The dynamic nature of the protons in H−ZSM-5 was examined by the temperature dependence of 1H MAS NMR in the range 298−473 K. The line width of 1H MAS NMR of acidic protons increased, and through maximum it decreased. The intensity of the spinning sidebands monotonically decreased, and they almost disappeared upon raising the temperature. This temperature dependence of the spectrum was explained by the thermal motion of protons. The correlation times and the activation energies for proton mobility were estimated. The estimated values of the activation energy are 17−20 kJ mol-1.

1H magic angle spinning NMR gave firm evidence for formation of acidic protons (4.0 ppm) and hydride species (−1.8 ppm), where the former exists as OH groups (acidic protons) and the latter has an interaction with three equivalent Ag atoms, existing as Ag3H when Ag+-exchanged A-zeolite is reduced with hydrogen. The formations of Ag3H and of acidic protons by the heterolytic dissociation of H2 over Ag3 + are reversible. The heterolytic dissociation of H2 was also observed over Ag-Y-zeolite, the silver hydride species being observed at −0.1 ppm.

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