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Direct observation of a new aluminum Lewis acid site in a zeolite

28 September 2022, Version 1
Working Paper
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

We report the formation of a new Lewis acid Al site in H-FAU zeolite upon 650 ⁰C thermal treatment, unknown for any zeolite. Spectroscopy and DFT calculations reveal this site is a naked Al+3 ion which is charge balanced by a triplet of adjacent framework oxygens with net charge of -1 for each Si-O-Al moiety. This is the first reported observation of a +3 cation stabilized in a zeolite and the first confirmation of existence of aluminum triplets (as opposed to Al pairs) in that can stabilize such cations in siliceous zeolites. This site forms a thermally stable carbonyl O3Al-CO complex with the highest known frequency at 2252 cm-1 for a carbonyl complex on any solid material. These findings open new horizons in zeolite chemistry and expand our understanding of polyvalent metals’ interactions with zeolites.

Keywords

zeolite
new aluminium Lewis acid site in zeolite
infrared spectroscopy
aluminum carbonyl and hydrides in zeolite
bare trivalent cation stabilized in zeolite
3 adjacent Al site in siliceous zeolite
Al triplet
first observation of an isolated +3 cation in zeolite

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Version History

Sep 28, 2022 Version 1

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The content is available under CC BY NC ND 4.0 [opens in a new tab]

DOI

10.26434/chemrxiv-2022-mgbnq
D O I: 10.26434/chemrxiv-2022-mgbnq [opens in a new tab]

Funding

The research described in paper is part of the Quickstarter Initiative at Pacific Northwest National Laboratory. It was conducted under the Laboratory Directed Research and Development Program at PNNL, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy (DOE) under Contract DE-AC05-76RL01830. The research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE's Office of Biological and Environmental Research. This work was supported by US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences, and Geosciences. SPG and HAA acknowledge the support by Bulgarian National Science Fund (project КП-06-Н59/5) and are also grateful for computational resources provided by the European Regional Development Fund within the Operational Programme "Science and Education for Smart Growth 2014 - 2020" under the Project CoE "National center of mechatronics and clean technologies" BG05M2OP001-1.001-0008". GNV acknowledges the support of the project EXTREME, funded by the Bulgarian Ministry of Education and Science (D01-76/30.03.2021).

Author’s competing interest statement

The author(s) have declared they have no conflict of interest with regard to this content

Ethics

The author(s) have declared ethics committee/IRB approval is not relevant to this content

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