Utilizing full-exchange capacity of zeolites by alkaline leaching: Preparation of Fe-ZSM5 and application in N2O decomposition
Utilizing full-exchange capacity of zeolites by alkaline leaching: Preparation of Fe-ZSM5 and application in N2O decomposition
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DOI：
10.1016/j.jcat.2005.11.034
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发表时间：
2006-03
影响因子：
7.3
通讯作者：
Melian-Cabrera;Silvia Espinosa;B. V. D. Linden;F. Kapteijn;J. Moulijn;I. Melián-Cabrera;D. Linden-
中科院分区：
文献类型：
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作者：
Melian-Cabrera;Silvia Espinosa;B. V. D. Linden;F. Kapteijn;J. Moulijn;I. Melián-Cabrera;D. Linden-
在温和的碱浸处理中，通过缩短扩散长度，实现了沸石的充分交换能力的利用。铁在ZSM5上通过液相离子交换完全结合，没有生成铁氧化物，从而提高了N2O分解反应的活性。结果表明，分子筛的大尺寸对FeIII-交换过程起主导作用。通过碱浸对工业样品进行后合成改性，可以降低ZSM5沸石的结晶度。在所研究的条件下，观察到两个现象：(I)在保持微孔率的同时，沸石团聚的尺寸显著减小；(Ii)随着处理时间的延长，形成了一个额外的中孔网络。介孔具有较宽的孔径分布和随机排列的介孔结构。在这两种情况下，MFI晶格都得到了很好的保存。根据表征数据和活性结果，得出沸石晶体的解聚有利于充分交换的结论。在更恶劣的条件下新形成的中孔并不是改善交换的原因。在较短的浸出时间内，FeIII达到了全交换负载(而非活性FeOx几乎可以忽略不计)，导致N2O分解活性显著提高。中孔的形成不会进一步改善N2O的分解性能。从活度的增加可以看出，部分额外的铁变得活泼起来，并且随着交换度的增加而增加。
Utilization of the full exchange capacity of zeolites has been achieved by shortening diffusional lengths on a mild alkaline leaching treatment. Iron was fully incorporated by liquid-phase ion exchange on ZSM5 without the formation of Fe-oxides, leading to improved activity in the N2O-decomposition reaction. It is demonstrated that the large crystal size of the zeolite dominates the FeIII-exchange process. The crystallinity of the ZSM5 zeolite can be tuned down by postsynthesis modification of commercial samples by caustic leaching. Under the study conditions, two phenomena were observed: (i) The size of the zeolite agglomerates is significantly reduced while the microporosity is preserved, and (ii) at prolonged treatment, an additional mesopore network is created. The mesopores display a wide pore size distribution with randomly organized mesopores. The MFI lattice is well preserved in both cases. Based on the characterisation data and activity results, it is concluded that deagglomeration of the zeolite crystals enables full exchange. The newly created mesopores at harsher conditions are not responsible for the improved exchange. At short leaching times, full-exchange loading of FeIIIis achieved (and negligible inactive FeOx), leading to a considerable enhancement of the activity for N2O decomposition. Mesopore formation does not further improve the performance of N2O decomposition. From the activity increase, it is concluded that a “fraction” of the extra Fe becomes active, which increases with the exchange degree.