In the presented study, H-Beta zeolite and H-Beta/meso (mesoporous Beta zeolite obtained by a mesotemplate-free method) were modified with Fe, FeCr, FeCr and Cr triple-metallic aggregates (oligocations) by ion-exchange method (for comparison modification with isolated Fe cations was also done). Successful synthesis of mesoporous Beta zeolite was confirmed by several techniques such as N-sorption, PXRD, AAS or NH-TPD. Modified porosity and acidity of the Beta zeolite, as well as the source of metals used, influenced the form (coordination and aggregation), content and reducibility of Fe– and Cr-species in the samples (UV–vis-DRS, AAS, H-TPR). The obtained samples were tested as catalysts in the process of selective catalytic oxidation of ammonia to dinitrogen (NH–SCO). The highest activity and selectivity for nitrogen was obtained for the bimetallic Fe–Cr samples prepared by deposition of suitable oligocations.