Method for the preparation of a metal-exchanged zeolites or mixtures of metal-exchanged zeolites, such as Cu-SSZ-13, Cu-ZSM-5, Cu-beta, or Fe-beta, comprising the steps of providing a dry mixture of a) one or more microporous zeotype materials that exhibit ion exchange capacity and b) one or more metal compounds; heating the mixture in a gaseous atmosphere containing ammonia to a temperature lower than 300° C. for a time sufficient to initiate and perform a solid state ion exchange of ions of the metal compound and ions of the zeolite material; and obtaining the metal-exchanged zeolite material.