Simulation Of Ammonia Oxidation Mechanism Of Zeolites With Different Topologies Based On Dft Method

Because of the growing voice for high quality life,environmental protection issues have become an important issue concerning people's livelihood.Air pollution is the top priority of environmental protection issues.Ammonia is one of the most important atmospheric pollutants.So far,a variety of ammonia gases Treatment methods have been proposed.Among them,the advantages of chemical treatment of ammonia gas are obvious,especially the selective catalytic oxidation of ammonia gas,which has the advantages of short time and high efficiency,and is considered to be ideal.The ion-exchange of zeolites has good efficiency on the selective catalytic oxidation of NH3,but there are few reports on the mechanism of NH3-SCO with different topologies.In this work,the catalytic oxidation of ammonia over three topological zeolites(MFI,BEA,MOR)were studied and the mechanisms were investigated by density functional theory(DFT).The results of a comparative study on the mechanism of three zeolites show that MFI(Cu-ZSM-5)exhibits the higher NH3 conversion under the same copper exchange rate.The DFT simulations suggest that the mechanism consists of three major parts:(1)adsorption of gaseous ammonia molecules,followed by interaction with reactive oxygen atoms to form OHNH2;(2)Then involving an E-R reaction pathway in which a gas phase NH3 molecule reacts with OHNH2 and active oxygen atoms to produce stable N2H4 species;(3)The N2H4 species and the active oxygen atoms continue to act,gradually dehydrogenate,and finally generate nitrogen and water.The energy required for the formation of OHNH2 species is the highest one,which is the rate-determining step of the reaction.In the rate-determining step,the activation energy required for MFI(Cu-ZSM-5)is the smallest among the three zeolites,while MOR(Cu-Mordenite)is the largest.The lower the activation energy is,the higher the catalytic efficiency becomes.