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Bulk TiO2 vs alternative Ti-based photocatalysts for the mild aerobic oxidation of alcohols

Abstract : A series of metal oxides semiconductors, including commercially available TiO2 or synthesized mesoporous samples, were tested as photocatalysts for the aerobic mild oxidation of alcohols in acetonitrile under UV. Benzyl alcohol, used as a reference, was oxidized mainly into benzaldehyde. Best yield (60%) was obtained with TiO2-P25. Unfortunately, this catalyst tended deactivate with time. The role of dioxygen solubility in the oxidation process was emphasized through the test of different solvents. Aliphatic alcohols were also studied. Among them, cyclohexanol gave mainly cyclohexanone with a yield of 70%. Parallely, a colloidal approach was developed for the deposition of titanium oxide nanoparticles on UV transparent mesoporous silica supports in order to take advantage of their important specific surface area and avoid aggregation phenomena during the photocatalysis tests. After optimizing the synthesis protocol (amount of water, nature of the acid and alcohol), spherical, non-crystalline stable nanoparticles with 5 nm diameter were obtained. Using the “two-solvents” impregnation method, these particles were successfully introduced in the mesopores of two SBA-15 silica samples differing by their mean pore diameter (either 6 or 8 nm). TEM measurements emphasized that the SBA-15 material with the largest pores led to the incorporation of more nanoparticles in its mesopores. Clearly, silica/ titanium dioxide interactions in the resulting materials appeared to play a positive role since lower amounts of TiO2 in the corresponding photocatalysis tests led to improved conversion rates of benzylalcohol compared to those performed with P25 or the parent suspension of colloids.
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Diaa Obaid. Bulk TiO2 vs alternative Ti-based photocatalysts for the mild aerobic oxidation of alcohols. Theoretical and/or physical chemistry. Université Pierre et Marie Curie - Paris VI, 2017. English. ⟨NNT : 2017PA066578⟩. ⟨tel-01913747⟩

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