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Quasielastic neutron scattering and molecular dynamics simulation study on the molecular behaviour of catechol in zeolite Beta

Hernandez Tamargo, Carlos, Silverwood, Ian P., O'Malley, Alexander J. and Leeuw, Nora H. de 2020. Quasielastic neutron scattering and molecular dynamics simulation study on the molecular behaviour of catechol in zeolite Beta. Topics in Catalysis 10.1007/s11244-020-01400-1

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Abstract

The dynamics of catechol in zeolite Beta was studied using quesielastic neutron scattering (QENS) experiments and molecular dynamics simulations at 393 K, to understand the behaviour of phenolic monomers relevant in the catalytic conversion of lignin via metal nanoparticles supported on zeolites. Compared to previous work studying phenol, both methods observe that the presence of the second OH group in catechol can hinder mobility significantly, as explained by stronger hydrogen-bonding interactions between catechol and the Brønsted sites of the zeolite. The instrumental timescale of the QENS experiment allows us to probe rotational motion, and the catechol motions are best fit to an isotropic rotation model with a Drot of 2.9 × 1010 s−1. While this Drot is within error of that measured for phenol, the fraction of molecules immobile on the instrumental timescale is found to be significantly higher for catechol. The MD simulations also exhibit this increased in ‘immobility’, showing that the long-range translational diffusion coefficients of catechol are lower than phenol by a factor of 7 in acidic zeolite Beta, and a factor of ∼3 in the siliceous material, further illustrating the significance of Brønsted site H-bonding. Upon reproducing QENS observables from our simulations to probe rotational motions, a combination of two isotropic rotations was found to fit the MD-calculated EISF; one corresponds to the free rotation of catechol in the pore system of the zeolite, while the second rotation is used to approximate a restricted and rapid “rattling”, consistent with molecules anchored to the acid sites through their OH groups, the motion of which is too rapid to be observed by experiment.

Item Type: Article
Date Type: Published Online
Status: In Press
Schools: Chemistry
Additional Information: This article is licensed under a Creative Commons Attribution 4.0 International License
Publisher: Springer Verlag
ISSN: 1022-5528
Funders: NERC and EPSRC
Date of First Compliant Deposit: 14 December 2020
Date of Acceptance: 13 November 2020
Last Modified: 15 Dec 2020 10:45
URI: http://orca.cardiff.ac.uk/id/eprint/136994

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