Interaction of hydrogen and carbon dioxide with sod-type zeolitic imidazolate frameworks: a periodic DFT-D study
Interaction of hydrogen and carbon dioxide with sod-type zeolitic imidazolate frameworks: a periodic DFT-D study
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DOI：
10.1039/c3ce42209g
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发表时间：
2014-01-01
期刊：
影响因子：
3.1
通讯作者：
Bell, Robert G.
中科院分区：
文献类型：
--
作者：
Fischer, Michael;Bell, Robert G.
分散校正的密度泛函理论（DFT-D）计算用于研究氢和二氧化碳与ZIF-8，一个典型的沸石咪唑骨架（ZIF）与方钠石拓扑结构的相互作用。四个不同的吸附位点被确定为两个客体物种。两个网站是与六环窗口，第三个网站位于接近一个咪唑部分，和第四个网站是位于两个甲基取代基的甲基咪唑连接器的紧密接近。对于氢的情况下，实验数据是可用的，在DFT-D计算中得到的位置和能量排序同意这些数据。调查，然后扩展到两组同构系统。第一组由两个硼咪唑酯框架（BIF）组成，其中四面体配位原子（T原子）不同于ZIF-8中的那些，而甲基咪唑酯连接基保持相同。计算表明，T原子的性质对与客体分子的相互作用只有非常有限的影响。第二组衍生物包含四个系统，其并入与ZIF-8（锌）相同的T原子，但具有不同取代基X的接头，其中X = -H、-NO2、-NH 2、-CHO。在这些情况下，在与取代基相关的吸附位点处，与CO2的相互作用以及在小得多的程度上与氢的相互作用增加，最显著的是在硝基官能化系统和脱硝基官能化系统中。吸附几何形状的详细分析是用来解释的取代基的有利效果。此外，它示出了如何可以从不同的吸附位点的加权平均值，占其可能占用的平均相互作用能的合理估计。在ZIF-8的情况下，这个平均值相比，实验吸附热，并讨论了偏差。最后讨论了其在储氢和CO_2/H_2分离中的应用。所有材料对氢显示出相似的亲和力，表明它们在H-2存储应用中的性能在很大程度上与所考虑的结构修饰无关。由于CO2/H-2选择性与对两种物质的亲和力差异有关，因此从DFT-D结果可以预期，硝基和脱硝官能化体系的性能将明显优于ZIF-8，特别是对于从氢气进料中去除相对少量的二氧化碳。这一发现是特别令人鼓舞的，因为这两个系统是合成访问。
Dispersion-corrected density-functional theory (DFT-D) calculations are used to study the interaction of hydrogen and carbon dioxide with ZIF-8, a prototypical zeolitic imidazolate framework (ZIF) with sodalite topology. Four distinct adsorption sites are identified for each of the two guest species. Two of the sites are associated with the six-ring windows, a third site is located close to one imidazolate moiety, and the fourth site is situated in the close proximity of two methyl substituents of the methylimidazolate linkers. For the case of hydrogen, where experimental data are available, the positions and the energetic ordering obtained in the DFT-D calculations agree well with these data. The investigation is then extended to two groups of isostructural systems. The first group consists of two boron imidazolate frameworks (BIFs), in which the tetrahedrally coordinated atoms (T atoms) differ from those in ZIF-8, while the methylimidazolate linker remains the same. The calculations show that the nature of the T atoms has only a very limited effect on the interaction with the guest molecules. The second group of derivatives comprises four systems that incorporate the same T atom as ZIF-8 (zinc), but linkers with different substituents X, with X = -H, -NO2, -NH2, -CHO. In these cases, the interaction with CO2 and, to a much lesser extent, hydrogen is increased at the adsorption site that is associated with the substituents, most prominently in the nitro-and aldehyde-functionalised systems. A detailed analysis of the adsorption geometries is used to explain the favourable effect of the substituents. Furthermore, it is shown how a reasonable estimate of the average interaction energy can be obtained from a weighted average over the different adsorption sites, accounting for their possible occupancy. In the case of ZIF-8, this averaged value is compared to experimental heats of adsorption, and the deviations are discussed. Finally, possible applications in hydrogen storage and CO2/H-2 separation are discussed. All materials show similar affinities for hydrogen, indicating that their performance in H-2 storage applications is largely independent of the structural modifications considered. Because the CO2/H-2 selectivity is related to the difference in affinity towards the two species, it can be expected from the DFT-D results that the nitro-and aldehyde-functionalised systems will perform considerably better than ZIF-8, especially for the removal of relatively small amounts of carbon dioxide from a hydrogen feed. This finding is particularly encouraging as both systems are synthetically accessible.