Fast detection and structural identification of carbocations on zeolites by dynamic nuclear polarization enhanced solid-state NMR†,Chemical Science

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Fast detection and structural identification of carbocations on zeolites by dynamic nuclear polarization enhanced solid-state NMR†
Chemical Science ( IF 7.6 ) Pub Date : 2018-10-02 00:00:00 , DOI: 10.1039/c8sc03848a
Dong Xiao _{1,

2,

3} , Shutao Xu ₄ , Nick J Brownbill ₃ , Subhradip Paul ₅ , Li-Hua Chen ₆ , Shane Pawsey ₇ , Fabien Aussenac ₈ , Bao-Lian Su _{6,

9} , Xiuwen Han ₁ , Xinhe Bao ₁ , Zhongmin Liu _{1,

4} , Frédéric Blanc _{3,

10}

Affiliation

State Key Laboratory of Catalysis , Dalian Institute of Chemical Physics , Chinese Academy of Sciences , 457 Zhongshan Road , Dalian 116023 , China.
University of Chinese Academy of Sciences , Beijing 100049 , China.
Department of Chemistry , University of Liverpool , Crown Street , Liverpool , L69 7ZD , UK . Email:
National Engineering Laboratory for Methanol to Olefins , Dalian National Laboratory for Clean Energy , Dalian Institute of Chemical Physics , Chinese Academy of Sciences , Dalian 116023 , China.
DNP MAS NMR Facility , Sir Peter Mansfield Imaging Centre , University of Nottingham , Nottingham NG7 2RD , UK.
State Key Laboratory of Advanced Technology for Materials Synthesis and Processing , Wuhan University of Technology , 122 Luoshi Road , 430070 , Wuhan , China.
Bruker BioSpin Corporation , 15 Fortune Drive , Billerica , Massachusetts 01821 , USA.
Bruker BioSpin , 34 rue de I'Industrie BP 10002 , 67166 Wissembourg Cedex , France.
CMI (Laboratory of Inorganic Materials Chemistry) , University of Namur , 61 rue de Bruxelles , B-5000 Namur , Belgium.
Stephenson Institute for Renewable Energy , University of Liverpool , Crown Street , Liverpool L69 7ZD , UK.

Acidic zeolites are porous aluminosilicates used in a wide range of industrial processes such as adsorption and catalysis. The formation of carbocation intermediates plays a key role in reactivity, selectivity and deactivation in heterogeneous catalytic processes. However, the observation and determination of carbocations remain a significant challenge in heterogeneous catalysis due to the lack of selective techniques of sufficient sensitivity to detect their low concentrations. Here, we combine ¹³C isotopic enrichment and efficient dynamic nuclear polarization magic angle spinning nuclear magnetic resonance spectroscopy to detect carbocations in zeolites. We use two dimensional ¹³C–¹³C through-bond correlations to establish their structures and ²⁹Si–¹³C through-space experiments to quantitatively probe the interaction between multiple surface sites of the zeolites and the confined hydrocarbon pool species. We show that a range of various membered ring carbocations are intermediates in the methanol to hydrocarbons reaction catalysed by different microstructural β-zeolites and highlight that different reaction routes for the formation of both targeted hydrocarbon products and coke exist. These species have strong van der Waals interaction with the zeolite framework demonstrating that their accumulation in the channels of the zeolites leads to deactivation. These results enable understanding of deactivation pathways and open up opportunities for the design of catalysts with improved performances.

中文翻译：

通过动态核极化增强固态 NMR 快速检测和结构鉴定沸石上的碳阳离子†

酸性沸石是多孔硅铝酸盐，广泛用于吸附和催化等工业过程。碳正离子中间体的形成在多相催化过程的反应性、选择性和失活中起着关键作用。然而，由于缺乏足够灵敏度的选择性技术来检测碳阳离子的低浓度，碳阳离子的观察和测定仍然是多相催化中的重大挑战。在这里，我们结合¹³ C 同位素富集和高效动态核极化魔角旋转核磁共振波谱来检测沸石中的碳正离子。我们使用二维¹³ C- ¹³ C 直通键关联来建立它们的结构，并使用²⁹ Si- ¹³ C 直通空间实验来定量探测沸石的多个表面位点与受限烃池物种之间的相互作用。我们表明，一系列不同的元环碳阳离子是不同微观结构β-沸石催化的甲醇到烃类反应的中间体，并强调存在形成目标烃类产物和焦炭的不同反应路线。这些物质与沸石骨架具有强烈的范德华相互作用，表明它们在沸石通道中的积累导致失活。这些结果有助于了解失活途径，并为设计具有改进性能的催化剂提供了机会。

更新日期：2018-10-02

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