Characterization of the balance between metallic and acidic properties of Cu-MFI catalysts by using the transformation of haloaromatic compounds: effect of copper loading and Si/Al ratio

The transformation of equimolar mixtures of m-bromofluorobenzene and chloro benzene was carried out over Cu-MFI catalysts at 400 degreesC under atmosph eric pressure in a fixed bed reactor. A reversible exchange of halogen atom s occurred between m-bromofluorobenzene and chlorobenzene leading to m-chlo rofluorobenzene and bromobenzene. The isomerization of m-bromofluorobenzene into o- and p-bromofluorobenzene was also observed. It was found that the activity in halogen exchange increased linearly with increasing copper cont ent up to a loading corresponding to the cationic exchange capacity of the zeolite, while the isomerization activity decreased symmetrically. It was c oncluded that the halogen exchange reaction between the aromatic compounds was catalyzed by the copper species located in the cationic exchange sites of the zeolite and that the isomerization reaction was catalyzed by the res idual protonic acidity. (C) 2001 Elsevier Science B.V. All rights reserved.