Abstract
The adsorption of different isotopic ozone mixtures on TiO2 at 77K was studied using FTIR spectroscopy and DFT calculations of cluster models. In addition to weakly bound ozone with band positions close to those of free or dissolved molecules, the spectrum of chemisorbed species was observed. The splitting of the ν1+3 combination band to eight maxima due to different isotopomers testified to the loss of molecule symmetry. The frequencies of all the isotopic modifications of the ozone molecules which form monodentate or bidentate complexes with four- or five-coordinated titanium atoms were calculated and compared with those of experimentally observed spectra. The four considered complexes adequately reproduced the splitting of the ν1+3 vibration band and the lowered anharmonism of chemisorbed O3. The energetically most favorable monodentate complex with four-coordinated titanium atoms showed good agreement with the observed spectra, although a large difference between the frequencies of ν1 and ν3 modes was found. For better coherence with the experiment, the interaction of the molecule with adjacent cations must be considered.
Highlights
The type of interaction of ozone with solid surfaces is a key factor determining the activity of different materials for catalyzing ozone decomposition and the reactivity towards other adsorbed molecules
The obtained data are compared with the results of DFT calculations of ozone complexes with TiO2 clusters to check the proposed assignment of the distinct components in the complex structure of the observed spectra of chemisorbed isotopically mixed ozone
If we adsorb the ozone prepared from a 50:50% isotopic mixture of 16 O and 18 O, in the region of the ν1+3 combination immediately after adsorption the structure of six bands arises, forming two triplets typical of symmetrical O3 molecules, as in the spectrum of ozone adsorbed on aerosolized SiO2 [1]
Summary
The type of interaction of ozone with solid surfaces is a key factor determining the activity of different materials for catalyzing ozone decomposition and the reactivity towards other adsorbed molecules. The problem is of extreme importance for industry and ecology, the number of spectral studies regarding ozone adsorption is limited, apparently because of the technical difficulties of working with this highly active and unstable compound. Using low-temperature FTIR spectroscopy it was possible to study ozone adsorbed on SiO2 [1,2,3], Al2 O3 [4], MgO [5], CaO [6], TiO2 [2,7,8], CeO2 [8,9], ZnO, and some zeolites [8].
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