Treating NOx emission of hydrogen fueled combustion engines by NOx storage and reduction catalysts: A transient kinetic study including PLIF measurements

NOx storage and reduction (NSR) catalysts are a well-known and broadly used technology to reduce NOx emissions from combustion engines, which may also be applied for hydrogen fueled engines in the future. In this study, Pt- and Pd-based NSR-catalysts were investigated in the absence and presence of water to understand how NO oxidation as well as the storage and reduction phases are influenced by the gaseous environment with H2 as a reductant. A planar channel configuration was chosen for conducting planar laser-induced fluorescence experiments during the storage phase in addition to steady-state oxidation measurements and transient lean/rich cycles in a packed bed reactor. The presence of steam significantly decreases the NO oxidation activity of both noble metal catalysts. The Pt/BaO/Al2O3 catalyst is more active during transient lean/rich cycles, however, it suffers an activity loss during repeated cycles, whereas the activity of the Pd/BaO/Al2O3 sample is slightly more stable in the wet gas feed over time. All experiments showed a strong correlation between the NO2 formation over the catalyst and its storage capability. The influence of water in the exhaust gas on the NSR-catalysts shows a strong temperature dependency on storage and reduction of NO for both catalysts containing Pt and Pd. The storage behavior is also strongly influenced by both the experimental configurations chosen revealing the significance of the interaction of intrinsic catalytic kinetics and mass transfer in the surrounding flow field.