Active site configurations within the NO decomposition catalyst, Cu-ZSM-5; the role of framework aluminium

Computer modelling techniques have been used to identify the extra-framework 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 species are strongly anchored to the zeolite wall via framework aluminium, in the absence of which the clusters undergo significant structural modifications. Specifically, we observe changes both in the Cu - O and Cu - Cu bond distances and also in the coordination numbers of the copper. We suggest that such changes are responsible, in part, for the relationship between the copper loading and Si/Al ratio and the catalytic activity of the material.