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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Reduction mechanisms of the CuO(111) surface through surface oxygen vacancy formation and hydrogen adsorption
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Reduction mechanisms of the CuO(111) surface through surface oxygen vacancy formation and hydrogen adsorption

机译：通过表面氧空位形成和氢吸附还原CuO（111）表面的机理

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摘要

We studied the reduction of CuO(lll) surface using density functional theory (DFT) with the generalized gradient approximation corrected for on-site Coulomb interactions (GGA + U) and screened hybrid DFT (HSE06 functional). The surface reduction process by oxygen vacancy formation and H2 adsorption on the CuO(111) surface is investigated as two different reduction mechanisms, it is found that both GGA + U and HSE06 predict the same trend in the relative stability of oxygen vacancies. We found that loss of the subsurface oxygen is initially thermodynamically favourable. As the oxygen vacancy concentration increases, mixture of subsurface and surface vacancies is energetically preferred over full reduction of the surface or subsurface monolayer. The reduction of Cu~(2+) to Cu~+ is found to be more favourable than that of Cu~+ to Cu~0 in the most stable vacancy structures at all concentrations. Consistent with the oxygen vacancy calculations, H2 adsorption occurs initially on under-coordinated surface oxygen. Water molecules are formed upon the adsorption of H2 and this gives a mechanism for H2 reduction of CuO to Cu. Ab initio atomistic thermodynamics shows that reducing CuO to metallic Cu at the surface is more energetically difficult than in the bulk so that the surface oxide protects the bulk from reduction. Using H2 as the reducing agent, it is found that the CuO surface is reduced to Cu2O at approximately 360 K and that complete reduction from Cu2O to metallic Cu occurs at 780 K.
机译：我们使用密度泛函理论（DFT）研究了CuO（III）表面的还原，并针对现场库仑相互作用（GGA + U）和筛选的混合DFT（HSE06功能）校正了广义梯度近似。作为两个不同的还原机理，研究了氧空位形成和H2在CuO（111）表面上的吸附引起的表面还原过程，发现GGA + U和HSE06都预测了氧空位的相对稳定性的相同趋势。我们发现地下氧的损失最初在热力学上是有利的。随着氧空位浓度的增加，在能量上优选地下表面和表面空位的混合，而不是表面或地下单层的完全还原。发现在所有浓度下最稳定的空位结构中，Cu〜（2+）还原为Cu〜+比Cu〜+还原为Cu〜0更有利。与氧空位计算一致，H2吸附最初发生在配位不足的表面氧上。水分子在吸附H2时形成，这提供了H2将CuO还原为Cu的机理。从头算起的原子热力学表明，从表面上将CuO还原为金属Cu的能量比在主体中更为困难，因此表面氧化物可保护主体免受还原。使用H2作为还原剂，发现CuO表面在约360 K时还原为Cu2O，并且在780 K时从Cu2O完全还原为金属Cu。

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