【作者】 邓秀娟；

【导师】 何鸣元； 刘月明；

【作者基本信息】 华东师范大学 ， 物理化学， 2014， 博士

【摘要】 钛硅分子筛TS-1自1983年成功合成以来,得到了广泛的研究。基于TS-1构建的TS-1/H2O2催化新体系也已在大宗化学品绿色化工新工艺技术中工业应用。TS-1/H2O2体系催化反应的化学本质探究一直是充分利用和发挥该体系催化性能的科学基础。本论文以TS-1/H2O2体系结构性因素决定其催化氧化性质为研究主线,从高性能TS-1的合成、高催化活性Ti中心的构筑、双氢键活性中间体的构建及结构稳定性的分析等方面进行系统研究,试图阐明该体系催化反应的化学本质,形成影响该体系催化氧化性能的系统认识,为进一步充分利用和发挥TS-1/H2O2体系的催化作用奠定科学基础。(1)从探索TS-1合成过程Ti活性中心的形成规律出发,通过水解过程的控制,采用两步或多步水解法,在较低TPAOH/SiO2(0.08或0.065)比时,合成出高性能Ts-1。发现,第一步水解过程决定了TS-1的催化氧化性能,而Ti的引入过程影响不大。通过XRD、UV-Vis、SEM、FT-IR、BET及TG的表征,可知得到的TS-1的物化和催化性质与传统的高TPAOH/SiO2(≥10.18)条件一步水解合成的“黑莓状”TS-1类似。在TS-1合成过程中,有机酯的水解是关键。在高TPAOH/SiO2比条件下,可形成较多晶核,是最终形成“黑莓状”TS-1的基础。第二步水解时,硅源可以是有机硅或无机硅,拓宽了高性能TS-1合成的原料来源,也能有效降低废弃物的排放和生产成本。两步或多步水解合成法为TS-1的低成本环境友好工业生产具有指导意义。(2)钛硅分子筛骨架Ti原子具有三种配位状态。通过水热处理方式,将TS-1分子筛骨架四配位Ti(Ⅳ)物种定向转化为骨架高配位Ti物种。通过UV-Vis、 UV-Raman、29Si MAS NMR、IR等表征,发现采用244nm光源激发时,UV-Raman谱中700cm-1处的振动峰归属为具有骨架六配位Ti(Ⅵ)物种(TiO6)的特征峰,此外,UV-Vis谱中-280nm处吸收峰及采用325nm光源激发时UV-Raman谱中130、650、670cm-1振动峰的出现均与高配位Ti存在相关；骨架高Ti物种的形成还表现在归属于骨架Ti(Ⅳ)结构特征的UV-Vis谱中-210nm、UV-Raman谱中960和1125cm-1处的吸收峰及IR谱中960cm-1处的吸收峰强度均随之降低。催化研究结果表明,骨架高配位Ti物种是具有明显高于骨架Ti(Ⅳ)物种催化活化H202能力的活性中心,进而显著提升其催化烯烃环氧化反应性能,其TON值为骨架Ti(Ⅳ)物种活性中心的2-3倍。(3)TS-1/H2O2催化体系中,由骨架Ti原子活性中心活化H2O2形成的反应活性中间体Ti-Oα-Oβ-Hend的稳定性直接影响其催化氧化能力。通过在反应体系中引入氢键受体,构建与反应活性中间体Ti-Oα-Oβ-Hend中的Hend原子相互作用的新氢键,进一步稳定活性中间体,形成了具有双氢键结构的新反应活性中间体。DFT模拟计算表明该双氢键活性中间体的存在的可能性。反应动力学研究表明,反应体系中双氢键活性中间体的形成,降低了催化活化H202的活化能,进而大幅度提高其催化烯烃环氧化反应性能,最高增幅达到约50%。构建新氢键的反应活性中间体在钛硅分子筛/H202催化体系中具有普适性。并且,采用水热法或浸渍法,可在TS-1分子筛孔道中成功原位构筑了氢键受体,具有良好的水热稳定性(≤373K)。(4)采用环己酮氨肟化浆态床连续反应考察了TS-1分子筛的结构稳定性。结果表明,在单程运行周期内,TS-1分子筛具有较高的结构稳定性,骨架Ti中心的流失极少,有机物堵塞孔道是造成TS-1分子筛失活的主要原因。加入多孔硅物种可吸附部分有机物,减缓了TS-1分子筛吸附有机物的速率,进而提高其运行周期。更多还原

