Sulaiman Kazeem O, Purves Randy W, Scott Robert W J
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada.
J Chem Phys. 2021 Aug 28;155(8):084301. doi: 10.1063/5.0060248.
Designing atom-precise bimetallic clusters with a relatively cost-effective and more abundant metal than Au (i.e., Ag) is desirable for the development of heterogeneous bimetallic cluster catalysts for industrial applications. Atom-precise Ag-based bimetallic clusters, which are analogs of the well-studied Au based clusters, are yet to be fully explored as catalysts. Establishing the Pd loading limit and the position of the Pd dopant in AgPd bimetallic clusters will further give an insight into the structure-activity relationships for these atom-precise AgPd heterogeneous catalysts. In this study, an improved single-pot co-reduction strategy was employed to prepare the bimetallic clusters, which were then characterized by mass spectrometry, x-ray photoelectron spectroscopy (XPS), and x-ray absorption spectroscopy (XAS) to identify the loading and position of the dopant metal. Our results show that only a single dopant Pd atom can be incorporated, and in comparison with monometallic Ag clusters, the absorption peaks of AgPd(SPhMe) bimetallic clusters are blue shifted due to the incorporation of Pd. The XPS and XAS results show that the AgPd(SPhMe) bimetallic clusters have multivalent Ag(0) and Ag(I) atoms and surprisingly show Pd(II) species with significant Pd-S bonding, despite the prevailing wisdom that the Pd dopant should be in the center of the cluster. The XAS results show that the singly doped Pd atom predominantly occupies the staple position, albeit we cannot unambiguously rule out the Pd atom in an icosahedral surface position in some clusters. We discuss the ramifications of these results in terms of possible kinetically vs thermodynamically controlled cluster formation.
设计具有比金（即银）成本效益更高且更丰富的金属的原子精确双金属簇，对于开发用于工业应用的多相双金属簇催化剂而言是很有必要的。原子精确的银基双金属簇是经过充分研究的金基簇的类似物，但作为催化剂尚未得到充分探索。确定钯负载极限以及钯掺杂剂在银钯双金属簇中的位置，将进一步深入了解这些原子精确的银钯多相催化剂的结构 - 活性关系。在本研究中，采用了一种改进的单锅共还原策略来制备双金属簇，然后通过质谱、X射线光电子能谱（XPS）和X射线吸收光谱（XAS）对其进行表征，以确定掺杂金属的负载量和位置。我们的结果表明，只能掺入单个掺杂钯原子，并且与单金属银簇相比，由于钯的掺入，AgPd(SPhMe)双金属簇的吸收峰发生蓝移。XPS和XAS结果表明，AgPd(SPhMe)双金属簇具有多价Ag(0)和Ag(I)原子，令人惊讶的是，尽管普遍认为钯掺杂剂应位于簇的中心，但仍显示出具有显著Pd - S键的Pd(II)物种。XAS结果表明，单掺杂的钯原子主要占据主链位置，尽管我们不能明确排除在某些簇中位于二十面体表面位置的钯原子。我们根据可能的动力学与热力学控制的簇形成来讨论这些结果的影响。
