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The energy efficiency of the photocatalytic conversion of gas-phase organic pollutants was studied using a redesigned and scaled-up photo-CREC-air reactor. This photocatalytic unit has the unique feature of allowing an accurate analysis of the irradiation field by establishing macroscopic balances and in situ measurements. The photo-CREC-air reactor operates in batch mode with the photocatalyst supported by a stainless steel mesh being irradiated by eight UV lamps. Kinetic modeling was performed, and quantum yields (QYs) and photochemical thermodynamic efficiency factors (PTEFs) were calculated using data for acetone and acetaldehyde photocatalytic degradation in ambient air utilizing a Degussa P25 (Aeroxide 25) photocatalyst. It was found that the photo-CREC-air reactor is suitable for the determination of kinetic and adsorption parameters, given a design with excellent irradiation usage and fluid−catalyst contact. In this respect, quantum yields for both acetone and acetaldehyde exceed the value of 1 (equivalent to 100%), with PTEFs in both cases remaining below the level of 1, as required by thermodynamics.

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The photocatalytic degradation of phenol and other phenolic compounds can follow different pathways depending on the reaction conditions. It is found that the photocatalytic oxidation of phenol is faster in acidic pHs with an optimum pH value of 3.2. On the basis of experimental data, it is concluded that the photocatalytic oxidation of phenol, ortho-dihydroxybenzene (o-DHB), para-dihydroxybenzene (p-DHB), and 1,4-benzoquinone (1,4-BQ) can all be described with a series − parallel reaction scheme. The present study reports a detailed reaction network incorporating possible reaction steps based on data obtained for the oxidation of phenol and its three aromatic intermediates. Four carboxylic acids (fumaric acid, maleic acid, oxalic acid, and formic acid) are detected as intermediates in the photocatalytic oxidation of phenol, o-DHB, p-DHB, and 1,4-BQ, suggesting that, in the oxidation of any phenolic compounds, these acids are part of the oxidation breakdown of more complex molecules. Additionally, two kinetic models are proposed with different degrees of complexity. A first model (KM#1) contains enhancements to that proposed by Salaices et al. (Chem. Eng. Sci. 2004, 59, 3) and helps predict the formation and disappearance of aromatic compounds only. In a second kinetic model (KM#2), a lumped acid concentration and CO2 formation are incorporated to account for the formation and disappearance of carboxylic acids as well as for the overall rate of mineralization. Both models provide a very good fit of the experimental data and work for a wide range of phenol concentrations (20−50 ppm C in phenol). Parameters estimates with statistical indicators for both models are also reported in this study.