Computational Study of Brønsted Acidity of Faujasite. Effect of the Al Content on the Infrared OH Stretching Frequencies
Computational Study of Brønsted Acidity of Faujasite. Effect of the Al Content on the Infrared OH Stretching Frequencies
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DOI：
10.1021/jp807623m
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发表时间：
2008-11
影响因子：
3.7
通讯作者：
Germán Sastre;N. Katada;Katsuki Suzuki;M. Niwa
中科院分区：
文献类型：
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作者：
Germán Sastre;N. Katada;Katsuki Suzuki;M. Niwa
在本研究中，我们使用了商业八面沸石样品(Si/Al∼2.5)的实验数据，并对组成为Si3 4Al14 O96H14(Si/Al=2.4)的八面沸石晶胞的红外OH伸缩能带与周期密度泛函计算进行了比较。在不填充04H的情况下，01H、02H和03H的计算结果分别为3588-3689、3555-3588和3517-3560 cm-1，分别与实验值3648、3571和3526 cm-1符合较好。我们研究了两个相邻Al中心(Si46Al2O96H2，Si/Al=23)对孤立情况(S147Al1O96H1，Si/Al=47)的OxH频率(x=1-4)的影响。实验红外谱带不能用高SiO_2模型(Si/Al=47，23)解释，只有考虑到(I)实验Al含量，(Ii)实验的OH布居和(Iii)实验的Si(NaL)(n=0-4)布居，才能解释实验的红外谱带。
In this study we use the experimental data from a commercial sample of faujasite (Si/Al ∼ 2.5) and we compare the infrared OH stretching bands with periodic density functional calculations of a faujasite unit cell of composition Si 34 Al 14 O 96 H 14 (Si/Al = 2.4). Assuming that 04H is not populated, the computational results show the following bands for O1H, 02H, and 03H: 3588-3689, 3555-3588, and 3517-3560 cm -1 , respectively, which are in good agreement with the experimental values of 3648, 3571, and 3526 cm -1 , respectively. We have studied how the OxH frequencies (x = 1-4) change due to the presence of two neighbor Al centers (Si 46 Al 2 O 96 H 2 , Si/Al = 23), with respect to the isolated case (S1 47 Al 1 O 96 H 1 , Si/Al = 47). The experimental infrared bands cannot be explained by the high silica models (Si/Al = 47, 23) and can only be explained when taking into account (i) the experimental Al content, by using a Si 34 Ali 4 O 96 H 14 model, (ii) the experimental OH population, and (iii) the experimental Si(nAl) (n = 0-4) population.