Role of Hydrated Cu Ion Complexes and Aluminum Distribution in the Framework on the Cu Ion Siting in ZSM-5

• Published in: The journal of physical chemistry. B Vol. 101; no. 49; pp. 10233 - 10240
• Main Authors: Dědeček, Jiří, Wichterlová, Blanka
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04.12.1997
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp971776y

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.