用于部分氧化反应活性中心定位的负载型钼酸根物种的还原性研究：原位Mo K-Edge XAS和DFT研究,The Journal of Physical Chemistry C

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用于部分氧化反应活性中心定位的负载型钼酸根物种的还原性研究：原位Mo K-Edge XAS和DFT研究
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2019-07-22 , DOI: 10.1021/acs.jpcc.9b02732
Hao Hu ₁ , Danilo Oliveira de Souza ₁ , Elise Berrier ₁ , Jean-François Paul ₁ , Camille La Fontaine ₂ , Valérie Briois ₂ , Sylvain Cristol ₁ , Asma Tougerti ₁

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我们已经研究了TiO ₂的分子和电子结构在甲醇或二氢气氛下还原后，生成负载型钼酸酯。原位Mo K边X射线吸收光谱法得到密度泛函理论（DFT）计算和从头算X射线吸收光谱法（XAS）光谱模拟的支持，表明负载型钼酸盐物种的可还原性与Cb的几何环境密切相关。钼原子。实际上，不涉及末端氧代位点的钼原子很容易还原，而钼二氧代物种不在我们应用的条件下。在这两种极端情况之间，参与单氧羰基末端位点的Mo原子表现出中等的还原性，这取决于它们的局部环境及其与载体的相互作用。自旋密度计算表明，在CH _3下在OH流动下，催化剂的表面被部分还原。将与甲醇反应后的还原相的结构与通过二氢还原后得到的相进行比较。我们的结果表明，在H ₂流动下的还原不会增加还原的Mo原子的数量，但会导致每个Mo原子具有更高的自旋密度。基于DFT和XAS光谱模拟绘制的Mo物种电子结构的个体映射，提出了详细描述甲醇选择性氧化过程中Mo活性位的结构的模型。

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Investigation of the Reducibility of Supported Oxomolybdate Species for Mapping of Active Centers of Partial Oxidation Reaction: In Situ Mo K-Edge XAS and DFT Study

We have investigated the molecular and electronic structure of a TiO₂-supported oxomolybdate phase upon reduction under methanol or dihydrogen atmosphere. In situ Mo K-edge X-ray absorption spectroscopy, supported by density functional theory (DFT) calculations and ab initio X-ray absorption spectroscopy (XAS) spectra simulation showed that the reducibility of supported molybdate species is closely related to the geometric environment of Mo atoms. Indeed, Mo atoms not involved in terminal oxo sites are easily reducible whereas Mo dioxo species are not under the conditions we have applied. Between those extreme cases, Mo atoms involved in mono-oxo terminal sites exhibit intermediate reducibility, which varies according to their local environment and their interaction with the support. Spin density calculations showed that under CH₃OH flow, the surface of the catalyst is partially reduced. The structure of the reduced phase after reaction with methanol was compared to that afforded after reduction by dihydrogen. Our results show that the reduction under H₂ flow does not increase the number of reduced Mo atoms but causes a higher spin density per Mo atom. On the basis of the individual mapping of the electronic structure of Mo species as drawn by DFT and XAS spectra simulation, a model that details the structure of the Mo active sites in the selective oxidation of methanol is proposed.

更新日期：2019-07-22

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