Effect of Nanoparticle Ligands on 4-Nitrophenol Reduction: Reaction Rate, Induction Time, and Ligand Desorption
Effect of Nanoparticle Ligands on 4-Nitrophenol Reduction: Reaction Rate, Induction Time, and Ligand Desorption
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DOI：
10.1021/acscatal.0c02759
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发表时间：
2020-09-04
期刊：
影响因子：
12.9
通讯作者：
Neretina, Svetlana
中科院分区：
文献类型：
--
作者：
Neal, Robert D.;Hughes, Robert A.;Neretina, Svetlana
配体是制备胶体金属催化剂的典型合成工具，可以合理地设计具有高活性和选择性的纳米结构表面。然而，这些试剂可以强烈影响金属纳米结构在水介质中的催化性能。在这方面，目前描述配体对模型催化反应的影响的文献是高度分散的，因为对反应速度、诱导时间和配体解吸现象的理解是不连贯的，有时是相互矛盾的。在这里，我们提出了一项研究，将三个化学上不同的配体应用到裸金催化剂上，然后将它们暴露在与4-硝基苯酚还原相关的水溶液中，同时跟踪配体的去向。结果表明，配体暴露在硼氢化物中会导致它们从金催化剂上几乎完全脱除。这反过来会对4-硝基苯酚的还原速率造成严重的干扰，因为在这种情况下，水中的反应物被清除掉了溶解氧，而配体解吸时间很慢。与之形成鲜明对比的是，当相同的反应物含有溶解氧时，反应速度几乎不受影响，因为由此产生的诱导期为配体在反应开始前提供了充足的解吸时间。此外，强结合配体被证明产生了诱导时间相似的特征，只有当反应物没有溶解氧时才能观察到。总而言之，这些发现倡导不同于当前最佳做法的催化基准程序，并强调了这样一点，即对4-硝基苯酚催化的基本理解必须采用一种考虑到配体-纳米结构相互依赖的整体方法。
Ligands are the quintessential synthesis tool in the preparation of colloidal metal catalysts, allowing for the rational design of nanostructured surfaces with high activity and selectivity. These same agents can, however, strongly influence the catalytic performance of metal nanostructures in aqueous media. In this regard, the current literature describing the influence of ligands on the model catalytic reaction that sees 4-nitrophenol reduced to 4-aminophenol by borohydride is highly fragmented in that the understanding of reaction rate, induction time, and ligand desorption phenomena is disconnected and, at times, contradictory. Herein, we present a study in which three chemically distinct ligands are applied to bare gold catalysts followed by their exposure to aqueous solutions of relevance to 4-nitrophenol reduction while simultaneously tracking the ligand whereabouts. It is shown that the exposure of ligands to borohydride leads to their near-complete removal from the gold catalyst. This, in turn, gives rise to severe disruptions to the rate of 4-nitrophenol reduction for the scenario where the aqueous reactants are purged of dissolved oxygen and ligand desorption times are slow. In sharp contrast, the reaction rate is little affected when the same reactants contain dissolved oxygen because the resulting induction period provides ample time for the ligands to desorb prior to the onset of the reaction. Moreover, strongly bound ligands are shown to give rise to an induction-time-like feature that is only observable when the reactants are free of dissolved oxygen. Collectively, these findings advocate procedures for catalytic benchmarking that differ from current best practices and underscore the point that a fundamental understanding of 4-nitrophenol catalysis must adopt a holistic approach that accounts for ligand-nanostructure interdependencies.