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The chemical and photochemical reactivity of modified and unmodified high area titania surfaces

The chemical and photochemical reactivity of modified and unmodified high area titania surfaces
The chemical and photochemical reactivity of modified and unmodified high area titania surfaces

The photocatalytic oxidation of CH3Cl with oxygen on a highly dehydroxylated high area TiO2 powder has been studied. A novel UHV apparatus equipped with transmission FTIR and QMS was commissioned for this investigation. Using CO adsorbed at 110 K as a probe molecule, considerable heterogeneity of the TiO2(Degussa P25) powder surface and dependency on the preannealing temperature were revealed. A linear relationship between the intensity of the νβ(C-O) and ν(Ti-O) bands was observed as a function of CO exposure, suggesting electronic perturbation of the Ti-O bond by CO adsorption. A unique surface structural model of the dehydroxylated TiO2 surface is presented.

The nature of the apparent two O2 photodesorption routes (α- and β-O2) were investigated via thermal- and photo-desorption of molecular oxygen. Photodesorption of α-O2 was not observed when the TiO2(Degussa P25) surface was heated above 200 K, while the β-O2 species was stable up to 450 K. IR results showed a weakening of the O-O bond and the formation of an ozone type species by the association of an oxygen adatom as a function of increasing sample temperature. This association accounts for the two apparent photodesorption features.

The photocatalytic oxidation of CH3Cl with oxygenate on the dehydroxylated TiO2(Degussa P25) powder surface at 110 K under UHV conditions showed the formation of surface CO, CO2 and (bi)carbonates with a concomitant disappearance of CH3Cl. The results indicate that the oxidation process does not require surface H2O nor OH and that the oxidation occurs on the surface. Kinetic analysis showed that the oxidation process is first order with respect to the concentration of CH3Cl. A probable site dependent oxidation sequence of CH3Cl to CO2 and (bi)carbonates was suggested.

University of Southampton
Yoshikawa, Naruo
c6d30bd6-9c23-4d22-bd70-6e57938d1de4
Yoshikawa, Naruo
c6d30bd6-9c23-4d22-bd70-6e57938d1de4

Yoshikawa, Naruo (2000) The chemical and photochemical reactivity of modified and unmodified high area titania surfaces. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The photocatalytic oxidation of CH3Cl with oxygen on a highly dehydroxylated high area TiO2 powder has been studied. A novel UHV apparatus equipped with transmission FTIR and QMS was commissioned for this investigation. Using CO adsorbed at 110 K as a probe molecule, considerable heterogeneity of the TiO2(Degussa P25) powder surface and dependency on the preannealing temperature were revealed. A linear relationship between the intensity of the νβ(C-O) and ν(Ti-O) bands was observed as a function of CO exposure, suggesting electronic perturbation of the Ti-O bond by CO adsorption. A unique surface structural model of the dehydroxylated TiO2 surface is presented.

The nature of the apparent two O2 photodesorption routes (α- and β-O2) were investigated via thermal- and photo-desorption of molecular oxygen. Photodesorption of α-O2 was not observed when the TiO2(Degussa P25) surface was heated above 200 K, while the β-O2 species was stable up to 450 K. IR results showed a weakening of the O-O bond and the formation of an ozone type species by the association of an oxygen adatom as a function of increasing sample temperature. This association accounts for the two apparent photodesorption features.

The photocatalytic oxidation of CH3Cl with oxygenate on the dehydroxylated TiO2(Degussa P25) powder surface at 110 K under UHV conditions showed the formation of surface CO, CO2 and (bi)carbonates with a concomitant disappearance of CH3Cl. The results indicate that the oxidation process does not require surface H2O nor OH and that the oxidation occurs on the surface. Kinetic analysis showed that the oxidation process is first order with respect to the concentration of CH3Cl. A probable site dependent oxidation sequence of CH3Cl to CO2 and (bi)carbonates was suggested.

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Published date: 2000

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Local EPrints ID: 464334
URI: http://eprints.soton.ac.uk/id/eprint/464334
PURE UUID: d79e60dd-d9e5-4ceb-a5a2-35d3eafd44de

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Date deposited: 04 Jul 2022 22:17
Last modified: 16 Mar 2024 19:25

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Author: Naruo Yoshikawa

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