CHARACTERIZATION OF H,NA-Y USING AMINE DESORPTION

We have examined series of partially ion-exchanged H, Na-Y zeolites using temperature-programmed desorption (TPD) and thermogravimetric analysis (TGA) of isopropylamine and n-propylamine in order to examine the acid sites in H-Y zeolites as a function of Na poisoning. Both amines desorbed from Na-Y, unreacted, below 500 K; however, samples containing protonic sites exhibited two additional desorption features. First, unreacted amine molecules were observed leaving the samples between ∼500 and 600 K. Second, reaction features appeared which were observed as the simultaneous desorption of propene and ammonia between 575 and 650 K for isopropylamine and between 625 and 700 K for n-propylamine. For a given sample, the number of both isopropylamine and n-propylamine molecules which desorbed in both features was identical. Furthermore, the number of molecules desorbing from the two high-temperature features was found to be equal to the number of protonic sites for the entire series, which indicates that both desorption features are associated with protonic sites. This finding was confirmed by infrared spectroscopy, which also demonstrated that the unreacting desorption feature was associated with the low-frequency, hydroxyl stretch at 3540 cm-1 and that the reacting amine molecules were adsorbed at the high-frequency. hydroxyl stretch near 3640 cm-1. The implications of these results for understanding the use of TPD-TGA of amines for the characterization of acidity is discussed. © 1993 Academic Press, Inc.