Infrared study of the adsorption of acetone on rutile

Abstract

The associative adsorption of acetone onto Lewis acidic Ti4+ ion sites on rutile is followed by the formation of a surface enolate complex which reacts with a further acetone molecule to give mesityl oxide. The enolate is also an intermediate in the exchange of hydrogen atoms between acetone and hydroxyl groups on rutile. The effects of dehydroxylation and dehydration of the rutile surface on the associative adsorption of acetone and on the formation of the enolate complex and mesityl oxide have been studied using infrared spectroscopy. The reversibility of the surface reactions has been established, in part by a study of the adsorption of mesityl oxide, which not only associatively adsorbs onto Ti4+ ion sites but also decomposes to enoIate complex and coordinatively liganded acetone molecules. Reduction of rutile in hydrogen decreases the Lewis acidity of the oxide surface but promotes the formation of surface acetate ions by the chemisorption of acetone.

Infrared Study of Acetophenone Adsorption on Mordenite and Dealuminated Mordenite

“…6) in order to test for H/D isotopic exchange involving surface hydroxyl groups and possibly resulting from enolisation reactions (17). In accordance with the expected band shift associated with the replacement of an OH-group by an OD group (18), a weak band appearing as a shoulder at ca.…”

“…Acetone on the pure rutile form of titanium dioxide undergoes slow enolization and condensation to give adsorbed mesityl oxide (17). In the present study of mordenite the spectra slowly changed with time for two possible reasons: first, diffusion of molecules into the zeolite pore structure, and second, the occurrence of chemical reactions.…”

Fourier-Transform Infrared and Raman Spectroscopy of Pure and Doped TiO2 Photocatalysts

“…Again there are significant differences in reported data, which appear to depend on reaction conditions. At high acetone coverages, aldol condensation reactions have also been reported on anatase TiO 2 nanoparticles [149,170], while at low coverages [9,19] and/or under vacuum conditions on TiO 2 (110), decomposition reactions have been observed [96,174]. From Figure 8.22, it is evident that the photocatalytic degradation of acetone proceeds very differently on rutile and anatase, and that again the photochemical processes have distinct particle-size dependence.…”

“…The acetone photochemistry is much more complex compared to the formic-acid adsorption system and may result in diverse reaction pathways that range from complete oxidation to condensation reactions. Thus, a variety of surface species have been suggested, based on IR spectroscopy on powder TiO 2 samples, ranging from radicals [14,168] to condensation products [169] such as mesityl oxide [149,[170][171][172] and polyacetone [100], or decomposition products such as carboxylate species (acetate and formate) [15,18,19,[171][172][173][174] and methoxy groups [18,19,174]. Further reactions between decomposition products are likely to occur, and a wide range of possibilities exist, depending on reaction conditions.…”

“…There are only a few IR spectroscopy studies of acetone photo-oxidation on TiO 2 nanoparticles [15,19,149,170,172]. Overall they all exhibit similar vibrational features, although the experimental conditions, samples and reported reaction mechanisms differ.…”