Tailoring the hierarchical architecture of beta zeolites using base leaching and pore-directing agents
Tailoring the hierarchical architecture of beta zeolites using base leaching and pore-directing agents
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DOI：
10.1016/j.micromeso.2017.12.023
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发表时间：
2018-06-01
影响因子：
5.2
通讯作者：
Zhang, Ke
中科院分区：
文献类型：
--
作者：
Fernandez, Sergio;Ostraat, Michele L.;Zhang, Ke
采用自上而下的碱浸法，以不同的阳离子四烷基铵盐（TAA）和有机胺为孔导向剂（PDA），系统地研究了不同Al含量（Si/Al：14-250）的β沸石中分级结构的调整，考察了它们在保护β沸石骨架的同时引导介孔形成的有效性。PDA结构和平均介孔尺寸之间的结构-性能关系建立在所得分级沸石中，特别是对于高Si β沸石，当PDA的存在是必要的，以避免在NaOH脱硅过程中的骨架非晶化。研究的所有PDA都有效地指导碱性溶液中的中孔形成，而没有经历母体β沸石的微孔性和结晶度的显着降低。对于高Si β沸石，具有非离子胺的分级结构具有比用TAA阳离子PDA（d（alpha）：2-6 nm）处理的那些更大的中孔（平均中孔尺寸，d（alpha）：5-8 nm），这应该是由于与有机胺相比，TAA型阳离子PDA在β骨架的内部通道内的更好的适应性以及母体骨架的更有利的相互作用和保护。对于类似结构的TAA阳离子，所得的中孔尺寸和表面积与不同阳离子的分子量相关，即较高分子量的阳离子导致较小的da和相应较大的表面积。因此，通过自上而下的碱浸并适当选择用于β沸石的PDA来定制中孔尺寸是可行的。与母体β催化剂相比，在β沸石中成功引入中孔还导致酸催化的α-蒎烯异构化的催化转化率显著提高。
The tailoring of hierarchical structures in beta zeolites of differing Al contents (Si/Al: 14-250) has been systematically investigated through a top-down base leaching process with various cationic tetraalkylammonium (TAA) salts and organic amines as pore-directing agents (PDAs) to examine their effectiveness in protecting beta zeolite framework while directing the formation of mesopores. The structure-property relationship was established between PDA structure and average mesopore sizes in resulting hierarchical zeolites, especially for high Si beta zeolites when the presence of PDA is necessary to avoid framework amorphization during NaOH desilication. All PDAs studied are effective in directing the mesopore formation in alkaline solutions without experiencing significant decrease in microporosity and crystallinity of parent beta zeolites. For high Si beta zeolites, hierarchical structures with non-ionic amines possess larger mesopores (average mesopore sizes, d(alpha): 5-8 nm) than those treated with TAA cationic PDAs (d(alpha): 2-6 nm), which should be due to better accommodation of TAA-type cationic PDAs within the inner channel of beta framework and more favorable interaction and protection of parent framework as compared to organic amines. For similarly structured TAA cations, the resulting mesopore sizes and surface areas are correlated with the molecular weights of different cations, i.e. higher molecular weight cations result in smaller da and correspondingly larger surface areas. Therefore, it is feasible to tailor the mesopore sizes by a top-down base leaching with an appropriate selection of PDAs for beta zeolites. The successful introduction of mesopores in beta zeolites also led to significantly improved catalytic conversion for the acid-catalyzed alpha-pinene isomerization, as compared to the parent beta catalysts.