Water adsorption in SAPO-34: elucidating the role of local heterogeneities and defects using dispersion-corrected DFT calculations.
Water adsorption in SAPO-34: elucidating the role of local heterogeneities and defects using dispersion-corrected DFT calculations.
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DOI：
10.1039/c5cp04189a
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发表时间：
2015-09
期刊：
影响因子：
--
通讯作者：
M. Fischer
中科院分区：
文献类型：
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作者：
M. Fischer
菱沸石型磷酸硅铝SAPO-34是一种很有前途的吸附剂，可用于水吸附-脱附循环的热能储存。为了发展对局部非均匀性和缺陷对水吸附性质的影响的微观理解，使用分散校正密度泛函理论（DFT-D）计算研究了不同模型的SAPO-34与水的相互作用。除了具有孤立硅原子的SAPO-34之外，计算还考虑了包含两种类型的异质性（硅岛，铝硅酸盐域）和两种含缺陷（部分和完全脱硅）系统的模型。对具有少量吸附水的系统进行DFT-D优化，其中所有H2O分子都可以与骨架质子相互作用，以及具有大量吸附水的系统（每个晶胞30个H2O分子）。在低负载下，对于具有孤立Si原子的SAPO-34计算的主体-客体相互作用能总计约为-90kJ mol（-1）。虽然存在的局部不均匀性导致创建一些吸附位点的能量稍微更有利，相互作用强度急剧降低的系统中的缺陷。在高水负荷下，所有模型的能量范围为-70 kJ mol（-1）。DFT-D相互作用能与实验测得的水吸附热吻合得很好。的平衡结构的详细分析被用来深入了解在低覆盖率的结合模式，并评估框架去质子化的程度和在高水负荷的铝原子的配位环境的变化。
The chabazite-type silicoaluminophosphate SAPO-34 is a promising adsorbent for applications in thermal energy storage using water adsorption-desorption cycles. In order to develop a microscopic understanding of the impact of local heterogeneities and defects on the water adsorption properties, the interaction of different models of SAPO-34 with water was studied using dispersion-corrected density-functional theory (DFT-D) calculations. In addition to SAPO-34 with isolated silicon atoms, the calculations considered models incorporating two types of heterogeneities (silicon islands, aluminosilicate domains), and two defect-containing (partially and fully desilicated) systems. DFT-D optimisations were performed for systems with small amounts of adsorbed water, in which all H2O molecules can interact with framework protons, and systems with large amounts of adsorbed water (30 H2O molecules per unit cell). At low loadings, the host-guest interaction energy calculated for SAPO-34 with isolated Si atoms amounts to approximately -90 kJ mol(-1). While the presence of local heterogeneities leads to the creation of some adsorption sites that are energetically slightly more favourable, the interaction strength is drastically reduced in systems with defects. At high water loadings, energies in the range of -70 kJ mol(-1) are obtained for all models. The DFT-D interaction energies are in good agreement with experimentally measured heats of water adsorption. A detailed analysis of the equilibrium structures was used to gain insights into the binding modes at low coverages, and to assess the extent of framework deprotonation and changes in the coordination environment of aluminium atoms at high water loadings.