Efficient NH3 Detection Based on MOS Sensors Coupled with Catalytic Conversion

A solution of NH3 detection based on catalytic conversion of NH3 into NOx was proposed by using MOS gas detectors and Pt-supported catalysts. The catalysts convert NH3 into NOx, which is a very sensitive analyte for MOS detectors. Catalysts based on Pt-loaded HZSM-5 and Al2O3 were prepared by wet impregnation. MOS detectors were fabricated from nanosized In2O3 and WO3 using screen-printing techniques. As expected, MOS sensors based on In2O3 and WO3 have an extremely high sensitivity to NO2; nevertheless, they have a relatively low response to NH3 and a large cross-sensitivity to typical interfering gases such as CO and ethanol. By the present solution, MOS sensors could very sensitively respond to NH3, even down to 0.25 ppm. In addition, it was also found that the catalysis also combusts the reducing gases into CO2 and water and consequently significantly improves the selectivity of NH3. Lastly, we would to like to stress that the proposed concept of the catalytic conversion method suggests the potential utility for broader measurements by using different catalysts and gas detectors and that only a part of the usage for NH3 was presented here.