| The combustion of fossil fuels to meet the society requirements of energy discharges large quantities of pollutants to the environment. Among these contaminants are the nitrogen oxides (NO_x) that are the source of severe environmental problems such as acid rain and smog formations. Great efforts have been made in research direct to find solutions for the NO_x removal. In the present study, to improve the catalysts'low temperature activities for NH3-SCR of NO_x, an Al-rich Beta zeolites synthesized from organotemplate-free route (provided by BASF) were employed to support Fe to build a series of Fe-Beta-9 catalysts. As compared with commercial Beta-19 zeolite supported Fe catalysts, Fe-Beta-9 catalysts exhibited much high low temperature activities, better hydrothermal stability and SO2 resistance. The main results obtained in the dissertation have been summarized as follows:(1) A series of Fe-Beta-9 catalysts with various Fe content had been prepared under anhydrous conditions, and were investigated for NH3-SCR of NO_x reaction. The effect of CO2, H2O and SO2 on Fe-Beta-9 catalyst during the SCR reaction was also investigated. For comparison, a commercial Beta zeolite with Si/Al ratio of 19 which had been synthesized by organo template method was employed as another carrier, and then the Beta-19 zeolite was modified by introducing iron in the same procedure for the same reaction. Meanwhile, combined with multiple characteristic techniques, i.e. XRD, EPR, UV-vis, Mossbaure, NMR, et al., we attempt to establish a correlation between catalysts'structure and catalytic performance. The results obtained clearly exhibit that the Fe-Beta-9 catalysts have better NH3-SCR activities at low temperature region and more durable SO2 resistance than the Fe-Beta-19 catalysts. In the feed gas consisting of 500 ppm NO,500 ppm NH3,10% O2, balance N2, GHSV=80000 h-1, NO conversion over Fe(2.1)-Beta-9 catalyst at 125 ? was 33% and that was 60%at 150 ?, and exceeded 90% at 200?-500?, which may be one of the most efficient Fe-zeolites for NH3-SCR of NO_x There are isolated Fe species, clustered Fe species and bulked Fe species in Fe-Beta catalysts, and Fe species will aggregate when Fe content increase in Beta zeolite. At a similar Fe loading, the amount of isolated Fe3+species in the zeolites was always higher over Fe-Beta-9 catalysts than over Fe-Beta-19 catalysts, which should be related to the higher amount of ion-exchange sites provided by Al-rich Beta zeolites. Correlating quantities of isolated Fe3+ species in Beta zeolites with NO conversion rate at 150 ?, there is a linear relationship suggesting that the isolated Fe3+ species affect the SCR activity directly. The sulfate deposited either on the Fe-Beta-9 or on the Fe-Beta-19 catalysts surface might not be the primary cause of the catalyst's deactivation during NH3-SCR reaction in the presence of SO2.(2) The hydrothermal stability of the Fe-Beta-9 and Fe-Beta-19 catalysts was also investigated. The Fe(2.1)-Beta-9 and Fe(2.3)-Beta-19 catalysts had been treated under 10% H2O/Ar at 750 ? and 850 ?, respectively. The aged Fe(2.1)-Beta-9 and the aged Fe(2.3)-Beta-19 catalysts were also investigated under the same NH3-SCR reactions and were characterized by multiple techniques. The results suggest that the Fe(2.1)-Beta-9 catalyst shows a better hydrothermal stability than the Fe(2.3)-Beta-19 catalyst. Hydrothermal treating at 750 ? has a less influence on catalytic properties of the Fe-Beta catalysts but hydrothermal treating at 850 ? has a severe effect on their activities. Upon hydrothermal treating at 850?, there is always more severe dealumination occurred, which is accompanied by the aggregating of Fe species. The decrease of isolated Fe3+species in the Fe-Beta catalysts leads to the decreased activity for SCR reaction. Hydrothermal treating Fe(2.1)-Beta-9 catalysts at 750 ? may be beneficial to its SO2 resistance.(3) By acid leaching of the parent Beta-9 zeolites, Beta zeolites with Si/Al ratio of 22 and 36 were obtained, and Fe(2.3)-Beta-22 and Fe(2.3)-Beta-36 catalysts had been prepared in the same procedure to the Fe(2.1)-Beta-9 catalyst, and they were also investigated under the same NH3-SCR reactions and they were characterized by multiple techniques. The results indicate that the NH3-SCR activities of the Fe(2.3)-Beta-22 and Fe(2.3)-Beta-36 catalysts decrease at low temperature region and at high temperature region and their SO2 resistance slightly reduce with respect to that of the Fe(2.1)-Beta-9 catalyst. It is found that the amount of isolated Fe species of the Fe(2.3)-Beta-22 and Fe(2.3)-Beta-36 catalysts decrease and the amount of aggregated Fe species increase with respect to the Fe(2.1)-Beta-9 catalyst, because the parent Beta-22 and Beta-36 catalysts have less ion-exchange site as compared to Beta-9 zeolites. The Fe(2.3)-Beta-22 and Fe(2.3)-Beta-36 catalysts had also been hydrothermal treated under 10%H2O/Ar at 750 ? and 850 ?, respectively, and the aged Fe(2.3)-Beta-22 and the aged Fe(2.3)-Beta-36 catalysts were also investigated under the same NH3-SCR reactions. The results suggest that the Fe(2.3)-Beta-22 and Fe(2.3)-Beta-36 catalysts exhibit a poorer hydrothermal stability than the Fe(2.3)-Beta-9 catalyst. Hydrothermal treatments at 850 ? lead to much more severe dealumination of Fe-Beta-22 and Fe-Beta-36 catalysts, and there is obvious loss of activity for NH3-SCR of NO_x. |
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