Substitution of Sn in place of Al in the framework of molecular sieve via treatment with fluoride salts

A process for preparing a molecular sieve having a three dimensional microporous framework structure which has a unit empirical formula on an anhydrous basis of:

• (Sn.sub.w Al.sub.x Si.sub.y)O.sub.2
• where "w", "x", and "y" are the mole fractions of tin, aluminum and silicon, respectively, present as framework tetrahedral oxide units, said mole fractions being such that they are within the trigonal area defined by points A, B, and C of FIG. 13, which points have the following values of w, x and y:
• ______________________________________ Point w x y ______________________________________ A 0.49 0.01 0.50 B 0.01 0.49 0.50 C 0.01 0.01 0.98 ______________________________________
• said molecular sieve characterized in that it has a cation equivalency of at least about 0.8 and an oxygen adsorption capacity of at least 70% of its theoretical capacity as measured at 100 torr and 90.degree. K. the process comprising contacting a crystalline microporous aluminosilicate zeolite having a framework structure of aluminum and silicon tetrahedral oxide units, pore diameters of at least about 3 Angstroms and a molar ratio of SiO.sub.2 /Al.sub.2 O.sub.3 of at least 2, with a fluoro salt of tin, said fluoro salt being in the form of an aqueous solution or slurry, at a pH of about 3 to about 7, whereby framework aluminum atoms of the zeolite are removed and replaced by extraneous tin atoms.