Redox modification of high-silica zeolites with chromium via multistep cluster synthesis

This paper examines the modification of zeolites with superstoichiometric amounts of metals using multistep cluster synthesis. Ion-exchange sites in zeolite MFI-50 (SiO2/Al2O3 molar ratio of 50) have been modified with hydrazonium cations. Subsequent redox reaction with chromate anions has yielded a chromium-containing zeolite. The sample prepared by three ion-exchange/redox cycles contains 10 wt % chromium (Cr-MFI-50). EPR results show that most of the chromium in Cr-MFI-50 is in the form of fine Cr2O3 particles. In addition, the material contains isolated Cr5+ ions and, presumably, Cr3+ stabilized at aluminum vacancies.