ACTIVE-SITE CONFIGURATIONS WITHIN THE NO DECOMPOSITION CATALYST, CU-ZSM-5 - THE ROLE OF FRAMEWORK ALUMINUM

Computer modelling techniques have been used to identify the extra-fra mework copper clusters which form the active sites in the Cu-ZSM-5 de- NOx catalysts. In particular, we suggest that both isolated copper and Cu-OH-Cu species represent useful models for the active site. These s pecies are strongly anchored to the zeolite wall via framework alumini um, in the absence of which the clusters undergo significant structura l modifications. Specifically, we observe changes both in the Cu-O and Cu-Cu bond distances and also in the coordination numbers of the copp er. We suggest that such changes are responsible, in part, for the rel ationship between the copper loading and Si/Al ratio and the catalytic activity of the material.