Zeolite H-ZSM-5: A Microporous Proton Conductor for the in situ Monitoring of DeNO <sub>x</sub>-SCR

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ABSTRACT

Impedance spectroscopy was applied on zeolite H-ZSM 5 as a proton conducting NH ₃ sensor material and DeNOx-SCR (selective catalytic reduction of NO _x with NH ₃) catalysts at the same time under SCR conditions. We show that in situ monitoring of the NH ₃ conversion with NO _x becomes feasible when the zeolite is loaded with NH ₃ first and NO _x is applied afterwards to the gas phase. Temperature dependent measurements allow discriminating NH ₃ desorption from catalytic conversion and time dependent measurement give first hints on the thermal activation of the conversion.

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Solvate-supported proton transport in zeolites.

Folker E Franke, Ulrich Simon (2004)

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 NH3 and H2O that depends on the concentration of the solvate molecule, temperature (298-773 K), and the SiO2/Al2O3 ratio of the zeolite (30-1000). In general, proton conductivity in H-ZSM-5 is most effectively supported in the presence of NH3 and H2O at high concentrations, low temperatures, and low SiO2/Al2O3 ratios (< or = 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 NH4+ and H3O+ vehicle conductivity depend on the SiO2/Al2O3 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.