Fernandez Eva M, Balbas Luis C
Departamento de Física Teórica, Atómica y Optica, Universidad de Valladolid, E-47011 Valladolid, Spain.
J Phys Chem B. 2006 Jun 1;110(21):10449-54. doi: 10.1021/jp060426l.
Aiming to understand the role of the substrate in the adsorption of carbon monoxide on gold clusters supported on metal-oxides, we have started a study of that process on two different alumina substrates: an amorphous-like fully relaxed stoichiometric (Al2O3)20 cluster and the Al terminated (0001) surface of alpha-(Al2O3) crystal. In this paper, we present first principles calculations for the adsorption of one Au atom on both alumina substrate and the adsorption of Au8 on (Al2O3)20. Then, we study the CO adsorption on the minimum energy structure of these three different gold/alumina systems. A single Au adsorbs preferably on top of an Al atom with low coordination, the binding energy being higher in the case of Au/(Al2O3)20. CO absorbs preferably on top of the Au atom, but in the case of Au/(Al2O3)20, Au forms a bridge with the Al and O substrate atoms after CO adsorption. We find other stable sites for CO adsorption on the cluster but not on the surface. This result suggests that the Au activity toward CO may be larger for the amorphous cluster than for the crystal surface substrate. For the most stable Au8/(Al2O3)20 configuration, two Au atoms bind to Al and a O atoms respectively and CO adsorbs on top of the Au which binds to the Al atom. We find other CO adsorption sites on supported Au8 which are not stable for the free Au8 cluster.
为了理解底物在一氧化碳吸附到负载于金属氧化物上的金团簇过程中的作用，我们开始了在两种不同氧化铝底物上对该过程的研究：一种类非晶态完全弛豫的化学计量比(Al2O3)20团簇以及α-(Al2O3)晶体的Al端接(0001)表面。在本文中，我们给出了一个金原子在两种氧化铝底物上的吸附以及Au8在(Al2O3)20上的吸附的第一性原理计算。然后，我们研究了这三种不同金/氧化铝体系的最低能量结构上的一氧化碳吸附。单个金原子优选吸附在低配位的铝原子顶部，在Au/(Al2O3)20的情况下结合能更高。一氧化碳优选吸附在金原子顶部，但在Au/(Al2O3)20的情况下，一氧化碳吸附后金与铝和氧底物原子形成桥键。我们在团簇上发现了其他一氧化碳吸附的稳定位点，但在表面上没有。该结果表明，对于非晶团簇，金对一氧化碳的活性可能比对晶体表面底物的活性更大。对于最稳定的Au8/(Al2O3)20构型，两个金原子分别与铝和一个氧原子结合，一氧化碳吸附在与铝原子结合的金原子顶部。我们在负载的Au8上发现了其他一氧化碳吸附位点，而这些位点对于游离的Au8团簇是不稳定的。
