Engineering the Mechanically Mixed BaMnO3-CeO2 Catalyst for NO Direct Decomposition: Effect of Thermal Treatment on Catalytic Activity

Abstract

A 5 wt% BaMnO3-CeO2 composite catalyst prepared by the one-pot method exhibits extraordinary catalytic performance for nitrogen monoxide (NO) direct decomposition into N2 and O2; however, the reasons for the high activity remain to be explored. Here, the catalyst was prepared by mechanical mixing and then subjected to thermal treatment at different temperatures (600–800 °C) to explore the underlying reasons. The thermal pre-treatment at temperatures higher than 600 °C can improve the catalytic activity of the mechanically mixed samples. The 700 °C-treated 5%BaMnO3-CeO2 sample shows the highest activity, with NO conversion to N2 of 13.4%, 40.6% and 57.1% at 600, 700, and 800 °C, respectively. Comparative activity study with different supports (ZrO2, TiO2, SiO2, Al2O3) reveals that CeO2 is indispensable for the high performance of a BaMnO3-CeO2 composite catalyst. The Ce species (mainly Ce3+) in CeO2 components diffuse into the lattice of BaMnO3, generating oxide ion vacancy in both components as evidenced by X-ray photoelectron spectroscopy and Raman spectra, which accelerates the rate-determining step and thus higher activity. The chemisorption results show that the interaction between BaMnO3 and CeO2 leads to higher redox activity and mobility of lattice oxygen. This work demonstrates that engineering the oxide ion vacancy, e.g., by thermal treatment, is an effective strategy to enhance the catalytic activity towards NO direct decomposition, which is expected to be applicable to other heterogeneous catalysts involving oxide ion vacancy.