13C nuclear magnetic resonance investigations of carbon monoxide in decationated zeolites of type Y

Abstract

The ¹³C n.m.r. of carbon monoxide adsorbed on decationated zeolites of type Y is characterized by extremely large resonance shifts to lower magnetic field. The strong dependence of this resonance shift on temperature and on coverage can be explained by means of an exchange model described in the literature. This treatment yields the resonance shift of carbon monoxide molecules in the adsorption complex (350 ppm relative to gaseous CO) and the number of sites in zeolites effective for the complex formation (0.07 active sites per cavity). Investigations of the ¹³C nuclear magnetic relaxation of CO and CO₂ adsorbed on zeolite NaY and its decationated forms suggest that the large resonance shifts are due to an interaction with Lewis-type centres in the form of extra-lattice aluminium ions. Thus, investigations of the CO adsorption by means of the ¹³C n.m.r. method are suitable for a characterization of Lewis-acid sites in zeolites.