RhNaY and RhHY zeolites have been prepared either by ion exchange with RhCl3 or by Rh-6(CO)(12) sublimation under vacuum. Except in the latter case, very small rhodium aggregates were obtained within the supercages of faujasitic zeolite. Photoelectron spectra and IR of chemisorbed carbon monoxide revealed that the interaction of these clusters with the zeolite matrix differs substantially, depending on the acidity of the zeolite. These clusters become aggregated during reduction or on-stream mainly at the outer zeolite surface irrespective of the degree of protonation of the zeolite. The RhNaYi catalyst proved to be interesting for the conversion of CO/H-2 mixtures to low carbon number alkenes and alkanes with a propensity to form butenes/butanes. However, the parent RhHYi homologue produced a higher proportion of saturated and branched hydrocarbons, mainly the C-4 fraction. These important differences in product distribution in the RhHYi zeolite have been associated with the presence of cationic rhodium species as revealed by X-ray photoelectron spectroscopy and carbon monoxide chemisorption.