Abstract The silanol defects in ZSM-5 zeolite have been recognized as an important factor in catalytic activity. Here, ZSM-5 zeolites with different amounts of silanol defect sites were synthesized from synthetic gels containing fluoride medium and were applied as catalysts for trioxane synthesis. The results of XRD, SEM, NH 3 -TPD, Py-IR, OH-IR, 27 Al MAS NMR, 1 H MAS NMR, and TG indicated that all ZSM-5 zeolites showed similar crystal size, relative crystallinity, porosity, and the number of Brønsted acid sites. However, the silanol defects reduced obviously and the number of Lewis acid sites reduced correspondingly when a little NH 4 F was added in the synthesis gels and both of them decreased slightly with increase of F/Si ratio. Compared with ZSM-5 zeolite prepared in hydroxide medium, ZSM-5 zeolite prepared in fluoride medium displayed higher selectivity to trioxane and increased gradually with increase of F/Si ratio. Moreover, the lifetime of ZSM-5 zeolite prepared in fluoride medium was longer than that of prepared in hydroxide medium. Thus, ZSM-5 zeolite prepared in fluoride medium which contained the few silanol defects and low Lewis acid sites is an efficient catalyst for trioxane synthesis. Graphic Abstract

中文翻译：

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ZSM-5沸石硅烷醇缺陷对甲醛合成三恶烷的影响

摘要 ZSM-5 沸石中的硅烷醇缺陷被认为是影响催化活性的重要因素。在这里，具有不同数量硅烷醇缺陷位点的 ZSM-5 沸石由含有氟化物介质的合成凝胶合成，并用作三恶烷合成的催化剂。XRD、SEM、NH 3 -TPD、Py-IR、OH-IR、 27 Al MAS NMR、 1 H MAS NMR 和 TG 的结果表明，所有 ZSM-5 沸石显示出相似的晶体尺寸、相对结晶度、孔隙率和Brønsted 酸位点的数量。然而，当合成凝胶中加入少量NH 4 F时，硅烷醇缺陷明显减少，路易斯酸位点数量相应减少，两者均随着F/Si比的增加而略有减少。与氢氧化物介质中制备的 ZSM-5 沸石相比，在氟化物介质中制备的 ZSM-5 沸石对三恶烷显示出较高的选择性，并且随着 F/Si 比的增加而逐渐增加。此外，在氟化物介质中制备的 ZSM-5 沸石的寿命比在氢氧化物介质中制备的长。因此，在含有少量硅烷醇缺陷和低路易斯酸位点的氟化物介质中制备的 ZSM-5 沸石是合成三恶烷的有效催化剂。图形摘要