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 exchan ge from Cu acetate and Cu chloride solutions in order to investigate t he complexation of the Cu ions in hydrated and dehydrated zeolites. VI S-NIR d-d spectra of the Cu2+ ions in hydrated and Cu+ luminescence sp ectra of the dehydrated zeolites were used to indicate the coordinatio n of the Cu ions in the zeolites. It has been found that the ''monoval ent'' [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 det ected by Cu+ emission at 540 nm in dehydrated zeolites exhibit the sam e trend in population in dependence on the Cu(Ca,Ce)/Al/Si composition s of the ZSM-5 zeolite. These Cu ions were in our previous work indica ted as those balanced by a single Al framework atom, exhibiting a rath er open, close to planar ligand field environment and low positive cha rge 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 fa r remote Al atoms in the zeolite framework. As is shown here, the simu ltaneous presence of a single positive charge in solution and single n egative charge in the framework for obtaining a complete or overexchan ge level of the Cu ions in the ZSM-5 zeolite is necessary.