Low temperature IR studies of CO sorbed in ZSM-5 zeolites

Abstract The properties of OH groups and cationic sites in CuZSM-5, CoZSM-5 and FeZSM-5 (and also in HZSM-5, NaZSM-5 and MgZSM-5, used as “reference zeolites”) were investigated by the sorption of CO at 170 K. The acid strength of Si–OH–Al groups increases with their amount, which is explained assuming heterogeneity of these OH groups in ZSM-5 zeolites. The positions of the C–O stretching bands of CO interacting with sites other than transition metal cations were determined and these data would be helpful in the correct analysis of the spectra of CO interacting with transition metal cations. The electronic properties of the adsorption site were studied by comparison of the C–O frequencies. In the case of CuZSM-5, two kinds of Cu + sites of various Cu–CO stretching frequencies were found.