Oxidizing, trapping and releasing NO x 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 MnO x (Mn 2 O 3 , Mn 3 O 4 and MnO 2 ) model Lean NO x Traps (LNT) catalysts at low temperatures (≤ 200 °C). Among these typical MnO x samples, Mn 2 O 3 has the high NO oxidizability, and can efficiently trap and release NO x in the alternative lean-burn/fuel-rich atmospheres. Our characterization results show that enrichment of the Mn 3+ cations and active surface oxygen species probably plays the important role for NO oxidation. Although MnO 2 has the biggest NO x storage capacity in the lean-burn atmosphere, the strong adsorption strength between MnO 2 and NO x inhibits the release of the stored NO x species in the fuel-rich atmosphere. The in situ DRIFTS and NO-TPD studies indicate that the trapped NO x on Mn 2 O 3 can transform from nitro compounds to nitrites, and then to nitrates along with the increased adsorption temperature.