采用晶格能极小化技术模拟计算了一系列结构的低硅沸石全硅骨架晶格，预测了它们的骨架结构和晶格能．计算结果与二氧化硅致密α一石英相比较，发现这些低硅沸石彼此间的晶格能相差很小（＜２５ｋＪ·ｍｏｌ－１），与α一石英相差４３～６８ｋＪ·ｍｏｌ－１这意味着在低硅沸石的合成中，特定结构骨架的形成仅需要较少的能量；可以解释低硅沸石骨架结构的相似性和多样性．同时讨论了计算晶格能和骨架结构间的关系，结果表明随着低硅沸石骨架密度的增大，全硅骨架晶格能呈降低趋势．分析这些低硅沸石的ＸＲＤ数据发现在它们的结构中包含较短的 Ｓｉ－Ｏ键长（０．１５５７ｎｍ），很长的 Ｓｉ－Ｏ键长（０１７６４ｎｍ）， Ｏ－Ｓｉ－Ｏ键角有大的分布范围（９３．３８～１３３．４１°），Ｓｉ－Ｏ－Ｓｉ键角平均在１４４°左右并且具有更大的分布范围（１２７～１８０°）。
The all-silica frameworks s lattice energy of a series of low-silica zeolites was determined by using the lattice energy minimization method. The results were compared to the lattice energy of dense polymorphs of SiO2. All low-silica zeolites frameworks are only 43-68kJ·mol-1 less stable thanα-quartz. This may imply that there is little energy barrier to the formation of lowsilica zeolites frameworks and explain the structural diversity observed for low-silica zeolites. The relationship of calculated lattice energies and framework structures was discussed. The results reveal that the lattice energy decreases and the relative stability of framework increases with the increase of framework densities. These XRD data of the low-silica zeolites contain very short Si-O bond length(0.1557nm), very long Si-O bond length(0.1764nm), and a large range of O-Si-O angles(93.38～133.41°), an average Si-O-Si angles close 144° and a larger range of Si-O-Si angles(127～180°).
参考文献
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