The zeolitic imidazolate frameworks (ZIFs) are chemically and thermally stable microporous materials that are being considered as ideal supports for the uniform encapsulation of noble metal nanoparticles. Our theoretical investigations started from the adsorption of the molecular precursor Au(CO)Cl in both ZIF-8 and ZIF-90; surprisingly, pore-B, with the diameter less than 2.2 Å in the two ZIFs, dramatically expanded as an energetically most favorable site for the location of Au(CO)Cl, whereas the well-known pore-A, with a diameter of about 3.5 Å, is less favorable. Then, ab initio molecular dynamics simulations showed that the confined Au_n cluster has a transition from two-dimensional to three-dimensional structures when n is larger than 12 in both ZIFs. Interestingly, the aldehyde groups in ZIF-90 were computed to be the main binding sites for Au clusters, whereas the imidazole rings were identified as the binding sites in ZIF-8. Compared to ZIF-90, the binding of Au clusters in ZIF-8 was stronger, accompanied by transfer of larger electrons from the frameworks to the confined Au clusters. Finally, the computed energy barriers for the CO oxidation using Au clusters confined in ZIFs as catalysts were found to be smaller than those for isolated Au clusters.

中文翻译：

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ZIF-8和ZIF-90包裹的Au团簇的结构和电子性质

沸石咪唑酸盐骨架（ZIF）是化学和热稳定的微孔材料，被认为是均匀封装贵金属纳米粒子的理想载体。我们的理论研究始于ZIF-8和ZIF-90分子对前体Au（CO）Cl的吸附。出乎意料的是，两个ZIF中直径小于2.2的B孔，在能量上最有利地扩展了Au（CO）Cl的位置，而众所周知的A孔的直径大约为2.2Å。 3.5Å较差。然后，从头分子动力学模拟表明，该受限的Au _Ñ簇具有从二维到三维结构时的过渡Ñ在两个ZIF中都大于12。有趣的是，计算得出ZIF-90中的醛基是Au团簇的主要结合位点，而咪唑环则被确定为ZIF-8中的结合位点。与ZIF-90相比，ZIF-8中的Au团簇的结合更强，伴随着更大的电子从骨架转移到受限的Au团簇中。最后，发现使用限制在ZIFs中的Au簇作为催化剂的CO氧化计算的能垒比孤立的Au簇小。