Core-shell-like structured α-MnO2@CeO2 catalyst for selective catalytic reduction of NO: Promoted activity and SO2 tolerance

Abstract MnO2 is effective to selectively catalytically reduce NO (SCR) at low-temperature as an environmental catalyst, but suffers seriously from SO2 poisoning. The α-MnO2@CeO2 catalyst with a core-shell-like structure was synthesized by a two-step hydrothermal method. The CeO2 shell with a depth of 10 nm was deposited outside α-MnO2, consisting of CeO2 nanoparticles with a diameter of less than 5 nm. The ultra-thin CeO2 shell was porous and did not affect the gaseous molecules diffusing. Furthermore, the valence of Mn decreased and the redox property improved due to the CeO2 shell, thus increasing the NO removal efficiency. Moreover, CeO2 shell could bind SO2 strongly in priority to the poisoning of MnO2, thus functioning as the sacrifice to protect the α-MnO2 core from SO2 poisoning. The preferential adsorption of SO2 on the CeO2 shell was because of its strong covalent binding with SO2. SO2 was oxidized and solidified by lattice oxygen, leaving the gas phase and avoiding further attack on active center Mn. This work offers a new route for the design of SO2-resistant Mn-based catalysts for SCR of NOx at low temperatures.