Fast detection and structural identification of carbocations on zeolites by dynamic nuclear polarization enhanced solid-state NMR. Issue 43 (17th October 2018)

• Record Type: Journal Article
• Authors: 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
• Is Part Of: Chemical science. Volume 9:Issue 43(2018)
• Page Start: 8184
• Page End: 8193
• Publication Date: 2018-10-17
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c8sc03848a
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : A fast NMR data acquisition strategy is explored to detect and characterize carbocations on solid zeolites. 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 13 C isotopic enrichment and efficient dynamic nuclear polarization magic angle spinning nuclear magnetic resonance spectroscopy to detect carbocations in zeolites. We use two dimensional 13 C– 13 C through-bond correlations to establish their structures and 29 Si– 13 C 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.