Photocatalysis with Ti-pillared clays for the oxofunctionalization of alkylaromatics by O2

Ti-pillared montmorillonite clays (Ti-PILCs) have been investigated as photocatalysts for the selective oxygenation of the following liquid alkylaromatics: toluene, para-xylene and ortho-xylene. The photocatalytic processes occur using O-2 as Oxidizing species, upon near UV light, in mild pressure and temperature conditions and with good stability of the catalytic materials. Accumulation of valuable carbonylic derivatives is possible since their over-oxidation to carbon dioxide is negligible. In particular, proper reaction conditions are found for obtaining carbonylic compounds with about 90% selectivity, which is significantly higher than that obtained when the same experiments are carried out with commercial TiO2 Degussa P25. Detailed results on the chemical-physical characterization of these materials are also presented. In this regard, particular attention is devoted to the effects of surface interaction with substrates and reaction intermediates on efficiency and selectivity of the photocatalytic processes. In particular, the hydrophobic nature of the Ti-PILCs as well as adsorption phenomena are beneficial for alkylaromatics to reach the photoactive sites. The results obtained in mixed alkylaromatics/cyclohexane reaction media show that the Ti-PILCs are also able to discriminate among the substrates in favour of the aromatic compounds. (C) 2008 Elsevier B.V. All rights reserved.