Methanol gas-sensing properties of CeO2-Fe2O3 thin films

Ce-doped iron oxide thin films have been prepared by a liquid-phase method (LPD) and tested as methanol gas sensors. Sensing tests have shown that the addition of Ce to Fe2O3 increases the response to methanol at low temperature (< 350 degrees C). The optimum loading of Ce was 50% in moles. At operating temperatures > 400 degrees C, the response of CeO2-doped Fe2O3 sensors is instead lower than that of pure Fe2O3. To find properties-sensitivity relationships, the microstructure, acid-base properties and reactivity of CeO2-Fe2O3 powders were investigated by X-ray diffraction (XRD), temperature-programmed desorption of adsorbed CO2 (TPD-CO2) and gas-phase oxidation of methanol. Ce-doped iron oxides powders have shown the formation of a FexCe1-xO2 solid solution, smaller grain size and an increase of the number of basic sites compared to pure Fe2O3. Moreover, the addition of Ce to Fe2O3 was found to promote the adsorption of methanol and its subsequent oxidation to CO2. Correlation between the amount of basic sites, oxidation activity and the response to methanol were reported. According to the obtained results, the role played by Cc on modifying the methanol-sensing properties of iron oxide thin films was related to its capability to: (a) form a solid solution and reduce the grain size; (b) enhance the number of basic sites and methanol adsorption; (c) promote the methanol oxidation activity of the sensing layer. This latter was found to be the factor limiting the sensors response at higher temperatures. (c) 2005 Published by Elsevier B.V.