Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Institute, Faradayweg 4-6, 14195 Berlin, Germany.
Chemistry. 2010 Sep 3;16(33):10007-13. doi: 10.1002/chem.201001330.
The catalytic oxidation of alcohols with molecular oxygen on supported nanometallic catalysts represents one of the green methods in a crucial process for the synthesis of fine chemicals. We have designed an experiment using physically mixed Au/AC and Pd/AC (AC=activated carbon) as the catalyst in the liquid-phase oxidation of benzyl alcohol by aerobic oxygen. The evolution of the physically mixed catalyst structures at different stages in the catalytic reaction was investigated by aberration-corrected high-resolution transmission electron microscopy and spatially resolved element mapping techniques at the nanometre scale, and they were also compared with the structure of the bimetallic alloy. For the first time we show the formation of surface Au-Pd bimetallic sites by reprecipitation of Pd onto Au nanoparticles. Negligible Au leaching was observed. The in situ structural evolution can be directly correlated to the great enhancement of the catalyst activity. Moreover, we distinguish the different behaviours of Au and Pd, thus suggesting an oxygen differentiating mechanism for Au and Pd sites. The findings are of great importance to both the understanding of the structure-activity correlation and the design of highly active catalysts in green chemistry.
负载型纳米金属催化剂上的分子氧催化醇的氧化是精细化学品合成中关键过程的绿色方法之一。我们设计了一个实验，使用物理混合的 Au/AC 和 Pd/AC（AC=活性炭）作为催化剂，在有氧氧气存在下液相氧化苯甲醇。通过在纳米尺度上使用像差校正的高分辨率透射电子显微镜和空间分辨元素映射技术研究了在催化反应的不同阶段物理混合催化剂结构的演变，并将其与双金属合金的结构进行了比较。我们首次展示了通过将 Pd 再沉淀到 Au 纳米粒子上形成表面 Au-Pd 双金属位。观察到几乎没有 Au 浸出。原位结构演变可以直接与催化剂活性的大幅增强相关联。此外，我们区分了 Au 和 Pd 的不同行为，从而为 Au 和 Pd 位点提出了一种氧区分机制。这些发现对于理解结构-活性关系以及设计绿色化学中的高效催化剂都具有重要意义。
