【作者】 王瑞璞；

【导师】 王祥生； 郭新闻；

【作者基本信息】 大连理工大学 ， 工业催化， 2004， 博士

【摘要】 常压、氢氧共存下，以银改性钛硅分子筛（TS-1）为催化剂，以丙烯气相氧化合成环氧丙烷反应为探针，研究了Ag／TS-1催化剂制备条件和丙烯气相环氧化反应条件以及催化剂改性对丙烯环氧化反应性能的影响；考察了反应过程中Ag／TS-1催化剂上内外表面银物种的作用以及TS-1中不同钛物种的作用；对催化剂的失活与再生进行了初步探讨；同时采用XRD、UV-Vis、FT-IR、TEM、ESR、ICP等手段对催化剂进行了表征。结果表明： 1．银与TS-1之间存在协同作用。以沉积-沉淀法制备的Ag／TS-1催化剂性能最佳，但是浸渍法也可以制备具有环氧丙烷选择性的催化剂，它们之间的差别关键在于银物种与载体TS-1之间不同的相互作用。 2．Ag／TS-1催化剂的最佳制备条件为：采用沉积-沉淀法；银负载量，2wt％；TS-1硅／钛摩尔比为64；Ag／TS-1催化剂在450℃空气中焙烧5h。最佳反应条件为：反应温度，150℃；气体空速，4000h^-1；n（C₃H₆）／n（O₂）／n（H₂）／n（N₂）为1：2：3：12。氢气在反应过程中起着重要的作用。 3．沉积-沉淀法制备催化剂时，AgNO₃为银盐制备的催化剂性能较好；采用乙酸银为原料，制备的催化剂活性稍有提高，但环氧丙烷选择性下降。碱金属碳酸盐是一种良好的沉淀剂，尤其是K₂CO₃为沉淀剂制备的催化剂性能最佳，钾离子的存在有利于提高催化剂的活性和选择性；以0.07mol／L K₂CO₃为沉淀剂制备的2％Ag／TS-1(n_Si／n_Ti=33)在最佳条件下反应时，可得到1.9％的丙烯转化率和90.9％的环氧丙烷选择性。 4．在Ag／TS-1催化丙烯气相氧化反应过程中，载体内外表面的银物种均具有环氧化性能，但分子筛孔道内的银物种起主要作用。 5．在Ag／TS-1催化丙烯气相氧化反应过程中，TS-1分子筛中的骨架钛与银协同作用后有较强的环氧化性能。锐钛矿型和金红石型的二氧化钛载体负载 大连理下人学博卜学位论文银后不具有环氧化性能，但某种形态的非骨架钦（紫外谱图中280一290nm）与银结合后具有一定的环氧化性能，而大量非骨架钦的存在会使催化剂的选择性下降。 6.载体经过硅烷化处理再负载Zwt%Ag后，其催化性能可得到提高。当510:负载量为Zwt%时，Ag/Ts一1催化剂的丙烯转化率和环氧丙烷选择性分别为2 .1%和98%。 7.Ag/TS一l催化剂失活主要是由沉积在催化剂上的环氧丙烷或丙烯的低聚物，以及反应过程中生成的水引起的。失活后的催化剂在空气中450℃焙烧可以再生，其再生性能可恢复到新鲜催化剂的指标水平。 8.催化剂外表面的银颗粒过大（大于10nm）或过小（小于snm）均不利于提高催化剂性能。小的银颗粒不具有催化活性，而大的单质银颗粒以及大量的单质银会降低环氧丙烷选择性;氧化态的银离子刁‘是丙烯气相氧化过程中的活性物种;UV一VIS中，银物种在400⁸00nm范围内的吸收波长红移（大于45Onm），不利于丙烯气相氧化反应合成环氧丙烷，吸收波长越长，环氧化性能越差。更多还原

【Abstract】 The epoxidation of propylene was carried out over silver modified titanium silicalites (TS-1) in the presence of hydrogen and oxygen at atmospheric pressure. The effects of the factors involved in the catalysts preparation and reaction conditions as well as the modification of Ag/TS-l catalyst on the catalytic properties have been investigated; Function of the internal and external silver species of the Ag/TS-1 catalyst and the titanium species for propylene epoxidation have also been investigated; The deactivation and regeneration of the Ag/TS-1 catalyst have been preliminarily discussed; at the same time the catalysts have been characterized by XRD?UV-Vis?FT-IR?TEM?ESR?ICP and GC-MS. The results show that:1. There is a synergy between Ag species and TS-1. The catalyst prepared by deposition-precipitation (DP) method is optimum, however the impregnation method can also get a moderate selective catalyst to propylene oxide (PO). The key factors for the two catalysts are the different interactions between silver species and TS-1 support.2. The optimum preparation conditions are: DP preparation method; Ag loading, 2wt%; the nsi/nTi of TS-1, 64; The Ag/TS-1 catalysts were calcined at 450℃ in air for 5h. The optimum reaction conditions are: 150℃; gas velocity 4000h-1; n (C3H6)/ n (O2)/ n (H2)/ n (N2) = 1:2:3:12. Moreover, hydrogen plays an important role in the gas-phase epoxidation of propylene.3. As a silver precursor, AgNO3 is better than Ag2SO4 and CH3COOAg; the selectivity to propylene oxide (PO) decreases drastically with a little increase in.the conversion of propylene, when CH3COOAg was used. Alkali metal carbonate, especially K2CO3, is favorable as the precipitator. Both the propylene conversion and the selectivity to PO can be improved with the existence of K+. Using 0.07mol/L K2CO3 as the precipitator, 1.9% propylene conversion with 90.9% PO selectivity is obtained over 2wt%Ag/TS-l (nsi/nTi-33) catalyst, when reacted at the optimum reaction conditions.4. Both internal and external silver species have catalytic properties, however, the internal silver species of Ag/TS-1 plays an important role in the gas-phase epoxidation of propylene.5. The framework titanium species of TS-1 in synergy with Ag plays an important role in the gas-phase epoxidation of propylene over Ag/TS-1 catalyst. Both anatase type and rutile type TiO2 are not effective supports for the propylene epoxidation; however, the extra framework titanium species (280~290nm in UV-Vis spectra) together with Ag also shows weak epoxidation activity, and the selectivity to PO decreases with large amount of it in the gas-phase epoxidation of propylene.6. During the direct gas-phase epoxidation of propylene, the catalytic properties of Ag/TS-1 can be increased when TS-1 was silylated. When 2wt%Si02 was loaded on TS-1, 2.1% propylene conversion with 98% selectivity to PO is obtained over Ag/TS-1 catalyst.7. Apart from the polymers of propylene or propylene oxide being the cause of the catalyst deactivation, the presence of water may be one of the reasons resulted in the deactivation of the Ag/TS-1 catalysts. The catalytic properties of the spent catalysts can be recovered to the original value, when the catalysts were calcined at450 in air.8. Neither big (larger than 10nm) nor small silver particles (less than 5nm) areIVbeneficial to the formation of PO. The small silver particles less than 5nm do not show any catalytic activities, however, the metal silver particles bigger than 10nm and large amount of metal silver can decrease the PO selectivity. The oxidized silver ions are the effective silver species for the gas-phase epoxidation of propylene. In UV-Vis spectra, that the shift of the silver species’ absorbance ranged at 400~800nm to a longer wavelength (longer than 450nm) does not favor the formation of PO. The longer the absorbance wavelength of the silver species has, the poorer the catalytic properties of the catalysts exhibit.更多还原