Yu Lili, Huang Shengjun, Miao Shu, Chen Fucun, Zhang Shuang, Liu Zhenni, Xie Sujuan, Xu Longya
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road No. 457, Dalian 116023 (P. R. China); University of Chinese Academy of Sciences, Beijing 100049 (P. R. China).
Chemistry. 2015 Jan 12;21(3):1048-54. doi: 10.1002/chem.201404817. Epub 2014 Nov 14.
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.
高铝含量是分级沸石合成后改性的主要障碍。本文提出了一种包括氟化和顺序碱处理的简便方法，用于富铝MFI分级沸石的合成后改性。通过该方法，在富铝MFI沸石（硅铝比=14.3）中引入了均匀的晶内介孔。所得分级沸石表现出以6 nm为中心的明显介孔尺寸分布，并且在大分子芳烃的催化裂化中显示出提高的转化率。氟化-碱处理方法的基本意义与在前述氟化步骤中形成含氟四面体铝物种有关，这减轻了铝位点对碱性介质的抗性，并在碱处理过程中导致铝-氟络合以调节铝物种的水解。这种自上而下的方法和由此得出的机理理解有望应用于具有其他骨架拓扑结构的富铝分级沸石的合成。
