Photocatalytic NOx abatement: The effect of high air flow velocity

In the literature, the abatement of nitrogen oxide (NOx) emissions by photocatalysis is rarely carried out at real-world air flow velocities. Here, we investigated the performance of two commercial photocatalysts, Aeroxide (R) TiO2 P25 (Evonik Industries, Germany) and FN NANO (R) 2 (Advanced Materials-JTJ, Czech Republic), P25 containing 88 % anatase and 12 % rutile, while FN 2 moreover 13 % of a binder. The degradation of NOx pollutants (0.1 and 1.0 ppmv) at air flow velocities ranging from 0.02 to 0.7 m s-1 was tested, the photocatalytic efficiency being determined for various slit heights (5-25 mm) and rate of volume flow (1500-11 000 cm3 min-1). The photocatalysts achieved substantial NO and NO2 abatement. Pollutant conversion decreased as the air flow velocity increased, with the highest conversion (80%) occurring at 0.1 m s-1. The NOx conversions were slightly higher for NO than for NO2, and significantly higher for the NO concentration of 0.1 ppmv. Slit height had a negligible effect, indicating a substantial degree of mixing in the direction perpendicular to the flow; consequently, the flow cannot be laminar in nature as the ISO standard (22197-1:2016) states. This finding is supported by the nanoindentation technique showing that the surface roughness contributed to the formation of vortexes and enhancement of the mass transport. To our best knowledge, this is the first study to test commercial photocatalysts under such a wide range of air velocities and, in doing so, it has identified considerable implications for outdoor air purification. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).