PURPOSE: To produce faujasite zeolite stable to hydrothermal treatment, by repeating the treatment with an aqueous solution of an ammonium salt and the calcination treatment.

CONSTITUTION: The objective modification can be carried out by (1) treating a faujasite zeolite containing alkali or alkaline earth metal with an aqueous solution of an ammonium salt (4.5W5pH) to convert about 50W67% of the metal to ammonium ion, and calcining the product at 400W600°C for 2W4hr, (2) treating the calcined zeolite again with an aqueous solution of an ammonium salt (4.5W 5pH) to decrease the amount of the alkali or alkaline earth metal remaining in the zeolite to ≤2wt% (in terms of oxide), (3) treating the product with a strongly acidic cation exchange resin to convert the ammonium-type zeolite to hydrogen-type zeolite and to elute aluminum, and (4) calcining the resultant dealuminized hydrogenated zeolite at 500W800°C for 1.5W8hr.