Selective detection of NH3 over NO in combustion exhausts by using Au and MoO3 doubly promoted WO3 element

Developing a semiconductor sensor to detect residual NH3 in combustion exhausts after NOx removal processes was attempted. It was found that, although the elements using WO3 were sensitive to both NH3 and NO, the NO sensitivity could be eliminated selectively by the addition of MoO3 to the elements. The best NH3-sensing performance was obtained with a doubly promoted element, Au (0.8 wt.%)–MoO3 (5 wt.%)–WO3 which could respond to NH3 (1–50 ppm) sensitively and selectively regardless of the presence of high concentration of NO in the temperature of 400–500°C. The role of MoO3 was assumed to poison the catalytic sites of WO3 to convert NO to NO2.