Role of additives in tin oxide-based sensors for alcohols

Using gas chromatographic analyses, the effects of additives (PdCl2, Al2O3, or La2O3) on the alcohol sensing properties of SnO2-based sensors were investigated with respect to the distribution and the reaction steps of the products formed from the reactions of alcohols over the SnO2-based powder. Ethanol was catalytically oxidized with the SnO2-based powders. With the PdCl2-doped SnO2, the C-C bond cleavage product, methane, was produced. This seems to be related with the significant promotional role of PdCl2-doping in ethanol sensing especially at temperatures below 300degreesC. For the La2O3-doped SnO2, relatively large amounts of CO and CO2 were produced, resulting in an enhanced sensitivity. On the other hand, for the Al2O3-doped SnO2, selective dehydration, which consumes smaller amounts of the adsorbed oxygen species (O-ads(-)), seems to degrade the sensitivity. When exposed to methanol, the SnO2-based sensors showed oxidation products consisting of CO, CO2 and H2O and sensing characteristics similar to those observed with ethanol.