分子筛限域孔道内C4中间体结构及其异构化机理的NMR实验和理论研究

发布时间：2018-05-27 16:27

本文选题：分子筛 + 固体核磁　；参考：《中国科学院大学(中国科学院武汉物理与数学研究所)》2017年硕士论文

【摘要】：分子筛具有可调节的酸性活性位点和孔隙结构,这使其成为广泛应用的工业催化剂,可以催化多种反应如催化裂化、加氢裂解、异构化等。分子筛的催化机理与其他酸性催化剂相同,都涉及碳正离子这种重要的中间体物种,所以可以通过在分子筛体系内捕捉碳正离子并观察其转化情况,来研究分子筛的催化机理。分子筛催化石油的裂解和汽油的重整一直备受关注,其催化反应机理主要涉及C4物种的转化,其中研究最多的是叔丁基碳正离子。这种具有支链结构的中间体,一直被认为可以用来揭示短链的碳氢物种在分子筛体系内的异构化机理。本文主要是在ZSM-5分子筛中观测叔丁基碳正离子并且研究其转化过程。(1)短链的碳正离子由于其活性高、寿命短,在分子筛体系内的观测一直是实验上的难点。本文采用共吸附碱性捕捉剂(氨气)的方法,在ZSM-5分子筛孔道内捕捉重要的C4中间体,并且通过13C-13C二维相关谱和理论计算对捕捉到的物种进行了结构分析,确定叔丁基碳正离子的存在。在此基础上,利用13C-27Al相关实验表征了叔丁基碳正离子与分子筛骨架的相互作用关系。(2)C4物种在分子筛孔道内的转化一直是研究的热点,本文利用原位固体核磁观测了选择性标记的2-13C-叔丁醇在ZSM-5分子筛内的转化情况,发现13C标记的季碳迁移到伯碳位置,而且标记碳在最终产物中混乱分布的现象。为了解释这两种实验现象,我们采取了理论计算的方法,给出了包含质子化的甲基环丙烷中间体的反应机理,并预测了可能存在的C4中间体物种。通过碱性捕捉剂法和过量吸附法观察到了理论计算预测的C4烯烃物种(2-13C-2-丁烯、1-13C-异丁烯、2-13C-异丁烯),在实验上印证了反应机理的正确性。通过实验和理论手段,我们观测到了 C4物种骨架异构化的实验现象,并且给出了合理的解释。
[Abstract]:Molecular sieve has adjustable acidic active sites and pore structure which makes it a widely used industrial catalyst which can catalyze many reactions such as catalytic cracking hydrocracking isomerization and so on. The catalytic mechanism of molecular sieve is the same as that of other acidic catalysts, which involves carbon ion as an important intermediate species. Therefore, the catalytic mechanism of molecular sieve can be studied by capturing carbon positive ion in molecular sieve system and observing its conversion. Molecular sieve catalyzes the cracking of petroleum and the reforming of gasoline. The mechanism of catalytic reaction is mainly related to the conversion of C4 species, among which the tertiary Ding Ji carbon ion is the most studied. This intermediate with branched structure has been thought to be used to reveal the isomerization mechanism of short-chain hydrocarbon species in molecular sieve system. In this paper, the observation of tert Ding Ji carbon positive ions in ZSM-5 molecular sieve and its conversion process. 1) because of its high activity and short lifetime, the observation in molecular sieve system is always difficult. In this paper, the important C4 intermediates were captured in the pore of ZSM-5 molecular sieve by the method of coadsorption alkaline catcher (ammonia), and the structure of the captured species was analyzed by 13C-13C two-dimensional correlation spectrum and theoretical calculation. The existence of tertiary Ding Ji carbon ion was determined. On this basis, the interaction between tertiary Ding Ji carbon cations and molecular sieve framework was characterized by 13C-27Al correlation experiments. The transformation of C 4 species in molecular sieve channels has been a hot topic. The transformation of selective labeled 2-13C- tert-butanol in ZSM-5 molecular sieve was observed by in situ solid state NMR. It was found that the 13C-labeled quaternary carbon migrated to the primary carbon position and the labeled carbon was misdistributed in the final product. In order to explain these two experimental phenomena, the reaction mechanism of methyl cyclopropane intermediates containing protonation is given by theoretical calculation, and the possible C4 intermediate species are predicted. The theoretical calculation of 2-13C-2-butene (2-13C-2-butene) 2-13C- (isobutene) -2-13C- (isobutene) was observed by alkaline trapping agent method and excessive adsorption method, which proved the correctness of the reaction mechanism. Through experimental and theoretical means, we observed the experimental phenomenon of the isomerization of C4 species skeleton, and gave a reasonable explanation.
【学位授予单位】：中国科学院大学(中国科学院武汉物理与数学研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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