金属氧化物表面甲烷C-H键活化的异裂裂解机理研究

IF 4.6 2区 化学 Q2 CHEMISTRY, PHYSICAL
Lu Cheng, Jiaye Lu, Qian Xiang and Xiao-Ming Cao*, 
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引用次数: 0

摘要

对C-H键活化机理的了解有助于改进甲烷转化为有价产物催化剂的设计。然而,其机制仍有争议,特别是关于金属氧化物。本研究旨在通过系统地研究甲烷C-H键在各种原始金属氧化物表面的激活,并重新审视普遍的异裂解理机制,来阐明这一问题。在金属氧化物表面上,甲烷活化的“异裂解机制”可分为两种不同的机制:在平面不可还原的碱和碱土金属氧化物表面上的真正异裂解机制(N-MOSs)和在可还原的金属氧化物表面上的配体到金属电荷转移(LMCT)激活的氢原子转移(HAT)机制(R-MOSs)。甲烷与表面在过渡态的库仑相互作用和LMCT (ELMCT)的能量决定了其主导机理。在裸态N-MOSs上,强库仑相互作用有利于异裂解机制,而在R-MOSs上则相反,有利于lmct激活的HAT机制。然而,在甲烷氧化反应条件下,由于双氧在碱和碱性金属氧化物表面的强化学吸附会使甲烷远离表面,从而显著削弱库仑相互作用,因此异裂解理机制可能难以发生。掺杂可以操纵晶格氧的电子结构,潜在地还原ELMCT,甚至绕过LMCT直接产生活性氧自由基,从而加速C-H活化。此外,这些不同的机制可以影响后续步骤,例如C-O耦合。通过lmct机制激活C-H键是触发C-O耦合的先决条件。该研究为设计具有所需活性和选择性的靶向催化剂以实现高效和受控的甲烷转化提供了有价值的见解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Revisiting Heterolytic Cleavage Mechanism of Methane C–H Bond Activation over Metal Oxide Surfaces

Revisiting Heterolytic Cleavage Mechanism of Methane C–H Bond Activation over Metal Oxide Surfaces

The understanding of C–H bond activation could facilitate the design of improved catalysts for the conversion of methane to valuable products. However, its mechanism remains controversial, particularly with regard to metal oxides. This study aims to shed light on this issue by systematically investigating methane C–H bond activation across various pristine metal oxide surfaces and revisiting the prevailing heterolytic cleavage mechanism. It is found that the so-called “heterolytic cleavage mechanism” for methane activation could be classified into two distinct mechanisms on bare metal oxide surfaces: the real heterolytic cleavage mechanism over flat nonreducible alkali and alkaline-earth metal oxide surfaces (N-MOSs) and a ligand-to-metal charge transfer (LMCT)-enabled hydrogen atom transfer (HAT) mechanism over reducible metal oxide surfaces (R-MOSs). The dominant mechanism is determined by the Coulomb interaction between methane and the surface at the transition state and the energy of LMCT (ELMCT). Strong Coulomb interactions favor the heterolytic cleavage mechanism on bare N-MOSs, while the opposite favors the LMCT-enabled HAT mechanism on R-MOSs. Nevertheless, the heterolytic cleavage mechanism might have difficulty occurring under the reaction conditions of methane oxidation since the strong chemisorption of dioxygen over alkali and alkaline metal oxide surfaces would render the methane far from the surface, significantly weakening the Coulomb interaction. Doping can manipulate the electronic structure of lattice oxygen, potentially reducing ELMCT and even bypassing LMCT to directly generate reactive oxygen radicals, thus accelerating C–H activation. Additionally, these distinct mechanisms can influence subsequent steps, such as C–O coupling. C–H bond activation through the LMCT-enabled mechanism would be a prerequisite to trigger C–O coupling. This study provides valuable insights into the design of targeted catalysts with desired activity and selectivity for efficient and controlled methane conversion.

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来源期刊
The Journal of Physical Chemistry Letters
The Journal of Physical Chemistry Letters CHEMISTRY, PHYSICAL-NANOSCIENCE & NANOTECHNOLOGY
CiteScore
9.60
自引率
7.00%
发文量
1519
审稿时长
1.6 months
期刊介绍: The Journal of Physical Chemistry (JPC) Letters is devoted to reporting new and original experimental and theoretical basic research of interest to physical chemists, biophysical chemists, chemical physicists, physicists, material scientists, and engineers. An important criterion for acceptance is that the paper reports a significant scientific advance and/or physical insight such that rapid publication is essential. Two issues of JPC Letters are published each month.
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