Abstract
We present a review on catalytic or electrical properties of materials based on rare earth (RE) oxides (CeO2 ,L a2O3, Lu2O3) or bismuth based composite systems CeO2-Bi2O3, susceptible to be integrated into catalytic microsystems or gas sensors. The polycrystalline solids can be used as catalysts allowing conversion of CO or CH4 traces in air-gas flows. Fourier Transform infrared spectroscopy is used to determine the conversion rate of CO or CH4 into CO2 through the variations versus time and temperature of vibrational band intensities. The time dependent reactivities are interpreted in terms of an adapted Avrami model. In these catalytic analyses the nature of surfaces of polycrystalline solids seems to play a prominent role in catalytic efficiency. Electrical impedance spectroscopy allows analyzing the variation of conductivity of the system CeO2-Bi2O3. In this system, the specific high ionic conduction of a Bi2O3 tetragonal phase might be linked to the high catalytic activity.
Highlights
In the case of rare earth (RE) oxide [1, 2] and CeO2-Bi2O3 materials [3, 4], infrared spectroscopy as a function of time (t) and temperature (T) has been used to determine the catalytic oxidation rates of CH4 or CO into CO2
We present a review on catalytic or electrical properties of materials based on rare earth (RE) oxides (CeO2, La2O3, Lu2O3) or bismuth based composite systems CeO2-Bi2O3, susceptible to be integrated into catalytic microsystems or gas sensors
In these catalytic analyses the nature of surfaces of polycrystalline solids seems to play a prominent role in catalytic efficiency
Summary
In the case of RE oxide [1, 2] and CeO2-Bi2O3 materials [3, 4], infrared spectroscopy as a function of time (t) and temperature (T) has been used to determine the catalytic oxidation rates of CH4 or CO into CO2. In the case of bismuth based system [(1 − x)CeO2 − (x/2)Bi2O3] with 0 < x < 1, electrical impedance spectroscopy (EIS) has been used to determine the conductivities as a function of bismuth fraction (x) and temperature (T). We try to give a general interpretation of the origin of abnormal catalytic effects in the case of methane or carbon monoxide oxidation in air, as these gases are in contact with the above RE or Bi based solids at high temperature. High temperature ionic conduction coupled to complex surface modifications of these solids might be at the origin of strongly different catalytic effects
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