Transferring concepts from classical catalysis to the new field of photocatalysis

Abstract

The aim of the study was to characterize the regime of operation of a newly constructed POLITEF flat-plate gas-phase continuous flow photocatalytic reactor in view of improving its construction and selecting the optimum set of operational conditions. The nanosized photocatalytic powder material (TiO2 Degussa P25, consisting of 75% anatase and 25% rutile with average anatase particle size 25 nm) was deposited as a thin film coating on a TLC aluminum sheet, pre-coated with silica gel (Merck, 0.2 μm SiO2 film), achieving loadings of 0.6 –2.0 mg TiO2/cm2. The reactor is operated either with UV light or visible light, penetrating through a quartz glass flat-plate illumination window (56 cm2 illuminated surface area). The time interval needed to reach steady-state operation conditions was established to be 5 min, applying the criterion of Wald–Wolfowitz. The model air pollutant was ethylene with a feed concentration of 1000 ppm. All the experimental runs were carried out at an optimal relative humidity of 30%, which was established in a previous work. Varying the operational parameters—ethylene contact time, ethylene/oxygen feed ratio, the kind of light and intensity of illumination—the optimum operating conditions were established, under which maximum ethylene conversion was observed. Corrigan’s criterion for the presence or absence of diffusion limitations was applied, proving that the reactor was operating in the kinetic region at low TiO2 loadings, but at high loadings, a diffusion retardation effect was observed. It was established that the flow through the reactor is laminar based on the values of the Reynolds number.