Synthesis And Catalytic Performances Of Titanium Silicate-1

Titanosilicalite-1 (TS-1) has attracted great attention due to its excellent catalytic properties. The synthesis of titanosilicalite-1 has become a hot spot in the zeolite catalytic fields.The most widely-used synthetic method of TS-1 is the hydrothermal synthesis improved by Thangaraj et al. Microwave irradiation (TS1-MI) is employed to synthesize zeolites and the advantage is utilized to get homogeneous nucleation and substantial reduction in crystallization time periods compared with the conventional hydrothermal method (TS1-CM) which is time-consuming and energy-consuming.To investigate the influence of the above two synthetic methods on the catalytic performance TS-1, in this paper, TS-1 zeolite samples with different Ti content were synthesized with TPAOH as the template, TEOS as the silicon source and tetrabutyl orthotitanate as the titanium source using the two methods respectively, and the effect of the amount of tetrapropyl ammonium hydroxide (TPAOH) and crystallization time on the properties of TS-1 zeolite prepared under microwave irradiation was studied.The amount of TPAOH (1Si:xTi:0.36TPAOH:50H2O) and the crystallization time (3.5hours) were established. The TS-1 samples were characterized by IR,XRD,SEM,UV-vis, and the results showed that the titanium element was incorporated into the framework of zeolites with low Ti content prepared by the two methods. The samples fabricated under microwave irradiation had higher Ti content and crystallinity, and the crystal particles of TS-1 samples from microwave irradiation were found to exhibit an adhered morphology. But with the Ti content increased, the Ti content in the samples synthesized by the two methods approached gradually, and the extra amount of Ti resulted in extra-framework anatase; grain size increased, but the crystals of the sample from TS1-MI stacked on top of one another to form a fibrous morphology, which showed that microwave irradiation facilitated the form of stacked morphology.To further study of the two methods, the TS-1 samples with various Ti content were applied in partial oxidation of n-hexane using aqueous hydrogen peroxide as the oxidant. The results indicated: with the Ti content increased, the catalytic activities of the TS-1 samples from the two synthesis methods both increased, the reaction products were both of the same trend, and both methods benefited the produce of 2-hexanone. However, the TS-1 samples from TS1-MI have higher catalytic activities than those from TS1-CM when the Ti content of the zeolites was low, and with the Ti content increased, the n-hexane reaction rate catalyzed by the TS1-MI sample increased but the selectivity decreased due to the stacked morphology.