Spectroscopic Evidence of Efficient Generation of Dicopper Intermediate in Selective Catalytic Reduction of NO over Cu-Ion-Exchanged Zeolites

The
key reactive sites in the selective catalytic reduction (SCR)
of NO using ammonia (NH3–SCR) are the Cu­(II)/Cu­(I)
ammine complexes encapsulated within zeolite catalysts. The reaction
intermediate in the important CuI → CuII reoxidation step has been proposed as the dicopper species. However,
obtaining the definitive spectroscopic probe for the dicopper intermediate
under NH3–SCR remains a quite challenging subject.
Here we report spectroscopic evidence of the efficient generation
of the dicopper intermediate in NH3–SCR over Cu-ion-exchanged
zeolites. The state of the Cu ion under the NH3–SCR
condition was analyzed using fiber-optic UV–vis–NIR
spectroscopy; a distinct spectroscopic fingerprint of the (μ–η2:η2-peroxo)­dicopper­(II) intermediate was
detected. Our spectroscopic assignment was rationalized by density
functional theory calculations. The intensity of the spectroscopic
fingerprints of dimeric copper was much higher than expected from
previous reports, and it was also found that such a spectroscopic
probe is observable only under the NH3–SCR conditions.
This finding strongly supports the previously suggested Cu dynamic
contributions to NH3–SCR catalysis.