SrSnO 3–WO 3 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 BaSnO 3 or SrSnO 3 mixed with WO 3 exhibits high sensitivity at temperature higher than 773 K. In particular, mixed oxide capacitor of SrSnO 3–WO 3 exhibited high sensitivity to NO and stable response at high temperatures. Furthermore, the capacitance of SrSnO 3–WO 3 is less sensitive to CO 2, H 2O, and CO compared to NO. Addition of small amount of Pt was effective for improving the response characteristics. Consequently, mixed oxide of SrSnO 3–WO 3 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 SrSnO 3 was undissociative and two adsorption species exist. In contrast, NO adsorption on WO 3 is dissociative. Addition of Pt was effective for decreasing the desorption temperature of oxygen from WO 3 which was formed by the dissociative adsorption of NO.