The decarbonylation of Co4-nRhn(CO)(12)/SiO2 and (Co-4(CO)(12) + Rh-4(CO)(12))/SiO2 catalysts was studied by temperature programmed reduction (TPR) and in-situ diffuse reflectance FT-IR techniques. Special attention was paid to the effect of the decomposition atmosphere on the supported catalysts. The temperature of decarbonylation depended on the precursor, and the CO desorption peak maxima during the TPR were as follows : Co2Rh2(CO)(12) = 123 degrees C, Co3Rh(CO)(12) = 125 degrees C, (Co4CO)(12) + Rh-4(CO)(12)) = 135 degrees C, Co-4(CO)(12) = 137 degrees C and Rh-4(CO)(12) = 178 degrees C, The CO desorption was greatest for Co-4(CO)(12), and less and similar for other catalysts. Thus, from rhodium containing catalysts less CO was desorbed at elevated temperatures indicating a stronger interaction of rhodium than of cobalt with the support. Correspondingly, according to FT-IR measurements, the stability of the tetranuclear carbonyls supported on silica decreased in the order Co-4(CO)(12) > bimetallic carbonyls > Rh-4(CO)(12) at room temperature.