Chinese Academy of Sciences (CAS) Key Laboratory of Nanosystem and Hierarchy Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China.
School of Science, Tianjin University, Tianjin 300072, China.
Nature. 2016 Nov 3;539(7627):76-80. doi: 10.1038/nature19763. Epub 2016 Oct 5.
Owing to the limited availability of natural sources, the widespread demand of the flavouring, perfume and pharmaceutical industries for unsaturated alcohols is met by producing them from α,β-unsaturated aldehydes, through the selective hydrogenation of the carbon-oxygen group (in preference to the carbon-carbon group). However, developing effective catalysts for this transformation is challenging, because hydrogenation of the carbon-carbon group is thermodynamically favoured. This difficulty is particularly relevant for one major category of heterogeneous catalyst: metal nanoparticles supported on metal oxides. These systems are generally incapable of significantly enhancing the selectivity towards thermodynamically unfavoured reactions, because only the edges of nanoparticles that are in direct contact with the metal-oxide support possess selective catalytic properties; most of the exposed nanoparticle surfaces do not. This has inspired the use of metal-organic frameworks (MOFs) to encapsulate metal nanoparticles within their layers or inside their channels, to influence the activity of the entire nanoparticle surface while maintaining efficient reactant and product transport owing to the porous nature of the material. Here we show that MOFs can also serve as effective selectivity regulators for the hydrogenation of α,β-unsaturated aldehydes. Sandwiching platinum nanoparticles between an inner core and an outer shell composed of an MOF with metal nodes of Fe, Cr or both (known as MIL-101; refs 19, 20, 21) results in stable catalysts that convert a range of α,β-unsaturated aldehydes with high efficiency and with significantly enhanced selectivity towards unsaturated alcohols. Calculations reveal that preferential interaction of MOF metal sites with the carbon-oxygen rather than the carbon-carbon group renders hydrogenation of the former by the embedded platinum nanoparticles a thermodynamically favoured reaction. We anticipate that our basic design strategy will allow the development of other selective heterogeneous catalysts for important yet challenging transformations.
由于天然资源的有限供应，调味剂、香料和制药行业对不饱和醇的广泛需求是通过从α，β-不饱和醛生产不饱和醇来满足的，通过选择性地氢化碳-氧基团（优先于碳-碳基团）。然而，开发这种转化的有效催化剂具有挑战性，因为氢化碳-碳基团在热力学上是有利的。对于一类主要的多相催化剂：金属氧化物负载的金属纳米粒子，这种困难尤其相关。这些系统通常无法显著提高对热力学不利反应的选择性，因为只有与金属氧化物载体直接接触的纳米粒子的边缘才具有选择性催化特性；大多数暴露的纳米粒子表面没有。这激发了使用金属有机骨架（MOFs）将金属纳米粒子封装在其层内或通道内，以在保持有效反应物和产物传输的情况下影响整个纳米粒子表面的活性，这是由于材料的多孔性质。在这里，我们表明 MOFs 也可以作为α，β-不饱和醛氢化的有效选择性调节剂。将铂纳米粒子夹在由具有 Fe、Cr 或两者的金属节点的 MOF（称为 MIL-101；参考文献 19、20、21）组成的内芯和外壳之间，得到稳定的催化剂，可高效转化一系列α，β-不饱和醛，并显著提高对不饱和醇的选择性。计算表明，MOF 金属位与碳-氧而不是碳-碳基团的优先相互作用使嵌入的铂纳米粒子对前者的氢化成为热力学有利的反应。我们预计，我们的基本设计策略将允许开发其他用于重要但具有挑战性的转化的选择性多相催化剂。
