Methane C–H Activation by [Cu 2 O] 2+ and [Cu 3 O 3 ] 2+ in Copper-Exchanged Zeolites: Computational Analysis of Redox Chemistry and X-ray Absorption Spectroscopy
Methane C–H Activation by [Cu 2 O] 2+ and [Cu 3 O 3 ] 2+ in Copper-Exchanged Zeolites: Computational Analysis of Redox Chemistry and X-ray Absorption Spectroscopy
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铜交换沸石中 [Cu 2 O] 2 和 [Cu 3 O 3 ] 2 的甲烷 C–H 活化：氧化还原化学和 X 射线吸收光谱的计算分析
DOI：
10.1021/acs.inorgchem.0c03693
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发表时间：
2021
影响因子：
4.6
通讯作者：
Odoh, Samuel O.
中科院分区：
文献类型：
--
作者：
Suleiman, Olabisi;Panthi, Dipak;Adeyiga, Olajumoke;Odoh, Samuel O.
[Cu 3 O3]2+在铜交换沸石催化甲烷转化为甲醇反应中的作用一直存在争议。在这里，我们进行电子结构分析和局域轨道成键分析，以探测其Cu和μ-氧代位点的氧化还原化学。此外，X射线吸收近边结构，XANES，甲烷活化[Cu 3 O3]2+相比，更普遍的[Cu 2 O]2+。甲烷C-H活化仅与[Cu 2 O]2+中的Cu 2 +/Cu+氧化还原电对有关。对于[Cu_3O_3]_2 ~+，在密度泛函理论的基态下，Cu ~（3+）/Cu ~（2+）对的参与是没有根据的.在[Cu_3O_3]_2 ~+中，存在许多可能的甲烷活化中间体。在我们研究的九种可能性中，甲烷活化是由Cu 2 +/Cu+和oxyl/O2-氧化还原对的组合驱动的。据此，[Cu_2O]_2 ~+和[Cu_3O_3]_2 ~+的Cu 1 s边XANES谱都具有甲烷活化过程中Cu ~（2+）→ Cu ~+还原的能量特征。这确实是我们从计算的XANES光谱中得到的。[Cu_2 O]~（2+）和[Cu_3 O_3]~（2+）中间体中只有一个Cu ~（2+）晶位，位移0.9- 1.7eV，而有两个Cu ~（2+）晶位的中间体位移3.0- 4.2eV。这些接近在甲烷与活化的铜交换沸石接触后实验观察到的2.5- 3.2eV的范围。因此，[Cu 3 O3]2+活化甲烷将导致Cu+位点的形成。重要的是，对于未来的定量XANES研究，[Cu 3 O3]2+中O-+ e-→ O2-的参与意味着整体反应性与Cu 2 +/Cu+氧化还原对中使用的电子数量之间的脱节。
There is an ongoing debate regarding the role of [Cu3O3]2+in methane-to-methanol conversion by copper-exchanged zeolites. Here, we perform electronic structure analysis and localized orbital bonding analysis to probe the redox chemistry of its Cu and μ-oxo sites. Also, the X-ray absorption near-edge structure, XANES, of methane activation in [Cu3O3]2+is compared to that of the more ubiquitous [Cu2O]2+. Methane C–H activation is associated with only the Cu2+/Cu+redox couple in [Cu2O]2+. For [Cu3O3]2+, there is no basis for the Cu3+/Cu2+couple’s participation at the density functional theory ground state. In [Cu3O3]2+, there are many possible intrazeolite intermediates for methane activation. In the nine possibilities that we examined, methane activation is driven by a combination of the Cu2+/Cu+and oxyl/O2–redox couples. Based on this, the Cu 1s-edge XANES spectra of [Cu2O]2+and [Cu3O3]2+should both have energy signatures of Cu2+→ Cu+reduction during methane activation. This is indeed what we obtained from the calculated XANES spectra. [Cu2O]2+and [Cu3O3]2+intermediates with one Cu+site are shifted by 0.9–1.7 eV, while those with two Cu+sites are shifted by 3.0–4.2 eV. These are near a range of 2.5–3.2 eV observed experimentally after contacting methane with activated copper-exchanged zeolites. Thus, activation of methane by [Cu3O3]2+will lead to formation of Cu+sites. Importantly, for future quantitative XANES studies, involvement of O–+ e–→ O2–in [Cu3O3]2+implies a disconnect between the overall reactivity and the number of electrons used in the Cu2+/Cu+redox couple.