A density functional theory based approach to extraframework aluminum species in zeolites
A density functional theory based approach to extraframework aluminum species in zeolites
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DOI：
10.1021/jp022331z
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发表时间：
2003-05-08
影响因子：
3.3
通讯作者：
Mota, CJA
中科院分区：
文献类型：
--
作者：
Bhering, DL;Ramírez-Solís, A;Mota, CJA
采用密度泛函理论方法研究了可能存在于沸石中的6种不同的框架外铝（EFAL）的结构。采用不同Si/Al比的T-6簇（T = Si, Al）模拟了真实的沸石Y型结构和所选EFAL组分(Al3+、Al(OH)（2+）、AlO+、AI(OH)(2)（+）、AlO（OH）和Al（OH)(3)）的配位。一价阳离子倾向于与骨架AlO4-部分实现双配位，二价和三价阳离子通常实现四配位。一个重要的结果是，在所有情况下，配位都发生在离框架铝原子最近的氧原子上。一个水分子加入到优化的Al3+中。T-6簇产生强烈的放热反应，导致在沸石上形成羟基铝阳离子和酸性位点。第二个水分子的加入只会产生微小的能量和结构变化。
The structures of six different extraframework aluminum (EFAL) species, possibly present in zeolites, were studied by density functional theory methods. A T-6 cluster (T = Si, Al), with different Si/Al ratios, was used to simulate the real zeolite Y structure and the coordination of the chosen EFAL species (Al3+, Al(OH)(2+), AlO+, AI(OH)(2)(+), AlO(OH), and Al(OH)(3)) The monovalent cations prefer to attain bicoordination with the framework AlO4- moiety, while di- and trivalent cations usually achieve tetracoordination. One important result is that, in all cases, coordination occurs with the oxygen atoms nearest to the framework aluminum ones. A single water molecule addition to the optimized Al3+.T-6 cluster produces a strongly exothermic reaction, leading to formation of a hydroxyaluminum cation and an acidic site on the zeolite. The addition of a second water molecule produces only minor energetic and structural changes.