【作者】 郑健；

【导师】 宋丽娟；

【作者基本信息】 中国石油大学(华东) ， 化学工程与技术， 2022， 博士

【摘要】 分子筛材料因具有高选择性吸附特性,被广泛应用于各种实际工业应用中产生了不可估量的经济价值。对分子吸附构象（是决定分离催化性能的关键特征）的精准调控是分子筛分离和催化材料设计的主要目标。本文采用巨正则蒙特卡罗、分子动力学和密度泛函理论方法,研究分子筛骨架组成、骨架和非骨架物种及孔道窗口对分子吸附构象的影响规律及调控本质。文中以不同孔道/孔笼结构的分子筛（MFI、FAU、BEA和EMT）为模型分子筛,烃类分子（烷烃、硫化物和芳烃）转化为应用背景,揭示了分子（正己烷、噻吩、甲苯）特定吸附构象对正己烷裂化、噻吩低聚和甲苯烷基化反应的调变机制。孔道组成调控正己烷分子吸附扩散机制的研究发现,正己烷在Silicate-1和高硅铝比HZSM-5分子筛（SAR=300、100、50和30）折型孔道中的吸附具有更高的概率分布。高浓度Br（?）nsted酸环境（HZSM-5分子筛,SAR=12.47、5.86和2.43）结合MFI特殊的孔道结构,改变了直孔道的电场环境,促进了正己烷分子在直孔道中的分布,提高了正己烷的吸附和扩散性能。此外,研究发现直孔道中的正己烷可以横贯孔道交叉处相邻十元环吸附,容易停留在孔道交叉处,而择型孔道中的正己烷则不会跨越孔道交叉处相邻十元环吸附,不容易在孔道交叉处停留。揭示了孔道交叉处的结构差异造成不同吸附构象是决定正己烷催化裂化选择性的关键。孔道内非骨架物种调控噻吩分子吸附转化机制的研究发现,FAU中非骨架铝物种（EFAls）的存在会对Br（?）nsted位吸附态噻吩施加弱的相互作用与Br（?）nsted酸协同作用噻吩分子,增加噻吩的吸附能,调控噻吩的吸附构象,改变噻吩与分子筛的作用模式,使噻吩发生电子重排,进一步影响噻吩的催化转化反应。Al（OH）²⁺羟基物种作为最优的单核非骨架铝物种,其结构和化学性质有优势与B酸位协同作用噻吩分子,实现对η¹S吸附模式（噻吩S原子与B酸H原子直接作用模式）优先吸附的调控,进一步调控噻吩的质子化反应,抑制噻吩的低聚。孔道窗口调控芳烃分子（苯和甲苯）吸附转化机制的研究发现,分子筛的十二元环（12MR）窗口对苯和甲苯分子具有分子识别效应,其中FAU分子筛笼中圆形的十二元环（12MR）与苯分子具有最高的结构匹配性和电子匹配性。且通过降低硅铝比,减小碱金属阳离子电负性,增加碱性共吸附化合物浓度均可实现苯和甲苯分子从碱金属阳离子吸附模式向12MR吸附模式的调控。参数的调控本质主要是通过增加12MR骨架氧原子（O_F）的电子密度或增加12MR面外物种与12MR吸附态甲苯的弱相互作用增进12MR窗口对苯分子的识别。在12MR对芳烃分子识别研究的基础上研究了FAU分子筛甲苯侧链烷基化反应的调变机制。研究发现12MR对甲苯的优先吸附可以优化侧链烷基化反应的性能。12MR位吸附态的甲苯和甲醇侧链烷基化反应能垒显著低于阳离子吸附态的甲苯和甲醇侧链烷基化反应能垒,可以有效抑制甲醛的进一步脱氢,从而提高甲苯和甲醛侧链烷基化的选择性。本文分别从分子、原子和电子层面理解并掌握了主体分子筛活性位点及其微环境的本征特性,精确分析了吸附过程分子吸附构象及电子性质的变化,阐述了参数对分子吸附模式的调变规律和调控本质,揭示了特定吸附模式调控催化反应的本质。此研究为设计和制造具有定制吸附位的优良催化剂和吸附剂提供了理论基础和有益指导。更多还原

