Effect of CeO2 for a high-efficiency CeO2/WO3–TiO2 catalyst on N2O formation in NH3-SCR: a kinetic study

Abstract

In this study, we investigated the effects of CeO₂ for a high-efficiency CeO₂/WO₃–TiO₂ catalyst on N₂O formation in NH₃-SCR reaction using a kinetic method. The results demonstrated that CeO₂ is very effective for enhancing the SCR (4NH₃ + 4NO + O₂ → 4N₂ + 6H₂O) reaction rate and thus suppressing the NSCR reaction (4NH₃ + 4NO + 3O₂ → 4N₂O + 6H₂O) due to the competition between these two reactions. Therefore, N₂O formation under SCR reaction conditions could be remarkably inhibited with the addition of CeO₂ to the catalyst. On the other hand, CeO₂ can also enhance the C–O reaction (4NH₃ + 5O₂ → 4NO + 6H₂O) over the catalyst, so N₂O formation under NH₃ oxidation conditions was promoted due to the lack of SCR reaction. In addition, we also found another interesting phenomenon wherein N₂O formation over WO₃–TiO₂ (without CeO₂) decreased gradually at high temperature from 350 to 450 °C, while N₂O formation over CeO₂/WO₃–TiO₂ kept increasing with the reaction temperature, which was also associated with the promotional effect of CeO₂ on SCR reaction and the competition between SCR and NSCR reactions.