Assessing the Accuracy of Isothermal Kinetic Tests in Reproducing Light-Off Profiles for Pd/Al₂O₃ Catalyzed NO–CO Reactions

This study investigated the kinetics of the reduction reaction of nitric oxide (NO) by carbon monoxide (CO), aiming to evaluate NOx emissions in automotive exhaust gases. Although the overall reaction leads to the formation of inert nitrogen gas (N₂), nitrous oxide (N₂O), a potent greenhouse gas, can arise as a byproduct, depending on the catalyst composition and operating conditions. The study demonstrates that light-off curves are an effective and practical method for determining the kinetic parameters and product distribution in the reduction of NO by CO over Pd/Al₂O₃. These curves provide results consistent with isothermal experiments, while requiring simpler and faster procedures. N₂O was identified as a reaction intermediate, formed in the partial conversion of NO and consumed as N₂ becomes the dominant product. Its formation occurs over a wide temperature range, which is especially relevant for cold start conditions in gasoline engines. The Pd/Al₂O₃ catalyst demonstrated high thermal stability and resistance to deactivation up to 500 °C. A first-order kinetic model successfully reproduced the main experimental trends, including the transient behavior of N₂O.