Novio Fernando, Monahan Daniele, Coppel Yannick, Antorrena Guillermo, Lecante Pierre, Philippot Karine, Chaudret Bruno
Laboratoire de Chimie de Coordination, UPR8241 CNRS, 205, Route de Narbonne, 31077 Toulouse (France).
Chemistry. 2014 Jan 27;20(5):1287-97. doi: 10.1002/chem.201303935.
The reactivity of two classes of ruthenium nanoparticles (Ru NPs) of small size, either sterically stabilized by a polymer (polyvinylpyrrolidone, PVP) or electronically stabilized by a ligand (bisdiphenylphosphinobutane, dppb) was tested towards standard reactions, namely CO oxidation, CO2 reduction and styrene hydrogenation. The aim of the work was to identify the sites of reactivity on the nanoparticles and to study how the presence of ancillary ligands can influence the course of these catalytic reactions by using NMR and IR spectroscopies. It was found that CO oxidation proceeds at room temperature (RT) on Ru NPs but that the system deactivates rapidly in the absence of ligands because of the formation of RuO2. In the presence of ligands, the reaction involves exclusively the bridging CO groups and no bulk oxidation is observed at RT under catalytic conditions. The reverse reaction, CO2 reduction, is achieved at 120 °C in the presence of H2 and leads to CO, which coordinates exclusively in a bridging mode, hence evidencing the competition between hydrides and CO for coordination on Ru NPs. The effect of ligands localized on the surface is also evidenced in catalytic reactions. Thus, styrene is slowly hydrogenated at RT by the two systems Ru/PVP and Ru/dppb, first into ethylbenzene and then into ethylcyclohexane. Selectively poisoning the nanoparticles with bridging CO groups leads to catalysts that are only able to reduce the vinyl group of styrene whereas a full poisoning with both terminal and bridging CO groups leads to inactive catalysts. These results are interpreted in terms of location of the ligands on the particles surface, and evidence site selectivity for both CO oxidation and arene hydrogenation.
测试了两类小尺寸钌纳米颗粒（Ru NPs）的反应活性，一类通过聚合物（聚乙烯吡咯烷酮，PVP）进行空间稳定，另一类通过配体（双二苯基膦丁烷，dppb）进行电子稳定，针对标准反应，即CO氧化、CO₂还原和苯乙烯氢化反应。这项工作的目的是确定纳米颗粒上的反应位点，并通过核磁共振（NMR）和红外光谱（IR）研究辅助配体的存在如何影响这些催化反应的进程。研究发现，CO氧化在室温（RT）下于Ru NPs上进行，但在没有配体的情况下，由于形成RuO₂，该体系会迅速失活。在有配体存在的情况下，反应仅涉及桥连CO基团，在催化条件下室温下未观察到整体氧化。逆反应，即CO₂还原，在120°C、有H₂存在的情况下实现，生成CO，其仅以桥连模式配位，因此证明了氢化物与CO在Ru NPs上配位的竞争。表面定位的配体的影响在催化反应中也得到了证明。因此，苯乙烯在室温下被Ru/PVP和Ru/dppb这两个体系缓慢氢化，首先生成乙苯，然后生成乙基环己烷。用桥连CO基团选择性地毒化纳米颗粒会导致催化剂只能还原苯乙烯的乙烯基，而用末端和桥连CO基团完全毒化会导致催化剂失活。这些结果根据配体在颗粒表面的位置进行了解释，并证明了CO氧化和芳烃氢化的位点选择性。
