The formation of a well defined rhodium dicarbonyl in highly dealuminated rhodium-exchanged zeolite Y by interaction with CO

I.r. spectra with unusually sharp (f.w.h.m. ≤ 5 cm-1) carbonyl bands and their corresponding 13CO satellites follow from the interaction of natural CO with both reduced and oxidized rhodium (1 wt %) introduced into dealuminated zeolite Y (US-Ex). Isotopic exchange with 13C16O, 12C18O, and 13C18O confirms the proposed formation of a well defined dicarbonyl compound with C2v symmetry and an angle of ca. 106° between the two CO groups. The formation of the dicarbonyl with reduced Rh/US-Ex at 300 K is accompanied by a loss of intensity of the hydroxyl bands of the zeolite, showing the participation of the hydroxyl groups in the formation of RhI from small rhodium clusters. The additional intensity increase of the dicarbonyl bands at 423 K proceeds without an intensity loss of the hydroxyl bands and indicates the formation of RhI by another process, presumably by CO dissociation. In addition to the carbonyl-stretching bands, combination bands are detected, which allow the estimation of other fundamental bands of the RhI(CO)2 system masked by strong bands of the zeolite framework. During the formation of the Rh dicarbonyl there are no significant changes in the far-i.r. region (400-50 cm-1) to be assinged to cation motions within the zeolite framework.