Small Rh clusters in NaY zeolite (Rh-c/NaY) produced by oxidation and subsequent reduction of Rh-6(CO)(16)/NaY were studied by NMR, in situ FTIR, and volumetric adsorption of CO and H-2. Hydrogen uptake on bare Rh clusters measured via H-1 NMR was 1.0(+/-0.2) hydrogen per rhodium (H/Rh), while the amount of CO determined volumetrically was 2.56(+/-0.1) CO/Rh. These values are consistent with very high Rh dispersion. Dosing of the Rh clusters with sufficient CO regenerated Rh-6(CO)(16). The catalyst was stable to further oxidation-reduction-CO adsorption treatment cycles. Two resonance peaks were observed in the H-1 NMR spectra of reduced Rh/NaY in the presence of H-2 : (i) a resonance at about 2 ppm due to hydrogen associated with the support and (ii) a broader upfield peak assigned to hydrogen adsorbed on Rh clusters. The NMR properties of hydrogen adsorbed on Rh clusters differed considerably from those observed for hydrogen on metallic Rh particles, e.g., particles produced by impregnation on NaY zeolite [Rh(imp)/NaY]. First, the intrinsic shift of the hydrogen adsorbed on Rh clusters was over 100 ppm further upfield than hydrogen adsorbed on catalysts with Rh particles larger than 2 nm. It is suggested that this increased shift reveals the paramagnetic character of Rh clusters. Second, the temperature dependence of this intrinsic shift indicated antiferromagnetic electron spin coupling. In contrast, the NMR shift of hydrogen adsorbed on Rh(imp)/NaY was nearly constant in the same temperature range (similar to 300-500 K). Finally, the second moment analysis showed that hydrogen was rigidly adsorbed on Rh clusters but was mobile on the surface of larger Rh particles. At a hydrogen coverage of 0.65 H/Rh, two hydrogen states on Rh clusters were indicated by this analysis and were proposed to be hydrogen adsorbed at face-bridging sites and edge-bridging sites.