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

• Published in: Catalysis today 2022-01, Vol.383, p.330-338
• Main Authors: Dacquin, J.P., Troncéa, S., Parvulescu, V.I., Granger, P.
• Format: Article
• Language: English
• Subjects: Ammonia; Catalysis; Catalytic reduction of nitrites; Ceria-zirconia mixed oxides; Chemical Sciences; Palladium; Water denitrification
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2020.05.054

[Display omitted] •Weak structure-sensitivity of nitrite reduction on Pd/CexZr1-xO2 due to strong support effect.•Ammonia re-oxidation assigned to reactive oxygen species bonded to cerium.•Density of active oxygen dependent on the preparation route: EISA vs. co-precipitation.•Correlation between kinetic rate constant of ammonia re-oxidation and Ce–O coverage. 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.