Gaseous By-Products Generated from UV-PCO Process-A Review
ASHRAE TRANSACTIONS 2021, VOL 127, PT 1(2021)
Abstract
Photocatalytic oxidation (PCO) based air filters have been receiving increased attention because of its potential for indoor air cleaning. However, the formation of undesired by-products leads to the slow commercialization of this technology. Acetaldehyde and formaldehyde were the two typical by-products. By literature review, a database of gaseous by-products generated from the PCO process was established to explain systemically, the impacts of operational conditions and catalyst features on the by-product formation. Generation of by-products relyed on the challenging VOC types and inlet concentrations. The levels of by-products increase with airflow rates (a decrease of residence time). Relative humidity (RH) would quantitively and qualitatively influence the by-product formation. The development of modified catalysts would help inhibit by-product generation. Compared with TiO2 and P25, Carbon-doped TiO2 or Ce-doped P25 showed better performance on both removal efficiency promotion and by-product prevention. However, some modified materials, such as fluorinated P25, aiming to increase the VOCs removal efficiency, would generate higher concentrations of by-products than P25. This review focuses on a better understanding of the PCO by-product generation mechanism, thereby assisting ASHRAE to establish a proficient testing and evaluation standard of PCO air cleaners.
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