Three different approaches have been used to characterize the state of exchanged copper ions in copper-ion-exchanged MFI (CuMFI) samples. (1) Two types of an ion-exchangeable site with different adsorption properties for N 2 or CO molecules were identified depending on the pre-treatment temperature (723 or 873 K) of a sample prepared by using an aqueous solution of CuCl2. (2) The state of the active sites formed by the evacuation of a sample at 873 K that had been prepared using a mixture solution of aqueous NH4CH3COO and Cu(CH3COO)2 was analysed utilizing both 13C18O and 12C 16O to identify the two types of active adsorption sites for CO molecules. (3) CuMFI samples prepared by the ion-exchange method employing anhydrous CuCH3COO showed a surprising adsorption feature characterized by a single IR band occurring at 2159 cm-1 due to the adsorbed CO molecules, but there was no corresponding IR band due to adsorbed N2 molecules. A successful preparation of CuMFI, in which the monovalent copper ions exclusively occupied another one of the two types of ion-exchangeable sites, was also carried out utilizing the solid-ion exchange method using Cu(CH3COO)2·H2O. This site exhibits an IR band occurring at 2151 cm-1 for CO molecules and also acts as an active site for N2 molecules. These experimental data correlate, and clearly indicate that there are at least two types of exchangeable sites for copper ions in MFI-type zeolites.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry