物理化学学报 >> 2020, Vol. 36 >> Issue (4): 1905035.doi: 10.3866/PKU.WHXB201905035

所属专题: 固体核磁共振

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Silicalite-1分子筛氢键诱导晶化机制的固体核磁共振研究

刘小龙1,2,王强1,王超1,徐君1,*(),邓风1,*()   

  1. 1 中国科学院精密测量科学与技术创新研究院,武汉物理与数学研究所,波谱与原子分子物理国家重点实验室,武汉磁共振中心,武汉 430071
    2 中山大学材料学院,广州 510275
  • 收稿日期:2019-05-08 录用日期:2019-06-14 发布日期:2020-03-12
  • 通讯作者: 徐君,邓风 E-mail:xujun@wipm.ac.cn;dengf@wipm.ac.cn
  • 基金资助:
    国家自然科学基金(21473246);国家自然科学基金(21622311);国家自然科学基金(21573278);国家自然科学基金(21673282);中国科学院前沿科学重点研究计划(QYZDB-SSW-SLH027);湖北省自然科学基金(2017CFA032)

Hydrogen-Bond Induced Crystallization of Silicalite-1 Zeolite as Revealed by Solid-State NMR Spectroscopy

Xiaolong Liu1,2,Qiang Wang1,Chao Wang1,Jun Xu1,*(),Feng Deng1,*()   

  1. 1 State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Centre for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, P. R. China
    2 School of Materials, Sun Yat-Sen University, Guangzhou 510275, P. R. China
  • Received:2019-05-08 Accepted:2019-06-14 Published:2020-03-12
  • Contact: Jun Xu,Feng Deng E-mail:xujun@wipm.ac.cn;dengf@wipm.ac.cn
  • Supported by:
    the National Natural Science Foundation of China(21473246);the National Natural Science Foundation of China(21622311);the National Natural Science Foundation of China(21573278);the National Natural Science Foundation of China(21673282);Key Program for Frontier Science of the Chinese Academy of Sciences(QYZDB-SSW-SLH027);Hubei Provincial Natural Science Foundation, China(2017CFA032)

摘要:

对分子筛晶化机理的理解对于定向合成具有理想结构与性质的分子筛具有重要意义,然而这仍然是目前材料研究领域中的一个重要挑战。在此工作当中,我们利用一维及二维固体核磁共振结合多种表征技术研究了Silicalite-1 (MFI结构)分子筛晶化过程,通过二维1H双量子(DQ)-单量子(SQ) MAS NMR以及一维2H MAS NMR实验发现[415262]笼中与层间两种SiO-···H―OSi氢键结构,其中层间氢键在分子筛的晶化过程中逐步转变为笼中氢键。这两种氢键分别具有不同作用:笼中氢键对四丙基氢氧化铵导向剂(TPA+)起到空间电荷平衡的作用,在长程有序结构还没有形成时期,这种静电相互作用是晶化过程中有机-无机复合物转变为MFI结构的关键因素;层间的SiO-···H―OSi氢键起到了“连接器”的作用,能够将合成体系中的硅物种不断的聚集在一起从而产生分子筛的骨架。此外,2H MAS NMR实验表明,即使在分子筛的长程有序结构(MFI结构)生成之后,在分子筛骨架上仍然会存在由于未完全聚合的硅物种而产生的Si―OH羟基巢缺陷位。

关键词: 分子筛, 晶化机理, 固体核磁共振, 结构导向剂, 氢键

Abstract:

The flexible chemical composition of the frameworks with tunable pore size and geometry of molecular dimensions makes zeolites widely used in chemical and petrochemical industry fields. The understanding of crystallization mechanism is important for a rational design of new zeolite with target structure and property, which however is still a big challenge in the field of material science. In this work, the specific spatial correlations/interactions between the SiO-···HO―Si hydrogen bonds within the charged framework of silicalite-1 (MFI topology) zeolite and the alkyl chains of tetrapropylammonium ion (TPA+) organic structure direction agents (OSDAs) were studied by one-dimensional (1D) and two-dimensional (2D) solid state-NMR spectroscopy in combination with other techniques, with the aim to shed light into the crystallization mechanism of silicalite-1. The "solvent-free" route was used to study the crystallization process. Silicalite-1 crystals were also prepared following the hydrothermal synthesis route. The structural properties of as-synthesized TPA-silicalite-1 samples during the crystallization were characterized by XRD and scanning electron microscopy (SEM) images, which showed the evolution of long-range periodic structure and cyrtal growth. The 1H-29Si CP/MAS NMR experiments showed that the reorganization of the silica or silicates occurred in the crystallization process. The lH-13C CP/MAS NMR experiments performed on the samples synthesized with different time indicated that the TPA+ ions in the amorphous samples experienced a constrained environment, forming the inorganic-organic composites. The splitting of the methyl carbon signal from TPA+ ions was observed in the 13C NMR spectra, which is the direct reflection of the interactions between the methyl groups and the silicate framework in the straight and zig-zag channels of silicalite-1. Two types of SiO-···H―OSi hydrogen bonds (SiO-···H―OSi hydrogen bond in-cage and SiO-···H―OSi hydrogen bond between lamellae) have been identified by 2D 1H double quantum (DQ)-single quantum (SQ) MAS NMR and 2H MAS NMR during the crystallization of silicalite-1. The SiO-···H―OSi hydrogen bonds between lamellae are formed and gradually transformed into the in-cage ones during the crystallization process. Their functions have been revealed in the formation of silicalite-1: the SiO-···H―OSi hydrogen bond in-cage provides the stereoscopic counterbalance for the positive charges from TPA+ ions and this stereoscopic electrostatic interaction is the key factor to transform inorganic-organic composites with the MFI structure property, even though the long-range periodic MFI structures have not been established yet; the SiO-···H―OSi hydrogen bond between lamellae acts as a connector to assemble the silicate species together to generate the zeolite framework. 2H MAS NMR spectra show that the SiOH nests exist in the zeolite framework even though the long-range periodic structures have been fully established.

Key words: Zeolite, Crystallization mechanism, Solid-state NMR, Structure direction agent, Hydrogen bond

MSC2000: 

  • O641