Selective catalytic reduction of NO over Cu-AFX zeolites: mechanistic insights from in situ/operando spectroscopic and DFT studies

Abstract

In situ/operando spectroscopic experiments and DFT calculations were combined to study the selective catalytic reduction of NO with NH₃ (NH₃-SCR) over Cu-AFX zeolites. Transient experiments (in situ/operando XANES, IR, and UV-vis) on the reduction half cycle show that the NH₃ coordinated to the Cu(II) center reacts with NO to produce N₂ and H₂O, and simultaneously Cu(II) is reduced to Cu(I). On the other hand, transient experiments on the oxidation half cycle indicate that the oxidation of Cu(I) to Cu(II) species occurs with O₂ as the sole oxidant. DFT calculations suggest plausible pathways for the oxidative activation of Cu(I) by O₂ as the only oxidant. It is proposed that the oxidation of Cu(I) by O₂ as the exclusive oxidant rather than the NO-assisted oxidation plays the key role in the standard NH₃-SCR reaction at low temperatures.