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Co3O4/TiO2 catalysts studied in situ during the preferential oxidation of carbon monoxide: the effect of different TiO2 polymorphs

Co3O4/TiO2 catalysts studied in situ during the preferential oxidation of carbon monoxide: the effect of different TiO2 polymorphs
Co3O4/TiO2 catalysts studied in situ during the preferential oxidation of carbon monoxide: the effect of different TiO2 polymorphs

Co3O4 nanoparticles were supported on different TiO2 polymorphs, namely, rutile, anatase, and a 15 : 85 mixture of rutile and anatase (also known as P25), via incipient wetness impregnation. The Co3O4/TiO2 catalysts were evaluated in the preferential oxidation of CO (CO-PrOx) in a H2-rich gas environment and characterised in situ using PXRD and magnetometry. Our results show that supporting Co3O4 on P25 resulted in better catalytic performance, that is, a higher maximum CO conversion to CO2 of 72.7% at 200 °C was achieved than on rutile (60.7%) and anatase (51.5%). However, the degree of reduction (DoR) of Co3O4 to Co0 was highest on P25 (91.9% at 450 °C), with no CoTiO3 detected in the spent catalyst. The DoR of Co3O4 was lowest on anatase (76.4%), with the presence of TixOy-encapsulated CoOx nanoparticles and bulk CoTiO3 (13.8%) also confirmed in the spent catalyst. Relatively low amounts of CoTiO3 (8.9%) were detected in the spent rutile-supported catalyst, while a higher DoR (85.9%) was reached under reaction conditions. The Co0 nanoparticles formed on P25 and rutile existed in the fcc and hcp crystal phases, while only fcc Co0 was detected on anatase. Furthermore, undesired CH4 formation took place over the Co0 present in the P25- and rutile-supported catalysts, while CH4 was not formed over the Co0 on anatase possibly due to encapsulation by TixOy species. For the first time, this study revealed the influence of different TiO2 polymorphs (used as catalyst supports) on the chemical and crystal phase transformations of Co3O4, which in turn affect its activity and selectivity during CO-PrOx.

2044-4753
2038-2052
Nyathi, Thulani M.
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Fadlalla, Mohamed I.
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Fischer, Nico
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York, Andrew P.E.
fbd1bacf-79f8-4e88-842e-af3e4ab7dd3d
Olivier, Ezra J.
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Gibson, Emma K.
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Wells, Peter P.
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Claeys, Michael
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Nyathi, Thulani M.
e5a3f8fb-63de-4b2c-a7d2-3b6be6f8107e
Fadlalla, Mohamed I.
f1188dbb-fe38-480c-ba6c-5395f7721a07
Fischer, Nico
35b81bb7-173c-4a45-a2fd-0a99910b1e5f
York, Andrew P.E.
fbd1bacf-79f8-4e88-842e-af3e4ab7dd3d
Olivier, Ezra J.
7564fc93-b3f1-49d2-bb37-ebb753e50548
Gibson, Emma K.
738c74e4-ab68-42fe-bda8-9d4a43669b31
Wells, Peter P.
bc4fdc2d-a490-41bf-86cc-400edecf2266
Claeys, Michael
19cb6adb-b243-4dba-b0a8-94fd2c1f9658

Nyathi, Thulani M., Fadlalla, Mohamed I., Fischer, Nico, York, Andrew P.E., Olivier, Ezra J., Gibson, Emma K., Wells, Peter P. and Claeys, Michael (2023) Co3O4/TiO2 catalysts studied in situ during the preferential oxidation of carbon monoxide: the effect of different TiO2 polymorphs. Catalysis Science and Technology, 13 (7), 2038-2052. (doi:10.1039/d2cy01699k).

Record type: Article

Abstract

Co3O4 nanoparticles were supported on different TiO2 polymorphs, namely, rutile, anatase, and a 15 : 85 mixture of rutile and anatase (also known as P25), via incipient wetness impregnation. The Co3O4/TiO2 catalysts were evaluated in the preferential oxidation of CO (CO-PrOx) in a H2-rich gas environment and characterised in situ using PXRD and magnetometry. Our results show that supporting Co3O4 on P25 resulted in better catalytic performance, that is, a higher maximum CO conversion to CO2 of 72.7% at 200 °C was achieved than on rutile (60.7%) and anatase (51.5%). However, the degree of reduction (DoR) of Co3O4 to Co0 was highest on P25 (91.9% at 450 °C), with no CoTiO3 detected in the spent catalyst. The DoR of Co3O4 was lowest on anatase (76.4%), with the presence of TixOy-encapsulated CoOx nanoparticles and bulk CoTiO3 (13.8%) also confirmed in the spent catalyst. Relatively low amounts of CoTiO3 (8.9%) were detected in the spent rutile-supported catalyst, while a higher DoR (85.9%) was reached under reaction conditions. The Co0 nanoparticles formed on P25 and rutile existed in the fcc and hcp crystal phases, while only fcc Co0 was detected on anatase. Furthermore, undesired CH4 formation took place over the Co0 present in the P25- and rutile-supported catalysts, while CH4 was not formed over the Co0 on anatase possibly due to encapsulation by TixOy species. For the first time, this study revealed the influence of different TiO2 polymorphs (used as catalyst supports) on the chemical and crystal phase transformations of Co3O4, which in turn affect its activity and selectivity during CO-PrOx.

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Accepted/In Press date: 23 February 2023
Published date: 24 February 2023
Additional Information: Funding Information: Johnson Matthey, the DSI-NRF Centre of Excellence in Catalysis (c*change), and the Science and Technology Facilities Council (STFC) via GCRF-START (Global Challenges Research Fund – Synchrotron Techniques for African Research and Technology (ST/R002754/1)) are gratefully acknowledged for their financial support. The authors would also like to thank the staff in the Analytical Laboratory, within the Chemical Engineering department (University of Cape Town), for conducting the ICP-OES analysis. Finally, M. Panchal (University College London and UK Catalysis Hub) and Dr. N. Ramanan (Diamond Light Source) are thanked for assisting with the XAS measurements on beamline B18 at Diamond Light Source (sessions: SP19850-3, SP19850-4, and SP19850-5). Publisher Copyright: © 2023 The Royal Society of Chemistry.

Identifiers

Local EPrints ID: 476651
URI: http://eprints.soton.ac.uk/id/eprint/476651
ISSN: 2044-4753
PURE UUID: 1399cf60-6d20-451d-9bbd-7de1788cd511
ORCID for Peter P. Wells: ORCID iD orcid.org/0000-0002-0859-9172

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Date deposited: 10 May 2023 17:07
Last modified: 18 Mar 2024 03:02

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Contributors

Author: Thulani M. Nyathi
Author: Mohamed I. Fadlalla
Author: Nico Fischer
Author: Andrew P.E. York
Author: Ezra J. Olivier
Author: Emma K. Gibson
Author: Peter P. Wells ORCID iD
Author: Michael Claeys

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