Influence of the chemical composition upon adsorption, coadsorption, and reactivity of ammonia and methanol on alkali-exchanged zeolites

The interaction of ammonia and methanol with several alkali zeolites was studied by means of IR spectroscopy, mass spectrometry, and thermogravimetry. While ammonia adsorbed identically on all zeolites investigated, the adsorption complex of methanol subtly depended upon the concentration of lattice aluminum in the zeolite. This is attributed to the variation of the polarizability of the zeolite lattice induced by the varying chemical composition. With respect to the reaction of methanol with ammonia, the differences in the sorption of methanol led to variations in the reactivity of these zeolites toward the primary products monomethylamine and dimethyl ether. On zeolites with a high aluminum content, both products were formed in approximately equal concentrations, while with silicon-rich zeolites monomethylamine was the dominating product. With all alkali zeolites investigated methanol was significantly stronger adsorbed than ammonia.