Mechanisms of small alkane activation and aromatization on zinc-modified zeolite catalysts

锌改性沸石催化剂上小烷烃活化及芳构化机理

• 批准号: 405567845
• 负责人: Professor Dr. Jürgen Haase
• 金额: --
• 依托单位: Boreskov Institute of Catalysis
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/405567845?language=en
• 关键词: Mechanisms; small; alkane; activation; aromatization

Light paraffins (C2−C4) are contained in oil and natural gas and can be processed on zeolite catalysts in a mixture of aromatic hydrocarbons (toluene, xylenes, etc.), which are widely used in the petrochemical industry to synthesize more valuable substances or improve the quality of motor fuels. Zeolite modifications with metals (e.g., zinc) increase the efficiency of light (small) alkane processing into aromatic hydrocarbons. Zinc-modified zeolites contain usually, besides Brønsted acid sites (BAS), different Zn species including Zn2+ cations or zinc oxide species of different dimensions and localizations in the zeolitic pores. The role of different Zn species in the primary activation of the alkane and the subsequent aromatization is still unclear.The project intends to perform a targeted synthesis of two zeolite samples of ZSM-5 or BEA type, containing exclusively one type of zinc species in the pores, either Zn2+cations or small zinc oxide species (ZnO) with a size by order of magnitude of 1 nm. This will help to establish differences in the mechanisms of activation and aromatization of C2−C4 alkanes on zeolites containing cations Zn2+ or ZnO species, and it will help us find out what particular zinc species ensure the efficient conversion of small alkanes into aromatic molecules.The implementation of the project includes the following main stages:1. Establishing the role of Brønsted acidic sites (BAS) and zinc species in the activation of the C-H bonds of alkanes. 2. Determination of synergistic action of BAS and zinc species in the activation of C-H bonds of small alkanes.3. Identification of primary intermediates formed during the interaction of alkanes with zinc species. Determination of the similarity and difference in the structure of these intermediates for Zn2+ - and ZnO-zeolites.4. Analysis of the evolution of primary intermediates into subsequent secondary intermediates, and further transformation in to aromatic products.An analysis of the nature and structure of the intermediates of the interaction of alkanes with zinc-containing zeolites will be performed by 13C MAS NMR in situ. Rationalization of the role of BAS and various zinc species in the activation of CH bonds of alkanes will be based on the analysis of both, the regioselectivity and the rate of H/D hydrogen exchange between BAS and various CHn (n = 1−3) fragments of alkanes obtained by monitoring the kinetics of this exchange by the 1H MAS NMR method in situ. 1H MAS NMR and 67Zn MAS NMR studies of the BAS and Zn sites complete the applied methods.The obtained fundamental information will make it possible to clarify the role of different zinc centers and BAS in the activation of particular C-H bonds of alkane and its aromatization on zeolite catalysts. The new information provides the basis for the rational design and operation of heterogeneous catalysts for aromatization of small alkanes based on zinc modified zeolites.

轻质石蜡（C2−C4）存在于石油和天然气中，可以在芳烃（甲苯、二甲苯等）混合物中通过沸石催化剂进行加工，广泛应用于石化工业中以合成更有价值的物质或提高发动机燃料的质量（例如锌），提高轻（小）烷烃加工成锌改性芳烃的效率。除了布朗斯台德酸中心（BAS）之外，沸石通常还含有不同的 Zn 物种，包括不同尺寸和在沸石孔中的不同 Zn2+ 阳离子或氧化锌物种。不同 Zn 物种在烷烃的初级活化和随后的芳构化中的作用是。仍不清楚。该项目打算对两种 ZSM-5 或 BEA 型沸石样品进行定向合成，其中仅含有一种类型的锌物质孔径为 1 nm 数量级的 Zn2+ 阳离子或小型氧化锌 (ZnO)，这将有助于确定含有 Zn2+ 或 ZnO 阳离子的沸石上 C2−C4 烷烃的活化和芳构化机制的差异。物种，这将有助于我们找出哪些特定的锌物种可以确保小烷烃有效转化为芳香分子。该项目的实施包括以下主要阶段： 1．布朗斯台德酸性位点（BAS）和锌物质在烷烃C-H键活化中的作用2.BAS和锌物质在小烷烃C-H键活化中的协同作用的测定。3．确定Zn2+-和ZnO-沸石中间体结构的相似性和差异。4．初级中间体演变为后续次级中间体，并进一步转化为芳香族产物的过程。将通过13C MAS NMR原位分析烷烃与含锌沸石相互作用的中间体的性质和结构。 BAS 和各种锌物质在烷烃 CH 键活化中的作用将基于对 BAS 和各种锌物质之间的区域选择性和 H/D 氢交换速率的分析。通过原位 1H MAS NMR 方法监测这种交换的动力学获得了烷烃的 CHn (n = 1−3) 碎片，并对 BAS 和 Zn 位点进行了 1H MAS NMR 和 67Zn MAS NMR 研究，完成了应用方法。这些信息将有助于阐明不同锌中心和 BAS 在烷烃特定 C-H 键的活化及其在沸石催化剂上的芳构化中的作用。为基于锌改性沸石的小烷烃芳构化多相催化剂的合理设计和运行提供依据。