Lee Hsuan, Liao Zhen-He, Hsu Po-Wei, Wu Yu-Cheng, Cheng Meng-Chin, Wang Jeng-Han, Luo Meng-Fan
Department of Physics, National Central University, 300 Jhongda Road, Jhongli District, Taoyuan 32001, Taiwan.
Phys Chem Chem Phys. 2018 Apr 25;20(16):11260-11272. doi: 10.1039/c8cp01714j.
The decomposition of methanol-d4 that was adsorbed on Au-Rh bimetallic nanoclusters grown by the sequential deposition of Au and Rh vapors onto ordered thin-film Al2O3/NiAl(100) at 300 K, occurred by means of dehydrogenation and primarily on the surface Rh. Nevertheless, the surface Rh atoms were not equally reactive; their reactivity altered with both structural and electronic effects arising from the alloying. The Au deposited on Rh clusters decorated the surface and deactivated Rh by not only directly obstructing them but also by neighboring them. As the initially incorporated Au tended to aggregate around reactive low-coordinated Rh atoms, such as corner Rh atoms, the reactivity of the cluster, indicated by the CO and deuterium (D2) produced per surface Rh, decreased markedly. In contrast, the Rh deposited on Au clusters promoted their reactivity. The reactivity was sharply enhanced by a few incorporated Rh atoms, as they preferentially decorated the edge Au atoms, resulting in their lower coordination, more positive charge, higher energetic d-band centers, and high reactivity. On the reactive Rh, the scission of the O-D bond in the initial dehydrogenation of methanol-d4 became more preferential than the competing desorption. The further incorporated Rh failed to promote the reactivity, but the clusters remained more reactive than those formed by Rh clusters incorporating Au as their structuring involved an active atomic segregation that yielded more low-coordinated and reactive surface Rh.
在300 K下，通过将金和铑蒸气依次沉积到有序薄膜Al2O3/NiAl(100)上生长的金-铑双金属纳米团簇上吸附的甲醇-d4，其分解是通过脱氢作用发生的，且主要发生在表面铑上。然而，表面铑原子的反应活性并不相同；它们的反应活性会因合金化产生的结构和电子效应而改变。沉积在铑团簇上的金不仅直接阻碍铑原子，还通过与它们相邻而使铑失活。由于最初掺入的金倾向于聚集在反应性低配位的铑原子周围，如角部铑原子，每个表面铑产生的一氧化碳和氘（D2）所表明的团簇反应活性显著降低。相比之下，沉积在金团簇上的铑提高了它们的反应活性。少数掺入的铑原子显著增强了反应活性，因为它们优先修饰边缘金原子，导致其配位降低、电荷更正、高能d带中心以及高反应活性。在反应性铑上，甲醇-d4初始脱氢过程中O-D键的断裂比竞争性脱附更具优势。进一步掺入的铑未能提高反应活性，但这些团簇仍比由掺入金的铑团簇形成的团簇更具反应活性，因为它们的结构涉及活性原子偏析，产生了更多低配位和反应性的表面铑。
