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The Investigation Of N2O Direct Decomposition Over ZSM-5 Zeolite

Posted on:2009-02-25Degree:MasterType:Thesis
Country:ChinaCandidate:H X KangFull Text:PDF
GTID:2121360245974565Subject:Chemical processes
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Based on the catalytic material of ZSM-5 zeolite,a series of zeolite catalyst for N2O direct decomposition were prepared by liquid ion-exchanged.The activity of zeolites was evaluated.The effect of the Si/Al molar ratio,modified metal ions species and technological conditions on the catalytic performance of modified zeolites were systemally investigated by some methods such as performance evaluation, NH3-TPD and FT-IR.Besides,the mechanism of NO assists the decomposition of N2O on Fe-ZSM-5 was researched.The experimental results for the effect of zeolite type and modified metal species on N2O direct decomposition showed that(1)the zeolite activity enhanced with the increasing of iron loading,but decreased with the increasing of Si/Al molar ratio.(2)The catalytic activity of Fe-ZSM-5 was better than that of Fe-MCM-22.(3)the activity of Cu-ZSM-5 was lower than Fe-ZSM-5 under the same operating temperature.(4)The activity of double metal modified zeolites was investigated also.there was no obvious effect on the Fe-ZSM-5 with the addition of Ce.However,the addition of La and Pd had an obvious effect on Fe-ZSM-5 catalytic performance.The results of NH3-TPD and FT-IR indicated that the iron ions located at the Br(?)nsted acid sites were the active component in the direct decomposition of N2O.The Fe ions mainly exchanged H protons that were in the center of Br(?)nsted acid,and formed the charge-balancing Fe-cation adsorbing on the surface of the zeolite.Based on the Fe-ZSM-5 zeolite,the experiments of the effect of impurity(such as NO,O2 and H2O)on the zeolite catalyst performance were carried out by the method of single factors.The results showed: (1)micro-content NO would obviously increase the catalytic activity of Fe-ZSM-5.(2)micro-content oxygen did not influence on the catalytic performance of Fe-ZSM-5.(3)Microcontent stream would result in the quick deactivation of zeolites.The reason might be that the steam of water occupied the active sites on the surface of zeolites.But,under the condition of He or N2O atmosphere,the activity of zeolites could be regenerated thorough.The adsorption behaviors of NO and N2O and the NO assisted mechanism to N2O decomposition over Fe-ZSM-5 zeolite were studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS),respectively.The results showed that(1)NO and N2O were both adsorbed on the Br(?)nsted acid sites and charge-balancing Fe-cation sites of the Fe-ZSM-5 zeolite.(2)NO and O2 could react to form N2O4, NO2,NO3- or NO2- over FeZSM-5 zeolite.(3)The existence of NO might both accelerate N2O decomposition and enhance Fe-ZSM-5 catalytic activity because it may consume the O produced by N2O decomposition.
Keywords/Search Tags:ZSM-5, N2O, catalytic decomposition, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)
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