Non-framework Al species in Y zeolites investigated by 27Al MAS NMR and by IR spectroscopy

Different signals of 27Al MAS NMR (at 0 ppm, 30 ppm and 60 ppm) detected on either dehydroxylated or under self-steaming conditions treated Y zeolites are discussed. Non-framework Al species exhibit not only octahedral but also tetrahedral coordination. During the treatment at higher temperature the octahedrally bonded species are successively transformed into species exhibiting coordination number 4. Non-framework Al species interact specifically with adsorbed carbon monoxide. The simple cations exhibiting strong L-acidity are the real reason of the high perturbation of CO molecules causing a shift of stretching vibration to 2225 cm-1. An interpretation of the correlation between NMR results and IR spectra of adsorbed CO is presented. 22 refs.; 6 figs