the resulting subcarbonyl species adsorbed on NaY and NaXzeolites have been investigated utilizing i.r., temperature-programmed decomposition and X.p.s. techniques. It was found that Mo(CO)6 encapsulated in the NaXzeolite was considerably less stable than that contained in the NaYzeolite, while intermediate subcarbonyl species, Mo(CO)3ads, showed a completely reversed thermalstability. The drastic