Study On Ag-Cu Based Catalysts For Selective Catalytic Oxidation Of Ammonia

Ammonia?NH₃?is a well-known atmospheric pollutant that has not only a serious danger to health and life but also result in serious environmental problems.The selective catalytic oxidation of NH₃?NH₃-SCO?into N₂ and H₂O is an ideal technology of ammonia remove from the economic and/or technical considerations.Up to now,sliver or copper based catalysts have been widely investigated in NH₃-SCO.Copper based catalysts possess relatively high N₂ selectivity,however,the disadvantages is low activity at temperatures below 350°C.Sliver based catalysts tend to have high activity below 350°C,while their low selectivity to N₂?NO/N₂O formation?has restrained their extensive application.Ag-Cu alloy structures have attracted great interest due to their unique catalytic properties.Furthermore,Ag-Cu alloy structures can effectively maintain the metallic state of Ag and Cu as well as structure stability,which might exhibit the high activity and thermal stability in NH₃ oxidation.Thus in this paper,Ag-Cu alloy bimetallic nanoparticles?NPs?as potential catalysts for NH₃-SCO was studied.Many characterizations are used to get deep insight into physical and chemical properties of catalysts,and this paper investigated the performance of different catalysts in NH₃-SCO reaction.The Ag-Cu alloy nanoparticle catalysts were successfully synthesized by a solventless mix–bake–wash approach,and investigate its NH₃-SCO reaction performance.The results showed that the Ag₂Cu₁ catalyst exhibited the best catalytic performance?NH₃ was completely oxidized at 200°C?and had the lowest apparent activation energy(Ea=53.5 kJ?mol^-1)and more excellent stability.The results of XRD?TEM?XPS and NH₃-TPD showed that the molar ratio of Ag to Cu was an important factor for the alloy structure and nanoparticle size.The Ag₂Cu₁ catalyst exhibited the smallest particle diameter and the perfect spherical alloy structure.the alloyed structure could effectively maintain the stability of Ag⁰?Cu⁰ metallic states,provided more surface chemisorbed oxygen?O??and was more conducive to NH₃ adsorption at lower temperatures.The kinetic test indicated that the difference of O₂reaction order is bigger than that of NH₃,indicated that the adsorption and activation of O₂ plays an important role in NH₃-SCO reaction.The results of DFT showed that the apply of alloyed structure significantly increases the adsorption amount and strength of NH₃ and O₂ on the catalyst surface.O₂ is more easily activated from the adsorption state to the transition state.This causes NH₃ to be more easily oxidized,increasing the reaction rate.The Ag₂Cu₁/H-ZSM-5 monolithic powder catalyst was prepared and applied to the low temperature NH₃-SCO reaction,which investigated the promotion of H-ZSM-5 zeolite.The results showed that the Ag₂Cu₁/H-ZSM-5exhibited the best low-temperature ammonia oxidation performance,and the values of T₅₀ and T₉₀ are reduced to 221 and 247°C,respectively.The results of XRD,BET,SEM,TEM,XPS and NH₃-TPD showed that MFI structure and Ag-Cu alloy structure remained intact.Ag-Cu alloy nanoparticles were highly dispersed on the surface of H-ZSM-5.The small Ag-Cu alloy nanoparticles?2¹4 nm?had strong interaction with the surface of H-ZSM-5,which promotes more active oxygen on the surface of the catalyst,enhances the adsorption of ammonia on its surface,and thus increases the reaction rate of NH₃-SCO.