Abstract: Mixed zeolites embedded in and strongly bound to a substrate and method for producing same are disclosed. The method comprises providing a plurality of seed zeolites, raw material for forming zeolites, the raw material comprising a source of silica, and a substrate, and combining the above, heat-treating the combination at a temperature and for a time sufficient to insure the formation of stable SiO.sub.2, and hydrothermally treating the heat-treated combination with alkali hydroxide, and optionally, a source of alumina as additional raw material at least when the combination is absent a source of alumina, to produce the mixed zeolites. The substrate can either enter into the reaction to form the zeolites, or they can be non-reactive.