Sorption and surface chemistry of aminoethanol and ethanediamine on H-mordenites

The sorption and surface chemistry of 2-aminoethanol and 1,2-ethanediamine on acidic mordenites was studied in situ by means of IR spectroscopy. Upon sorption on the hydroxyl groups of the zeolite, the amino group of aminoethanol and one amino group of ethanediamine is protonated. The extent of interaction of the second functional group with the zeolite decreases with increasing Si/Al ratio. On mordenites with a high acid site density the OH group of aminoethanol was strongly hydrogen bonded to the zeolite, while this interaction was less pronounced in the samples with a low site density. For ethanediamine sorbed on mordenites with a high acid site density the fraction of double-protonated molecules was higher than for samples with a low aluminum content. When aminoethanol and ammonia were coadsorbed on Si-rich mordenite with a large-pore volume, aminoethanol was preferentially adsorbed. On Al-rich samples with a small pore volume, the formation of a coadsorption complex is indicated in which aminoethanol and ammonia are sorbed on neighboring acid sites and interact via hydrogen bonding. During TPD of aminoethanol from H-mordenites, the molecule eliminated water at approximately 600 K. The formed intermediate decomposed further into ammonia and hydrocarbons. During TPD of ethanediamine from H-mordenites, the desorption of more weakly bound species and the increased mobility at higher temperatures enabled all ethanediamine molecules to be protonated on both amino groups. The double protonated species then desorbed at temperatures above 600 K upon decomposition into ammonia and hydrocarbons.