Hollow MnOx-CeO2 mixed oxides as highly efficient catalysts in NO oxidation

- A hollow sphere structure was established over MnOx-CeO2 mixed oxide.
- ∼82% NO conversion could be attained over MnOx-CeO2-CS1 sample at 220 °C when GHSV = 120,000 h−1.
- The redox property and the oxygen vacancies are the key factors to determine the performance.

A series of hollow MnOx-CeO2 mixed oxide catalysts were prepared by employing carbon as hard templates. The activity tests reveal that the catalytic performance of MnOx-CeO2(CS) samples are more active than that of MnOx-CeO2(AC) sample, indicating carbon sphere (CS) as a more effective carbon template. Among these samples, MnOx-CeO2(CS1) sample exhibits the best activity, for which a maximal NO conversion (∼82%) could be attained at 220 °C when GHSV = 120,000 h−1. In addition, the NO conversion could be further improved with lower NO initial concentration or higher O2 content. Under the simulated flue gas condition, the activity of MnOx-CeO2(CS1) sample is barely affected by the presence of CO2, but the influence of H2O and SO2 couldn't be neglected. The characterization result proves that the core-shell hollow structure has been successfully synthesized over MnOx-CeO2 binary oxides. For the hollow MnOx-CeO2 sample, the mesopore structures are formed and the MnOx oxides are highly dispersed on CeO2 support. Among these samples, MnOx-CeO2(CS1) sample possesses the largest SBET and Vtotal values. The result of H2-TPR and oxygen pulse measurement indicates that MnOx-CeO2(CS) samples, especially MnOx-CeO2(CS1) exhibits the best redox property. Moreover, more amount of high valence Mn as redox active sites and more oxygen vacancies exist in MnOx-CeO2(CS1) proved by XPS technique. Overall, these properties may contribute to the excellent activity.