ON THE CU SITE IN ZSM-5 ACTIVE IN DECOMPOSITION OF NO - LUMINESCENCE,FTIR STUDY, AND REDOX PROPERTIES

Cu+ photoluminescence spectra and IR spectra of NO adsorbed on Cu2+ in ion exchanged Cu-ZSM-5 of various Cu/Al and Si/Al ratios were employe d to identify two main Cu sites (denoted as Cu-<alpha> and Cu-beta) an d their redox properties. The Cu-alpha site, preferably occupied at lo w Cu loadings, exhibits more packed environment, higher positive charg e, and is proposed to be balanced by two framework Al atoms, while the Cu-beta site, occupied in the whole concentration range, but predomin antly at high loadings approaching and exceeding 100% degree of ion ex change is in more open coordination, possesses lower positive charge, and is suggested to be balanced by a single framework Al atom. The red ucibility of these Cu sites differs substantially and depends on the l ocal negative framework charge, controlled by both the local Si-Al ord ering adjacent to the Cu ion and on the total framework charge given b y the Si/Al ratio. The correlation of the catalytic activity and reduc ibility of the Cu-ZSM-5 of various Cu/Al/Si compositions and populatio ns of the Cu-alpha and Cu-beta sites identified the Cu-beta site as th e active center for NO decomposition. (C) 1997 Academic Press.