An investigation by EXAFS of the thermal dehydration and rehydration of cerium- and erbium-exchanged Y-zeolite

Abstract

The changes in the local environments of cerium and erbium in rare-earth exchanged Y-zeolites which are induced by dehydration and rehydration processes have been investigated by extended X-ray absorption fine structure (EXAFS). The cerium L 3-edge EXAFS recorded from ca. 6 wt.% cerium-exchanged Y-zeolite show the hydrated cerium ion to be located in the large spaces in the supercages of the zeolite framework. Treatment in vacuo at 300 °C induces limited dehydration but the EXAFS study shows a closer approach of cerium to the zeolite framework. Washing of the material in ammonium chloride removes most of the cerium ions which are weakly held within the zeolite supercages but does not affect the ions located within the small cages. Treatment of the sample in vacuo at 300 °C induces the migration of most of the cerium into multiple site occupation of the small cages of the zeolite structure. Treatment in steam causes further changes in site occupancy and the migration of the cerium ions from the supercages in the zeolite framework. The erbium L 3-edge EXAFS data recorded from ca. 8 wt.% erbium-exchanged Y-zeolite following identical treatments are essentially similar to those recorded from cerium-exchanged Y-zeolite.