Solvate‐Supported Proton Transport in Zeolites

Solvate‐supported proton transport in zeolite H‐ZSM‐5 was studied by means of complex impedance spectroscopy. The zeolite shows enhanced proton mobility in the presence of NH 3 and H 2 O that depends on the concentration of the solvate molecule, temperature (298–773 K), and the SiO 2 /Al 2 O 3 ratio of the zeolite (30–1000). In general, proton conductivity in H‐ZSM‐5 is most effectively supported in the presence of NH 3 and H 2 O at high concentrations, low temperatures, and low SiO 2 /Al 2 O 3 ratios (≤80). For the aluminum‐rich samples desorption measurements reflect different transport mechanisms that depend on the respective temperature range. Up to about 393 K a Grotthus‐like proton transport mechanism is assumed, whereas at higher temperatures (393–473 K) vehiclelike transport seems to dominate. The activation energies for NH 4 + and H 3 O + vehicle conductivity depend on the SiO 2 /Al 2 O 3 ratio, and the values are in the range of 49–59 and 39–49 kJ mol −1 , respectively, and thus significantly lower than those for “pure” proton conduction in solvate‐free samples.