Photooxidation of Acetone on TiO2(110): Conversion to Acetate via Methyl Radical Ejection

Journal Article · Thu Jun 23 04:00:00 EDT 2005 · Journal of Physical Chemistry B

DOI:https://doi.org/10.1021/jp0507546· OSTI ID:15020629

Henderson, Michael A

It is generally held that radicals form and participate in heterogeneous photocatalytic processes on oxide surfaces, although understanding the mechanistic origins and fates of such species is difficult. In this study, photodesorption and thermal desorption techniques show that acetone is converted into acetate on the surface of TiO(110) in a two step process that involves, first, a thermal reaction between acetone and coadsorbed oxygen to make a surface acetone-oxygen complex, followed second by a photochemical reaction that ejects a methyl radical from the surface and converts the acetone-oxygen complex into acetate. Designation of the photodesorption species to methyl radicals was confirmed using isotopically labeled acetone. The yield of photodesorbed methyl radicals correlates well with the amount depleted of acetone and with the yield of acetate left on the surface, both gauged using post-irradiation temperature programmed desorption (TPD). The thermal reaction between adsorbed acetone and oxygen to form the acetone-oxygen complex exhibits an approximate activation barrier of about 10 kJ/mol. A prerequisite to this reaction is the presence of surface Ti?? sites that enable O? adsorption. Creation of these sites by vacuum reduction of the surface prior to acetone and oxygen co-adsorption results in an initial spike in the photodecomposition rate, but replenishment of these sites by photolytic means (i.e., by trapping excited electrons at the surface) appears to be a slow step a sustained reaction. Evidence in this study for the ejection of organic radicals from the surface during photo-oxidation catalysis on TiO provides support for mechanistic pathways that involve both adsorbed and non-adsorbed species.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 15020629
• Report Number(s): PNNL-SA-44160; 11105; KC0302010
• Journal Information: Journal of Physical Chemistry B, Journal Name: Journal of Physical Chemistry B Journal Issue: 24 Vol. 109
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ACETATES
ACETONE
ADSORPTION
CATALYSIS
METHYL RADICALS
OXIDATION
PHOTOCHEMICAL REACTIONS
TITANIUM OXIDES
TiO₂ (110)
acetone
environmental molecular sciences laboratory
photocatalysis
surface science