A method for improving the stability of a composition of matter comprising an inorganic, porous, non-layered crystalline phase exhibiting an X-ray diffraction pattern with at least one peak at a d-spacing greater than about 18 Angstrom Units and having a benzene adsorption capacity after stabilization of greater than 15 grams benzene per 100 grams of said material at 50 torr and 25.degree. C. includes contacting the crystalline material with a compound M'X.sub.2 Y.sub.n wherein M' represents B, Al, Si, or Ti; X represents halides or alkoxides of C.sub.1-6 ; Y represents X or alkyls of C.sub.1-12 ; and n=1-2; said contacting occurring under sufficient contacting conditions to result in a thermally and/or hydrothermally stable crystalline product.