Low-temperature NOx capture and reduction via NO oxidation by O3 on Cu-CHA

Abstract

We studied the transient reduction of NOx with NH3 over Cu-exchanged CHA zeolite (Cu-CHA) assisted by the catalyst-free oxidation of NO by O3. The room-temperature catalyst-free oxidation of NO by O3 yielded NO2 at low O3/NO ratio and N2O5 as the main product at higher ratios. DFT calculations verified the reaction of NO2 +O3 to N2O5 proceeding with low activation energies. Transient operando IR measurements demonstrated that Cu-CHA exposure to NO+O3 at 100 °C resulted in the storage of NOx as NO3− on the Cu2+ site. The stored NOx reacted with NH3 to yield N2 and NH4NO3. Preadsorbed NH3 on Cu-CHA was oxidized by O3 to yield N2 and N2O. The reaction of preadsorbed NH3 with NO+O3 caused the selective formation of N2. The obtained results may aid in developing a new O3-assisted unsteady-state lean De-NOx process involving reactions of captured NOx with NH3 or reduction of NOx with stored NH3.