MICROPOROUS AND MESOPOROUS MATERIALS ELSEVIER Microporous and Meaoporous Materials 70 ( 1998) 259 767 A refined model for the active site within the NO decomposition catalyst, Cu-ZSM-5 Dean C. Sayle ‘**, C. Richard, A. Catlow ‘, Marc -A. Perrin b, Patrice Nortier b a D~~~~~-Furudq Lahortrtor~~. Th Roy/ hstitutim of Grtrt Rrituiw. 21 AI~FM~c Strut. LOFILIOFI. WI .Y 4B.S. UK b CLJFI trc tk Rccherck rie Rhti~le-~~)lrli,ni,, 52 Rw tie lrr Huic C’O~. Y3308, Auhert:illi~r.c. C’tvk~. Frmcr Received 9 July 1997: accepted 3 September 1997 Abstract 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 comprises a copper pair. bridged by OH and forming a six membered ring, specifically, I-O-Cu( II )---OH--Cu( I )POPAIL}, within the zeolite framework. The six-membered ring arises from the strong association of both of the copper species with a 0 single aluminium in the zeolite framework and consequently the ring is strained. reflected in the low ( 3. I A) intercoppct distance in the cluster. Indeed. this Cu-Cu distance compares well with the experimentally determined value of 3.0. In addition. it is expected that the strain in the cluster influences the activity of the cluster. uhich we suggest may be responsible for its unique activity for NO decomposition. :i;, 1998 Elsevier Science R.V. K~~~wortl.s; Alumina-silicate; Cu -Cu clusters; MFI: Solution enthalpy 1. introduction The Cu-ZSM-5 system has been shown by Iwamoto et al. [ I ] to catalyse effectively the decom- position of NO, although various inadequacies of this material preclude its use commercially [2]. A knowledge of the structure of the active site would provide a useful basis for the development ol future catalysts which do not suffer the deficiencies of the present material. Various models [%8] have been proposed for * Corresponding ;luthor. Present address: Department of Environmental and Ordnance Systems. Cranlield University. Royal Military College of Science. Shrivenham, Swindon. SNh XLA. UK; tel. +44 l7Y? 785264: e-mail: wylekr~rmck cranfield.ac.uk the configuration of the active site and it has been suggested that isolated Cu species together with copper pairs, bridged by extra-lattice oxygen or hydroxyl groups, are present in the active catalyst. These copper specieshave also been shown to be strongly associated with framework aluminium [6.9]. A detailed study by Grunert et al. [ IO] allowed the identification of six different copper species with respect to environment, location or aggregation. Furthermore, they argue that both the isolated copper and copper clusters are neces- sary to provide optimum catalytic performance, but the composition, detailed structure and loca- tion of these clusters remains at present ill defined. In a previous study. we used simulation tech- niques to probe the structure of Cu-ZSM-5, and 13X7-IXI IW:$lY.OW~ I998 Elrevier Science B.V. All rlghta reserved. P/I Sl3X7-1x1 I (97)0000’~-7