Add time:08/05/2019         Source:sciencedirect.com

This work is aimed at elaborating a route for co-modification of acidic and catalytic sites on the surface of nanocrystalline tin oxide with the aim to enhance the sensitivity to ammonia gas. Sulfated tin oxide with controlled amount 0–10 wt.% of SO42− as the acidic modifier was synthesized by wet chemical deposition. It was modified by the catalytic additive of ruthenium oxide (0–5 wt.% Ru). Surface acidity was evaluated by temperature-programmed desorption and in situ infrared spectroscopy of adsorbed ammonia. The concentration of Lewis and Broensted acid sites was strongly dependent on sulfate content. Increasing amount of ruthenium oxide depressed surface acidity of catalytically-modified materials. Sensor response to 2–100 ppm NH3 in air was measured depending on the materials composition. At Ru-loading lower 0.5 wt.% the sensor signal was detected at temperature 200–300 °C and its value was monotonously dependent on SO42− content. The highest ammonia sensitivity was detected at lower temperature of 140–150 °C for co-functionalized tin oxide with comparable contents of Ru and SO42− (1–3 wt.%). From the sensing tests and in situ infrared spectroscopy data it was deduced that the improved sensing of ammonia gas was provided by equivalent impacts from the processes of target molecules adsorption on sulfate-promoted acid sites and NH3 oxidation on the catalytic clusters of ruthenium oxide.

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