Electronic spectroscopic studies of transition metal-enriched zeolites: I. Nickel-exchanged zeolite L

Abstract

Electronic reflectance spectra of Ni-L at various stages of dehydration, rehydration in contact with water vapor, and sorption of ammonia are investigated. In the fully hydrated crystal nickel is present as Ni(H 2O) 6 2+ complexes in the main channels. As dehydration proceeds the nickel ions relocate and two successive coordination states are observed. Ni(H 2O) 6 2+ complexes gradually reform after long periods of rehydration by water vapor in samples partially outgassed at 373°K and lower temperatures. As the outgassing temperature increases however the Ni 2+ ions become increasingly inaccessible to NH 3 or H 2O molecules sorbed from the vapor phase.