Efficient NH₃ Detection Based on MOS Sensors Coupled with Catalytic Conversion

A solution of NH₃ detection based on catalytic conversion of NH₃ into NO was proposed by using MOS gas detectors and Pt-supported catalysts. The catalysts convert NH₃ into NO, 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.