Surface chemistry of methanol and ammonia on HNaK erionites

Abstract

The adsorption and interaction of ammonia and methanol on HNaK erionites have been found to depend strictly on the nature of the zeolite acid sites. Adsorbed alone, ammonia and methanol were found to be protonated on H-erionite at ambient temperature and to be bound coordinately to the alkali-metal cation on NaK erionite. Coadsorption experiments indicated that ammonia is preferentially adsorbed on H-erionite and methanol on NaK erionite. Thus, ammonia was found to displace adsorbed methanol from the Brønsted acid sites of H-erionite, generating surface ammonium ions, which act as adsorption sites for methanol. On NaK erionite, ammonia is bound to methanol which is adsorbed on Na⁺ or K⁺ cations. The sequence of the adsorption did not influence the final coadsorption complex.