Crystallographic study of the distribution of chromium cations in X and Y zeolites

Abstract

The crystal structures of four CrY zeolites and one CrX zeolite containing 1,2 wt% chromium have been determined by powder X-ray crystallography. The results demonstrate that the Cr³⁺ cations occupy preferentially the site I' of these samples after dehydration. The cations at this site are three-coordinate.

The frameworks of the chromium-containing zeolite samples were found to be relatively unstable and a major amount of decomposition was common. This decomposition precluded similar crystal structure determinations for CrA zeolites at this Cr concentration.

Attempts to observe cationic migration and the formation of nitrosyl complexes upon addition of nitric oxide to a dehydrated CrY sample were inconclusive.