核壳结构Fe-ZSM-5的制备及脱硝性能研究

发布时间：2018-04-10 17:12

本文选题：NH_3-SCR + Fe-ZSM-5　；参考：《南京理工大学》2015年硕士论文

【摘要】：本文通过水热法一步合成了粒径约200 nm的Fe-ZSM-5,并通过不同的方法在其外表包覆了硅壳并考查核壳分子筛在NH3-SCR中的不同性能。首先,利用TPAOH作为模板剂,通过二次水热晶化在Fe-ZSM-5表面包覆一层较薄的silicalite-1壳层,并在在该过程中调节TEOS的用量以控制壳层的厚度。二次晶化过程中,随着模板剂TPAOH用量的增加,Fe-ZSM-5溶解的程度也逐渐增加,而另一方面,TPAOH的使用也能明显提高silicalite-1壳层的结晶度。溶解到晶化液中的Fe3+参与了壳层的构建,在后续的煅烧过程中,Fe3+进一步聚合形成低聚Fe或者簇。由于silicalite-1几乎不具有酸性,因此壳层的包覆使得核壳分子筛Fe-ZSM-5@silicalite-1的酸性较Fe-ZSM-5有一定的降低,而分散在壳层中的Fe物种明显增强了核壳样品的NO吸附能力。比较Fe-ZSM-5@silicalite-1与Fe-ZSM-5的活性以及抗水性可以发现壳层的包覆可以提高样品的活性,同时也能提高样品的疏水性。同样利用Fe-ZSM-5作为核相分子筛,通过醇／水体系中的自组装在其表面包覆了一层介孔硅壳,再向其中负载Ce,并且研究了不同壳层厚度和不同Ce负载量对于活性的影响。在自组装过程中,壳层的厚度主要取决于正硅酸乙酯的用量,但是过量的正硅酸乙酯会使得壳层孔道的规整性出现明显的下降甚至形成独立的介孔硅球。Ce主要以四配位的形式存在于介孔壳层的孔道中,并且具有较高的分散度,在Fe-ZSM-5的孔道中几乎不存在Ce的氧化物,由于干燥过程中壳层孔道中溶液的浓缩使得Ce更多地存在于壳层的内部。相比于Fe-ZSM-5,核壳分子筛对于NO以及O2均具有更好的吸附能力,在SCR过程中,一部分通过壳层的NO与O2发生反应生成NO2,这部分NO2与剩余的NO以快速SCR机理在Fe-ZSM-5核上反应。由于快速SCR的反应速率比标准SCR高,因此Fe-ZSM-5@Ce-mesosilica的活性相对于Fe-ZSM-5有了明显的提升。但是由于转化为NO2的NO不到50%,因此在反应过程中快速SCR过程与标准SCR过程是共存的。同时,核壳分子筛具有较好的抗水抗硫性能,在撤去H2O和SO2后,样品的活性均能够得到很好的恢复。
[Abstract]:Fe-ZSM-5 with a diameter of about 200nm was synthesized by hydrothermal method. The silicon shell was coated on the surface of Fe-ZSM-5 by different methods and the different properties of core-shell molecular sieve in NH3-SCR were examined.Firstly, TPAOH was used as template, and a thin layer of silicalite-1 shell was coated on the surface of Fe-ZSM-5 by secondary hydrothermal crystallization, and the thickness of the shell was controlled by adjusting the amount of TEOS in the process.In the process of secondary crystallization, the dissolution degree of Fe-ZSM-5 increases with the increase of the amount of TPAOH, and on the other hand, the crystallinity of silicalite-1 shell can be improved by the use of TPAOH.The Fe3 dissolved in the crystallization solution was involved in the construction of the shell, and Fe _ 3 was further polymerized to form oligomeric Fe or clusters during the subsequent calcination process.Because silicalite-1 has almost no acid, the Fe-ZSM-5@silicalite-1 acidity of core-shell molecular sieve is lower than that of Fe-ZSM-5, and Fe species dispersed in the shell obviously enhance the no adsorption ability of core-shell samples.Comparing the activity and water resistance of Fe-ZSM-5@silicalite-1 and Fe-ZSM-5, it is found that the coating of the shell can improve the activity of the sample and the hydrophobicity of the sample.Using Fe-ZSM-5 as a nuclear molecular sieve, a mesoporous silicon shell was coated on its surface by self-assembly in alcohol / water system and then loaded with Ce. the effects of different shell thickness and ce loading on the activity were studied.In the process of self-assembly, the thickness of shell depends mainly on the amount of ethyl orthosilicate.However, excessive amount of ethyl orthosilicate can decrease the regularity of the shell pore and even form an independent mesoporous silica ball. Ce mainly exists in the pore channel of the mesoporous shell in the form of four coordination positions, and has a high dispersion.There is almost no ce oxide in the pore of Fe-ZSM-5. The concentration of solution in the pore channel of the shell during drying makes the ce exist more in the interior of the shell.Because the reaction rate of fast SCR is higher than that of standard SCR, the activity of Fe-ZSM-5@Ce-mesosilica is obviously higher than that of Fe-ZSM-5.However, since the amount of no converted to NO2 is less than 50%, the rapid SCR process and the standard SCR process coexist in the reaction process.At the same time, the core-shell molecular sieve has good water resistance and sulfur resistance. After removing H _ 2O and SO2, the activity of the samples can be recovered very well.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ426;X701

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