Unexpected kinetic behavior of structured Pd/CeO2-ZrO2 toward undesired ammonia formation and consumption during nitrites reduction: Role of the reactivity of oxygen from ceria

This study deals with the kinetics of successive ammonia production and unexpected consumption in the course of the catalytic water denitrification over Pd/CexZr1-xO2 catalysts. A fast conversion of nitrites to ammonium ions was found weakly dependent of the particle size of palladium likely due to the juxtaposition of electronic effects stabilizing electron-rich Pd active sites more prone to produce ammonia instead of nitrogen. Subsequent slow consumption of ammonia in anaerobic conditions occurred on Pd/CexZr1-xO2 whereas Pd/ZrO2 was found inactive for this sequential reaction. Kinetic measurements from semi batch experiments led to the estimation of rate constants. Particular attention was paid to ammonia oxidation reaction with a pseudo rate constant depending on the surface coverage of reactive oxygen from ceria then revealing the importance of the synthesis route of CexZr1-xO2 and peculiar interaction with Pd.

Automated summary

This study investigates the kinetics of successive ammonia production and consumption during the catalytic water denitrification process over Pd/CexZr1-xO2 catalysts. The fast conversion of nitrites to ammonium ions is found to be weakly dependent on palladium particle size, while subsequent slow consumption of ammonia in anaerobic conditions highlights the importance of ammonia oxidation reaction with a pseudo rate constant depending on the surface coverage of reactive oxygen from ceria. The study emphasizes the significance of the synthesis route of CexZr1-xO2 and its peculiar interaction with Pd in the overall reaction kinetics.