关键词: Ti-ZSM-5, 气固相反应, 反应机理

Several samples of Ti-ZSM-5 from HZSM-5 (SiO₂/Al₂O₃=280) were prepared using TiCl₄ gas-solid reaction, and characterized by FT-IR, UV-vis, XRD, TG, ICP-AES and chemical analysis. FT-IR and UV-vis results show that Ti-ZSM-5 samples with no extra framework titanium were obtained. An obvious increment in UCV (Unit Cell Volume) of Ti-ZSM-5, compared with that of HZSM-5, is found by XRD. Further experimental result indicates that Ti-ZSM-5 exhibits good catalytic performance in allyl chloride epoxidation. Chemical analysis of the catalyst shows that there is only a small decrease of Al content (1.6% to total Al content in HZSM-5) in Ti-ZSM-5, which has been confirmed by ICP-AES. However, TG analysis shows a difference in losing of weight between Ti-ZSM-5 and HZSM-5 from 130 to 698℃, and dehydration of "hydroxyl nests" should be responsible for that. Based on TG analysis result and according to a formula (n_Ti=n_OH/4=n_H2O/2) (99.8%), we suppose that Ti incorporation into framework of molecular sieves is mainly through the reaction of "hydroxyl nests" with TiCl₄ (99.68%), and the contribution that Ti replaces framework Al is very little only0.32%).

Key words: Ti-ZSM-5, gas-solid reaction, reaction mechanism