Interplay between active sites of modified nanocrystalline tin dioxide and selectivity to CO and NH3 gases

A specific effect of surface modifiers on the active sites of sol-gel synthesized nanocrystalline tin dioxide improving its selectivity to CO and NH₃ gases was demonstrated. Introducing PdO_x clusters led to the increase of OH-groups concentration, while that of RuO_y - to accumulation of active oxygen species on the SnO₂ surface. This interplay contributes to increased low-temperature CO-sensitivity of SnO₂/PdO_x and to high NH₃-sensitivity of SnO₂/RuO_y at raised temperature. Cross-sensitivity tests to CO+NH₃ mixtures in air revealed the possibility to discriminate the reductive gases by modified SnO₂-based sensors operated at appropriate temperature. The impact of different active sites to the selectivity improvement was estimated. In situ DRIFT studies indicated a key role of catalytic clusters in promoting selective SnO₂/PdO_x-CO and SnO₂/RuO_y-NH₃ interactions. Possible sensor signal formation processes were suggested regarding the modifiers catalytic action and their distinctive influence on tin dioxide active sites.