Study On TS-1, TS-1/Cordierite And Their Catalytic Properties Synthesized By Adding Nonionic Surfactants

Titanium silicalite (TS-1) has attacted much attention because of its unique catalytic properties in selective oxidation reactions such as oxidation of alkanes and alcohols,epoxidation of alkenes,hydroxylation of aromatic compounds using diluted hydrogen peroxide as the oxidant. However,it is too costly for industry to make TS-1 in commercial process.So it is crucial to find suitable routes that help to lower the cost of TS-1 as well as suitable ways to synthesize supported TS-1 that can be easily recycled. In this dissertation ,titanium silicalite (TS-1) was synthesized using small amount of TPAOH(nTPAOH/nSiO2=0.10) as template in the presence of small amount of nonionic surfactant such as Tween20,Tween40,Tween60,Tween80,Triton X100 and Span20. The samples were characterized by XRD, FTIR, UV-Vis and SEM techniques, and the propylene epoxidation was used as probe reaction to evaluate the catalytic properties of TS-1 samples. Compared with the traditional sample synthesized in the same condition,it was showed that the addition of these nonionic surfactants could not only greatly reduce the amount of TPAOH and avoid the formation of anatase (TiO₂),but also improve the catalytic properties,and Tween40 was found to be the most effective.In the presence of Tween40,when the TPAOH/SiO2 ratio lowered to 0.05,the zeolite with good crystalization and catalytic properties could be obtained . When synthesize powdery TS-1,the effect of the amount of Tween40,the ratio of SiO₂/TiO₂ and H₂O/SiO₂ as well as the cystallization time has been investigated. Besides ,H₂PO₄^-,NO₃^-,Cl-and SO₄^2- ions were introduced into the jel and the effect of these ions on the cystallization of TS-1 were studied. The results indicated that the catalytic performance increased with the amount of Tween40,but droped a little when more Tween40 was added. When an appropriate amount of Tween40 was added (nTween40/nTPAOH=0.02),the conversion ratio of hydrogen peroxide ( XH 2O2) was 98.1%,and the selectivity and yield of propene oxide(SPO,YPO)could reach 96.1% and 94.3% respectively. A suitable crystallization time was about 30～50 hours. It was found that when TS-1 were synthesized with different SiO₂/TiO₂ and H₂O/SiO₂ ratios,the synthetic gel was clear without precipitation of the oxides of titanium(TiO₂) throughout the dissolution of materials. when the SiO2/TiO2 ratio was lower than 33,the presence of extra-framework titanium in the sample was confirmed by the characterization of UV-Vis spectra, which suggested that there was a suitable SiO2/TiO2 ratio in this synthesis system (SiO2/TiO2 =33),whereas the H2O/SiO2 ratio had little effect on the catalytic properties of TS-1. The catalytic performance droped greatly when H2PO4-,NO3-,Cl-and SO42-ions were introduced into the synstem. Nonionic surfactants couldn't be used as template of TS-1,and we speculated that it helped to reduce the surface tension,and when the surfactant molecules aggregated into miclles, the template molecules in and around the "miclle shell", such type of arrangement may increased the interaction between template and silica and/or titanium species.As a result the addition of surfactant helped to avoid the formation of anatase(TiO2) and reduced the amount of TPAOH. the cooperative behavior between the surfactant and template molecules could increase the chances of interaction between template and silica and(or)titanium species,also induced orientation reaction between them,which helped to avoid the formation of anatase(TiO2) and reduce the amount of TPAOH. TS-1 membrane was successfully in-situ synthesized on the surface of cordierite substrates by hydrothermal mathod,which was confirmed by characteristic experiments using XRD,IR ,UV-Vis and SEM,as well as the probe reaction of propylene epoxidation. And the results showed that when the molar ratio of SiO2/TiO2 was 35 and the molar ratio of H2O/SiO2 was 50,the thickness of membrane was about 14μm, the conversion of hydrogen peroxide( XH 2O2)and the selectivity of propene oxide(PO)could reach 31.5% and 100% respectively. Compared with the sample without Tween40,the sample synthesized in the presence of Tween40 has better catalytic properties, XH 2O2for per unit of membrane thickness was 1% higher,while SPO remained 100%.