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Understanding the mechanochemical synthesis of the perovskite LaMnO3 and its catalytic behaviour

Understanding the mechanochemical synthesis of the perovskite LaMnO3 and its catalytic behaviour
Understanding the mechanochemical synthesis of the perovskite LaMnO3 and its catalytic behaviour
Mechanochemistry offers a solventless, ‘waste free’ route to preparing metal oxide catalysts, however, there is limited information on the chemical steps involved. In this work, the perovskite LaMnO3 has been successfully synthesized via mechanochemistry from metal oxide powders, La2O3 and Mn2O3, at room temperature, using a planetary ball mill. Separate ex situ ‘time slices’ were taken during the milling procedure to provide insights into the underlying chemistry. The crystalline material was assessed using XRD, which identified 100% perovskite phase after 3 h of milling. Conversely, characterization by X-ray absorption spectroscopy (XAS) at both the Mn K-edge and La L3-edge provides a very different picture. The XAS data shows that there are significant structural alterations as early as 30 min of milling, with the La precursor dispersed over Mn2O3. Increasing milling time then allows for mechanical activation of both precursors and the formation of powdered LaMnO3, with no calcination step required. The XAS highlights that there is a significant amount of amorphous, oxygen deficient, content even when XRD has identified 100% perovskite phase. The samples were tested for the decomposition of the environmental pollutant N2O; at a milling time of 3 h, the LaMnO3 catalyst displays a much early onset production of N2 compared to a traditional sol–gel synthesized LaMnO3, resulting from increased oxygen deficiency at the surface, confirmed by XPS and STEM-EELS. This is an encouraging sign that mechanochemical routes can be harnessed to provide a sustainable route to preparing mixed metal oxide catalysts with enhanced catalytic performance.
0300-9246
232-240
Blackmore, Rachel H.
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Rivas, Maria Elena
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Erden, Tugce Eralp
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Tran, Trung Dung
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Marchbank, Huw R.
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Ozkaya, Dogan
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Briceno de Gutierrez, Martha
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Wagland, Alison
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Collier, Paul
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Wells, Peter P.
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Blackmore, Rachel H.
3584b852-92ac-4341-b303-786f67e41f77
Rivas, Maria Elena
08dfefa0-544f-4c89-a1c8-7a58560a59e1
Erden, Tugce Eralp
758531fc-bdd2-4122-bc1b-2e4438b1a282
Tran, Trung Dung
249e2322-c163-48cd-9c3e-23b0b7acbbec
Marchbank, Huw R.
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Ozkaya, Dogan
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Briceno de Gutierrez, Martha
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Wagland, Alison
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Collier, Paul
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Wells, Peter P.
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Blackmore, Rachel H., Rivas, Maria Elena, Erden, Tugce Eralp, Tran, Trung Dung, Marchbank, Huw R., Ozkaya, Dogan, Briceno de Gutierrez, Martha, Wagland, Alison, Collier, Paul and Wells, Peter P. (2020) Understanding the mechanochemical synthesis of the perovskite LaMnO3 and its catalytic behaviour. Dalton Transactions, 49 (1), 232-240. (doi:10.1039/C9DT03590G).

Record type: Article

Abstract

Mechanochemistry offers a solventless, ‘waste free’ route to preparing metal oxide catalysts, however, there is limited information on the chemical steps involved. In this work, the perovskite LaMnO3 has been successfully synthesized via mechanochemistry from metal oxide powders, La2O3 and Mn2O3, at room temperature, using a planetary ball mill. Separate ex situ ‘time slices’ were taken during the milling procedure to provide insights into the underlying chemistry. The crystalline material was assessed using XRD, which identified 100% perovskite phase after 3 h of milling. Conversely, characterization by X-ray absorption spectroscopy (XAS) at both the Mn K-edge and La L3-edge provides a very different picture. The XAS data shows that there are significant structural alterations as early as 30 min of milling, with the La precursor dispersed over Mn2O3. Increasing milling time then allows for mechanical activation of both precursors and the formation of powdered LaMnO3, with no calcination step required. The XAS highlights that there is a significant amount of amorphous, oxygen deficient, content even when XRD has identified 100% perovskite phase. The samples were tested for the decomposition of the environmental pollutant N2O; at a milling time of 3 h, the LaMnO3 catalyst displays a much early onset production of N2 compared to a traditional sol–gel synthesized LaMnO3, resulting from increased oxygen deficiency at the surface, confirmed by XPS and STEM-EELS. This is an encouraging sign that mechanochemical routes can be harnessed to provide a sustainable route to preparing mixed metal oxide catalysts with enhanced catalytic performance.

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Accepted/In Press date: 23 October 2019
e-pub ahead of print date: 9 December 2019
Published date: 7 January 2020

Identifiers

Local EPrints ID: 436994
URI: http://eprints.soton.ac.uk/id/eprint/436994
ISSN: 0300-9246
PURE UUID: dc3b2558-56fb-4c12-9c6c-56488e3698a3
ORCID for Peter P. Wells: ORCID iD orcid.org/0000-0002-0859-9172

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Date deposited: 14 Jan 2020 18:35
Last modified: 07 Oct 2020 01:51

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Contributors

Author: Rachel H. Blackmore
Author: Maria Elena Rivas
Author: Tugce Eralp Erden
Author: Trung Dung Tran
Author: Huw R. Marchbank
Author: Dogan Ozkaya
Author: Martha Briceno de Gutierrez
Author: Alison Wagland
Author: Paul Collier
Author: Peter P. Wells ORCID iD

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