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A Computational Study of Lowenstein’s Rulein ZeoliteA
Li Baohui,Jin Qinghua,Sun Pingchuan,Guo Zhenya,Ding Datong
Author NameAffiliation
Li Baohui Department of Physics,Tianjin 300071 
Jin Qinghua Department of Physics,Tianjin 300071 
Sun Pingchuan State Key Laboratory of Functional Polymer Materials for Adsorption and Separation,Institute of Polymer Chemistry,Nankai University,Tianjin 300071 
Guo Zhenya Department of Physics,Tianjin 300071 
Ding Datong Department of Physics,Tianjin 300071 
Abstract:
The Si,Al ordering in zeolite A(formula Na96Al96Si96O384)has been studied theoretically using steric energy minimization by simulated annealing.The consistent molecular mechanics force field is used.Calculations are performed on four kind of Si,Al distributions:i)the 4:0 ordered structure,in which Lowenstein's rule is obeyed and no Al-O-Al bridges occur,ii)and iii)two hypothetical structures having 3:1 framework ordering,i.e.,each silicon is connected by oxygen to three aluminum atoms and one silicon atom,iv)a structure with random Si,Al distribution and three kind of cation occupations:i)The experimental Na+ occupation;i.e.,Na+ occupy sites I ,II and III with 64,24 and 8 per unit cell,respectively;ii)and iii)Na+ occupy sites I,II and III randomly.The steric energy,the heat of formation and unit cell parameter of each refined structure are obtained.An energetic preference for the Lowensteinian Si,Al distribution and the experimental Na+ occupation are found.
Key words:  Zeolite A Lowenstein’s rule Si,Al ordering
FundProject:国家自然科学基金资助项目(29603004)
A型沸石中Lwenstein规则的能学研究
李宝会,金庆华,孙平川,郭振亚,丁大同
摘要:
通过模拟退火方法,使用协合分子力学力场对Si、Al分布分别为4:0序、两种3:1序和随机分布的NaA型沸石结构进行了能量最小化计算,获得了不同结构的位能及其生成热大小。计算结果表明,4:0序结构的位能和生成热在所讨论的几种序结构中最低,从而在理论上证实了Lwenstein规则是分子筛结构中能量最小化的自然结果。
关键词:  A型沸石  Lwenstein规则  Si、Al分布
DOI:10.1088/1674-0068/13/1/43-48
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