Oxidizing, trapping and releasing NOx over model manganese oxides in alternative lean-burn/fuel-rich atmospheres at low temperatures

Abstract

Herein, we report the performance of the catalytic oxidizing, trapping and releasing NO over the MnOx (Mn2O3, Mn3O4 and MnO2) model Lean NOx Traps (LNT) catalysts at low temperatures (≤200°C). Among these typical MnOx samples, Mn2O3 has the high NO oxidizability, and can efficiently trap and release NOx in the alternative lean-burn/fuel-rich atmospheres. Our characterization results show that enrichment of the Mn3+ cations and active surface oxygen species probably plays the important role for NO oxidation. Although MnO2 has the biggest NOx storage capacity in the lean-burn atmosphere, the strong adsorption strength between MnO2 and NOx inhibits the release of the stored NOx species in the fuel-rich atmosphere. The in situ DRIFTS and NO-TPD studies indicate that the trapped NOx on Mn2O3 can transform from nitro compounds to nitrites, and then to nitrates along with the increased adsorption temperature.