Spectroscopic study of surface properties of various NH4-exchanged X zeolites

Abstract

The nature of hydroxyl groups formed during deammoniation of three NH₄-X zeolites has been investigated in terms of their stability during dehydroxylation and their acidity towards bases like pyridine. It appears that besides the two principal bands at 3660 and 3560 cm^–1 always observed in spectra of decationated X and Y zeolites, a third band is present at 3625 cm^–1, the intensity of which depends on the percentage of Na⁺ ions exchanged and, for a given sample, on the outgassing temperature. This band is attributed to hydroxyl groups which show acidic properties, are very accessible to large molecules, and are therefore probably located inside the large cavities of the network, but which are very sensitive to dehyroxylation at relatively low outgassing temperatures.