CaMnO3 perovskite-derived porous γ-MnO2 for highly efficient oxidation of NH3 and NO

Selective dissolution is highly promising for tailoring the structures and functions of metal oxides toward various applications. Here, we demonstrate a successful fabrication of porous γ-MnO 2 by selectively dissolving Ca in a CaMnO 3 perovskite (CMO) via dilute HNO 3 treatment. The perovskite-derived γ-MnO 2 (denoted as CMO-72 h) outperformed drastically the pristine CaMnO 3 and a commercial γ-MnO 2 in the catalytic oxidation of NH 3 and NO, two representative gaseous pollutants in the atmosphere. Physicochemical characterization by X-ray photoelectron spectroscopy and temperature-programmed techniques (including H 2 -TPR, O 2 -TPD and NH 3 -TPD) suggests that the excellent catalytic performance of CMO-72 h is associated with its low–temperature reducibility and abundant surface–active oxygen species. Specifically, acid treatment led to the oxidation of Mn 3+ to Mn 4+ on the surface, increasing significantly the Mn 4+ /Mn 3+ ratio from 0.76 (for CMO) to 1.45 (for CMO-72 h) and, meanwhile, generating additional surface oxygen vacancies . As a result, O 2 molecules can be easily adsorbed and activated on the CMO-72 h, leading to improved performance in NH 3 and NO oxidation. This study may offer new opportunities in the synthesis of high-performance Mn oxide catalysts for environmental applications.