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Isolated Molybdenum(VI) and Tungsten(VI) Oxide Species on Partly Dehydroxylated Silica: A Computational Perspective
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-01-22 , DOI: 10.1021/acs.jpcc.9b09586 Kamil Kurleto 1 , Frederik Tielens 2 , Jarosław Handzlik 1
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-01-22 , DOI: 10.1021/acs.jpcc.9b09586 Kamil Kurleto 1 , Frederik Tielens 2 , Jarosław Handzlik 1
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Although silica-supported molybdenum and tungsten oxide systems are widely used in catalysis, the nature of the surface metal oxide species is still not fully recognized. In this work, comprehensive periodic and cluster density functional theory (DFT) studies of the isolated Mo(VI) and W(VI) oxide species on dehydrated amorphous silica have been performed to give insight into their heterogeneity. It is shown that the relative stabilities of the metal oxide species strongly depend on their location that influences their geometry and the strain of the dehydrated silica surface. The favorable located monooxo W(VI) species are clearly more stable than the dioxo W(VI) species, whereas no strong thermodynamic preference is predicted in the case of the Mo(VI) species. The relative stability of the monoxo species increases in the order: Cr < Mo < W. However, due to geometrical constraints on the silica surface, formation of the tetragrafted monooxo species is hampered, compared to the digrafted dioxo species and the latter are expected to be in majority. The monografted hydroxy dioxo Mo(VI) species are unstable. Based on the vibrational frequency analysis, some details regarding the structure of the experimentally observed dioxo species in the MoOx/SiO2 catalyst are proposed, while the results for the WOx/SiO2 system are somewhat ambiguous.
中文翻译：
部分脱羟基的二氧化硅上的分离的钼（VI）和钨（VI）物种：计算的角度
尽管二氧化硅负载的钼和氧化钨体系广泛用于催化，但仍未充分认识到表面金属氧化物的性质。在这项工作中，已经对脱水的无定形二氧化硅上分离的Mo（VI）和W（VI）氧化物物种进行了全面的周期性和簇密度泛函理论（DFT）研究，以深入了解它们的异质性。结果表明，金属氧化物种类的相对稳定性在很大程度上取决于其位置，从而影响其几何形状和脱水二氧化硅表面的应变。位置优越的单氧W（VI）物种显然比二氧W（VI）物种更稳定，而对于Mo（VI）物种则没有强烈的热力学偏好。一氧化碳物种的相对稳定性按以下顺序增加：Cr <Mo <W。然而，由于二氧化硅表面上的几何约束，与二接枝的二氧代物种相比，四接枝的一氧代物种的形成受到阻碍，并且后者预计将占多数。单接枝的羟基二氧杂Mo（VI）种类不稳定。基于振动频率分析，有关MoO中实验观察到的二恶英物种结构的一些细节提出了x / SiO 2催化剂，而WO x / SiO 2体系的结果有些模棱两可。
更新日期：2020-01-23
中文翻译：
部分脱羟基的二氧化硅上的分离的钼（VI）和钨（VI）物种：计算的角度
尽管二氧化硅负载的钼和氧化钨体系广泛用于催化，但仍未充分认识到表面金属氧化物的性质。在这项工作中，已经对脱水的无定形二氧化硅上分离的Mo（VI）和W（VI）氧化物物种进行了全面的周期性和簇密度泛函理论（DFT）研究，以深入了解它们的异质性。结果表明，金属氧化物种类的相对稳定性在很大程度上取决于其位置，从而影响其几何形状和脱水二氧化硅表面的应变。位置优越的单氧W（VI）物种显然比二氧W（VI）物种更稳定，而对于Mo（VI）物种则没有强烈的热力学偏好。一氧化碳物种的相对稳定性按以下顺序增加：Cr <Mo <W。然而，由于二氧化硅表面上的几何约束，与二接枝的二氧代物种相比，四接枝的一氧代物种的形成受到阻碍，并且后者预计将占多数。单接枝的羟基二氧杂Mo（VI）种类不稳定。基于振动频率分析，有关MoO中实验观察到的二恶英物种结构的一些细节提出了x / SiO 2催化剂，而WO x / SiO 2体系的结果有些模棱两可。
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