Structural characterization of a non-heme iron active site in zeolites that hydroxylates methane
Structural characterization of a non-heme iron active site in zeolites that hydroxylates methane
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DOI：
10.1073/pnas.1721717115
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发表时间：
2018-04
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通讯作者：
Benjamin E. R. Snyder;L. Böttger;Max L. Bols;James J. Yan;Hannah M. Rhoda;A. Jacobs;Michael Y. Hu;Jiyong Zhao;E. Alp;B. Hedman;K. Hodgson;K. Hodgson;R. Schoonheydt;B. Sels;E. Solomon;E. Solomon
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作者：
Benjamin E. R. Snyder;L. Böttger;Max L. Bols;James J. Yan;Hannah M. Rhoda;A. Jacobs;Michael Y. Hu;Jiyong Zhao;E. Alp;B. Hedman;K. Hodgson;K. Hodgson;R. Schoonheydt;B. Sels;E. Solomon;E. Solomon
意义 了解沸石中形成的铁活性位点的结构对于了解铁沸石催化剂的极端反应性至关重要，铁沸石催化剂在重要的工业应用中显示出前景。这项研究定义了铁沸石活性位点的几何结构，该活性位点在室温下裂解甲烷的惰性 C-H 键以形成甲醇。该位点的高反应性源自催化剂刚性基质所强制的约束配位几何形状。对催化剂结构和功能之间关系的深入了解是迈向具有成本效益的甲醇燃料和源自天然气的化学原料的重要一步。含铁沸石在甲烷低温羟基化形成甲醇的过程中表现出前所未有的反应活性。反应发生在单核亚铁活性位点 α-Fe(II)，它被 N2O 激活形成反应中间体 α-O。这已被定义为 Fe(IV)=O 物种。使用核共振振动光谱与 X 射线吸收光谱耦合，我们探测了铁中心、其沸石晶格衍生的配体和活性氧之间的键合相互作用。 α-O被发现含有异常强的Fe(IV)=O键，这是由沸石晶格强制的约束配位几何结构产生的。密度泛函理论计算阐明了实验确定的活性位点几何结构如何导致高度激活以执行 H 原子提取的电子结构。
Significance Understanding the structure of iron active sites that form in zeolites is critical to understanding the extreme reactivity of Fe-zeolite catalysts, which show promise in important industrial applications. This study defines the geometric structure of an Fe-zeolite active site that cleaves the inert C–H bond of methane at room temperature to form methanol. The high reactivity of this site derives from a constrained coordination geometry enforced by the rigid matrix of the catalyst. This insight into the relationship between catalyst structure and function is an important step toward cost-effective methanol fuels and chemical feedstocks derived from natural gas. Iron-containing zeolites exhibit unprecedented reactivity in the low-temperature hydroxylation of methane to form methanol. Reactivity occurs at a mononuclear ferrous active site, α-Fe(II), that is activated by N2O to form the reactive intermediate α-O. This has been defined as an Fe(IV)=O species. Using nuclear resonance vibrational spectroscopy coupled to X-ray absorption spectroscopy, we probe the bonding interaction between the iron center, its zeolite lattice-derived ligands, and the reactive oxygen. α-O is found to contain an unusually strong Fe(IV)=O bond resulting from a constrained coordination geometry enforced by the zeolite lattice. Density functional theory calculations clarify how the experimentally determined geometric structure of the active site leads to an electronic structure that is highly activated to perform H-atom abstraction.