Reduction of NO with CH₄ Effected by Copper Oxide Clusters in the Channels of ZSM-5

Fine structures of the copper oxide clusters involved in catalytic reduction of NO were studied by X-ray absorption spectroscopy. The Extended X-ray absorption fine structural (EXAFS) spectra indicate that about 2.89 nearest oxygen atoms bond to the Cu central atoms with a Cu-O bond distance of 1.96 Å for the oxidized Cu-ZSM-5 catalyst. Reduction of the catalyst in hydrogen at 573 K led to the formation of mainly Cu-Cu (2.54 Å) species with the coordination number (CN) of 2.91. The Cu₄O₂ clusters in the channels of ZSM-5 observed by EXAFS were formed in the NO reduction process via incorporation of oxygen into the metallic copper matrix with desorption of N₂. Due to the restricted channel structure of ZSM-5, the Cu₄O₂ clusters were reduced promptly by CH₄.