Catalytic Decomposition Of Nitrous Oxide Over Supported Ru And Rh Catalysts

In this paper,N₂O decomposition is studied over Ru and Rh catalysts using a fixed bed reaction system.Different metal promoters and support materials are used to accommodate N₂O decomposition catalytic activity;the effects of Ru dispersion and support surface acidity are further investigated.Influence of MO_x on Ru dispersion and N₂O decomposition activitySBA-15 and alumina supported Ru and Rh catalysts are modified with Zr by impregnation method and then evaluated in N₂O decomposition.Based on characterization results,introducing of Zr improves the dispersion status of Ru and Rh catalysts,as well as N₂O decomposition activity.Excessive Zr loading leads to limited activity as decreasing surface area and pore size.On alumina support,Zr inhibits the activity of Ru and Rh catalysts due to decreased dispersion status of Ru and Rh on alumina.Differences in dispersion status result in variation of catalytic activity.On SBA-15,catalytic activities of Ru and Rh catalysts are significantly promoted by Zr modification,the temperature required for 50%N₂O conversion are 592 K and 640 K respectively,at least 50 K lower than the one before Zr modification.However, alumina slightly modified by Zr leads to decreased N₂O decomposition activity,the more Zr loading the less catalytic activity;this is mainly attributed to agglomeration of active species.Zn and Ce with proper concentrations are also proved beneficial to N₂O decomposition activity over SBA-15 supported Ru catalysts.The improvement of the catalytic performance was supposed to connect with higher Ru dispersion.However, excessive promoter will block the tunnel and go against with the N₂O decomposition ability. Impact of surface acidity on N₂O decomposition activity over Ru based catalystsBased on Ru/SBA-15 catalyst,series of Ru catalysts modified by Al and K are prepared and evaluated in N₂O decomposition.Al modification shows great effect on promoting surface acidity and N₂O decomposition activity,N₂O conversion is promoted from 6%to 86%at 623 K,while doping potassium on catalyst neutralizes the acidity,and leads to decreased catalytic performance.N₂O decomposition activity drops drastically to the level before Al modification with slightly K loading.HZSM-5,NaZSM-5 and alumina are selected as support material for further investigation on the effect of surface acidity.Among ZSM-5 and alumina supported Ru catalysts,influence of surface acidity on N₂O decomposition activity is also observed.It is proposed that acidic site activates N-O bond hence accelerates N₂O decomposition rate.