Insight into the sulfur resistance of manganese oxide for NH3-SCR: Perspective from the valence state distributions

The multiple valence states distributions (VSDs) endowed the catalyst with excellent low temperature de-NOx activity, while little is known about whether the SO2 resistance can be affected by VSDs modulation. In this context, three model manganese oxide catalysts (MnO2, Mn2O3 and Mn3O4) with different valence state distributions were fabricated and evaluated in the NH3-SCR reaction under the presence of SO2. The results show that the three catalysts exhibited a valance-state-dependent SO2 resistance (Mn3O4 > Mn2O3 > MnO2) under the SCR atmosphere with the presence of 100 ppm SO2 at 100 C within 7 h. Thermal regeneration analysis revealed the overall deactivation was dominated by the remarkably different reversible activity loss proportions, which were found proportionally correlated to the superficial Mn4+/Mnn+ content of the catalysts. Further characterizations indicated the Mn3O4 catalyst with more basic sites and less bulk-like sulfate formation could be the reason for its more slowly deactivation within the limited test period. However, the overall number of basic sites on MnOx is still critically insufficient for longer SO2 resistance test. This work clarified the deactivations details of MnOx from the perspective of valence state distributions, which can provide references for the design of better low temperature SO2-tolerant de-NOx catalyst.