Catalytic impact of RuOx clusters to high NH3 sensitivity of tin dioxide

A comparative study of NH3-sensing properties of blank and modified nanocrystalline SnO2 was performed. Tin dioxide modified by ruthenium displayed outstanding ammonia sensitivity with a maximum signal at 200 0C. The modifier was shown by XPS to possess mixed valence states of oxidized ruthenium. The RuOx-modified material was shown by EPR to contain up to 14 at. % of Ru3+ distributed between the surface and the bulk of SnO2 crystallites. From EPR study of SnO2/RuOx interaction with NH3/air mixture Ru3+ to Ru4+ oxidation was deduced. This could be due to oxidative products of NH3 conversion, that was supported by the oxidative-like gas response during sensing tests using the NH3/air gas flow passed through a preconcentrator with RuOx-modified tin dioxide heated to 200 °C.