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Combined spatially resolved operando spectroscopy: new insights into kinetic oscillations of CO oxidation on Pd/γ-Al2O3

Combined spatially resolved operando spectroscopy: new insights into kinetic oscillations of CO oxidation on Pd/γ-Al2O3
Combined spatially resolved operando spectroscopy: new insights into kinetic oscillations of CO oxidation on Pd/γ-Al2O3
Spatially resolved, combined energy dispersive EXAFS (EDE) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements have been performed over a fixed catalyst bed of Pd/γ-Al2O3 during kinetic oscillations of CO oxidation. The kinetic oscillations of CO oxidation over Pd (or for that matter Pt or Rh) catalysts are a complicated phenomenon that require characterisation techniques with high time resolution and spatial resolution in order to make links between catalyst structure and surface reactivity. By measuring the extent of Pd oxidation at the nanoparticle surface, from Pd K-edge EDE, and matching this with the CO coverage, from DRIFTS spectra, at multiple positions of the fixed bed reactor it is found that the majority of the catalyst undergoes a sharp transition from the CO poisoned catalyst to the highly active, oxidised Pd surface. This transition occurs initially at the end of the catalyst bed, nearest the outlet, and propagates upstream with increasing temperature of the reactor. The oscillations in Pd surface oxide formation and CO coverage are observed only in the first ∼1 mm of the bed, which gives rise to oscillations in CO2 and O2 concentrations observed by end-pipe mass spectrometry after the light-off temperature. The catalyst initially exists as less active, CO poisoned metallic Pd nanoparticles before light-off which transition to a highly active state after light-off when the Pd nanoparticle surface becomes dominated by chemisorbed oxygen. Kinetic oscillations only occur at the front of the catalyst bed where there is sufficient concentration of CO in the gas phase to compete with O2 for adsorption sites at the catalyst surface. We demonstrate the complex nature of the evolving catalyst structure and surface reactivity during catalytic operation and the need for spatially resolved operando methods for understanding and optimising catalyst technologies.
XAFS, DRIFTS, CO oxidation, Pd/AlO, Operando spectroscopy
0021-9517
201-208
Dann, Ellie K.
6418a9ec-735e-472e-a8fe-985c330d1b81
Gibson, Emma K.
738c74e4-ab68-42fe-bda8-9d4a43669b31
Catlow, C. Richard A.
50b88125-9415-4b37-9146-af6783e42510
Celorrio, Veronica
5ebb7fb5-a74c-4872-9795-5830dc915d0b
Collier, Paul
d5a98bd6-227c-421e-92b3-80993e175998
Eralp, Tugce
b37e8b72-16f9-4971-9890-3ffa087c9336
Amboage, Monica
f1f91840-c149-4732-b396-0c20e11aaeb6
Hardacre, Christopher
0715f59a-c82e-4844-a9f8-6a06fb36320f
Stere, Cristina
f9a4e54a-79b5-4bed-86f9-e3c6f3a94884
Kroner, Anna
625fc30b-2e38-438a-8098-634cf2d5898f
Raj, Agnes
860391d6-4201-4664-b1c2-5c2b9ddee929
Rogers, Scott
e01e36f3-0b45-4362-b822-1c98157d4206
Goguet, Alexandre
4de6e217-9733-4d26-b041-ab996672d919
Wells, Peter P.
bc4fdc2d-a490-41bf-86cc-400edecf2266
Dann, Ellie K.
6418a9ec-735e-472e-a8fe-985c330d1b81
Gibson, Emma K.
738c74e4-ab68-42fe-bda8-9d4a43669b31
Catlow, C. Richard A.
50b88125-9415-4b37-9146-af6783e42510
Celorrio, Veronica
5ebb7fb5-a74c-4872-9795-5830dc915d0b
Collier, Paul
d5a98bd6-227c-421e-92b3-80993e175998
Eralp, Tugce
b37e8b72-16f9-4971-9890-3ffa087c9336
Amboage, Monica
f1f91840-c149-4732-b396-0c20e11aaeb6
Hardacre, Christopher
0715f59a-c82e-4844-a9f8-6a06fb36320f
Stere, Cristina
f9a4e54a-79b5-4bed-86f9-e3c6f3a94884
Kroner, Anna
625fc30b-2e38-438a-8098-634cf2d5898f
Raj, Agnes
860391d6-4201-4664-b1c2-5c2b9ddee929
Rogers, Scott
e01e36f3-0b45-4362-b822-1c98157d4206
Goguet, Alexandre
4de6e217-9733-4d26-b041-ab996672d919
Wells, Peter P.
bc4fdc2d-a490-41bf-86cc-400edecf2266

Dann, Ellie K., Gibson, Emma K., Catlow, C. Richard A., Celorrio, Veronica, Collier, Paul, Eralp, Tugce, Amboage, Monica, Hardacre, Christopher, Stere, Cristina, Kroner, Anna, Raj, Agnes, Rogers, Scott, Goguet, Alexandre and Wells, Peter P. (2019) Combined spatially resolved operando spectroscopy: new insights into kinetic oscillations of CO oxidation on Pd/γ-Al2O3. Journal of Catalysis, 373, 201-208. (doi:10.1016/j.jcat.2019.03.037).

Record type: Article

Abstract

Spatially resolved, combined energy dispersive EXAFS (EDE) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements have been performed over a fixed catalyst bed of Pd/γ-Al2O3 during kinetic oscillations of CO oxidation. The kinetic oscillations of CO oxidation over Pd (or for that matter Pt or Rh) catalysts are a complicated phenomenon that require characterisation techniques with high time resolution and spatial resolution in order to make links between catalyst structure and surface reactivity. By measuring the extent of Pd oxidation at the nanoparticle surface, from Pd K-edge EDE, and matching this with the CO coverage, from DRIFTS spectra, at multiple positions of the fixed bed reactor it is found that the majority of the catalyst undergoes a sharp transition from the CO poisoned catalyst to the highly active, oxidised Pd surface. This transition occurs initially at the end of the catalyst bed, nearest the outlet, and propagates upstream with increasing temperature of the reactor. The oscillations in Pd surface oxide formation and CO coverage are observed only in the first ∼1 mm of the bed, which gives rise to oscillations in CO2 and O2 concentrations observed by end-pipe mass spectrometry after the light-off temperature. The catalyst initially exists as less active, CO poisoned metallic Pd nanoparticles before light-off which transition to a highly active state after light-off when the Pd nanoparticle surface becomes dominated by chemisorbed oxygen. Kinetic oscillations only occur at the front of the catalyst bed where there is sufficient concentration of CO in the gas phase to compete with O2 for adsorption sites at the catalyst surface. We demonstrate the complex nature of the evolving catalyst structure and surface reactivity during catalytic operation and the need for spatially resolved operando methods for understanding and optimising catalyst technologies.

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Accepted/In Press date: 23 March 2019
e-pub ahead of print date: 8 April 2019
Published date: May 2019
Keywords: XAFS, DRIFTS, CO oxidation, Pd/AlO, Operando spectroscopy

Identifiers

Local EPrints ID: 430207
URI: https://eprints.soton.ac.uk/id/eprint/430207
ISSN: 0021-9517
PURE UUID: 320dc85d-3b6b-4421-a8db-1a681e988c53
ORCID for Peter P. Wells: ORCID iD orcid.org/0000-0002-0859-9172

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Date deposited: 16 Apr 2019 16:30
Last modified: 20 Jul 2019 00:55

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