incorporated
up to Si/Ti = 50 successfully without forming any extra framework TiO2. Cyclohexene epoxidation reaction with dry tert-butyl hydroperoxide (TBHP) as an oxidant has been studied to evaluate the catalytic properties of Ti substituted mesoporous
catalysts. The effect of molar ratio of substrate:oxidant in this reaction has been studied and high conversion, high selectivity
were achieved at 2: 1 molar ratio with TiMCM-41 (Si/Ti =25). Dry TBHP (in dichloromethane) and chloroform were found as good
oxidant and solvent system for this reaction. Pure siliceous mesoporous silica and low `Ti' substituted mesoporous silicas
were found to be efficient catalysts for oxidation of cyclohexene. An interesting variation of the selectivity from allylic
oxidation to epoxidation during oxidation of cyclohexene was observed with an increase in the Ti amount in the mesoporous
framework. The allylic oxidation of cyclohexene has been carried out using molecular oxygen as an oxidant and in the presence
of a small amount of TBHP as initiator. Siliceous HMS materials gave better conversion compared to MCM-41 type of materials
and other conventional silicas like silica gel, fumed silica etc. in allylic oxidation of cyclohexene. Epoxidation of higher
cyclic olefins like cyclooctene, cyclododecene, cis-cyclododecene and linear olefins 1-Heptene, cis-2-hexene, 1-undecene was
carried out over TiMCM-41 (Si/Ti = 25). Ti substituted mesoporous catalysts were characterized by elemental analysis, XRD,
FTIR, UVDRS, 29SiMASNMR, BET surface area and pore size distribution techniques. |
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Keywords: | TiMCM-41 TiHMS Epoxidation Allylic oxidation TBHP and molecular oxygen |
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