Detection of side‐products on heavy metal cations loaded zeolites by XRD measurements

During the high loading of A, X, and Y zeolites with heavy metal cations by ion‐exchange undesired hydroxides are formed at the crystal surface. The precipitation is caused by the alkaline reaction of the parent sodium modification of zeolites in aqueous solutions and the low solubility product of heavy metal hydroxides. During the calcination of the samples the hydroxides are transformed into oxides. Exemplified by zeolite ZnNaA, a stepwise exchange in strongly diluted salt solutions may hinder the formation of hydroxides/oxides. XRD measurements enable a direct monitoring also of smallest amounts of zinc hydroxide/zinc oxide. The framework adopted ZnO causes a change of the symmetry of the zeolite lattice. The side product does not influence the formation of the new crystalline phases during the calcination of ZnNaA.