Modification of zeolites by multi-charged cations by the use of in-situ formed "active gas-phase species"

A new way of the modification of zeolites is discussed which is based on th e use of active gas-phase species formed in situ upon thermal treatment of a [H-zeolite+modifier oxide] mixture with an air flow containing CCl4. The chemical transport reaction, with the formation of reactive and mobile oxyc hloride fragments in the zeolitic bed, provides effective dissipation of th e oxide phase and migration of active species into the zeolitic channels at temperatures as low as 150-300 degrees C. ESR is used as an informative an d sensitive method to monitor transformations in systems containing paramag netic ions. The peculiarities of the introduction of Mo5+ ions into the H-f orms of several zeolites (ZSM-5, beta, ferrierite, USY) differing in channe l size and structure are discussed. Some transformations of H-ZSM-5 contain ing Fe3+ and Gd3+ ions are also studied. (C) 1998 Elsevier Science B.V. All rights reserved.