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Study On The Effect Of Different Titanium Species In Low-cost TS-1 Zeolite For Propylene Epoxidation

Posted on:2017-05-23Degree:MasterType:Thesis
Country:ChinaCandidate:Q Y JiaFull Text:PDF
GTID:2311330488958172Subject:Industrial Catalysis
Abstract/Summary:PDF Full Text Request
Titanium silicalite (TS-1) possess unique catalytic properties in oxidation reactions under mild conditions, especially with the use of hydrogen peroxide (H2O2) as the oxidant. It is commonly believed that the isolated titanium species in the framework of the TS-1 zeolite is the active center for the selective oxidation. However, the role of the nonframework Ti species, especially that of amorphous Ti species in the epoxidation reactions is still debated. Different synthetic methods may result in the formation of different titanium species, which increases the complexity of the research. Therefore, a systematic study on the function of the different titanium species in titanium silicalite (TS-1) is highly required.The low-cost TS-1 zeolites with different titanium species were synthesized and characterized by ultraviolet visible (UV-Vis) diffuse reflectance spectroscopies, ultraviolet (UV)-Raman, pyridine adsorption Fourier-transform infrared (Py-IR) and NH3-TPD method. The roles of different Ti species in TS-1 samples have been investigated by gas chromatography-Raman spectrometry (GC-Raman) during the propylene epoxidation process. By building the correlation among the concentration of framework Ti species, the amount of active intermediate Ti-OOH(?2), the conversion of propylene and the yield of PO, the influence of the different titanium species to the Ti-OOH(?2) and the PO was investigated.The results give evidence that the framework titanium species is the active center, and the concentration of framework Ti species is positively realted to the amount of active intermediate Ti-OOH(rj2). The presence of extraframework anatase TiO2 species is harmful to propylene epoxidation reaction because of its ability of decomposing H2O2 solution. Furthermore, the Py-IR and NH3-TPD results reveal that the extraframework Ti species are more acidic and should be mainly responsible for the further side conversion and the low yield of PO.It is proved that the extraframework Ti species can be eliminated by acid/alkali treatment while the framework Ti species remain unchanged. Many irregular hollows are generated during the alkali (TPAOH) modification and the pore structures are changed. Through the post treatment, the catalytic properties of low-cost TS-1 zeolites have been improved.
Keywords/Search Tags:Low-cost TS-1 zeolites, Titanium species, Active Intermediate, In-situ UV-Raman, Propylene Epoxidation
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