Atomic and electronic structure of molybdenum carbide phases: bulk and low Miller-index surfaces
Atomic and electronic structure of molybdenum carbide phases: bulk and low Miller-index surfaces
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DOI：
10.1039/c3cp51389k
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发表时间：
2013-01-01
影响因子：
3.3
通讯作者：
Illas, Francesc
中科院分区：
文献类型：
--
作者：
dos Santos Politi, Jose Roberto;Vines, Francesc;Illas, Francesc
催化相关的碳化钼相（立方δ-MoC，六方α-MoC，和正交β-Mo 2C）和它们的低米勒指数表面的几何和电子结构已经通过基于周期密度泛函理论（DFT）的计算与Perdew-Burke-Ernzerhof（PBE）交换相关功能进行了研究。比较现有的实验数据表明，这种功能是特别适合于研究这些材料。计算表明，β-Mo 2C具有比其他两种多晶型更强的金属特性，β-Mo 2C和d-MoC都具有较大的离子贡献，δ-和α-MoC表现出最强的共价特性。在探索的各种表面中，计算揭示了delta-MoC（001）非极性表面、α-MoC的Mo-和C-封端的（001）极性表面以及β-Mo 2C的非极性（011）表面的高稳定性。预测β-Mo 2C（011）的功函数相当低，仅为3.4 eV，这表明该系统特别适合于表面->吸附物电子转移至关重要的（电）催化过程。这些碳化钼纳米粒子的非均相催化反应的整体影响进行了讨论。
The geometric and electronic structure of catalytically relevant molybdenum carbide phases (cubic delta-MoC, hexagonal alpha-MoC, and orthorhombic beta-Mo2C) and their low Miller-index surfaces have been investigated by means of periodic density functional theory (DFT) based calculations with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. Comparison to available experimental data indicates that this functional is particularly well suited to study these materials. The calculations reveal that beta-Mo2C has a stronger metallic character than the other two polymorphs, both beta-Mo2C and d-MoC have a large ionic contribution, and delta- and alpha-MoC exhibit the strongest covalent character. Among the various surfaces explored, the calculations reveal the high stability of the delta-MoC(001) nonpolar surface, Mo- and C-terminated (001) polar surfaces of alpha-MoC, and the nonpolar (011) surface of beta-Mo2C. A substantially low work function of only 3.4 eV is predicted for beta-Mo2C(011), suggesting that this system is particularly well suited for (electro) catalytic processes where surface -> adsorbate electron transfer is essential. The overall implications for heterogeneously catalysed reactions by these molybdenum carbide nanoparticles are also discussed.