Highly mesoporous SAPO-11 molecular sieves with tunable acidity: facile synthesis, formation mechanism and catalytic performance in hydroisomerization of n-dodecane
Highly mesoporous SAPO-11 molecular sieves with tunable acidity: facile synthesis, formation mechanism and catalytic performance in hydroisomerization of n-dodecane
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酸度可调的高介孔SAPO-11分子筛：正十二烷加氢异构化的简易合成、形成机制和催化性能
DOI：
10.1039/c7cy01819c
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发表时间：
2017-12-07
影响因子：
5
通讯作者：
Tian, Zhijian
中科院分区：
文献类型：
--
作者：
Tao, Shuo;Li, Xiaolei;Tian, Zhijian
沸石材料的孔结构和酸性对催化反应的活性和选择性起着至关重要的作用。本文采用干凝胶转化（DGC）法制备了具有均匀晶间介孔（约4.3 nm）和可调酸度的SAPO-11分子筛微球。采用XRD、SEM、TEM、N2吸附-脱附、NH3-TPD、吡啶吸附IR （Py-IR）、TG、29Si MAS NMR等多种技术对产物进行了表征。结果表明，通过简单地调整合成中所用的水的含量，可以在很宽的范围内精确地调节产物的酸度。这种分级SAPO-11的生长经历了介孔的重排：在结晶初期，前驱体的原始介孔（约17 nm）被塌陷，产物的最终介孔由有机硅烷引导。更重要的是，Pt/分级SAPO-11催化剂在正十二烷的加氢异构化过程中表现出更强的异构化选择性，这要归功于分级孔网络带来的优异扩散特性。这项工作证明了一种简单的方法来合成具有可调酸度的分级沸石，这有利于涉及大分子的催化反应。
The pore architecture and acidity of zeolite materials play crucial roles in the activity and selectivity of catalytic reactions. Herein, hierarchical SAPO-11 molecular sieve microspheres with uniform intercrystalline mesoporosity (ca. 4.3 nm) and tunable acidity were synthesized via dry-gel conversion (DGC) of a silicoaluminophosphate–organosilane composite. The products were comprehensively characterized using multiple techniques, including XRD, SEM, TEM, N2 adsorption–desorption, NH3-TPD, pyridine-adsorbed IR (Py-IR), TG and 29Si MAS NMR measurements. It is revealed that the products' acidity can be precisely tuned in a wide range by simply adjusting the water content used in the synthesis. The growth of such hierarchical SAPO-11 underwent a rearrangement of the mesopores: the original mesopores (ca. 17 nm) of the precursor were collapsed at the initial stage of crystallization and the final mesopores of the products were directed by the organosilane. More importantly, the Pt/hierarchical SAPO-11 catalysts exhibited enhanced isomerization selectivity in the hydroisomerization of n-dodecane, attributed to their excellent diffusion properties resulting from the hierarchical pore network. This work demonstrates a facile approach to synthesize hierarchical zeolites with tunable acidity, which is beneficial for catalytic reactions involving bulky molecules.