Fluorescence characteristics of Cu-ZSM-5 zeolites in reactive gas mixtures: mechanisms for a fiber-optic-based gas sensor

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Abstract
In situ measurements of the fluorescence spectra,intensity, and response time were made at elevated temperatures(∼500 °C) for samples of Cu-ZSM-5 exposed to dilute mixturesof O2 in N2 and to variousO2-reductant combinations in N2. Theresults of these experiments are interpreted with a physical model ofthe oxidation/reduction kinetics of the copper ions. Thefluorescence signal depends strongly on the gas composition, providinga mechanism for a gas composition sensor. A prototype sensorconfiguration is described that uses a visible (488-nm) excitationsource and a fiber-optic geometry to generate and detect thefluorescence. The results indicate that for a weakly reducing gasthe fluorescence signal correlates well with the oxygen concentration,whereas for strongly reducing gases the signal correlates more closelywith the reductant-to-oxidant ratio.