Multiphase photo-capillary reactors coated with TiO2 films: Preparation, characterization and photocatalytic performance

摘要

Quartz capillaries were assessed as multiphase photocatalytic reactors. The tested reaction was thesalicylic acid (2-dihidroxibenzoic acid) oxidation. The catalyst (TiO2) was either in slurry or immobilizedby sol-gel method onto the capillary wall. All experiments were conducted under oxygen flow and Taylorflow hydrodynamic regime. TiO2 Films were characterized by Raman spectroscopy, diffuse reflectanceUV-Vis spectroscopy and scanning electronic microscopy. The effect of two synthesis variables wasestablished. These variables were volumetric ratio of precursors solutions (i-PrO:2-propanol:nitric acid)and number of capillary coating cycles. These variables were found to importantly affect filmhomogeneity and oxidation rate. The highest initial reaction rate (106.32x10-6 mol dm-3s-1) was obtainedwhen using the TiO2 as film prepared with a precursors volumetric ratio of 1:15:1 and with two coatingcycles. For comparison purposes, the same oxidation process was conducted in a stirred reactor and it wasfound that the reaction rate value is diminished by almost four times in comparison with that obtainedunder Taylor flow in the capillary reactor. Selectivity was found to be dependant on the type of catalystaddition, slurry or immobilized. Catalytic films employed in this non-common reaction system were2reused three times losing less than 10% of their photocatalytic activity. The photonic efficiency wasfound to be two orders of magnitude higher in the coated capillary reactor than in the slurry stirred reactor.