As the selective catalytic reduction (SCR) catalysts for NOx removal, various Mn-based catalysts have been widely investigated in the academic world. However, few studies focus on the identification of MnOx species and Mn valence states in Mn-based catalysts. In this study, Mn-based catalysts, which were prepared by using different precursors or pure MnOx species, were investigated for their activities for SCR of NO by NH3. Meanwhile, according to XRD, TG and H-2-TPR measurement, a mass of crystalline and/or amorphous MnOx species were detected, while a very small amount of amorphous MnOx species could be observed with the TG-DSC-MS by detecting the oxygen coming from manganese oxides because of the decomposition. In addition, the contents and distributions of Mn2+, Mn3+ and Mn4+ as well at the average valences of manganese in catalysts were tested with the chemical titration method, while the XPS results could not identify the MnOx species, showing a semi-quantitative assessment of Mn2+, Mn3+ and Mn4+ contents. Furthermore, based on the SCR performance, Mn2O3 and Mn3O4 species were active for NOx reduction. (C) 2015 Elsevier B.V. All rights reserved.