Zeolite NaY-supported Ir-4(CO)(12) was prepared by direct deposition onto the outside surface of the zeolite crystals and by reductive carbonylation of Ir(CO)(2)(acac) sorbed in its pores. These samples and the products of their decarbonylation and subsequent recarbonylation were characterized by infrared and extended X-ray absorption fine structure spectroscopies. The data show that the clusters in the zeolite pores were molecularly dispersed and could be reversibly decarbonylated and recarbonylated, whereas those on the outer surface outside the pores were aggregated under decarbonylation condition (300 degreesC in He) and could not be reversibly recarbonylated. The results demonstrate stabilization of the molecular clusters entrapped in the pores.