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Combining theoretical and experimental methods to probe confinement within microporous solid-acid catalysts for alcohol dehydrations

Combining theoretical and experimental methods to probe confinement within microporous solid-acid catalysts for alcohol dehydrations
Combining theoretical and experimental methods to probe confinement within microporous solid-acid catalysts for alcohol dehydrations

Catalytic transformations play a vital role in the implementation of chemical technologies, particularly as society shifts from fossil-fuel-based feedstocks to more renewable bio-based systems. The dehydration of short-chain alcohols using solid acid catalysts is of great interest for the fuel, polymer, and pharmaceutical industries. Microporous frameworks, such as aluminophosphates, are well-suited to such processes, as their framework channels and pores are a similar size to the small alcohols considered, with many different topologies to consider. However, the framework and acid site strength are typically linked, making it challenging to study just one of these factors. In this work, we compare two different silicon-doped aluminophosphates, SAPO-34 and SAPO-5, for alcohol dehydration with the aim of decoupling the influence of acid site strength and the influence of confinement, both of which are key factors in nanoporous catalysis. By varying the alcohol size from ethanol, 1-propanol, and 2-propanol, the acid sites are constant, while the confinement is altered. The experimental catalytic dehydration results reveal that the small-pore SAPO-34 behaves differently to the larger-pore SAPO-5. The former primarily forms alkenes, while the latter favors ether formation. Combining our catalytic findings with density functional theory investigations suggests that the formation of surface alkoxy species plays a pivotal role in the reaction pathway, but the exact energy barriers are strongly influenced by pore structure. To provide a holistic view of the reaction, our work is complemented with molecular dynamics simulations to explore how the diffusion of different species plays a key role in product selectivity, specifically focusing on the role of ether mobility in influencing the reaction mechanism. We conclude that confinement plays a significant role in molecular diffusion and the reaction mechanism translating to notable catalytic differences between the molecules, providing valuable information for future catalyst design.

DFT, alcohol, dehydration, heterogeneous, molecular dynamics, porous materials, solid acid
2155-5435
5955–5968
Armstrong, Lindsay-Marie
db493663-2457-4f84-9646-15538c653998
Potter, Matthew E.
34dee7dc-2f62-4022-bb65-fc7b7fb526d2
Amsler, Jonas
7874017d-7277-4a2d-bca5-3ea0480a0b41
Spiske, Lucas
982dac5a-a3e7-4157-be33-fd223447462c
Plessow, Philipp N.
2d1b0099-9a39-49a7-a97c-80439881c0d6
Asare, Theresah
b2f42749-fd07-4c3c-9409-4721042105b6
Carravetta, Marina
1b12fa96-4a6a-4689-ab3b-ccc68f1d7691
Raja, Robert
74faf442-38a6-4ac1-84f9-b3c039cb392b
Cox, Paul A.
eb5c4562-4843-4bc6-a95c-d06084d87c67
Studt, Felix
960c61b7-4d49-4f73-8483-a61c1e4c4fa2
Armstrong, Lindsay-Marie
db493663-2457-4f84-9646-15538c653998
Potter, Matthew E.
34dee7dc-2f62-4022-bb65-fc7b7fb526d2
Amsler, Jonas
7874017d-7277-4a2d-bca5-3ea0480a0b41
Spiske, Lucas
982dac5a-a3e7-4157-be33-fd223447462c
Plessow, Philipp N.
2d1b0099-9a39-49a7-a97c-80439881c0d6
Asare, Theresah
b2f42749-fd07-4c3c-9409-4721042105b6
Carravetta, Marina
1b12fa96-4a6a-4689-ab3b-ccc68f1d7691
Raja, Robert
74faf442-38a6-4ac1-84f9-b3c039cb392b
Cox, Paul A.
eb5c4562-4843-4bc6-a95c-d06084d87c67
Studt, Felix
960c61b7-4d49-4f73-8483-a61c1e4c4fa2

Armstrong, Lindsay-Marie, Potter, Matthew E., Amsler, Jonas, Spiske, Lucas, Plessow, Philipp N., Asare, Theresah, Carravetta, Marina, Raja, Robert, Cox, Paul A. and Studt, Felix (2023) Combining theoretical and experimental methods to probe confinement within microporous solid-acid catalysts for alcohol dehydrations. ACS Catalysis, 13 (9), 5955–5968. (doi:10.1021/acscatal.3c00352).

Record type: Article

Abstract

Catalytic transformations play a vital role in the implementation of chemical technologies, particularly as society shifts from fossil-fuel-based feedstocks to more renewable bio-based systems. The dehydration of short-chain alcohols using solid acid catalysts is of great interest for the fuel, polymer, and pharmaceutical industries. Microporous frameworks, such as aluminophosphates, are well-suited to such processes, as their framework channels and pores are a similar size to the small alcohols considered, with many different topologies to consider. However, the framework and acid site strength are typically linked, making it challenging to study just one of these factors. In this work, we compare two different silicon-doped aluminophosphates, SAPO-34 and SAPO-5, for alcohol dehydration with the aim of decoupling the influence of acid site strength and the influence of confinement, both of which are key factors in nanoporous catalysis. By varying the alcohol size from ethanol, 1-propanol, and 2-propanol, the acid sites are constant, while the confinement is altered. The experimental catalytic dehydration results reveal that the small-pore SAPO-34 behaves differently to the larger-pore SAPO-5. The former primarily forms alkenes, while the latter favors ether formation. Combining our catalytic findings with density functional theory investigations suggests that the formation of surface alkoxy species plays a pivotal role in the reaction pathway, but the exact energy barriers are strongly influenced by pore structure. To provide a holistic view of the reaction, our work is complemented with molecular dynamics simulations to explore how the diffusion of different species plays a key role in product selectivity, specifically focusing on the role of ether mobility in influencing the reaction mechanism. We conclude that confinement plays a significant role in molecular diffusion and the reaction mechanism translating to notable catalytic differences between the molecules, providing valuable information for future catalyst design.

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Accepted/In Press date: 17 April 2023
e-pub ahead of print date: 17 April 2023
Published date: 17 April 2023
Additional Information: Funding Information: The authors acknowledge the TotalEnergies “Consortium on Metal Nanocatalysis” project for funding. J.A., P.N.P., and F.S. gratefully acknowledge support from GRK 2450, by the state of Baden-Württemberg through bwHPC (bwUniCluster and JUSTUS, RV bw17D01), and by the Helmholtz Association. Publisher Copyright: © 2023 The Authors. Published by American Chemical Society.
Keywords: DFT, alcohol, dehydration, heterogeneous, molecular dynamics, porous materials, solid acid

Identifiers

Local EPrints ID: 476954
URI: http://eprints.soton.ac.uk/id/eprint/476954
ISSN: 2155-5435
PURE UUID: 061d7fe9-6756-4cab-a4a0-3d06062b726b
ORCID for Matthew E. Potter: ORCID iD orcid.org/0000-0001-9849-3306
ORCID for Marina Carravetta: ORCID iD orcid.org/0000-0002-6296-2104
ORCID for Robert Raja: ORCID iD orcid.org/0000-0002-4161-7053

Catalogue record

Date deposited: 22 May 2023 16:34
Last modified: 06 Jun 2024 01:44

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Contributors

Author: Jonas Amsler
Author: Lucas Spiske
Author: Philipp N. Plessow
Author: Theresah Asare
Author: Robert Raja ORCID iD
Author: Paul A. Cox
Author: Felix Studt

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