Alcohol dehydrogenation, photo

Catalysts containing niobia supported on various oxides have been the subject of considerable recent interest [1-4]. The molecular structures and reactivity of niobium oxides supported on alumina, titania, zirconia and silica have been intensively investigated over the last few years. Niobia supported on silica has been shown to be active for the dehydrogenation and dehydration of alcohols, photo-oxidation of propene and oxidative decomposition of methyl tertiary butyl ether. Titania supported niobia is active for the selective catalytic reduction (SCR) of NO by NH3. 

A similar mechanism was formulated for the catalytic oxidation of hydrocarbons and for the photo-sensitized oxidation of 2-propanol. (2) A pure dehydrogenation can be depicted in which the platinum cleaves the hydrogen from the substrate alcohol. 

Photo-oxygenation of (— )-citronellonitrile (74) followed by reduction of the intermediate hydroperoxides gave a 1 1 mixture of two allylic alcohols, (75) and (76). This mixture upon treatment with acid provided the diene (77) and recovered (76). Pyrolysis of (77) effected an intramolecular Diels-Alder reaction and a dehydrogenation to yield (78). 

Summary The kinetic study of the solid-liquid reaction between photocatalytic titanium dioxide (photo-Ti02) and H- siloxane was investigated. The results showed that the solid-liquid reaction was inhibited in the presence of water, alcohol, ether, or other polar molecules, and supported its characterization as a dehydrogenation condensation reaction. The synthesized silicone-modified photo-TiOa by the solid-liquid reaction was initially hydrophobic, but became super-hydrophilic after irradiation by BLB light. Both ESR and Si-NMR studies suggested that this effect was caused by the photocatalytic oxidation of the silicone present on the photo-Ti02. 

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