Abstract: The effects on the properties of ZSM-5 zeolite modified by steam. H₃PO₄and Mg(Ac)₂were studied. It is shown that middle strong acid sites were the active sites for ethyla-tion of toluene with ethanol. It is possible to cover the external surface acid sites selectively and keep the channel structure essentially by depositing an adequate amount of Pand Mg on the steam-treated zeolite. This is assumed in favour of increasing the shape-selectivity .to remain the activity as the unmodified zeolite. In this case,the so called "opposite effect" may be overcome. The modified catalyst P₁Mg₁HZ is stable at an average activity of 16.5% with the 85% p-selectivity and >97% alkylation selectivity for 100 hours on streaming.

Key words: ZSM-5,P-Mg modification, Ethylation of toluene