Characterization of extraframework aluminum in H-mordenite dealuminated with ammonium hexafluorosilicate
Characterization of extraframework aluminum in H-mordenite dealuminated with ammonium hexafluorosilicate
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DOI：
10.1016/j.cattod.2004.01.007
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发表时间：
2004-10
期刊：
影响因子：
5.3
通讯作者：
H. Kao;Yun-Chu Chen;Chun-Chiang Ting;Po Tuan Chen;Jyh‐Chiang Jiang
中科院分区：
文献类型：
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作者：
H. Kao;Yun-Chu Chen;Chun-Chiang Ting;Po Tuan Chen;Jyh‐Chiang Jiang
在用六氟硅酸铵脱铝的H-丝光沸石中骨架外Al（EFA 1）物种的状态和性质（即，（NH_4）_2SiF_6，AHFS）。从AHFS脱铝的实验条件，即，在存在和不存在的乙酸铵（NH 4 OAc），观察到相当大的差异。这两种处理方法在去除骨架铝方面都不是很有效。27 Al和19 F固态NMR被用来检测AHFS脱铝产生的不同骨架外铝氟络合物。在NH 4 OAc存在下，AHFS进行的脱铝过程的关键部分是大部分提取的Al 3+与F-反应形成（NH 4）3AlF 6。另一方面，在不存在NH 4 OAc的情况下，在脱铝之后形成除（NH 4）3AlF 6之外的至少两种不同形式的铝氟络合物。这些铝氟配合物在19 F NMR谱中显示出位于−144至− 156 ppm范围内的多条谱线。在6-31+G ~+基组水平上，采用Hartree-Fock和Hybrid Hartree-Fock密度泛函方法，用从头算方法计算了19 F NMR位移，并对铝氟配合物进行了分析。我们的结果表明，核磁共振和从头计算的结合为利用它们研究未知组成和结构的EFAl物种提供了基础。
The status and nature of extraframework Al (EFAl) species in H-mordenite dealuminated by ammonium hexafluorosilicate (i.e., (NH4)2SiF6, AHFS) was investigated. Considerable difference arising from the experimental conditions of AHFS dealumination, that is, in the presence and absence of ammonium acetate (NH4OAc), was observed. Both treatments were not very effective in removing framework aluminum.27Al and19F solid-state NMR was used to detect different extraframework aluminum fluoro-complexes resulting from the AHFS dealumination. In the presence of NH4OAc, the essential part of the dealumination process carried on with AHFS was that most of the extracted Al3+reacted with F−to form (NH4)3AlF6. In the absence of NH4OAc, on the other hand, at least two different forms of aluminum fluoro-complexes other than (NH4)3AlF6were formed after dealumination. These aluminum fluoro-complexes showed multiple lines located in the range of −144 to −156ppm in the19F NMR spectrum. An ab initio method that used both Hartree-Fock and hybrid Hartree-Fock density functional methods at the 6-31+G∗basis set level was used to calculate the19F NMR shifts for discriminating possible aluminum fluoro-complexes. Our results indicated that a combination of NMR and ab initio calculations provided a basis for using them to study EFAl species of unknown compositions and structures.