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.

催化活性位点的精准确定，对于阐明催化反应机理、指导开发更高性能的催化剂具有至关重要的意义。然而，负载型金属纳米催化剂（supported metal nanocatalysts）的结构极为复杂，涵盖载体、金属表面与金属-载体界面三部分，这仍为相关研究带来巨大挑战。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。本研究填补了这一空白，证实硫掺杂碳负载型金属纳米催化剂中的金属-硫界面，是多种催化加氢反应的核心活性位点。我们首先制备并表征了一系列金属粒径相近但金属-硫界面数量各异的纳米催化剂。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。进一步的实验与密度泛函理论（DFT）计算表明，喹啉的吸附与活化过程发生于Ir-S界面处的Ir原子上。类似现象也出现在Pt-S界面催化对氯硝基苯加氢、Ru-S界面催化苯甲酸加氢的体系中。上述所有发现均验证了金属-硫界面在催化加氢反应中的主导活性，并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。