WO₃ enhanced surface acidity of RuO₂/ZrO₂ and its performance in selective catalytic oxidation of NH₃

In this paper, RuO₂/ZrO₂ catalyst and WO₃ doped RuO₂/WO₃-ZrO₂ catalysts with different WO₃ loadings were designed and prepared for selective catalytic oxidation of ammonia. Among the catalysts, RuO₂/ZrO₂ catalyst exhibits excellent catalytic activity but poor N₂ selectivity. It is worth noting that the activity of RuO₂/ZrO₂ catalyst remains unchanged after 5% or 10% WO₃ doping, while the N₂ selectivity at high temperature is significantly improved, and NH₃ is completely transformed at 225 ℃. However, when WO₃ content rises to 15% and 20%, the catalytic activity of RuO₂/ZrO₂ catalyst decreases slightly, while N₂ selectivity is not further improved at high temperature. Therefore, it can be judged that the optimal WO₃ content is 10%. In addition, it is found that WO₃ doping can change the microstructure of the catalyst and the corresponding specific surface area increases with the increase of WO₃ content through BET analysis. XRD, H₂-TPR and XPS show that WO₃ doping can change the crystal structure of ZrO₂, increase the stability of the catalyst. According to the DRIFT spectra results, as WO₃ is doped into the catalyst, the amount of surface acid sites on the catalyst increase. More surface acid sites can facilitate the adsorption of ammonia species, inhibit the rapid reaction between ammonia and oxygen, and avoid formation of more by-products, which are the key factors to improve the N₂ selectivity.