Controllable Synthesis and Structure-Performance Relationship of Silicalite-1 Nanosheets in Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime
Controllable Synthesis and Structure-Performance Relationship of Silicalite-1 Nanosheets in Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime
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DOI：
10.1007/s10562-020-03404-8
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发表时间：
2020-10
影响因子：
2.8
通讯作者：
Chao Ge;Xiaojuan Sun;D. Lian;Zhikai Li-;Jianbing Wu
中科院分区：
文献类型：
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作者：
Chao Ge;Xiaojuan Sun;D. Lian;Zhikai Li-;Jianbing Wu
大分子硅分子筛-1对环己酮肟气相Beckmann重排反应具有很高的催化活性。然而，它往往失活迅速，结构与性能的关系不清楚。本文以双季铵盐[CnH 2n +1-N+（CH 3）2-C6 H12-N+（CH 3）2-C6 H13]（Br−）2（n = 6-18）为结构导向剂，可控合成了一系列从三维微米颗粒（n < 10）到二维纳米片（10 ≤ n ≤ 18）的结晶良好的silicalite-1催化剂。采用XRD、SEM、TEM、原位真空IR、29 Si MAS NMR和N2吸附/脱附等温线等手段研究了催化剂的形貌对活性中心分布的影响以及孔限制效应对己内酰胺选择性和催化剂稳定性的影响。具有相对高结晶度的silicalite-1纳米片表现出几乎100%的优异的上级催化活性和显著高的己内酰胺选择性（92%）。与体积较大的silicalite-1沸石相比，silicalite-1纳米片的催化寿命可以增加28倍。随着表面活性剂尾长从C6增加到C18，催化剂的比表面积和中孔体积显著增加，活性中心增加，抗积炭能力增强。结果表明，催化剂的寿命与硅醇巢面积和介孔体积的乘积（Asilanol·nest*Vmeso）几乎呈线性关系，相关系数为0.97，这有力地支持了纳米片的优异性能是由于其高活性位和高抗积炭能力的协同作用。图形摘要通过调节双季铵盐的烷基尾长，可控合成Silicalite-1纳米片，使其具有较大的介孔体积和比表面积，有效提高了催化剂的高抗积炭能力和活性中心，具有较长的催化寿命和较高的选择性.
AbstractBulky silicalite-1 shows high catalytic activity for vapor phase Beckmann rearrangement of cyclohexanone oxime. However, it often deactivates rapidly and the structure-performance relationship is unclear. Here, a series of well-crystallized silicalite-1 catalysts from three-dimensional micron particles (n < 10) to two-dimensional nanosheets (10 ≤ n ≤ 18) were controllably synthesized using diquaternary ammoniums [CnH2n+1-N+(CH3)2-C6H12-N+(CH3)2-C6H13](Br−)2(n = 6–18) as the structure directing agent. The influence of morphology of catalysts on active sites distribution and the pore confinement effect on caprolactam selectivity and the catalytic stability were studied by XRD, SEM, TEM, In situ vacuum IR,29Si MAS NMR and N2adsorption/desorption isotherms. The silicalite-1 nanosheets with relatively high crystallinity exhibited superior catalytic activity to almost 100% and remarkably high caprolactam selectivity (92%). The catalytic lifetime of silicalite-1 nanosheets could be increased by 28 times in comparison to bulky silicalite-1 zeolite. The external surface area and mesopore volume of the synthesized catalyst dramatically increase with increasing the tail length of surfactant from C6to C18, leading to high active sites and coke tolerance capacity. It was found the lifetime of the catalysts is almost linearly related to the product of area of silanol nest and volume of mesopore (Asilanol·nest*Vmeso) with correlation coefficient of 0.97, which strongly supports the excellent performance of nanosheets results from the synergetic effect of its high active sites and high coke tolerance capacity. This provides a theoretic guide for designing new catalysts with high catalytic activity.Graphical AbstractSilicalite-1 nanosheets were controllable synthesized through adjusting alkyl tail length of diquaternary ammoniums, resulting in large mesoporous volume and external surface area, which effectively improve high coke tolerance capacity and active sites of catalysts and exhibit much longer catalytic lifetime and high selectivity.