Bis(mu-oxo)dicopper as key intermediate in the catalytic decomposition of nitric oxide.

Abstract

The direct decomposition of NO into N2 and O2 is the simplest and most desirable approach to NO abatement. Although no catalysts are known that fulfill all criteria required for application, some materials show a high NO conversion and could be potential catalysts in the near future. 2] The copper-loaded ZSM5 zeolite is the most studied catalyst with a high and stable NO decomposition activity. Since its discovery in 1986, considerable research efforts have been made in order to unravel the reaction mechanism and the active sites in Cu-ZSM-5. A growing consensus is found that a redox process cycling between Cu ions and Cu -ELO species is present (ELO extra lattice oxygen). 4±6] However, the nature of the Cu -ELO species has so far not unequivocally been identified. 4±7] Here, we report on the elucidation of this catalysis by identifying the bis( -oxo)dicopper species as the key intermediate that allows the smooth formation and desorption of O2. The detection of the bis( -oxo)dicopper species and its role was made possible by in situ spectroscopy, that is, under real reaction conditions. Firstly, UV/Vis monitoring of the catalyst using optical fiber technology was combined with on-line GC analysis. Secondly, direct structural information of the catalyst under working conditions was obtained with XAS (X-ray absorption spectroscopy). 11] So far, the bis( -oxo)dicopper core had only been characterized in homogeneous, synthetic complexes. Its isomerized ( 2 : -peroxo)dicopper core is present in natural actin membrane skeleton mesh. In addition, the raft may keep the Lck concentrations high at and near the TCR cluster. Lck may partition into the TCR-cluster raft and/or the rafts with Lck may coalesce with those containing the TCR cluster, which would raise the Lck concentration in the neighborhood of the TCR cluster. These possibilities are now under investigation in our laboratories.