INFLUENCE OF COMBINED ACID TREATMENT ON PHYSICOCHEMICAL CHARACTERISTICS OF ULTRASTABLE ZEOLITE-Y AND ON ITS CATALYTIC PROPERTIES IN THE DISPROPORTIONATION OF ETHYLBENZENE

Ultrastable zeolites (USY) have been treated with sulphuric and/or pho sphoric acids, aiming at the determination of the interaction of both acids with either framework (FAL) or extraframework (EFAL) aluminas, a s well as the effect of such modifications on catalytic properties in ethylbenzene disproportionation. Zeolites have been characterized by m eans of several physicochemical techniques (XRD, XRF; FTIR, Si-29, Al- 27 and P-31-MAS/NMR, nitrogen adsorption and AA). Results revealed tha t the treatment with H2SO4 removes EFAL located in supercavities witho ut attacking the zeolitic framework. Treatment with H3PO4 incorporates P in two quite distinct ways: as a monomeric phosphate associated to framework aluminium atoms (for low EFAL concentrations) and as a polym eric phosphate originated from the reaction of EFAL with H2PO4 (for hi gh EFAL concentrations). Regarding catalytic properties, initial activ ities are higher for H2SO4 leached samples when compared to those whic h have just been calcined. Nevertheless,initial activities of samples treated with H3PO4 depend strongly on the P2O5 content incorporated in to the zeolite. With respect to isomers (ortho-, meta- and para-diethy lbenzenes) generally formed in this disproportionation reaction, no co nsiderable para-selectivity has been observed.