Experimental investigation of NO reduction by H2 on Pd using planar laser-induced fluorescence

Abstract

This study investigates the NO reduction by H2 on a Pd/Al2O3 catalyst in a temperature range of 100–300 °C and NO/H2 ratios from 0.5–2, aiming to gain a deeper understanding of the reaction kinetics and its interaction with mass transfer. Planar laser-induced fluorescence (PLIF) is used to visualize the NO distributions over the catalyst, supplemented by end-of-pipe gas analysis of other components. The reduced Pd-based catalyst undergoes a slow deactivation after exposure to the reactive flow, leading to reduced overall NO conversion and decreased selectivity towards N2. The NO-PLIF measurements are only conducted on the reduced catalyst without considering the temporal evolutions. Despite the overall NO conversion varying only around 50%–65% across all the investigated conditions, the spatially resolved NO distributions reveal three distinct regimes that limit the overall NO conversion: the regime governed by intrinsic reaction rates, the regime constrained by H2 availability, and the regime restricted by NO diffusion. These findings, demonstrating the interaction between reaction kinetics and mass transfer over a heterogeneous catalyst, highlight the significance of analyzing spatially resolved concentration distributions obtained through PLIF measurements. This approach complements the conventional end-of-pipe analysis, offering a more comprehensive understanding of the underlying processes.