Issue 34, 2023

The need for operando modelling of 27Al NMR in zeolites: the effect of temperature, topology and water

Abstract

Solid state (ss-) 27Al NMR is one of the most valuable tools for the experimental characterization of zeolites, owing to its high sensitivity and the detailed structural information which can be extracted from the spectra. Unfortunately, the interpretation of ss-NMR is complex and the determination of aluminum distributions remains generally unfeasible. As a result, computational modelling of 27Al ss-NMR spectra has grown increasingly popular as a means to support experimental characterization. However, a number of simplifying assumptions are commonly made in NMR modelling, several of which are not fully justified. In this work, we systematically evaluate the effects of various common models on the prediction of 27Al NMR chemical shifts in zeolites CHA and MOR. We demonstrate the necessity of operando modelling; in particular, taking into account the effects of water loading, temperature and the character of the charge-compensating cation. We observe that conclusions drawn from simple, high symmetry model systems such as CHA do not transfer well to more complex zeolites and can lead to qualitatively wrong interpretations of peak positions, Al assignment and even the number of signals. We use machine learning regression to develop a simple yet robust relationship between chemical shift and local structural parameters in Al-zeolites. This work highlights the need for sophisticated models and high-quality sampling in the field of NMR modelling and provides correlations which allow for the accurate prediction of chemical shifts from dynamical simulations.

Graphical abstract: The need for operando modelling of 27Al NMR in zeolites: the effect of temperature, topology and water

Associated articles

Supplementary files

Article information

Article type
Edge Article
Submitted
16 May 2023
Accepted
02 Aug 2023
First published
03 Aug 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2023,14, 9101-9113

The need for operando modelling of 27Al NMR in zeolites: the effect of temperature, topology and water

C. Lei, A. Erlebach, F. Brivio, L. Grajciar, Z. Tošner, C. J. Heard and P. Nachtigall, Chem. Sci., 2023, 14, 9101 DOI: 10.1039/D3SC02492J

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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