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

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.