A facile top-down protocol for postsynthesis modification of hierarchical aluminum-rich MFI zeolites.
A facile top-down protocol for postsynthesis modification of hierarchical aluminum-rich MFI zeolites.
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DOI：
10.1002/chem.201404817
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发表时间：
2015-01
期刊：
影响因子：
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通讯作者：
Li-li Yu;Shengjun Huang;S. Miao;Fucun Chen;Shuang Zhang;Zhenni Liu;Sujuan Xie;Longya Xu
中科院分区：
文献类型：
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作者：
Li-li Yu;Shengjun Huang;S. Miao;Fucun Chen;Shuang Zhang;Zhenni Liu;Sujuan Xie;Longya Xu
高铝含量是分级沸石合成后改性的主要障碍。提出了一种简单的方案，包括氟化和顺序碱处理，用于分级富铝 MFI 沸石的合成后改性。凭借该方案，在富铝 MFI 沸石 (Si/Al = 14.3) 中引入了均匀的晶内介孔性。所获得的分级沸石表现出显着的介孔尺寸分布，以 6 nm 为中心，并且在大体积芳族分子的催化裂化中表现出改进的转化率。氟化-碱处理方案的根本含义与先前氟化步骤中含氟四面体铝物质的形成有关，这减轻了铝位点对碱性介质的抵抗力，并导致铝-氟络合，从而在碱处理过程中调节铝物质的水解。这种自上而下的协议和衍生的机理理解预计将应用于具有其他框架拓扑的分层富铝沸石的合成。
High aluminum content constitutes a major hurdle for the postsynthesis modification of hierarchical zeolites. A facile protocol comprising fluorination and sequential alkaline treatment is presented for the postsynthesis modification of hierarchical Al-rich MFI zeolites. By virtue of this protocol, uniform intracrystalline mesoporosity is introduced in an Al-rich MFI zeolite (Si/Al = 14.3). The obtained hierarchical zeolites exhibit a significant mesopore size distribution, centered around 6 nm, and show improved conversions in catalytic cracking of bulky aromatic molecules. The fundamental implications of the fluorination-alkaline treatment protocol are related to the formation of F-bearing tetrahedral aluminum species in the antecedent fluorination step, which alleviates the resistance of Al sites to the alkaline medium and causes Al-F complexation for regulated hydrolysis of the Al species during the alkaline treatment process. This top-down protocol and the derived mechanistic understandings are expected to be applied in the synthesis of hierarchical Al-rich zeolites with other framework topologies.