Temperature Dependent Electrical Properties and Catalytic Activities ofLa2O3–CO2–H2OPhase System

Bahcine Bakiz,Abdeljalil Benlhachemi,Sylvie Villain,Madjid Arab,Frédéric Guinneton,Jean Raymond Gavarri

doi:10.1155/2009/612130

Abstract

We present a study of electrical properties and catalytic activities of materials belonging to the hydrated carbonated systemLa2O3–CO2–H2O. The polycrystalline hydroxycarbonate, dioxycarbonate, and oxide are prepared via a coprecipitation route followed by heat treatment. The electrical conduction of the phases obtained by thermal decomposition fromLaOHCO3,H2Ois analyzed by electrical impedance spectroscopy, from25°Cto950°C, under air. The catalytic properties ofLaOHCO3,La2O2CO3andLa2O3polycrystalline phases are studied by FTIR spectroscopy, in presence of gas mixtures CO-air andCH4-air, at temperatures ranging between100°Cto525°C. The three materials behave differently in presence of CO orCH4gases.

Highlights

The general aim of this study is to test the reactivity of materials sensitive to environmental water and CO2, and interacting with toxic gases (CO, CH4)
The electrical conduction of the phases obtained by thermal decomposition from LaOHCO3, H2O is analyzed by electrical impedance spectroscopy, from 25◦C to 950◦C, under air
The catalytic properties of LaOHCO3, La2O2CO3 and La2O3 polycrystalline phases are studied by FTIR spectroscopy, in presence of gas mixtures CO-air and CH4-air, at temperatures ranging between 100◦C to 525◦C

Summary

Introduction

The general aim of this study is to test the reactivity of materials sensitive to environmental water and CO2, and interacting with toxic gases (CO, CH4). We deal with the system La2O3–CO2–H2O that presents hydrated and carbonated phases, stable at various temperatures [1,2,3,4,5,6]; the hydroxycarbonate phase LaOHCO3 stable up to 380◦C [7]; the dioxycarbonate phase La2O2CO2 stable up to 700◦C, and the La2O3 phase stable above this temperature, under air atmosphere. Each phase can be sensitive to partial pressure of H2O or CO2. These phases can be used as sensing materials reacting with wet air and CO2. We try to determine the evolution of electrical conduction of these phases with increasing temperature; in a second step, we compare the temperature and time dependent catalytic efficiencies of LaOHCO3, La2O2CO3, and La2O3, to convert CH4 and CO present in air-CH4 and air-CO flows.

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Conclusion