Catalytic Performance Study Of Selective Catalytic Oxidation Of Ammonia Over Ferric-based Catalysts

Ammonia is widely used in preparing the ammonium hydroxide,soda,ammonium salt,nitric acid and so on.In addition,ammonia,as an effective reducer of de-NO_x technology,is well accepted in vehicle exhaust after-treatment system.Especially in recent years,the production and utilization of NH₃ increased rapidly with the enhancement of the industrial development,people's living standards and the motor vehicle industry,while a more serious environmental problem arises at the same time.The increasing amount of NH₃ leaks is a serious threat to the ecological environment and human health.NH₃ emission control issues are on the agenda.NH₃selective catalytic oxidation technology,as a kind of high efficiency,eco-friendly,and promising NH₃ treatment technology,is widely used in industrial and motor vehicle exhaust treatment system.The research point of this article is preparing the catalysts possessed the high catalytic performance,which used for the selective catalytic oxidation of ammonia to nitrogen and water,realizing effective removal of NH₃.This paper prepared the CuO-Fe₂O₃,RuO₂-Fe₂O₃ and RuO₂-WO₃-Fe₂O₃ catalysts with high catalytic performance by adopting the sol-gel method.Moreover,we systematically investigate the influences of elements ratio,reaction temperature and active component of catalyst on the catalytic activity of ammonia selective catalytic oxidation.At the same time,the relationship between the microstructure properties and catalytic activity of the catalyst is studied by means of BET,XRD,H₂-TPR,XPS,Raman,SEM and DRIFTS,and the main results were as follows:?1?Cu/Fe molar ratio of CuO-Fe₂O₃ composite oxides significantly influences the catalytic activity.The results of catalytic activity demonstrate that higher Cu/Fe ratio in CuO-Fe₂O₃ catalysts led to higher activity for NH₃ oxidation and the lower Cu/Fe ratio improved the N₂ selectivity.The optimal catalyst with a Cu/Fe molar ratio of 5:5 displayed a low complete conversion temperature?<250°C?with a relatively high N₂ selectivity?>91%?.H₂-TPR results indicated that the synergistic effect existed between Fe₂O₃ and CuO,which was beneficial to the catalytic performance.The results of the DRIFTS showed that NH₃-SCO reaction mainly followed the internal SCR?i-SCR?mechanism.The adsorbed NH₃ was first activated and reacted with atomic oxygen to form the nitrosyl?-HNO?.Then the-HNO was oxidized by oxygen atoms from O₂ to form NO species.Meanwhile,the in situ-formed NO could react with-NH₂ to form the main product of N₂.?2?The promoting effects of WO₃ on Ru O₂-Fe₂O₃ catalyst were systematically investigated for the selective catalytic oxidation of ammonia to nitrogen.It was found that the introduction of 5 wt.%WO₃ led to a dramatic promoting effect on the high-temperature N₂ selectivity of Ru O₂-Fe₂O₃ catalyst,giving 100%NH₃ conversion at 250°C and 94%N₂ selectivity at a high temperature of 400°C.In depth analysis using XRD,Raman and H₂-TPR revealed that the addition of WO₃ into the Ru O₂-Fe₂O₃ catalyst could strongly inhibit the crystallanity of Fe₂O₃ and decrease the reducibility of Ru O₂-Fe₂O₃catalyst,which were related to the strong interaction between WO ₃ and Fe₂O₃.Moreover,in situ DRIFTS studies illustrated that the introduction of WO ₃ not only promoted the formation of more acid sites on the catalyst surface but also restrained the formation of nitrate species at high temperature,with few NO _x formed,which contributed to the high N₂ selectivity.