SrSnO3–WO3 as capacitive-type nitrogen oxide sensor for monitoring at high temperature

Abstract Capacitive-type NO sensor, which is operable at high temperature, was investigated in this study for monitoring NO in flue gases from a gasoline engine. Oxide capacitor consisting of BaSnO3 or SrSnO3 mixed with WO3 exhibits high sensitivity at temperature higher than 773 K. In particular, mixed oxide capacitor of SrSnO3–WO3 exhibited high sensitivity to NO and stable response at high temperatures. Furthermore, the capacitance of SrSnO3–WO3 is less sensitive to CO2, H2O, and CO compared to NO. Addition of small amount of Pt was effective for improving the response characteristics. Consequently, mixed oxide of SrSnO3–WO3 is as promising as the capacitive-type NO sensor operable at high temperatures. The NO adsorption state was further investigated with TPD measurement. It became clear that NO adsorbed on SrSnO3 was undissociative and two adsorption species exist. In contrast, NO adsorption on WO3 is dissociative. Addition of Pt was effective for decreasing the desorption temperature of oxygen from WO3 which was formed by the dissociative adsorption of NO.