Effect of Coadsorbed Water on the Photodecomposition of Acetone on TiO2(110)

Journal Article · Tue Jun 10 04:00:00 EDT 2008 · Journal of Catalysis, 256(2):287-292

DOI:https://doi.org/10.1016/j.jcat.2008.03.020· OSTI ID:936202

Henderson, Michael A

The influence of coadsorbed water on the photodecomposition of acetone on TiO2 was examined using temperature programmed desorption (TPD) and the rutile TiO2(110) surface as a model photocatalyst. Of the two major influences ascribed to water in the heterogeneous photocatalysis literature (promotion via OH radical supply and inhibition due to site blocking), only the negative influence of water was observed. As long as the total water and acetone coverage was maintained well below the first layer saturation coverage (‘1 ML’), little inhibition of acetone photodecomposition was observed. However, as the total water+acetone coverage exceeded 1 ML, acetone was preferentially displaced from the first layer to physisorbed states by water and the extent of acetone photodecomposition attenuated. The displacement originated from water compressing acetone into high coverage regions where increased acetone-acetone repulsions caused displacement from the first layer. The immediate product of acetone photodecomposition was adsorbed acetate, which occupies twice as many surface sites per molecule as compared to acetone. Since the acetate intermediate was more stable on the TiO2(110) surface than either water or acetone (as gauged by TPD) and since its photodecomposition rate was less than that of acetone, additional surface sites were not opened up during acetone photodecomposition for previously displaced acetone molecules to re-enter the first layer. Results in this study suggest that increased molecular-level repulsions between organic molecules brought about by increased water coverage are as influential in the inhibiting effect of water on photooxidation rates as are water-organic repulsions.

• 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: 936202
• Report Number(s): PNNL-SA-58704; 19811; KC0302010
• Journal Information: Journal of Catalysis, 256(2):287-292, Journal Name: Journal of Catalysis, 256(2):287-292 Journal Issue: 2 Vol. 256; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ACETATES
ACETONE
ADSORPTION
CATALYTIC EFFECTS
Environmental Molecular Sciences Laboratory
PHOTOCATALYSIS
PHOTOLYSIS
TITANIUM OXIDES
WATER