【Abstract】 Since TS-1was successfully synthesized in1983, titanosilicate zeolite has been widely studied as a heterogeneous catalyst in various hydrocarbon oxidations. TS-1/H2O2catalytic system has also been carried out in green industrial application of the bulk chemicals. The research of catalytic nature in the TS-1/H2O2catalytic reaction system has provided scientific basis to fully utilization of the catalytic properties. In this dissertation, based on the structural factors of TS-1/H2O2on the catalytic oxidation activity, we have a systematic research on the TS-1/H2O2catalytic reaction system, such as synthesis of high-perfrmance TS-1, formation of high-coordination Ti species with high catalytic activity, build of intermediates with double hydrogen bonds and the structural stability of TS-1. Through the study of the TS-1/H2O2catalytic reaction system, the further understanding was attempted to gain about the influencing factors to the catalytic activity.In the first part, starting from the exploration on the formation law of Ti active site in the systhesis of TS-1, TS-1has been successfully synthesized in ultralow molar ratio of TPAOH/SiO2(0.08and0.065) by two-step and multistep hydrolysis process through a controlled hydrolysis process. We found that the catalytic activity depends on hydrosis of the first step. Combined characterization of XRD, UV-Vis, SEM, FT-IR, BET and TG shows that currently synthesized TS-1samples have the typical "blackberry" morphology, similar to that of the conventional TS-1synthesized at a high molar ratio of TPAOH/SiO2(>0.18). The hydrolysis of the organic esters is the key step in the synthesis of TS-1. Fast hydrolysis of a small part of TEOS at a high concentration of TPA+in the first step induces more nuclei In the second step, the silicon source could be either organic or inorganic silicon, which broadens synthetic raw sources of TS-1. This strategy can greatly reduce waste emissions and the synthesis cost of TS-1, which is suitable for synthesis of TS-1on an industrial scale.In the second part, there are three coordinated state of Ti species in TS-1zeolite. Part of framework four-coordination Ti(IV) species are inverted to framework high-coordination Ti(VI) species through hydrothermal posttreatment. Combined characterization of UV-Vis, UV-Raman, FT-IR,29Si MAS NMR shows that the vibration peak at700cm-1excited at244nm laser line in UV-Raman spectra are assigned to the characteristic peak of hexacoordinated Ti species (TiO6). The absorption band at～280nm in UV-Vis spectra and the vibration peak at130,650,670cm"1excited at325nm laser line in UV-Raman spectra are related with the formation of framework high-coordination Ti. Moreover, the intensity of the absorption band at210nm in UV-Vis spectra and the vibration peak at960and1125cm-1in UV-Raman spectra are decreased. The catalytic results show that the framework high-coordination Ti species exhibite more excellent catalytic activity in H2O2activation, thereby significantly enhancing its catalytic epoxidation of alkene. The TON in epoxidation is also2-3times higher than the four-coordination Ti(IV) species.In the third part, the stability of the intermediate Ti-Oα-Oβ-Hend is related with the catalytic activity of titanosilicates. A new intermediate with double hydrogen bonds is formed in a catalytic system over titanosilicates by introducing a hydrogen bond acceptor, and the catalytic activity is enhanced significantly as a result of the new intermediate with suitable stability. Furthermore, DFT result indicates the possibility of double hydrogen-banding reactive intermediates. The result of reaction kinetics shows that the apparent activation energy of Ti-Oα-Oβ-Hend formed over TS-1was decreased when the hydrogen bond acceptor was introduced into the catalytic oxidation system. Its catalytic performance is improved and the relatively highest increase is almost50%. This new intermediate is universal in titanosilicate/H2O2catalytic system. Except that, the new intermediate with good hydrothermal stability(≤373K) could successfully be in situ built in the pores of TS-1by hydrothermal or impregnation method. In the fourth part, we examine the structural stability of TS-1using the continuous reaction of cyclohexanone ammoximation. The results shows that in the single-run period, TS-1has a high structural stability with little loss of framework Ti species, and the main reason of TS-1inactivation is due to blockage of the pore. The introduced porous silicon may adsorb part of organic compounds, further to slo w the adsorption rate of TS-1, and to improve its operating life.更多还原