In Situ UV Raman Spectroscopic Study on the Reaction Intermediates for Propylene Epoxidation on TS-1

The reaction intermediates for propylene epoxidation were investigated by in situ UV Raman spectroscopy. A feature at 837 cm –1, which has been assigned to the O–O stretching mode in the Ti–OOH (η 2 ) species, was observed in Raman study for the first time. The physisorbed H 2 O 2 and triangular Ti(O 2 ) species are also present at different stages during the in situ measurement. The results obtained by gas chromatography-Raman spectrometry (GC-Raman) during the propylene epoxidation process give direct evidence that the 6-coordinated Ti–OOH (η 2 ) intermediates are important active sites for propylene epoxidation. After adding CH 3 OH to the TS-1/H 2 O 2 /H 2 O/system, the Raman spectra show the existence of a Ti–O–CH 3 moiety and 6-coordinated Ti–OOH (η 2 ) species. The five-numbered ring titanium hydroperoxo intermediate was not detected in this study. The results showed that the 6-coordinated Ti–OOH (η 2 ) species are active sites in the methanol-included epoxidation reaction process.