Abstract
A series of V- and/or Ti-loading MCM-41 catalysts are successfully synthesized with a hydrothermal method. The photocatalytic and thermal epoxidations of cyclohexene in the presence of tert-butyl hydroperoxide (t-BuOOH) were investigated with real-time monitored by NIR-Raman spectroscopy. It suggests that both V- and Ti-loading can be responsible for the cyclohexene epoxidation. Moreover, the complementary behavior of V- and Ti-loading may be related to a similar role of activation. Interestingly, the progress of the photo-epoxidation on V0.25Ti2/MCM-41 photocatalyst was monitored by changes in intensity of the characteristic Raman bands without interference from the UV-light irradiation. The result, for the first time, reveals that cyclohexene was directly photo-epoxidized to 1,2-epoxycyclohexane by t-BuOOH during the reaction. A possible mechanism of cyclohexene photo-epoxidation is also proposed for this study.
Highlights
Nowadays, major epoxide chemicals, which are produced by epoxidation of olefins such as ethylene, propylene and cyclohexene, etc., have become considerably more important, valuable and versatile intermediates in industrial organic synthesis [1,2,3,4,5,6]
The results proved that our procedure to incorporate vanadium and titanium-containing catalysts did not deteriorate the MCM-41 structure
We might conclude that both V- and Ti-loading can be responsible for the cyclohexene epoxidation
Summary
Major epoxide chemicals, which are produced by epoxidation of olefins such as ethylene, propylene and cyclohexene, etc., have become considerably more important, valuable and versatile intermediates in industrial organic synthesis [1,2,3,4,5,6]. The separation process of by-products when using t-BuOOH is much easier than with others [9] Another approach, which is based on utilizing clean and abundant photo-energy, instead of thermal energy, has been gained considerable interest. Cyclohexane 1,2-diol, 2-cyclohexene-1-ol and 2-cyclohexene-1-one might be observed by gas chromatography analyses, Raman result suggested that 1,2-epoxycyclohexane was the only product obtained in the reaction. Considering them together in this study, gas chromatography is used to screen the catalytic activity by determining cyclohexene conversion values while Raman technique is used to identify the reactants and selective products of epoxidation in real-time. The photocatalytic and thermal catalytic cyclohexene epoxidation behaviors of these catalysts were further investigated using real-time Raman spectroscopy. A possible mechanism for cyclohexene photo-epoxidation was proposed based on the results of Raman technique
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