A wide-line 1H nuclear magnetic resonance approach was used to study the rates of proton-transfer reactions between extra-framework species in hydrated ammonium-substituted zeolites (chabazite, clinoptilolite). In both samples, intense proton exchange between water molecules was detected; with no sign of cross-exchange with ammonium ions. The observed exchange was interpreted as being the result of proton-transfer reaction between H2O molecules and chemical defects; represented by Brønsted acid sites. Temperature measurements revealed that the barrier to this reaction was equal to about 40 and 60kJ/mol in NH4-chabazite and NH4-clinoptilolite, respectively. The proton conductivity that was associated with this reaction was equal to about 1% of the contribution arising from NH4+ migration.

Proton Transfer in Hydrated Ammonium Zeolites - a 1H NMR Study of NH4-Chabazite and NH4-Clinoptilolite. I.S.Afanassyev, N.K.Moroz: Solid State Ionics, 2003, 160[1-2], 125-9