Dynamic structure of highly disordered manganese oxide catalysts for low-temperature CO oxidation

The dynamic structures of a highly disordered manganese oxide catalyst (HDMO) and intermediates were thoroughly studied from precursor to working catalyst. Excellent CO oxidation activity at low temperatures (T-50 = 83 degrees C) was performed over a HDMO in the presence of H2O and CO2 . The specific reaction rate of 4.56 mu mol(CO).g(cat)(1).s(-1) at 90 degrees C was approximately 25 times and 15 times higher than those of bixbyitetype alpha-Mn2O3 and cryptomelane-type alpha-MnO2, respectively. With X-ray photon electron spectroscopy (XPS), we reveal that more surface oxygen vacancies (O-v) and adsorbed oxygen species from the highly disordered structure could promote the redox property and oxygen release capability. In situ Raman and DRIFTS spectroscopy were used to identify a dynamic surface phase transformation during CO adsorption and oxidation. In combination with kinetic studies of CO oxidation, we conclude that there are two mixed mechanisms for CO oxidation over HDMO: the Langmuir-Hinshelwood (L-H) mechanism and the Mars-van Krevelen (MvK) mechanism. (C) 2021 Elsevier Inc. All rights reserved.