负载到二氧化钛和二氧化锆表面上的金团簇的结构
发布时间：2018-11-07 07:08
【摘要】：从1987年Haruta等人发现TiO_2或Fe2O3衬底上的金团簇在低温下的高效催化活性以来,近三十年来纳米金催化剂得到了人们的广泛关注。到目前为止,人们发现纳米金担载到一些金属氧化物上能催化很多化学反应,包括烯烃制氢、硝基还原、醇类的选择性氧化、一些耦合反应、胺化反应等等。众所周知,催化剂的催化效率和纳米金团簇的形状、尺寸、以及与金属氧化物界面之间的电荷转移有关。本论文中我们用密度泛函理论方法,研究了Aun(n=1-20)团簇在金红石相TiO_2(110)面的稳定结构及其电荷转移机理。我们分别计算了金团簇在自然状态下和负载到表面上的形状和尺寸,并且分析了它们之间的联系,发现在自然状态下Aun(n≤13)时,团簇倾向于二维平面结构稳定,二维(2D)到三维的转变(2D-3D)发生在n=13或15。Au20团簇呈现四面体结构稳定,可以看做是面心立方体相金的一部分,对于中等尺寸的金团簇是类面心立方、二层、笼状结构,或者是拥挤的对称性极低的壳状结构稳定。同时,我们也研究了金团簇在表面上的生长模式,但是金团簇在表面上的生长模式和在自然状态下的生长模式很不相同。由于我们计算的金团簇相对比较大,所以在计算过程中我们的模型也相对很大,大的由几百个原子组成,尤其是要保证团簇和团簇之间没有相互作用,表面就会相应增大,团簇越大,计算模型也越大,这样对于计算机耗时量也相对很大。在这篇文章中,我们用更大的表面,进一步系统地计算了Aun/TiO_2(n=1-20)团簇在TiO_2(110)面的生长模式。我们想知道团簇Aun(n≥7)在金红石相TiO_2(110)面上的稳定吸附构型,进一步了解团簇和表面的相互作用机理,同时也讨论了电子结构和电荷分布。我们发现Aun团簇在表面上倾向于平面或类平面结构,并且这些平面结构和实验是相符的,色散力决定了Aun团簇和表面的相互作用,从而形成了Aun团簇的平面结构。TiO_2表面上的所有Aun团簇都带正电荷,但是由于团簇所含原子奇偶数不同,团簇所带电荷随着n的增大会出现振荡,尤其是n12。当n为偶数时我们能观察到明显的电荷不一致性,在一些偶数个金原子的Aun团簇中,部分Au原子带有明显的负电荷。同时我们也研究了Aun(n=1-14)团簇负载在ZrO_2(111)面的生长模式。我们进行了比较,金团簇在这两种表面上的稳定吸附都是倾向于平面结构,但是稳定构型有很大不同,而且从电荷分析来看,金团簇在二氧化锆表面吸附时随着团簇的增大,电荷分布几乎呈直线型,而不会出现振荡。
[Abstract]:Since 1987, when Haruta et al. discovered the high catalytic activity of gold clusters on TiO_2 or Fe2O3 substrates at low temperature, nanocrystalline gold catalysts have attracted much attention in recent 30 years. Up to now, it has been found that gold nanoparticles supported on some metal oxides can catalyze many chemical reactions, including olefin hydrogen production, nitro reduction, selective oxidation of alcohols, some coupling reactions, amination and so on. It is well known that the catalytic efficiency of the catalysts is related to the shape and size of the gold nanoclusters and to the charge transfer between the metal oxide interfaces. In this paper, we study the stable structure and charge transfer mechanism of Aun (nni1-20) clusters on the TiO_2 (110) surface of rutile phase by using density functional theory (DFT). We calculate the shape and size of gold clusters in natural state and load to surface, and analyze the relationship between them. It is found that when Aun (n 鈮，
本文编号：2315602
[Abstract]:Since 1987, when Haruta et al. discovered the high catalytic activity of gold clusters on TiO_2 or Fe2O3 substrates at low temperature, nanocrystalline gold catalysts have attracted much attention in recent 30 years. Up to now, it has been found that gold nanoparticles supported on some metal oxides can catalyze many chemical reactions, including olefin hydrogen production, nitro reduction, selective oxidation of alcohols, some coupling reactions, amination and so on. It is well known that the catalytic efficiency of the catalysts is related to the shape and size of the gold nanoclusters and to the charge transfer between the metal oxide interfaces. In this paper, we study the stable structure and charge transfer mechanism of Aun (nni1-20) clusters on the TiO_2 (110) surface of rutile phase by using density functional theory (DFT). We calculate the shape and size of gold clusters in natural state and load to surface, and analyze the relationship between them. It is found that when Aun (n 鈮，
本文编号：2315602
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