Multinuclear Solid-State NMR Studies on the Formation Mechanism of Aluminophosphate Molecular Sieves in Ionic Liquids

详细信息    查看全文

• 作者：Renshun Xu ; Weiping Zhang ; Jun Xu ; Zhijian Tian ; Feng Deng ; Xiuwen Han ; Xinhe Bao
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：March 21, 2013
• 年：2013
• 卷：117
• 期：11
• 页码：5848-5854
• 全文大小：512K
• 年卷期：v.117,no.11(March 21, 2013)
• ISSN：1932-7455

文摘

In the present work, multinuclear solid-state NMR techniques together with power X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to monitor the crystallization process of aluminophosphate AlPO₄-11 molecular sieves in 1-ethyl-3-methylimidazolium bromide ([emim]Br) ionic liquids (ILs). The local environments of the selected solid samples were probed by one-dimensional ²⁷Al, ³¹P, and ¹⁹F MAS NMR experiments, and more information was obtained from two-dimensional ²⁷Al鈫?sup>31P heteronuclear correlation (HETCOR) and ²⁷Al triple-quantum MAS (3Q MAS) experiments. It is found that a large amount of amorphous aluminophosphates was formed with the F鈥揂l_oct鈥揙鈥揚_par and Al_tet鈥揙鈥揚_par structures in the initial stage of aging. With increasing crystallization time, the partially condensed framework phosphorus species disappeared gradually and became fully condensed. Meanwhile, the octahedral Al was transformed into the pentahedral and tetrahedral Al species with the structures of F鈥揂l_penta鈥揙鈥揚_ful and Al_tet鈥揙鈥揚_ful in the AlPO₄-11 frameworks. During the crystallization process, [emim] cations acting as the structure-directing agents were occluded into the channels, and F^{鈥?/sup> anions were connected with pentahedral Al in the final AlPO4鈥?1 phase. All of these findings can allow proposing a possible formation mechanism for the synthesis of AlPO₄-11 in ionic liquids.}