【作者】 张东顺；

【导师】 王日杰；

【作者基本信息】 天津大学 ， 工业催化， 2012， 硕士

【摘要】 本文对改性Al-MCM-41分子筛上气相贝克曼重排反应进行了研究。采用等体积浸渍法,制备了磷酸和硼酸改性的Al-MCM-41分子筛催化剂。使用固定床反应器,对催化剂的活性进行了评价,并采用XRD,SEM,N2吸附,FT-IR,NH₃-TPD,MAS NMR,UV-Vis,XPS,TGA以及GC-MS等表征手段对反应前后的催化剂进行了一系列的表征,研究了催化剂表面的积碳情况和催化剂的活性位点,并采用化学计算的方法,探索了磷改性Al-MCM-41分子筛的结构以及气相贝克曼重排可能的反应历程。磷改性Al-MCM-41分子筛提高了催化剂的活性,己内酰胺的选择性由64%提高至80%左右。腈类和酮类是气相贝克曼重排的主要副产物,随着反应温度的升高,腈类增多,酮类减少。在所考察的40小时内,催化剂的活性基本没有发生改变,磷改性Al-MCM-41分子筛有着良好的稳定性。提高弱酸中心的数量有利于提高己内酰胺的选择性。硼改性Al-MCM-41分子筛也提高了催化剂的活性,己内酰胺的选择性最大可达到78%。硼的引入可以提高己内酰胺的选择性,但其选择性与硼加入量并不成线性关系。硼在分子筛中积聚会降低己内酰胺的选择性并容易导致催化剂失活。己内酰胺的选择性与分子筛中弱酸中心,尤其是弱Br（?）nsted酸中心有密切关系,它是气相贝克曼重排的活性中心。积碳是催化剂失活的主要因素。积碳在催化剂表面以无定形形态存在,主要以软积碳和硬积碳两种类型沉积在催化剂的表面;积碳优先在催化剂的酸中心上形成,尤其是较强的酸中心上;反应后催化剂表面积碳的成分主要是脂肪烃类,而不是芳香烃类化合物;由于脱氢和聚合反应,分子筛表面形成脱氢碳物种或者碳结焦产物,堵塞了活性位点或者孔道,从而导致催化剂失活。通过计算化学分析,构型B是磷改性Al-MCM-41分子筛的可能结构;Nguyen等人提出的气相贝克曼重排的反应机理是合理的。但是,烷基基团的迁移是该反应的速率决定步骤,而1,2-H转移反应不是决定步骤。更多还原

【Abstract】 Vapor phase Beckmann rearrangement reaction of cyclohexanone oxime to caprolactam was studied over modified Al-MCM-41 catalysts in this thesis. A series of phosphorus （P） and boron （B） modified Al-MCM-41 molecular sieves were prepared using impregnation method. The activity of these catalysts was studied by a continuous flow fixed-bed reactor. All the catalysts were characterized by XRD, SEM, N₂ adsorption, FT-IR, NH3-TPD, MAS NMR, UV-Vis, XPS, TGA, and GC-MS. The coke and catalytic activity sites of the catalyst were also studied. The possible molecular structure of P modified Al-MCM-41 catalyst and the possible reaction mechanism was investigated by computational chemistry method.P modified Al-MCM-41 catalyst can improve the selectivity for caprolactam. It increased from 64% to 80%. Nitriles and ketones are main side products. With increased temperature, more nitriles and less ketones were generated. No conversion decline was observed during the 40 hours process time, indicating the high stability of PAM-3 catalyst. More weak acid sites are favorable for caprolactam selectivity.B modified Al-MCM-41 catalyst can also improve the selectivity for caprolactam. It can reach 78% in this work. Boron can improve caprolactam selectivity. However, boron content does not linearly influence caprolactam selectivity. The acitivity of boron modified Al-MCM-41 catalyst was influenced by boron distribution in the catalyst. The conglomeration of boron on the catalyst decreased the selectivity of caprolactam and finally led to catalyst deactivation. There is a close relationship between caprolactam and weak acid sites, especially weak Br?nsted acid sites. And these acid centers are acitive sites.Coke formation on the catalyst is the main reason for its deactivation. The coke was mainly amorphous structure. Both soft coke and hard coke were deposited on the used boron modified Al-MCM-41 catalyst. And the coke was deposited preferentially on acid sites, especially the strong acid sites. The coke deposited on the catalyst is mainly aliphatic-type carbonaceous compounds and no aromatic-type coke formed. The catalyst deacitivition was attributed to the pore and active sites being blocked by the excessive dehydrogenated carbon species.The Computational Chemistry results reveal that the Geometry B is the possible structure of P modified Al-MCM-41 catalyst. The vapor phase Beckmann rearrangement reaction mechanism proposed by Nguyen et al is reasonable. A transfer of R1 group is a rate determining step, wihle 1,2-H shift reaction is not.更多还原