Rigid Arrangements of Ionic Charge in Zeolite Frameworks Conferred by Specific Aluminum Distributions Preferentially Stabilize Alkanol Dehydration Transition States
Rigid Arrangements of Ionic Charge in Zeolite Frameworks Conferred by Specific Aluminum Distributions Preferentially Stabilize Alkanol Dehydration Transition States
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DOI：
10.1002/anie.202007790
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发表时间：
2020-08-18
影响因子：
16.6
通讯作者：
Hibbitts, David
中科院分区：
文献类型：
--
作者：
Hoffman, Alexander J.;Bates, Jason S.;Hibbitts, David
沸石的反应性取决于其微孔的溶剂化环境和其布朗斯台德酸位点的接近程度。甲醇和乙醇脱水的转化率（每个 H+）随着共享菱沸石 (CHA) 沸石六元环的 H(+) 位点比例的增加而增加。密度泛函理论 (DFT) 表明，活化势垒随 Al 的数量和排列而变化很大（每 36 个 T 位晶胞 1-5 个），但不能仅通过 Al-Al 距离或密度来描述。某些铝分布产生阴离子电荷的刚性排列，通过氢键稳定阳离子中间体和过渡态以减少势垒。这是沸石溶剂中酸催化的一个关键特征，沸石溶剂缺乏液体溶剂的各向同性。极性过渡态对其溶剂化环境中电荷的特定排列的敏感性以及以越来越高的精度将这些电荷定位在沸石晶格中的能力预示着不同Al排列的沸石之间丰富的催化多样性。
Zeolite reactivity depends on the solvating environments of their micropores and the proximity of their Bronsted acid sites. Turnover rates (per H+) for methanol and ethanol dehydration increase with the fraction of H(+)sites sharing six-membered rings of chabazite (CHA) zeolites. Density functional theory (DFT) shows that activation barriers vary widely with the number and arrangement of Al (1-5 per 36 T-site unit cell), but cannot be described solely by Al-Al distance or density. Certain Al distributions yield rigid arrangements of anionic charge that stabilize cationic intermediates and transition states via H-bonding to decrease barriers. This is a key feature of acid catalysis in zeolite solvents, which lack the isotropy of liquid solvents. The sensitivity of polar transition states to specific arrangements of charge in their solvating environments and the ability to position such charges in zeolite lattices with increasing precision herald rich catalytic diversity among zeolites of varying Al arrangement.