Titanium silicalite (TS-1)was successfully synthesized by using tetra-propylammonium bromide (TPABr) and n-butylamine as the template and the base, respectively. XRD, IR, SEM, 13C CP/MAS NMR, UV-VIS, and UV-Raman techniques were used to characterize the synthesized products. The results show that TS-1 has MFI structure with high crystallinity and large crystal size, and with two kinds of titanium species. Using epoxidation of propylene as the probe, the catalytic properties of TS-1 in the present work were investigated. The crystal size of TS-1 affects much the initial reaction rate of propylene oxide (PO) formation. The effects of reaction conditions on PO reveal that the PO formation is greatly influenced by the solvent and the solution pH value. Methanol is the most preferable solvent, and a portion of water (<30%) in solution does not have much impact on the reaction. Moreover, the addition of base used to neutralize the residual acidity of the catalyst favor the reaction, the catalyst shows high activity and selectivity upon the adequate amount of base and the catalyst can be used repeatedly without regeneration. In the fixed-bed reactor, using ammonium water as the neutralizer, after 200 h of reaction, both the conversion and the utilization of H2O2 is about 95%, the selectivity of PO is about 90%.

Propylene epoxidation catalyzed by titanium silicalite is easily influenced by acidic or basic impurities. The effect of sodium ions on the reaction was systematically investigated. It has been shown that a proper amount of sodium salt additive can inhibit the further reaction of propylene oxide (PO) with the solvent and can increase the selectivity of PO. But a slightly excessive amount of sodium salt can be a poison to the titanium silicalite catalyst. The sodium salt additive can accumulate on the catalyst in repeated runs of propylene epoxidation in an autoclave, so the catalyst may be poisoned if an equal amount of sodium salt is added in each run. The excessive sodium ions on titanium silicalite can deactivate the catalyst in calcination, while acid treating can restore the activity of titanium silicalite. If the propylene epoxidation is carried out in a fixed bed, the sodium ions on titanium silicalite can gradually come loose and the PO selectivity decreases with time on-stream. A small amount of supplement of sodium salt in the raw material can make the PO selectivity stable for a longer period.

Titanium silicalites have been synthesized in the TPABr

Titanium silicalite (TS-1) is used as catalyst in selective oxidation of thiophene by hydrogen peroxide at 333K. Fourier transform infrared (FT-IR) and UV-vis characterization shows the presence of framework titanium in all TS-1 samples we prepared with different SiO2/TiO2 ratio. Catalytic test over these catalysts confirms that framework Ti species does influence the oxidation of thiophene. The role of non-framework titanium was discussed by studying acid treating of the catalyst. If TS-1 is treated using HCl (2mol/1) four times, part of the non-framework titanium species will be washed off and the activity of the catalyst increases greatly. These results suggest that framework titanium was crucial for thiophene oxidation. Non-framework titanium is not the active site, but provides steric hindrance for this reaction. Obvious diffusive restriction on the thiophene oxidation was also observed when using TS-1 with different crystal size.

Thiophene is a typical thiophenic sulfur compound in gasoline. Using n-octane containing thiophene as the model compound, the oxidation of thiophene, which is a key step for the oxidative deep desulfurization of gasoline, was carried out to study the reactivity of thiophene in oxidation reactions. It has been observed that thiophene oxidation can occur using water or t-butanol as solvent. Kinetics of the reaction shows a pseudo-first-order toward thiophene or catalyst and a zero order toward hydrogen peroxide. The mechanism for this unique reaction was proposed as the activation of conjugated electron in thiophene ring.