Synthesis of Pure Silica MWW Zeolite in Fluoride Medium by Using an Imidazolium‐Based Long Dication,Chemistry - A European Journal

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Synthesis of Pure Silica MWW Zeolite in Fluoride Medium by Using an Imidazolium‐Based Long Dication
Chemistry - A European Journal ( IF 3.9 ) Pub Date : 2018-12-27 , DOI: 10.1002/chem.201804973
Peng Lu _{1,

2} , Luis Gómez-Hortigüela ₃ , Miguel A. Camblor ₁

Affiliation

As the spacer length in 1,2‐dimethylimidazolium‐based dications increases beyond a specific point (six methylene units), they fail in structure‐directing towards STW zeolites in any synthetic conditions. These dications can instead produce, under fluoride concentrated conditions, either *BEA [in the case of the eight‐methylene‐unit structure‐directing agent (SDA)] or MWW (ten methylene units) zeolites. For any length of the dication, the default zeolite (MTW) is a relatively dense zeolite containing a unidimensional channel, whereas the zeolite demanding most specificity (STW, *BEA or MWW) is more porous, affording a larger concentration of the dication to be occluded. This work provides the first reported fluoride synthesis of pure silica MWW zeolites. Charge balance of the organic dications in this zeolite was achieved by combining “structural” silanolates, regular “connectivity defects” and occluded fluoride. Molecular mechanics calculations showed a perfect fit of the decamethylenebis(dimethylimidazolium) dication in the sinusoidal intralayer pore system of MWW. The calculations showed also that the dication is able to stabilize the interlayer space without disturbing the hydrogen‐bonding system that holds the layers together in the as‐made material. The ¹⁹F magic‐angle spinning (MAS) NMR presented two distinct resonances at −71 and −83 ppm, which, on the basis of DFT calculations, we tentatively assigned to fluoride occluded in [4⁶6²] and [4¹5²6²] cages of the MWW structure, respectively. The same DFT study determines a different chemical shift of one methyl ¹³C nuclear magnetic resonance according to the imidazolium ring residing in the sinusoidal channels or in the large cup cavities, thus explaining an experimentally observed splitting of that resonance.

中文翻译：

咪唑基长阳离子在氟介质中合成纯净的二氧化硅MWW沸石

当基于1,2-二甲基咪唑鎓的指示剂中的间隔基长度增加超过一个特定点（六个亚甲基单元）时，在任何合成条件下，它们都无法在结构上指向STW沸石。这些指示剂可以在氟化物浓缩条件下产生* BEA [对于八亚甲基单元结构导向剂（SDA）]或MWW（十个亚甲基单元）沸石。对于任何长度的指示剂，默认的沸石（MTW）是包含一维通道的相对致密的沸石，而对特异性要求最高的沸石（STW，* BEA或MWW）则更多孔，从而提供更大浓度的指示剂。被遮挡。这项工作提供了首次报道的纯二氧化硅MWW沸石的氟化物合成。该沸石中有机指示剂的电荷平衡是通过结合“结构性”硅烷醇盐，规则的“连接性缺陷”和封闭的氟化物来实现的。分子力学计算表明十甲基双（二甲基咪唑鎓）指示剂非常适合MWW的正弦层内孔系统。计算结果还表明，该指示剂能够稳定层间空间，而不会干扰将氢键结合在一起的氢键系统，该氢键键合系统将各层保持在制成的材料中。这计算结果还表明，该指示剂能够稳定层间空间，而不会干扰将氢键结合在一起的氢键系统，该氢键键合系统将各层保持在制成的材料中。这计算结果还表明，该指示剂能够稳定层间空间，而不会干扰将氢键结合在一起的氢键系统，该氢键键合系统将各层保持在制成的材料中。这¹⁹ F魔角旋转（MAS）NMR在-71和-83 ppm处表现出两个不同的共振，根据DFT计算，我们暂时将其归因于[4 ⁶ 6 ² ]和[4 ¹ 5 ² MWW结构分别为6 ² ]的笼子。相同的DFT研究根据正弦通道或大杯腔中的咪唑环确定了一个甲基¹³ C核磁共振的不同化学位移，从而解释了实验观察到的该共振的分裂。

更新日期：2018-12-27

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