Experimental and Mechanistic Understanding of Aldehyde Hydrogenation Using Au25 Nanoclusters with Lewis Acids: Unique Sites for Catalytic Reactions
Experimental and Mechanistic Understanding of Aldehyde Hydrogenation Using Au25 Nanoclusters with Lewis Acids: Unique Sites for Catalytic Reactions
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DOI：
10.1021/jacs.5b07716
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发表时间：
2015-11-18
影响因子：
15
通讯作者：
Kim, Hyung J.
中科院分区：
文献类型：
--
作者：
Li, Gao;Abroshan, Hadi;Kim, Hyung J.
研究了 Au-25(SR)(18) 纳米团簇 (R = C2H4Ph) 在碱（例如氨或吡啶）和过渡金属离子 Mz+（例如 Cu+、Cu2+、Ni2+ 和 Co2+）存在下作为路易斯酸对醛氢化反应的催化活性。研究发现添加路易斯酸可显着提高 Au-25(SR)(18)/CeO2 在苯甲醛及其多种衍生物氢化反应中的催化活性。基质辅助激光解吸电离 (MALDI) 和电喷雾电离 (ESI) 质谱与紫外-可见光谱相结合，证实了在路易斯酸存在下新物质 Au25-n(SR)(18-n) (n = 1-4) 的生成。通过密度泛函理论（DFT）方法研究了Au-24（SR）（17）从其母体Au-25（SR）（18）纳米团簇的形态形成途径及其结构。 M(z+) 吸附到 Au-25(SR)(18) 的硫醇盐配体“-SR-”上，然后“-SR-”和与“-SR-”键合的金原子逐步脱离（从而形成“Au-SR”单元），这被认为是 Au-24(SR)(17) 生成的最可能机制。这反过来又将 Au-24(SR)(17) 的 Au-13 核暴露于反应物，为催化氢化提供活性位点。 DFT 计算表明，Mz+ 也能够吸附到 Au13 核表面，产生可能的不同类型的活性金属位点来催化醛氢化反应。这项研究首次表明，具有开放金属位点的物质，例如加合物 [纳米颗粒-M]((z-1)+) 或 Au25-n(SR)(18-n) 片段，而不是完整的 Au-25(SR)(18) 充当催化剂。
The catalytic activity of Au-25(SR)(18) nanoclusters (R = C2H4Ph) for the aldehyde hydrogenation reaction in the presence of a base, e.g., ammonia or pyridine, and transition-metal ions Mz+, such as Cu+, Cu2+, Ni2+ and Co2+, as a Lewis acid is studied. The addition of a Lewis acid is found to significantly promote the catalytic activity of Au-25(SR)(18)/CeO2 in the hydrogenation of benzaldehyde and a number of its derivatives. Matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) mass spectrometry in conjunction with UV-vis spectroscopy confirm the generation of new species, Au25-n(SR)(18-n) (n = 1-4), in the presence of a Lewis acid. The pathways for the speciation of Au-24(SR)(17) from its parent Au-25(SR)(18) nanocluster as well as its structure are investigated via the density functional theory (DFT) method. The adsorption of M(z+) onto a thiolate ligand "-SR-" of Au-25(SR)(18), followed by a stepwise detachment of "-SR-" and a gold atom bonded to "-SR-" (thus an "Au-SR" unit) is found to be the most likely mechanism for the Au-24(SR)(17) generation. This in turn exposes the Au-13-core of Au-24(SR)(17) to reactants, providing an active site for the catalytic hydrogenation. DFT calculations indicate that Mz+ is also capable of adsorbing onto the Au13-core surface, producing a possible active metal site of a different kind to catalyze the aldehyde hydrogenation reaction. This study suggests, for the first time, that species with an open metal site like adducts [nanoparticle-M]((z-1)+) or fragments Au25-n(SR)(18-n) function as the catalysts rather than the intact Au-25(SR)(18).