Theoretical modeling of a copper site in a Cu(II)-Y zeolite

Model clusters of a Cu(II)-Y zeolite have been studied using a density func tional theory based method in order to investigate the electronic propertie s of the metal site involved in the catalytic activity of this zeolite. Thi s work has shown that different Si/Al ratios, sizes, and shapes of the mode ls do not induce significant changes in the electronic propel-ties of the C u site, whereas the influence of its coordination is emphasized. A large ch arge transfer (CT) from the zeolite to the metal has been found in the case of a formal Cu(II) cation. Comparable net charges on Cu are thus obtained for models of Cu(II) and Cu(I)-zeolite. However, these two systems differ b y their frontier orbital patterns, which are characterized by a low lying e mpty orbital localized on the zeolite and on Cu in the case of Cu (II), whe reas the lowest virtual molecular orbital of the Cu(I) model has a much hig her energy. Addition of NH3 molecules to the Cu(II) model is accompanied by a rearrangement in the electron distribution of the whole system, underlyi ng the non negligible role of the zeolite ill the catalytic process.