Development of novel catalytic materials based on fine structure analysis of novel multi-dimensional, large-pore zeolite

高硅mse型分子筛YNU-2具有由12×10×10-membered环（MR）组成的三维微孔结构。以N，N，N‘，N’-四乙基双环[2.2.2]辛-7-烯-2,3:5,6-二吡咯烷鎓离子（TEBOP^<2+>）为有机结构导向剂（SDA），采用干凝胶转化法合成了它。前驱体YNU-2（即YNU-2P）在骨架中包含大量的Si原子缺陷（超过单位胞中所有Si原子的10%）。SDA分子位于12-MR直通道和超级笼中。虽然MSE拓扑由8个不同的t位点组成，但通过结构分析确定了框架中4个可能的位点缺陷（T1, T3， T6和T7位置）。由于明显的位置缺陷，YNU-2P结构在煅烧时容易坍塌。我们通过在酸性条件下使用四甲基氧基硅烷（TMOS）气相硅化来克服这一问题。后来发现，只有蒸汽处理，不加酸，也有助于稳定框架。一些研究结果表明，蒸汽处理导致硅原子在缺陷硅烷醇和硅原子碎片之间的迁移和缩聚。研究了蒸汽处理对YNU-2P骨架稳定性的影响。采用粉末XRD、固体NMR、TG-DTA、氮气吸附实验等研究了相应的结构变化。结果表明，在不添加硅源的情况下，250℃24h的蒸汽处理可以部分修复微孔YNU-2P的缺陷。这可能为理解高硅沸石的结构稳定性提供新的见解。

High-silica MSE-type zeolite YNU-2 has a three-dimensional micropore structure composed of 12×10×10-membered ring (MR). It has been synthesized by dry-gel conversion, using N,N,N',N'-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium cation (TEBOP^<2+>) as an organic structure-directing agent (SDA). The precursor YNU-2 (i.e. YNU-2P) includes a large number of Si atom defects (over 10% of all the Si atoms in a unit cell) in the framework. SDA molecules are located in a 12-MR straight channel and the supercage. Although the MSE topology consists of eight distinct T-sites, four probable site defects (T1, T3, T6, and T7 positions) in the framework were identified by structure analysis. Due to the significant site defects, the YNU-2P structure readily collapse upon calcination. We overcame this problem by vapor-phase silylation using tetramethoxysilane (TMOS) under acidic conditions. Afterwards, it was found that only the steam treatment without acid also helped stabilize the framework. Several findings suggest that the steam treatment causes Si-atom migration and condensation between silanols of site defects and Si atom fragments. We investigated the effect of steam treatment on the framework stability of YNU-2P. The corresponding structural changes were also investigated using powder XRD, solid-state NMR, TG-DTA, and nitrogen gas adsorption experiments. As a result, it was con- firmed that the site defects in microporous YNU-2P were partially restored by steam treatment at 250℃ for 24 h without any additional Si source. This may afford new insights into the understanding of structural stability of high-silica zeolites.