The framework basicity of zeolites
The framework basicity of zeolites
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DOI：
10.1039/c2jm31366a
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发表时间：
2012-08
影响因子：
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通讯作者：
R. Schoonheydt;P. Geerlings;E. Pidko;R. A. Santen
中科院分区：
文献类型：
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作者：
R. Schoonheydt;P. Geerlings;E. Pidko;R. A. Santen
与金属阳离子交换的沸石可以被认为是固体刘易斯酸-碱材料。刘易斯酸性与可交换阳离子有关，刘易斯碱性与晶格氧有关。这种刘易斯碱性可以通过以下吸附的分子，如CO2，吡咯，甲醇，碘甲烷和N2 O 4的光谱变化和DFT建模来探测。最好的分子是那些不成比例地分成阳离子和阴离子的分子。阴离子取代可交换阳离子。阳离子吸附到沸石骨架的晶格氧上并探测这些氧的碱性。沸石分子筛的碱性可以在概念密度泛函的框架内进行描述。局部硬度不足以敏感地描述沸石中的碱度趋势。局部软度，近似的局部和全局的状态密度的比率，被认为是一个很好的描述框架的碱度，但它只被计算在一个集群模型。此外，骨架氧的福井函数是一个很好的碱度描述符，但它只在半经验EEM水平上计算。在文献中提出的其他参数中，氧原子处的分子静电势的最小值正确地描述了碱度趋势，而氧上的电荷不是一个好的碱度描述符。
Zeolites exchanged with metal cations can be considered as solid Lewis acid–base materials. Lewis acidity is associated with the exchangeable cations and Lewis basicity with the lattice oxygens. This Lewis basicity can be probed by following the spectral changes of adsorbed molecules such as CO2, pyrrole, methanol, methyl iodide and N2O4 and by DFT modeling. The best molecules are those which disproportionate into cations and anions. The anions immobilize the exchangeable cations. The cations adsorb onto the lattice oxygens of the zeolitic framework and probe the basicity of these oxygens. Basicity of zeolites can be described in the frame of conceptual DFT. Local hardness is not sensitive enough to describe basicity trends in zeolites. Local softness, approximated by the ratio of the local and global density of states, is found to be a good descriptor of framework basicity, but it has only been calculated on a cluster model. Also the Fukui function of the framework oxygens is a good basicity descriptor, but it is only calculated at the semi-empirical EEM level. Of the other parameters that have been proposed in the literature the minimum of the molecular electrostatic potential at the oxygen atoms describes the basicity trends correctly, whereas the charge on the oxygens is not a good basicity descriptor.