Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
J Phys Chem A. 2010 Mar 25;114(11):3802-10. doi: 10.1021/jp905761s.
When going from periodic surfaces to isolated clusters or nanoparticles, there is a big increase in the reactivity of Au and Cu toward SO(2). Density functional calculations indicate that the enhancement in the SO(2) adsorption energy is due to the presence of corner sites (i.e., metal atoms with a low coordination number) and the fluxionality of the nanoparticles. Therefore, small Au particles bind SO(2) stronger than a periodic Au(100) surface. However, the S <--> Au and O <--> Au interactions are not strong enough to induce the rupture of the S-O bonds. In contrast, the dissociation of SO(2) on Cu particles is a very exothermic process, even more exothermic than on a periodic Cu(100) surface. Experiments of synchrotron-based high-resolution photoemission and X-ray absorption spectroscopy show big differences in the DeSOx activity of Au and Cu nanoparticles dispersed on MgO(100) and CeO(2)(111). The heat of adsorption of the SO(2) on Au nanoparticles supported on MgO(100) or CeO(2)(111) was 0.2 to 0.4 eV larger than on Au(100) with negligible dissociation of the molecule. The full decomposition of SO(2) was observed only after O vacancies were introduced in the ceria support. The O vacancies in ceria either played a direct role in the dissociation of SO(2) (cracking of the molecule at the oxide-metal interface) or enhanced the chemical activity of the supported Au nanoparticles. The addition of Cu particles to MgO(100) or CeO(2)(111) generates systems that are extremely active for the destruction of SO(2). At 100-150 K, the SO(2) adsorbs molecularly on the supported Cu particles. Heating to temperatures above 200 K leads to massive dissociation of the SO(2). A comparison of the behavior of SO(2) on Cu/MgO(100) and Cu/CeO(2-x)(111) shows how important the reducibility of the oxide support in DeSOx operations can be.
从周期性表面到孤立的簇或纳米粒子，金和铜对 SO(2)的反应性会大大增强。密度泛函计算表明，SO(2)吸附能的增强是由于存在角位（即配位数较低的金属原子）和纳米粒子的流变性。因此，小金颗粒比周期性的 Au(100)表面更能吸附 SO(2)。然而，S <--> Au 和 O <--> Au 相互作用不够强，无法导致 S-O 键的断裂。相比之下，SO(2)在 Cu 粒子上的解离是一个非常放热的过程，甚至比在周期性的 Cu(100)表面上更放热。基于同步加速器的高分辨率光电子能谱和 X 射线吸收光谱实验表明，负载在 MgO(100)和 CeO(2)(111)上的 Au 和 Cu 纳米粒子的 DeSOx 活性存在很大差异。SO(2)在负载于 MgO(100)或 CeO(2)(111)上的 Au 纳米粒子上的吸附热比在 Au(100)上大 0.2 到 0.4 eV，分子几乎没有解离。只有在 CeO(2)载体中引入氧空位后，才观察到 SO(2)的完全分解。CeO(2)中的氧空位要么直接在 SO(2)的解离中起作用（在氧化物-金属界面处裂解分子），要么增强了负载的 Au 纳米粒子的化学活性。将 Cu 颗粒添加到 MgO(100)或 CeO(2)(111)上会生成对 SO(2)破坏极为活跃的体系。在 100-150 K 时，SO(2)在负载的 Cu 颗粒上以分子形式吸附。加热到 200 K 以上温度会导致 SO(2)的大量解离。比较 SO(2)在 Cu/MgO(100)和 Cu/CeO(2-x)(111)上的行为表明，氧化物载体的还原能力在 DeSOx 操作中是多么重要。
