SHAPE SELECTIVITY OF HYDROTHERMALLY TREATED H-ZSM-5 IN TOLUENE DISPROPORTIONATION AND XYLENE ISOMERIZATION

Controlled hydrothermal treatment of H-ZSM-5 at 500°C causes a transformation of framework into non-framework aluminium, as indicated by means of cation exchange and IR spectroscopy. After treatment with nitric acid, partial extraction of non-framework aluminium was observed. The non-framework aluminium-containing samples showed an enhanced p-xylene selectivity in the catalytic disproportionation of toluene and in the isomerization of m-xylene. The subsequently extracted samples had lost this property. A model of the decisive role of non-framework aluminium in shape selectivity is discussed. © 1990.