Surface science studies of rhodium gen-dicarbonyl on TiO₂(110) using FT-RAIRS and XPS
Surface science studies of rhodium gen-dicarbonyl on TiO₂(110) using FT-RAIRS and XPS
Reactions of the rhodium gem-dicarbonyl species, Rh(CO)2, deposited by MOCVD, on TiO2(110) have been studied under UHV conditions using FT-RAIRS, XPS and LEED. The application of FT-RAIRS to the structural characterization of absorbates on semiconductors and insulators has been developed. The alignment of surface species on TiO2(110) has been established, for the first time, through the coupling of the tangential component of the p-polarized radiation, or the parallel component of the s-polarized radiation, to vibrational modes with parallel surface components. Coupling of this mode results in an azimuthal dependence of the band intensity.
P-polarized and s-polarized FT-RAIRS have been used to look at the variation of the intensity of the absorption band due to the Rh(CO)2 asymmetric stretch (ν=2030cm-1) as a function of azimuthal angle. The Rh(CO)2 unit has been found to be aligned in the <11̅;0> direction of the surface, P-polarized FT-RAIRS has also been used to study the adsorption of formic acid onto the TiO2(110) surface. Azimuthal variation of the infrared bands (ν~1550, ~1380cm-1) due to adsorbed formate has identified two formate species on the surface. One species is absorbed aligned in the <001> direction and bridging two five-fold Ti4+ sites. The other is aligned perpendicular to this and is assigned to a formate bridging between one Ti4+ site and a defect (that is produced on adsorption of formic acid) in a bridging oxygen row. Further, complementary, structural studies of Rh(CO)2 are reported using the NIXSW technique at Daresbury Laboratories.
Several reactions of the Rh(CO)2 species have also been studied. For the reaction of Rh(CO)2 with H2 two steps have been identified. In the first step, which occurs at 300K and requires predissociation of H2, one O molecule is displaced leading to an intermediate RhH(CO) species (ν=2065cm-1) on highly dispersed rhodium. In the second step partial disproportionation of the remaining CO occurs to give carbidic carbon and reduced rhodium on the surface. The second step is activated on increasing the temperature, and this is proposed to be mediated by the production of defects on the TiO2(110) surface, which aid the CO dissociation reaction.
Reaction of NO with the Rh(CO)2 species occurs to give a Rh(NO+) species (ν=1920cm-1) on a highly dispersed rhodium site. This reaction has been shown to be reversible and complete regeneration of Rh(CO)2 occurs on exposure of the Rh(NO+) to CO.
The Rh(CO)2 species has also been found to undergo a reversible reaction with O2 to give a highly dispersed and oxidised rhodium species. This species has been assigned RhO2.
Both MeI and MeCl have been shoen to dissociatively absorb on rhodium particles deposited as Rh(CO)2 at 300K, but MeCl requires the carbonyl groups to be thermally desorbed before it will absorb. Decomposition of CH3 fragments and desorption of both HI and HCl from the surface have been proposed.
University of Southampton
King, Alex
0f4baad6-e009-461c-86b6-2b2e39248e56
1997
King, Alex
0f4baad6-e009-461c-86b6-2b2e39248e56
King, Alex
(1997)
Surface science studies of rhodium gen-dicarbonyl on TiO₂(110) using FT-RAIRS and XPS.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Reactions of the rhodium gem-dicarbonyl species, Rh(CO)2, deposited by MOCVD, on TiO2(110) have been studied under UHV conditions using FT-RAIRS, XPS and LEED. The application of FT-RAIRS to the structural characterization of absorbates on semiconductors and insulators has been developed. The alignment of surface species on TiO2(110) has been established, for the first time, through the coupling of the tangential component of the p-polarized radiation, or the parallel component of the s-polarized radiation, to vibrational modes with parallel surface components. Coupling of this mode results in an azimuthal dependence of the band intensity.
P-polarized and s-polarized FT-RAIRS have been used to look at the variation of the intensity of the absorption band due to the Rh(CO)2 asymmetric stretch (ν=2030cm-1) as a function of azimuthal angle. The Rh(CO)2 unit has been found to be aligned in the <11̅;0> direction of the surface, P-polarized FT-RAIRS has also been used to study the adsorption of formic acid onto the TiO2(110) surface. Azimuthal variation of the infrared bands (ν~1550, ~1380cm-1) due to adsorbed formate has identified two formate species on the surface. One species is absorbed aligned in the <001> direction and bridging two five-fold Ti4+ sites. The other is aligned perpendicular to this and is assigned to a formate bridging between one Ti4+ site and a defect (that is produced on adsorption of formic acid) in a bridging oxygen row. Further, complementary, structural studies of Rh(CO)2 are reported using the NIXSW technique at Daresbury Laboratories.
Several reactions of the Rh(CO)2 species have also been studied. For the reaction of Rh(CO)2 with H2 two steps have been identified. In the first step, which occurs at 300K and requires predissociation of H2, one O molecule is displaced leading to an intermediate RhH(CO) species (ν=2065cm-1) on highly dispersed rhodium. In the second step partial disproportionation of the remaining CO occurs to give carbidic carbon and reduced rhodium on the surface. The second step is activated on increasing the temperature, and this is proposed to be mediated by the production of defects on the TiO2(110) surface, which aid the CO dissociation reaction.
Reaction of NO with the Rh(CO)2 species occurs to give a Rh(NO+) species (ν=1920cm-1) on a highly dispersed rhodium site. This reaction has been shown to be reversible and complete regeneration of Rh(CO)2 occurs on exposure of the Rh(NO+) to CO.
The Rh(CO)2 species has also been found to undergo a reversible reaction with O2 to give a highly dispersed and oxidised rhodium species. This species has been assigned RhO2.
Both MeI and MeCl have been shoen to dissociatively absorb on rhodium particles deposited as Rh(CO)2 at 300K, but MeCl requires the carbonyl groups to be thermally desorbed before it will absorb. Decomposition of CH3 fragments and desorption of both HI and HCl from the surface have been proposed.
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Published date: 1997
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Local EPrints ID: 463175
URI: http://eprints.soton.ac.uk/id/eprint/463175
PURE UUID: 48e77ecd-7ef9-4832-80c1-609f49d7ad83
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Date deposited: 04 Jul 2022 20:46
Last modified: 04 Jul 2022 20:46
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Author:
Alex King
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