Metal–Sulfur Interfaces as the Primary Active Sites for Catalytic Hydrogenations

The determination of catalytically active sites is crucial for understanding the catalytic mechanism and providing guidelines for the design of more efficient catalysts. However, the complex structure of supported metal nanocatalysts (e.g., support, metal surface, and metal–support interface) still presents a big challenge. In particular, many studies have demonstrated that metal–support interfaces could also act as the primary active sites in catalytic reactions, which is well elucidated in oxide-supported metal nanocatalysts but is rarely reported in carbon-supported metal nanocatalysts. Here, we fill the above gap and demonstrate that metal–sulfur interfaces in sulfur-doped carbon-supported metal nanocatalysts are the primary active sites for several catalytic hydrogenation reactions. A series of metal nanocatalysts with similar sizes but different amounts of metal–sulfur interfaces were first constructed and characterized. Taking Ir for quinoline hydrogenation as an example, it was found that their catalytic activities were proportional to the amount of the Ir–S interface. Further experiments and density functional theory (DFT) calculations suggested that the adsorption and activation of quinoline occurred on the Ir atoms at the Ir–S interface. Similar phenomena were found in p-chloronitrobenzene hydrogenation over the Pt–S interface and benzoic acid hydrogenation over the Ru–S interface. All of these findings verify the predominant activity of metal–sulfur interfaces for catalytic hydrogenation reactions and contribute to the comprehensive understanding of metal–support interfaces in supported nanocatalysts.

催化活性位点的确定，对于阐明催化反应机制、指导高效催化剂的设计均具有关键意义。然而，负载型金属纳米催化剂（载体、金属表面以及金属-载体界面）的复杂结构，仍是该领域的一大研究难题。尤为关键的是，诸多研究已证实，金属-载体界面亦可作为催化反应的主要活性位点；这一结论在氧化物负载型金属纳米催化剂中已得到充分阐释，但在碳负载型金属纳米催化剂中却鲜有报道。本研究填补了上述研究空白，证实硫掺杂碳负载型金属纳米催化剂中的金属-硫界面，是数种催化加氢反应的核心活性位点。本研究首先构建并表征了一系列尺寸相近但金属-硫界面数量各异的金属纳米催化剂。以喹啉加氢反应中的铱（Ir）基催化剂为例，研究发现其催化活性与Ir-S界面的数量呈正相关关系。后续实验与密度泛函理论（DFT）计算结果表明，喹啉的吸附与活化过程均发生于Ir-S界面处的铱原子上。在对氯硝基苯加氢反应的Pt-S界面以及苯甲酸加氢反应的Ru-S界面中，亦观测到了一致的现象。上述研究结果证实了金属-硫界面在催化加氢反应中的主导活性，有助于深化对负载型纳米催化剂中金属-载体界面的全面认知。