FTIR study of novel Pd 6 carbonyl clusters encaged in zeolite 5A

Abstract

Infrared absorption spectra are compared with palladium carbonyl clusters encaged in zeolites Y and 5A. Marked differences are attributed, in terms of a dynamic model, to different sizes of the α-cage windows which control migration of primary clusters. Under conditions in which Pd 13(C0) x clusters prevail in zeolite Y, Pd 6(C0) x dominates the IR spectrum in 5A. Higher reduction temperatures cause formation of larger particles in zeolite Y, but in 5A the small window size prevents particle growth. Whereas doubly-bridged CO is abundant on Pd 13 carbonyls in zeolite Y, terminal and triply-bridged CO prevail in Pd 6(CO) x , as they do in Rh 6(C0) 16. Peak positions indicate different extents of electron deficiency. Marked color changes of calcined, reduced and CO-treated samples further illustrate the electronic interaction of Pd ions and clusters with the zeolite matrix.