This invention relates to a method for modifying a synthetic composition of ultra-large pore crystalline material, e.g., silicate, comprising an inorganic, porous, non-layered crystalline phase material exhibiting, after calcination, an X-ray diffraction pattern with at least one peak at a d-spacing greater than 18 Angstrom Units and having a benzene adsorption capacity of greater than 15 grams benzene per 100 grams of said material at 6.7 kPa (50 torr) and 25.degree. C., by contacting with a treatment composition comprising an inorganic oxide of a trivalent element X, e.g., sodium aluminate, or precursor of said inorganic oxide, under sufficient conditions so that the trivalent element X is incorporated in the crystalline phase material. The composition is suited to use for catalytic conversion of organic compounds or as a sorbent.