One Oxygen Vacancy, Two Charge States: Characterization of Reduced α-MoO3(010) through Theoretical Methods,The Journal of Physical Chemistry Letters

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One Oxygen Vacancy, Two Charge States: Characterization of Reduced α-MoO3(010) through Theoretical Methods
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2018-04-27 00:00:00 , DOI: 10.1021/acs.jpclett.8b00536
Marcos Rellán-Piñeiro ₁ , Núria López ₁

Affiliation

Molybdenum oxides are finding increasing applications that rely on their redox character. For the most common polymorph, α-MoO₃, oxygen vacancy formation leaves two electrons on the surface that can be stored as small polarons. Detailed density functional theory calculations that properly account for the self-interaction term, U_eff = 3.5 eV, show that the vacancy generates two different configurations: either two Mo⁵⁺ centers (Mo⁵⁺□ and Mo⁵⁺═O) or a single double-reduced Mo⁴⁺. These states are separated by 0.22 eV with a barrier for interconversion of 0.33 eV, and thus both are populated at catalytic temperatures, as shown by first-principles molecular dynamics. At higher reduction levels, vacancies can only be accumulated along a preferential direction and the energy difference between the 2×Mo⁵⁺ and Mo⁴⁺ configurations is reduced. These results point out the need for a revision of the experimental assignments based on our characterization that includes charges, vibrational frequencies, and XPS signatures.

中文翻译：

一个氧空位，两个电荷态：减少α茂的表征₃（010）通过理论方法

氧化钼正依赖于其氧化还原特性而得到越来越多的应用。对于最常见的多晶型物，α-的MoO ₃，氧空位形成在表面上留下两个电子可以存储作为小极化子。详细的密度泛函理论计算适当地考虑了自相互作用项U _eff = 3.5 eV，表明空位产生两种不同的构型：两个Mo ⁵⁺中心（Mo ⁵⁺ □和Mo ⁵⁺ ═O）或单双还原Mo ⁴⁺。这些状态之间相隔0.22 eV，且相互转换的势垒为0.33 eV，因此，这两种状态都在催化温度下分布，如第一性原理分子动力学所示。在较高的还原水平下，空位只能沿优先方向累积，并且2×Mo ⁵⁺和Mo ⁴⁺构型之间的能量差会减小。这些结果指出，需要根据我们的特征（包括电荷，振动频率和XPS签名）对实验任务进行修订。

更新日期：2018-04-27

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