Utilizing super-atom orbital ideas to understand properties of silver clusters inside ZSM-5 zeolite
Utilizing super-atom orbital ideas to understand properties of silver clusters inside ZSM-5 zeolite
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DOI：
10.1039/c6ra26492a
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发表时间：
2017-01
期刊：
影响因子：
3.9
通讯作者：
T. Yumura;Mitsuhiro Kumondai;Y. Kuroda;T. Wakasugi;Hisayoshi Kobayashi
中科院分区：
文献类型：
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作者：
T. Yumura;Mitsuhiro Kumondai;Y. Kuroda;T. Wakasugi;Hisayoshi Kobayashi
采用密度泛函理论（DFT）方法，采用B3 PW 91泛函对ZSM-5分子筛中Agn团簇的能量性质进行了研究.用该方法得到了几种优化的几何构型（Agn-ZSM-5（Alm），3 ≤ n ≤ 6和1 ≤ m ≤ 5），其中m为ZSM-5中Al原子取代Si原子的数目。密度泛函理论计算发现，在n = m + 2时，Agn团簇在ZSM-5（Alm）空腔中稳定性很好. Agm+2-ZSM-5（Alm）分子筛的HOMO是由银原子上完全对称的5s轨道组成的，因此可以用前线轨道理论解释其稳定化条件。完全对称的5s轨道对应于团簇化学中的超原子S轨道。因此，Agm+2-ZSM-5（Alm）沸石具有S2电子构型，类似于气相中的幻数银簇。含时DFT计算发现，在5s基轨道之间的电子跃迁从全对称轨道（S-轨道）的一个节点（P-轨道）显着的振子强度。Agm+2-ZSM-5（Alm）中S → P电子跃迁遵循裸团簇电子跃迁的选择规则。由于激发能（λmax）随所含银原子数的增加而变化，Agm+2-ZSM-5（Alm）的S → P电子跃迁可用来鉴别内部银原子的状态。
The energetic properties of Agn clusters in ZSM-5 zeolite were investigated using density functional theory (DFT) calculations with the B3PW91 functional. Several optimized geometries (Agn–ZSM-5(Alm), 3 ≤ n ≤ 6 and 1 ≤ m ≤ 5) were obtained using this method, where m is the number of Al atoms substituted for Si atoms of a ten-membered ring of ZSM-5. DFT calculations found that an Agn cluster is well stabilized within a ZSM-5(Alm) cavity at n = m + 2. The stabilization conditions can be explained by frontier orbital theory because the HOMO of Agm+2–ZSM-5(Alm) zeolites is composed by totally symmetric 5s-based orbitals on silver atoms. The totally symmetric 5s-based orbital corresponds to a superatom S-orbital in cluster chemistry. Accordingly, the Agm+2–ZSM-5(Alm) zeolites have an S2 electronic configuration, being similar to magic-number silver clusters in the gas phase. Time-dependent DFT calculations found significant oscillator strength at the electronic transition between 5s-based orbitals from the totally symmetric orbital (S-orbital) to that with one node (P-orbital). The S → P electronic transitions in Agm+2–ZSM-5(Alm) follow the selection rule of electronic transitions of bare clusters. Because the excitation energies (λmax) change with an increase in the number of contained silver atoms, the S → P electronic transitions of Agm+2–ZSM-5(Alm) could be used to identify the state of the inner silver atoms.