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首页> 外文会议>International Zeolite Conference pt.C; 20040425-30; Cape Town(ZA) >ELUCIDATING THE DEALUMINATION MECHANISM OF ZEOLITE H-Y BY SOLID-STATE NMR SPECTROSCOPY
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ELUCIDATING THE DEALUMINATION MECHANISM OF ZEOLITE H-Y BY SOLID-STATE NMR SPECTROSCOPY

机译：固态NMR光谱法测定H-Y分子筛的脱铝机理

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摘要

Hydrothermally treated zeolites H-Y were investigated by XRD, ~(29)Si MAS NMR, ~(27)Al MQMAS NMR, high-field ~(27)Al MAS NMR, and ~1H MAS NMR spectroscopy. Upon adsorption of ammonia on the hydrothermally treated materials, a reversible change of octahedrally coordinated to tetrahedrally coordinated aluminum atoms was found. Quantitative ~(29)Si, ~(27)Al, and ~1H MAS NMR measurements indicated that this coordination change is accompanied by the formation of bridging OH groups (SiOHAl) in the dehydrated materials, while only a weak decrease in the amount of silanol (SiOH) groups and no systematic change of AlOH groups occurred. Based on these results, a model for the reversible coordination change of aluminum atoms in the framework of hydrothermally treated zeolites H-Y is proposed assuming local structures consisting of threefold-coordinated framework aluminum atoms with SiO~- defect sites in their vicinity, which are coordinated to extra-framework aluminum species. After adsorption of ammonia at the threefold-coordinated framework aluminum atoms, the SiO~- defect sites are healed to Si-O-Al~- bridges leading to a transformation of the threefold-coordinated aluminum atoms to tetrahedrally coordinated atoms. Upon thermal decomposition of the ammonium ions formed at these Si-O-Al~- bridges, SiOHAl groups occur.
机译：通过XRD，〜（29）Si MAS NMR，〜（27）Al MQMAS NMR，高场〜（27）Al MAS NMR和〜1H MAS NMR研究了水热处理过的沸石H-Y。将氨吸附到水热处理的材料上后，发现八面体配位至四面体配位的铝原子可逆变化。 〜（29）Si，〜（27）Al和〜1H MAS NMR定量测量表明，这种配位变化伴随着脱水材料中桥连OH基团（SiOHAl）的形成，而仅少量地降低了硅烷醇（SiOH）基团和AlOH基团未发生系统变化。基于这些结果，提出了在水热处理沸石HY骨架中铝原子可逆配位变化的模型，假设局部结构由三配位骨架铝原子组成，且它们附近有SiO〜-缺陷位点，且与额外的铝框架。氨在三重配位的铝原子上吸附后，SiO--缺陷位点被修复成Si-O-Al--桥，导致三重配位的铝原子转变为四面体配位的原子。在这些Si-O-Al--桥上形成的铵离子热分解后，会出现SiOHAl基。

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