A REFINED MODEL FOR THE ACTIVE-SITE WITHIN THE NO DECOMPOSITION CATALYST, CU-ZSM-5

Static atomistic simulation techniques have been employed to identify a model for the active site configuration and its location within the NO decomposition catalyst, Cu-ZSM-5. We propose that the active site c omprises a copper pair, bridged by OH and forming a six membered ring, specifically, (-O-Cu(II)-OH-Cu(I)-O-Al-), within the zeolite framewor k. The six-membered ring arises from the strong association of both of the copper species with a single aluminium in the zeolite framework a nd consequently the ring is strained, reflected in the low (3.1 Angstr om) intercopper distance in the cluster. Indeed, this Cu-Cu distance c ompares well with the experimentally determined value of 3.0. In addit ion, it :is expected that the strain in the cluster influences the act ivity of the cluster, which we suggest may be responsible for its uniq ue activity for NO decomposition. (C) 1998 Elsevier Science B.V.