A research group led by Prof. DING Yunjie from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) developed a strategy to disperse atoms from activated carbon supported noble metal nanoparticles (NPs) to realize formation of mononuclear complexes.

Supported noble metal catalysts have been broadly used in heterogeneous catalysis, and the catalyst deactivation often occurred due to sintering and agglomeration. Scientists have developed methods to reverse this process, such as oxidation and reduction, chlorination and oxychlorination. However, disadvantages still exist in these methods.

In this study, noble metal nanoparticles of Rh, Ir, Pt, Pd, Ru and Ag with 5 wt% loading supported on activated carbon (AC) could be completely dispersed into stable mononuclear complex through the thermal treatment of CO and CH₃I.

The dispersive process and mechanism were investigated with Rh metal as an example. The researchers found that Rh NPs supported on AC could be efficiently transferred into stable mononuclear complexes of Rh(CO)₂I₃(O-AC) and Rh(CO)I₄(O-AC), in which O-AC representing oxygen-containing groups on the surface of AC.

The combined action of proper temperature, CO, CH₃I and the oxygen-containing groups on the surface of AC are indispensable for the atomic dispersion of supported NPs. Hemolytic cleavage of CH₃I on the surface of Rh NPs produces large amount of free radicals (I·).

The synergetic effect of CO and I· promotes the breakage of Rh-Rh bond and the formation of mononuclear complexes, leading to the gradual dispersion and decrease of Rh NPs. The O-AC provides the anchoring site for the detached mononuclear complexes.

The dispersive process of nanoparticles through the thermal treatment of CO and CH3I mixture. (Image by FENG Siquan)  

This work shares a simple strategy to regenerate sintered catalyst and synthesize supported mononuclear complexes of most precious metal. It will bring new insights and points for the design of single-metal-site catalyst.

This study, published in Nature Communication, was supported by the National Key R&D Program of China and the Strategic Priority Research Program of the Chinese Academy of Sciences.