Catalytic compositions

A method for preparing phosphorus-containing ultrastable Y-zeolite which comprises:

• (a) ion-exchanging and washing sodium Y zeolite having a unit cell dimension of about 24.53 to 24.72 .ANG. with an ammonium salt solution and water to obtain a Y-zeolite which contains 1 to 5 weight percent Na.sub.2 O;
• (b) combining the washed Y-zeolite of step (a) with an aqueous solution of a phosphorus compound selected from the group consisting of H.sub.3 PO.sub.4, NH.sub.4 H.sub.2 PO.sub.4, (NH.sub.4).sub.2 HPO.sub.4, and Na H.sub.2 PO.sub.4 to obtain a Y-zeolite that contains about 0.1 to 5 weight percent P.sub.2 O.sub.5 ;
• (c) heating the phosphorus-containing Y-zeolite of step (b) in the presence of steam to obtain a phosphorus-containing ultrastable Y-zeolite having au nit cell dimension of about 24.45 to 24.60 .ANG.;
• and
• (d) washing the phosphorus-containing ultrastable Y-zeolite of step (c) to remove sodium ions.