| DOI: | 10.2172/1162136
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| 报告号: | DOE-EMORY-15461
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| 报告题名: | Principles of water oxidation and O2-based hydrocarbon transformation by multinuclear catalytic sites |
| 作者: | Musaev, Djamaladdin G; Hill, Craig L; Morokuma, Keiji
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| 出版年: | 2014
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| 发表日期: | 2014-10-28
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| 国家: | 美国
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| 语种: | 英语
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| 英文关键词: | Catalysis
; Water oxidation
; O2-based hydrocarbon transformation
; Polyoxometalates
; Multinuclear catalytic sites
; Theory and Experiment
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| 中文主题词: | 剥蚀
; 离子
; 甲烷
; 元素
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| 主题词: | DEGRADATION
; IONS
; METHANE
; ELEMENTS
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| 英文摘要: | Abstract The central thrust of this integrated experimental and computational research program was to obtain an atomistic-level understanding of the structural and dynamic factors underlying the design of catalysts for water oxidation and selective reductant-free O2-based transformations. The focus was on oxidatively robust polyoxometalate (POM) complexes in which a catalytic active site interacts with proximal metal centers in a synergistic manner. Thirty five publications in high-impact journals arose from this grant. I. Developing an oxidatively and hydrolytically stable and fast water oxidation catalyst (WOC), a central need in the production of green fuels using water as a reductant, has proven particularly challenging. During this grant period we have designed and investigated several carbon-free, molecular (homogenous), oxidatively and hydrolytically stable WOCs, including the Rb8K2[{Ru4O4(OH)2(H2O)4}(Îł-SiW10O36)2]¡25H2O (1) and [Co4(H2O)2(Îą-PW9O34)2]10- (2). Although complex 1 is fast, oxidatively and hydrolytically stable WOC, Ru is neither abundant nor inexpensive. Therefore, development of a stable and fast carbon-free homogenous WOC, based on earth-abundant elements became our highest priority. In 2010, we reported the first such catalyst, complex 2. This complex is substantially faster than 1 and stable under homogeneous conditions. Recently, we have extended our efforts and reported a V2-analog of the complex 2, i.e. [Co4(H2O)2(Îą-VW9O34)2]10- (3), which shows an even greater stability and reactivity. We succeeded in: (a) immobilizing catalysts 1 and 2 on the surface of various electrodes, and (b) elucidating the mechanism of O2 formation and release from complex 1, as well as the Mn4O4L6 âcubaneâ cluster. We have shown that the direct O-O bond formation is the most likely pathway for O2 formation during water oxidation catalyzed by 1. II. Oxo transfer catalysts that contain two proximal and synergistically interacting redox active metal centers in the active site form another part of considerable interest of our grant because species with such sites [including methane monooxygenase (MMO) and more] are some of the most effective oxygenase catalysts known. Our team conducted the following research on Îł-M2-Keggin complexes: (a) investigated stability of the trimer [{Fe3(OH)3(H2O)2}3(Îł-SiW10O36)3]15-, 4, in water, and developed the chemistry and catalysis of the di-iron centered POM, [Îł(1,2)-SiW10{Fe(OH)}2O38]6-, 5, in organic solvents (Figure 2). We also study the thermodynamic and structural stability of Îł-M2-Keggin in aqueous media for different Mâs (d-electron metals). We have defined two structural classes of POMs with proximally bound d-electron metal centers. We refer to these structural isomers of the {Îł-M2SiW10} family of POMs as âin-pocketâ and âout-of pocketâ. We have elucidated the factors controlling the structure and stability of the V, Fe, Ru, Tc, Mo and Rh derivatives of [(SiO4)M2(OH)2W10O32]4- using a range of computational tools. We have: (a) demonstrated that heteroatom X in these polyanions may function as an âinternal switchâ for defining the ground electronic states and, consequently, the reactivity of the Îł-M2-Keggin POM complexes; (b) elucidated reactivity of divacant lacunary species and polyperoxotungstates (PPTs), {Xn+O4[WO(O2)2]4}n-, which could be degradation products of Îł-M2-Keggin complexes in aqueous media; (c) elucidated the role of the POM ligand in stabilization of {Ru2} and {(Ru-oxo)2} fragments in the reactant and product of the reaction of {Îł-[(Xn+O4)Ru2(OH)2W10O32]}(8-n)- (where X = Si4+, P5+ and S6+) with O2, and (d) the mechanisms of olefin epoxidation catalyzed by these di-d-transition metal substituted and divacant lacunary Îł-M2-Keggin complexes. III. Complementing the efforts presented above was the development of less time-consuming but reasonably accurate computational methods allowing one to explore more deeply large catalytic systems. We developed Reactive Force Field (ReaxFF) to study interaction of the targeted POMs with water, proton and hydroxide ions in the liquid phase. We tested our ReaxFF parameters on the Lindqvist POMs, M6O19n-, where M = Nb and Ta. These parameters are made available as part of the ReaxFF code. In addition, we have developed parameters for Sc, Ti, Fe, Co and Ni in combination with H, C, N, O, as well as the same metal (M-M) for the spin-polarized self-consistent-charge density-functional tight-binding (DFTB) method. Test calculations showed that the DFTB method with the present parameters in most cases reproduces structural properties very well. These parameters are made available as part of the DFTB code. Thus, this DOE BES funded research project has clarified several key areas impacting (a) water oxidation and O2-based hydrocarbon transformation, (b) stabilization of key structures and catalytic intermediates in such processes, (c) immobilization of molecular catalysts on metal oxide surfaces, and (d) application of optimal computational methods to study reaction dynamics in large systems. |
| URL: | http://www.osti.gov/scitech/servlets/purl/1162136
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| Citation statistics: |
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| 资源类型: | 研究报告
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| 标识符: | http://119.78.100.158/handle/2HF3EXSE/41384
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| Appears in Collections: | 过去全球变化的重建
影响、适应和脆弱性
科学计划与规划
气候变化与战略
全球变化的国际研究计划
气候减缓与适应
气候变化事实与影响
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作者单位: | Chemistry, Emory University
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| Recommended Citation: | |
Musaev, Djamaladdin G,Hill, Craig L,Morokuma, Keiji. Principles of water oxidation and O2-based hydrocarbon transformation by multinuclear catalytic sites. 2014-01-01.
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