【Abstract】 Zeolites are widely used in various practical industrial applications because of their high selective adsorption characteristics,which have produced immeasurable economic value.The precise regulation of molecular adsorption conformation（the key feature to determine the separation and catalytic performance）is the main goal of separation and catalytic material design.The grand canonical Monte Carlo（GCMC）,molecular dynamics（MD）,and density functional theory（DFT）simulations are carried out to study the effect of framework composition,framework and extra-framework species,and windows in zeolites on the molecular adsorption conformation.The zeolites with different channel/pore structures（MFI,FAU,BEA and EMT）are selected as model zeolites and the conversion of hydrocarbon molecules（alkanes,aromatics and sulfides）is used as the application background to reveal the regulation mechanism of specific adsorption conformations of molecules（n-hexane,thiophene,benzene and toluene）on n-hexane cracking,thiophene oligomerization and toluene alkylation.The study on the adsorption and diffusion mechanism of n-hexane molecules regulated by the channel/cage composition shows that the n-hexane in the sinusoidal channels of Silicate-1and HZSM-5 zeolites with high SAR（SAR=300,100,50 and 30）has a higher probability distribution.The high-concentration Br（?）nsted acid sites（HZSM-5,SAR=12.47,5.86 and 2.43）combined with the special channel composition of MFI improve the electric field environment of the straight channels,promote the distribution of n-hexane in the straight channels,and increase the adsorption and diffusion performance of n-hexane.It also can be found that n-hexane in the straight channels can be adsorbed across the adjacent ten-membered rings at the channel intersection and is easy to stay at the channel intersection,while n-hexane in the sinusoidal channels will not be adsorbed across the adjacent ten-membered rings at the channel intersection and is difficult to stay at the channel intersection.It is revealed that the structural differences at the channel intersection lead to different adsorption conformations of n-hexane,which is the key to determine the selectivity of n-hexane cracking.The study on the adsorption and conversion mechanism of thiophene molecules regulated by the extra-framework species represents that the existence of extra-framework aluminum species（EFAls）will exert weak interactions on the adsorbed thiophene at the Br（?）nsted acid site,increase the adsorption energies of thiophene,cooperate with Br（?）nsted acid site to regulate the adsorbed conformation of thiophene,alter the interaction modes between the thiophene and the zeolite,occur the electron rearrangement of thiophene,and further affect the catalytic conversion of thiophene.The Al（OH）²⁺hydroxyl species,as the optimal mononuclear extra-framework aluminum species,has advantages in its structure and chemical properties to synergize with the Br（?）nsted acid site interacting with thiophene,realizing the regulation of preferentialη¹S adsorption mode（direct interaction mode between S atom of thiophene and H atom of Br（?）nsted acid site）,further regulate the protonation reaction of thiophene and inhibit the oligomerization of thiophene.The study on the adsorption and conversion mechanism of aromatics regulated by windows depicts that the twelve-membered ring（12MR）windows of zeolites have recognition effect on benzene and toluene molecules.The circular 12MR windows in the supercage of the FAU zeolite have the highest structural and electronic matching with benzene molecules.Benzene and toluene molecules can be regulated from alkali-metal cationic adsorption mode to12MR adsorption mode by decreasing SAR,reducing the electronegativity of alkali-metal cations,and increasing the concentration of alkaline co-adsorption compounds.The change of parameters is mainly to improve the recognition ability of 12MR windows to benzene molecules by increasing the electronic density of framework oxygen atoms or increasing the weak interaction between acidic species and toluene adsorbed on 12MR.Based on the molecular recognition of aromatics by 12MR,the regulation mechanism of the toluene side-chain alkylation of FAU zeolites is studied.It can be found that preferential adsorption of toluene on 12MR can optimize the performance of the side-chain alkylation reaction.The reaction barrier of the side-chain alkylation of toluene（adsorbed on 12MR window）and formaldehyde is significantly lower than that of the side-chain alkylation of toluene（adsorbed on alkali-metal cation）and formaldehyde,which can effectively inhibit the further dehydrogenation of formaldehyde,thereby increasing the selectivity of side-chain alkylation.This work shows that the intrinsic properties of the active sites and surrounding microchemical environment over zeolites at molecular-level,atomic-level and electronic level,accurately analyzes the changes of adsorption conformations and electronic properties of the guest-molecules during the adsorption process,expounds the regulation essence of the parameters to the adsorption conformations,reveals the regulation mechanisms of the catalytic reaction by the specific adsorption conformations.These findings provide the theoretical basis and useful guidance for the design and fabrication of excellent catalysts and adsorbents with tailored adsorption sites更多还原