The surface organometallic chemistry of rhodium and palladium supported on inorganic oxides
The surface organometallic chemistry of rhodium and palladium supported on inorganic oxides
Extended X-ray Absorption Fine Structure (EXAFS), Energy Dispersive EXAFS (LDE), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and Temperature Programmed Desorption (TPD) have been employed to investigate the surface organometallic chemistry of rhodium and palladium supported on high area alumina and titania surfaces.
All the supported organometallic systems in this study have been prepared by Metallo-Organic Chemical Vapour Deposition (MOCVD). Metal loadings of between 2% and 5% were used.
DRIFTS and EDE data suggest that the [Rh(CO)2Cl]2 dimer is chemisorbed onto both the TiO2 and Al2O3 surfaces as a [O]Rh(CO)2(Cl) unit. DRIFTS, EDE and TPD studies show that the carbonyl ligands are removed by heating the system under an inert atmosphere up to 220°C, or under a hydrogen atmosphere up to 90°C. This results in the formation of small rhodium clusters on the oxide surface, shown by EDE spectroscopy. The gem-dicarbonyl species can be regenerated by exposure of the thermolysed sample to CO at room temperature. Reaction with NO results in substitution with the CO ligands to form a [O]2Rh(NO)-(Cl) species which exhibits greater thermal stability than the gem-dicarbonyl species, requiring temperatures of 300°C to remove the ligands and cluster the rhodium. The pre-treatment of the titania and alumina surfaces has been shown to affect the nature of nitrosyl species generated. The gem-dicarbonyl species is regenerated by exposure to CO.
Rh(CO)2(acac) has been shown to be physisorbed intact on the surfaces of titania and alumina. Thermolysis under helium and hydrogen results in evolution of firstly the carbonyl and then the acac ligands. Regeneration of the gem- dicarbonyl ligands occurs with exposure to CO at room temperature. Reaction of NO results in the formation of a Rh(NO)- species, with gem-dicarbonyl regeneration occurring after exposure at CO.
University of Southampton
Burnaby, Daryl George
ee4df7cd-ef74-4218-8759-d077f2778626
2000
Burnaby, Daryl George
ee4df7cd-ef74-4218-8759-d077f2778626
Burnaby, Daryl George
(2000)
The surface organometallic chemistry of rhodium and palladium supported on inorganic oxides.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Extended X-ray Absorption Fine Structure (EXAFS), Energy Dispersive EXAFS (LDE), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and Temperature Programmed Desorption (TPD) have been employed to investigate the surface organometallic chemistry of rhodium and palladium supported on high area alumina and titania surfaces.
All the supported organometallic systems in this study have been prepared by Metallo-Organic Chemical Vapour Deposition (MOCVD). Metal loadings of between 2% and 5% were used.
DRIFTS and EDE data suggest that the [Rh(CO)2Cl]2 dimer is chemisorbed onto both the TiO2 and Al2O3 surfaces as a [O]Rh(CO)2(Cl) unit. DRIFTS, EDE and TPD studies show that the carbonyl ligands are removed by heating the system under an inert atmosphere up to 220°C, or under a hydrogen atmosphere up to 90°C. This results in the formation of small rhodium clusters on the oxide surface, shown by EDE spectroscopy. The gem-dicarbonyl species can be regenerated by exposure of the thermolysed sample to CO at room temperature. Reaction with NO results in substitution with the CO ligands to form a [O]2Rh(NO)-(Cl) species which exhibits greater thermal stability than the gem-dicarbonyl species, requiring temperatures of 300°C to remove the ligands and cluster the rhodium. The pre-treatment of the titania and alumina surfaces has been shown to affect the nature of nitrosyl species generated. The gem-dicarbonyl species is regenerated by exposure to CO.
Rh(CO)2(acac) has been shown to be physisorbed intact on the surfaces of titania and alumina. Thermolysis under helium and hydrogen results in evolution of firstly the carbonyl and then the acac ligands. Regeneration of the gem- dicarbonyl ligands occurs with exposure to CO at room temperature. Reaction of NO results in the formation of a Rh(NO)- species, with gem-dicarbonyl regeneration occurring after exposure at CO.
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Published date: 2000
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Local EPrints ID: 464241
URI: http://eprints.soton.ac.uk/id/eprint/464241
PURE UUID: 285e42fa-02fb-4c77-9a7a-48026b0f7735
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Date deposited: 04 Jul 2022 21:42
Last modified: 16 Mar 2024 19:21
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Author:
Daryl George Burnaby
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