Gas-sensing properties of Pd/SnO2 sensors dipped in a diethoxydimethylsilane sol solution

Dipping a sintered Pd/SnO2 sensor in a diethoxydimethylsilane sol solution, followed by calcination at 600 degrees C, resulted in a considerable enhancement of gas sensitivity to H-2 but a marked decrease to CH4 and C3H8. In good accordance with the variations in the gas-sensing properties, catalytic activity of the sensor material markedly decreased for CH4 and C3H8 oxidation but increased for H-2 oxidation. TEM observation and EDX analysis revealed that the fine SnO2 particles were coated with thin SiO2 layers 2-3 nm in thickness after dipping. Temperature programmed desorption chromatograms (TPD) of O-2 and H2O were markedly influenced by the formation of thin SiO2 layers; that is, the amount of active O- or O2- species on SnO2 became considerably small, and the adsorbed species of H2O changed from surface hydroxyl groups to molecular species hydrogen-bonded on the surface oxygen ions. The mechansim of the H-2 gas sensitivity enhancement was discussed from the viewpoint of the modifications in TPD characteristics.