Simultaneous time resolved XAS, IR and mass spectrometric characterisation of catalytic systems : an investigation into the structure-function behaviour of supported rhodium catalysts
Simultaneous time resolved XAS, IR and mass spectrometric characterisation of catalytic systems : an investigation into the structure-function behaviour of supported rhodium catalysts
The techniques of Energy Dispersive Extended X-ray Absorption Fine structure (EDE), Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) and mass spectrometry have been successfully combined in an in situ, time resolved manner to investigate the structure function surface chemistry of γ-Al2O3 supported Rh catalysts.
Catalysts with a low meal loading (2.5 wt%) were subject to facile disruption upon exposure to CO; the formation of discrete Rh(CO)2 units was facilitated at higher temperatures. The proportion of dicarbonyl adopting this site was significantly less at higher metal loading (5 wt%), this was reflected by the IR and unchanging EXAFS data.
The formation of ‘high wavenumber’ Rh(NO)- and Rh(NO)2 species could be correlated to the rapid, extensive oxidation of Rh at low temperatures upon exposure to NO. The reactive turnover of NO and increased rate of oxidation were observed at higher temperatures, and evidence for a highly transient form of Rh(NO)2 to yield a linear Rh(NO)+ ‘spectator’ species was derived. Re-reduction of the oxide proceeded at temperatures as low as 373K.
A gas switching regime between CO and NO showed an almost static oxidic Rh phase to exist at low temperatures; structural changes were more substantial at higher temperatures and followed the pattern of switching more closely. With NO in excess the Rh clusters oxidised rapidly to yield the Rh(NO)+ species; reclustering was observed under CO, which also adopted linear and bridging sites on the metallic particles.
The poisoning of the catalysts reported SO2 to subtly modify the structure of the Rh but did not adversely affect the reduction of NO by H2. In contrast, complete and irreversible sulfidation of the nanoparticles rapidly curtailed catalysis upon exposure to H2S.
University of Southampton
Jyoti, Bhrat
9e00e347-0864-48fa-9bb8-f44f98161fd0
2006
Jyoti, Bhrat
9e00e347-0864-48fa-9bb8-f44f98161fd0
Jyoti, Bhrat
(2006)
Simultaneous time resolved XAS, IR and mass spectrometric characterisation of catalytic systems : an investigation into the structure-function behaviour of supported rhodium catalysts.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The techniques of Energy Dispersive Extended X-ray Absorption Fine structure (EDE), Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) and mass spectrometry have been successfully combined in an in situ, time resolved manner to investigate the structure function surface chemistry of γ-Al2O3 supported Rh catalysts.
Catalysts with a low meal loading (2.5 wt%) were subject to facile disruption upon exposure to CO; the formation of discrete Rh(CO)2 units was facilitated at higher temperatures. The proportion of dicarbonyl adopting this site was significantly less at higher metal loading (5 wt%), this was reflected by the IR and unchanging EXAFS data.
The formation of ‘high wavenumber’ Rh(NO)- and Rh(NO)2 species could be correlated to the rapid, extensive oxidation of Rh at low temperatures upon exposure to NO. The reactive turnover of NO and increased rate of oxidation were observed at higher temperatures, and evidence for a highly transient form of Rh(NO)2 to yield a linear Rh(NO)+ ‘spectator’ species was derived. Re-reduction of the oxide proceeded at temperatures as low as 373K.
A gas switching regime between CO and NO showed an almost static oxidic Rh phase to exist at low temperatures; structural changes were more substantial at higher temperatures and followed the pattern of switching more closely. With NO in excess the Rh clusters oxidised rapidly to yield the Rh(NO)+ species; reclustering was observed under CO, which also adopted linear and bridging sites on the metallic particles.
The poisoning of the catalysts reported SO2 to subtly modify the structure of the Rh but did not adversely affect the reduction of NO by H2. In contrast, complete and irreversible sulfidation of the nanoparticles rapidly curtailed catalysis upon exposure to H2S.
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Published date: 2006
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Local EPrints ID: 466102
URI: http://eprints.soton.ac.uk/id/eprint/466102
PURE UUID: 626f82a6-9e6a-4c6a-a1cc-21ceb4ab9edd
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Date deposited: 05 Jul 2022 04:21
Last modified: 16 Mar 2024 20:31
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Author:
Bhrat Jyoti
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