Photocatalytic NOx abatement: Mathematical modeling, CFD validation and reactor analysis

Highlights: • A CFD model was implemented and validated for the investigation of ${NO}_x$ abatement. • Profiles obtained with CFD deviated substantially from the plug flow model. • A nonlinear behavior was observed when the height of the reactor was varied. • The CFD predictions are especially better in non-ideal flow conditions. • The CFD model can be used for scale-up (scale-out) of photocatalytic ${NO}_x$ abatement. -- Abstract: A 2D CFD model was implemented for the numerical simulation of ${NO}_x$ abatement in a photocatalytic reactor, considering the effect of relative humidity (10–60%), light intensity (0.3–13 W⋅m⁻²) and inlet $NO$ concentration (0.1–1.0 ppm). Significant differences of ${NO}_x$ concentration at the catalytic surface and bulk gas were found (${\Delta }_{max}$ of ∼12% and ∼16% for $NO$ and ${NO}_2$, respectively) and corrections were proposed to achieve intrinsic rate laws from a model available in the literature. An analysis of the reactor performance was conducted and a nonlinear behavior was observed when the channel height ($H$) was varied. A point of maximum for the integral rate of $NO$ and ${NO}_2$ consumption as a function of $H$ was found (${\Delta }_{NO}$ of $\sim 2\%$ and $\sim -1\%$ for $H\to 2H$$\to 4H$; ${\Delta }_{{NO}_2}$ of $\sim 46\%$ and $-8.5\%$ for $H\to 2H$$\to 4H$). Additionally, the $NO$ conversion decreased from $\sim 29\%$ to $\sim 7\%$ and the selectivity decreased from $\sim 85\%$ to $\sim 80\%$ (passing through a point of minimum at $2H$) when the height was varied in the range $H-4H$. When comparing the results from the CFD simulations and the predictions of a plug flow model, deviations for $NO$ conversion and selectivity increased with $H$ (${\Delta }_{max}$ of ∼2% and ∼45%, respectively).