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

Abstract

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 Cu 4 O 2 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 N 2 . Due to the restricted channel structure of ZSM-5, the Cu 4 O 2 clusters were reduced promptly by CH 4 .

In Situ Speciation Studies of Copper–Humic Substances in a Contaminated Soil during Electrokinetic Remediation

“…X‐ray absorption near edge structure spectroscopy can also provide information of oxidation states of an excited atom, the coordination geometry, and the bonding of its local environment in environmental solids. By in situ EXAFS, we found that Cu oxides (in ZSM‐5 or ZSM‐48) were involved in the catalytic decomposition of NO (Huang and Wang, 1999; Huang et al, 2003) and oxidation of chlorophenols in supercritical water (Lin and Wang, 1999, 2000). Speciation of CuO during mineralization of CCl 4 was also studied by in situ EXAFS spectroscopy (Chien et al, 2001).…”

In situ EXAFS study of copper in the electrokinetic remediation process

“…A bump in the pre-edge region and an obvious shoulder in the edge jump were observed in XANES spectra of tetrahedral complex. The preedge XANES spectra of the Cu-contaminated soil exhibited a very weak absorbance band for the 1s to 3d transition (8975-8980 eV) which is forbidden by the selection rule in the case of perfect octahedral symmetry (Denise et al, 1989;Lin & Wang, 1999;Huang & Wang, 1999;Lin & Wang, 2000). A shoulder at 8984-8988 eV and an intense feature at about 8995-9002 eV were attributed to the 1s to 4p transition that indicated the existence of Cu(II) species.…”

EXAFS study of copper in waste incineration fly ashes

“…EXAFS can provide structural information including the coordination number, bond distance, and oxidation state (Yu et al, 1990;Oday et al, 1994;Mosselmans et al, 1995;Foster et al, 1998). By EXAFS, we found that copper oxides involved in the catalytic decomposition of NO (Huang and Wang, 1999) and oxidation of chlorophenols in supercritical water (Lin and Wang, 1999). These molecular scale data were very useful in revealing the structure of catalysts in the catalysis process.…”