采用密度泛函方法研究了水分子在Au, Cu和AuCu二元金属合金表面的不同吸附状态和裂解反应路径, 并且比较不同表面的催化性能. 结果表明, 研究中所考虑4种模型的反应活性顺序如下(以反应活化能为比较标准): Au(111) < AuCu(111)-Cu < AuCu(111)-Au < Cu(111). 相对于AuCu(111)-Cu表面和Au(111)表面, 这与水分子的分子吸附状态在AuCu(111)-Au表面和Cu(111)表面的吸附能相对较小, 而解离吸附状态时的吸附能相对较大有关. 根据金属催化剂表面与吸附物的电子转移和成键电子结构, 认为电子转移越多, 与表面的相互作用越强; 而金属原子的d电子态与水分子1b1电子态或者裂解产物的类1b1电子态之间的重叠、杂化程度决定了两者之间相互作用的强弱. 在实际反应体系中, 用AuCu二元金属合金替代贵金属Au催化剂不仅可以降低材料成本, 还可以提高反应活性.
In order to reduce the amount and cost of gold catalyst in practical application, it is an effective technical strategy to construct binary metal alloy with gold and transition metals. In this work, the adsorption behaviors and dissociation reaction path of water on the different surfaces of Au, Cu, and AuCu binary alloy were studied by using DFT calculations. Based on the calculations, the corresponding catalytic performance of each model was further analyzed. The calculated results showed that the catalytic activity of the considered four surface models is on the following order: Au(111) < AuCu(111)-Cu < AuCu(111)-Au < Cu(111), if using the active energy as comparison standard. The underlying reason of this phenomenon is closely related with the adsorption behavior: the molecular adsorptions of water on Cu(111) and AuCu(111)-Au surfaces have relatively small adsorption energies; while at the same time, the dissociation adsorptions of water on these two surfaces have relatively large adsorption energies. Based on the electron transfer and bonding electronic structure, it could be found that the more electrons transfer between surface and water or H+OH groups, the more strong interaction between catalyst and adsorbate. Furthermore, the overlapping or hybridization between the d states of metal atoms on the surface and the 1b1 states of water or lb1-like states of H+OH groups also determines this interaction. Therefore, using AuCu binary alloy to replace Au as catalyst or co-catalyst reduces cost, and enhances the catalytic activity.