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

Xiao, Dong; Xu, Shutao; Brownbill, Nick J.; Paul, Subhradip; Chen, Li-Hua; Pawsey, Shane; Aussenac, Fabien; Su, Bao-Lian; Han, Xiuwen; Bao, Xinhe; Liu, Zhongmin; Blanc, Frédéric

Abstract

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.

Citation

Xiao, D., Xu, S., Brownbill, N. J., Paul, S., Chen, L.-H., Pawsey, S., Aussenac, F., Su, B.-L., Han, X., Bao, X., Liu, Z., & Blanc, F. (2018). Fast detection and structural identification of carbocations on zeolites by dynamic nuclear polarization enhanced solid-state NMR. Chemical Science, 9(43), 8184-8193. https://doi.org/10.1039/c8sc03848a

• Journal Article Type: Article
• Acceptance Date: Oct 2, 2018
• Online Publication Date: Oct 2, 2018
• Publication Date: Nov 21, 2018
• Deposit Date: Nov 22, 2018
• Publicly Available Date: Nov 26, 2018
• Journal: Chemical Science
• Print ISSN: 2041-6520
• Electronic ISSN: 2041-6539
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 9
• Issue: 43
• Pages: 8184-8193
• DOI: https://doi.org/10.1039/c8sc03848a
• Keywords: General Chemistry
• Public URL: https://nottingham-repository.worktribe.com/output/1301603
• Additional Information: : This document is Similarity Check deposited; : Supplementary Information; : Dong Xiao (ORCID); : Shutao Xu (ORCID); : Subhradip Paul (ORCID); : Li-Hua Chen (ORCID); : Bao-Lian Su (ORCID); : Xinhe Bao (ORCID); : Frédéric Blanc (ORCID); : Frédéric Blanc (ResearcherID); : Single-blind; : Received 28 August 2018; Accepted 2 October 2018; Accepted Manuscript published 2 October 2018; Advance Article published 17 October 2018; Version of Record published 7 November 2018
• Contract Date: Nov 26, 2018