SORPTION OF MONOMETHYLAMINE, DIMETHYLAMINE, AND TRIMETHYLAMINE ON ZK-5 AND Y-ZEOLITES STUDIED BY DEUTERIUM NMR

Deuterium NMR is used to study the sorption complexes formed by (methyl-deuterated) mono-, di-, and trimethylamine (MMA-d3, DMA-d6, and TMA-d9) in the acid forms of the zeolites HZK-5 and HY, as well as in dehydroxylated HY and DHY, obtained by high-temperature calcination of HY. The measurements were made in the range -140 to 160°C on samples loaded up to twice the equivalent of the number of Al atoms per unit cell. For HZK-5 the uptake of MMA and DMA is rapid at room temperature, but sorption of TMA requires thermal activation. In HY and DHY all amine gases are readily absorbed upon exposure at room temperature. In all samples a variety of species are identified, roughly divided into chemi- and physisorbed. The former corresponds to sites in which the amine molecules are firmly bound to the zeolite framework but can still undergo various types of local motions. The nature of these motions is studied by analysis of the deuterium NMR line shape. In HZK-5 and HY similar species to those previously found in HRHO are observed. Their structure may be understood in terms of H-bonded complexes with the Brønsted acid site of the zeolites. In DHY other chemisorbed species are observed which appear to be formed by semipolar bonding of the amines with Lewis acid sites formed by the dehydroxylation process. © 1990 American Chemical Society.