Journal of Physical Chemistry B, Vol.101, No.49, 10233-10240, 1997
Role of Hydrated Cu Ion Complexes and Aluminum Distribution in the Framework on the Cu Ion Siting in ZSM-5
A series of CuNa-ZSM-5 zeolites with different Cu/Al and Si/Al ratios and CuCaNa- and CuCeNa-ZSM-5 zeolites were prepared by Cu2+ ion exchange from Cu acetate and Cu chloride solutions in order to investigate the complexation of the Cu ions in hydrated and dehydrated zeolites. VIS-NIR d-d spectra of the Cu2+ ions in hydrated and Cu+ luminescence spectra of the dehydrated zeolites were used to indicate the coordination of the Cu ions in the zeolites. It has been found that the "monovalent" [Cu2+-ligand](+) complexes are present and predominate in ZSM-5 with low content of aluminum and high Cu loading and in those zeolites where Ca2+ or Ce3+ ions were preexchanged. Similarly, the Cu ions detected by Cu+ emission at 540 nm in dehydrated zeolites exhibit the same trend in population in dependence on the Cu(Ca,Ce)/Al/Si compositions of the ZSM-5 zeolite. These Cu ions were in our previous work indicated as those balanced by a single Al framework atom, exhibiting a rather open, close to planar ligand field environment and low positive charge on the Cu2+ ions, and easily reduced compared to the other Cu ions present in the zeolite. The population of these Cu ions requires the presence of the [Cu2+-ligand](+) species (like Cu2+-acetate or Cu2+-OH complexes) in the exchange solution and the presence of the single far remote Al atoms in the zeolite framework. As is shown here, the simultaneous presence of a single positive charge in solution and single negative charge in the framework for obtaining a complete or overexchange level of the Cu ions in the ZSM-5 zeolite is necessary.
Keywords:NO DECOMPOSITION;NITRIC-OXIDE;CATALYTIC DECOMPOSITION;IR INVESTIGATIONS;GASEOUS CUCL;COPPER IONS;ZEOLITES;PHOTOLUMINESCENCE;COORDINATION;SILICA