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自Haruta和Hutchings发现负载的纳米金催化剂的催化活性后,负载型金催化剂一直是非均相催化的研究重点之一.近年来,单原子催化剂因其优异的活性、选择性,超高的原子利用效率,引起了科学家们的广泛关注.越来越多的单原子金催化剂被成功制备,并被证实具有很好的催化活性.水,作为环境中最常见的物质,在实际的催化体系中往往难以避免,即使在超高真空环境中也会有痕量的水气存在.水的解离不仅是水煤气反应的重要步骤之一,而且对别的反应也有一定的促进作用.尽管水和纳米团簇催化剂之间的研究已经颇有成效,但水和单原子金催化剂之间的作用还不是非常清晰.因此,我们采用密度泛函理论从原子尺度研究了水和Au1/CeO_2单原子催化剂的相互作用.我们首先研究了水在完美CeO_2表面和含有一个氧空位的CeO_(2-x)表面上的解离过程,研究发现分子态的水和解离态的水在完美CeO_2表面可以共存,而一旦在表面形成氧空位后,由于较低的能垒和极大的放热,解离态的水将占据绝对优势.接下来探索了水在完美Au1/CeO_2表面和含有一个氧空位的Au1/CeO_(2-x)表面上的解离过程,发现结论恰好和CeO_2表面相反.水的解离过程在完美的Au1/CeO_2表面几乎是一个无能垒的过程,并且解离会放出大量的热量.而一旦在表面形成氧空位后,单原子Au的轨道处于满占状态,无法提供水的吸附位点.水的解离过程在Ce位点进行,分子吸附能与解离吸附能相当,分子态与解离态共存.为了进一步理解单原子金在水的解离过程中起到的作用,我们分析了水和Au_1/CeO_2之间的电子相互作用.研究结果表明,单原子金不仅为水的吸附提供了位点,金的5d轨道和水的2p轨道之间的相互作用还有效减弱了水中氧氢键的强度,使水的解离更容易进行.由此可见,在涉及到水解离的反应中,以Au_1/CeO_2为代表的单原子催化剂有望带来新的突破.最后,我们还测试了范德华力对研究体系的影响.研究发现尽管范德华力会使吸附能的绝对值增加,但是并不影响我们得到的结论.
Since the discovery of the catalytic activity of supported gold nanoparticles by Haruta and Hutchings, supported gold catalysts have been the focus of heterogeneous catalysis.In recent years, monatomic catalysts have been widely used in many fields due to their excellent activity, selectivity and ultra-high atom utilization Efficiency has aroused widespread concern of scientists.An increasing number of single-atom gold catalysts have been successfully prepared and proved to have good catalytic activity.Water, as the most common material in the environment, often in the actual catalytic system It is difficult to avoid trace amounts of water vapor even in ultra-high vacuum environment. Dissociation of water is not only one of the important steps in the reaction of water gas, but also can promote other reactions .Although water and nanoclusters However, the interaction between water and monatomic Au catalysts is not yet very clear, so we used density functional theory to study the interaction between water and Au1 / CeO_2 monatomic catalysts from atomic scale We first study the dissociation of water on a perfect CeO 2 surface and a CeO 2 (2-x) surface containing an oxygen vacancy. It was found that the molecular water and dissociation state Water can coexist on the perfect CeO 2 surface, and once the oxygen vacancies are formed on the surface, the dissociated water will have an absolute advantage due to the lower energy barrier and extreme heat release.Next, The results show that the dissociation process on the surface of Au1 / CeO_ (2-x) with an oxygen vacancies is opposite to that of CeO_2 surface. The dissociation process of water is almost a barrierless process on the perfect Au1 / CeO_2 surface, And dissociation will release a lot of heat.Once the formation of oxygen vacancies on the surface, the monatomic Au orbit full occupancy, can not provide water adsorption sites.The water dissociation process at the Ce site, the molecular adsorption energy Which is equivalent to the dissociative adsorption energy, and the molecular states and the dissociative states coexist.In order to further understand the role of monatomic gold in the dissociation of water, we analyze the electronic interaction between water and Au_1 / CeO_2. It is indicated that the monatomic gold not only provides the site for the adsorption of water, but also the interaction between the 5d orbit of gold and the 2p orbit of water effectively weakens the strength of oxygen-hydrogen bond in water and makes the dissociation of water easier. This can be seen in reactions involving hydrolysis , The single atom catalyst represented by Au_1 / CeO_2 is expected to bring about a new breakthrough.Finally, we also test the influence of van der Waals forces on the research system.The study found that although van der Waals forces will increase the absolute value of the adsorption energy, it does not affect We got the conclusion.