Identification of MnOx species and Mn valence states in MnOx/TiO2 catalysts for low temperature SCR

•Using different precursors or pure MnOx species, Mn-based catalysts were prepared.•A mass of crystalline or amorphous MnOx species were found by XRD, TG and H2-TPR.•A very small amount of amorphous MnOx species could be observed by TG–DSC-MS.•Contents and distributions of Mnn+ were tested with the chemical titration method.•Mn2O3 and Mn3O4 species were active for NOx reduction.

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 H2-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 as 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.