Preparation, Characterization Of Ti-ZSM-5 And Its Catalytic Application For Olefins Selective Oxidation And Phenol Hydroxylation

The synthesis of titanium-silicates (TS) and their application for the catalytic selective oxidation of hydrocarbons have attracted much attention recently. The hydrothermal synthesis method of TS has a character of complex operation and expensive cost, however, TiCl4 gas-solid isomorphous substitution, being reported by few papers, is a good way of obtaining cheaper TS.· This thesis uses TiCl4 gas-solid isomorphous substitution of ZSM-5 to prepare Ti-ZSM-5. Through investigating effect of various parameters such as silicon source materials, temperature, time, and conditions of pretreating and activating by vapour on the property of Ti-ZSM-5 firstly, we have obtained an excellent Ti-ZSM-5. In catalytic selective oxidation of styrene, H2O2 utilization ratio and selectivity of producing PhC2H3O can reach 60.9% and 93.6% respectively. On the basis of pretreating and activating by vapour and the characterization of Ti-ZSM-5 using XRD, XPS and UV-Vis so on, we propose the mechanism of Ti incorporation into ZSM-5 framework:· The studies show the FT-IR spectrums of Ti-ZSM-5 activated by vapour don't exhibit 970cm-1 band, which was attributed to the skeletal Ti by the reports of literature, but it is proved that there are only skeletal Ti and absence of nonskeletal Ti by UV-Vis spectrum. So we propose that it is not validly to reckon the 970cm" band as the direct indication of Ti atom incorporation into framework of TS molecular sieves, however UV-Vis spectrum is more credible to detect the skeletal and nonskeletal Ti atom.· In the selective oxidation of styrene, Ti-ZSM-5 exhibits a remarkable properties with H2O2 utilization ratio being 75.51% and PhC2H3O selectivity being 90.88% under optimum conditions, which are both higher than the results in the recent reports. At the same, the maincomposition of PhC2H3O is phenylacetaldehyde being 95.72%, but styrene oxide being only 4.28%. So the selective oxidation of styrene catalyzed by Ti-ZSM-5 is rational to produce phenylacetaldehyde.· Due to styrene oxide having two enantio-isomers, this thesis firstly investigates the effect of various reaction parameters on the enantioselectivity of styrene epoxidation. It is found that there mainly is R-configure styrene oxide being —3% in the products. When reaction temperature being ≤40℃, e.e. value can reach 100%. Whereas reaction time, adding amount of Ti-ZSM-5 and 30%H2O2 is invalid to affect the enantioselectivity of styrene epoxidation.· We study on the kinetics of styrene oxidation with H2O2 catalyzed by Ti-ZSM-5 indetails. It is showed that reaction rate equation is R = k[Ti - ZSM -5][Styrene][H2O2]1/2 andthe apparent activation energy is 48.14kJ/mol. From these, the reaction mechanism is followed to Ridel-Freundich isotherms. Being combining with products distribution in styrene oxidation, we propose the styrene epoxidation carry out with Ti metallacyclo intermediates, And at the same time Ti-ZSM-5 have properties both catalytic epoxidation and acid-catalysis, namely the skeletal Ti can catalyze styrene epoxidation to styrene oxide and the skeletal Ti and Al can provide Lewis acid site to cause the rearrangement of styrene oxide to phenylacetaldehyde rapidly, the solvolysis to glycols and the cleavage of C = C double bond. Ti-ZSM-5 can also provide Bransted acid site simultaneously, which is also catalytic center for the solvolysis to glycols.· The epoxidation of allyl chloride on Ti-ZSM-5 has been too studied. The results show that in the products there is only epichlorohydrin (100%), and exists no hydrolysate of epichlorohydrin (C1CH2CH(OH)CH2OH, which is ever reported in the literatures). Methanol is the best solvent in the epoxidation of allyl chloride. Under the optimum conditions, H2O2utilization ratio can reach 99.5%, which is higher than the results of previous literature. Thereaction rate equation with R = k[Ti-ZSM -5][C3H5Cl][H2O2]1/2 and the apparent activationenergy being 63.462kJ/mol are obtained according to the kinetics study, and the reaction mechanism is also consistent with Ridel-Freundich isotherms.· In the hydroxylation of phenol with H2O2 in the presence of Ti-ZSM-5, water is best solvent. It produces catechol and hydroquinone simultaneously, and catechol/hydroquinone ratio is approximately 0.85. The results show H2O2 utilization ratio increase 14%, when nonoxidizable weak acid H Ac is added into the reaction system. Under the conditions of Ti-ZSM-5 as catalyst, phenol/H2O2 ratio being 10, a little HAc, temperature 75 ℃, reaction time 6h, H2O2 utilization ratio reaches 74.6mol% in the reaction.