Sensing properties to nitrogen oxides of CeO{sub}2-In{sub}2O{sub}3 composite sensor

摘要

NO{sub}x sensing properties of In{sub}2O{sub}3 semiconductor sensors modified with CeO{sub}2 have been investigated with respect to the exhaust monitoring. The addition of CeO{sub}2 enhanced the NO sensitivity when CeO{sub}2 was added with In{sub}2O{sub}3 at 5-35 wt%. The highest sensitivity of 10 (=Ra/Rg) to 50 ppm NO was obtained for the CeO{sub}2 (20 wt%) In{sub}2O{sub}3 sensor at 300℃. On the other hand, the sensor responded complicatedly to NO{sub}2. The electrical resistance decreased upon exposure to NO{sub}2, then steeply increased and reached the slightly higher value than the initial resistance, suggesting the low sensitivity to NO{sub}2. Thus, the CeO{sub}2- In{sub}2O{sub}3 sensor was found to exhibit high NO sensitivity as well as high selectivity at 300℃. The electrical resistance decreased upon exposure to NO in the presence of O{sub}2 (2-20%), while the resistance increased in the absence of O{sub}2. This suggests that NO behaves as a reducing gas in O{sub}2-containing atmosphere, i.e., reacts with adsorbed oxygen to be oxidized into NO{sub}2. It is assumed that CeO{sub}2 enhances the catalytic oxidation of NO on In{sub}2O{sub}3 surface.