Adsorption and photocatalytic oxidation of acetone on TiO{sub 2}: An in situ transmission FT-IR study
In situ transmission Fourier-transform infrared spectroscopy has been used to study the mechanistic details of adsorption and photocatalytic oxidation of acetone on TiO{sub 2} surfaces at 298 K. The adsorption of acetone has been followed as a function of coverage on clean TiO{sub 2} surfaces (dehydrated TiO{sub 2}). Infrared spectra at low acetone coverages ({theta} < 0.05 ML) show absorption bands at 2,973, 2,931, 1,702, 1,448, and 1,363 cm{sup {minus}1} which are assigned to the vibrational modes of molecularly adsorbed acetone. At higher coverages, the infrared spectra show that adsorbed acetone can undergo an Aldol condensation reaction followed by dehydration to yield (CH{sub 3}){sub 2}C{double_bond}CHCOCH{sub 3}, 4-methyl-3-penten-2-one or, more commonly called, mesityl oxide. The ratio of surface-bound mesityl oxide to acetone depends on surface coverage. At saturation coverage, nearly 60% of the adsorbed acetone has reacted to yield mesityl oxide on the surface. In contrast, on TiO{sub 2} surfaces with preadsorbed water (hydrated TiO{sub 2}), very little mesityl oxide forms. Infrared spectroscopy was also used to monitor the photocatalytic oxidation of adsorbed acetone as a function of acetone coverage, oxygen pressure, and water adsorption. Based on the dependence of the rate of the reaction on oxygen pressure, acetone coverage, and water adsorption, it is proposed that there are potentially three mechanisms for the photooxidation of adsorbed acetone on TiO{sub 2}. In the absence of preadsorbed H{sub 2}O, one mechanism involves the formation of a reactive O{sup {minus}}(ads) species, from gas-phase O{sub 2}, which reacts with adsorbed acetone molecules. The second mechanism involves TiO{sub 2} lattice oxygen. In the presence of adsorbed H{sub 2}O, reactive hydroxyl radicals are proposed to initiate the photooxidation of acetone.
- Research Organization:
- United Arab Emirates Univ., Al-Ain (AE)
- Sponsoring Organization:
- National Science Foundation (NSF); USDOE
- DOE Contract Number:
- FG02-98ER62580
- OSTI ID:
- 20030512
- Journal Information:
- Journal of Catalysis, Vol. 119, Issue 1; Other Information: PBD: 1 Apr 2000; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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