The Progress of Research on Catalytic Mechanism of Nanocrystals Nanocrystals in China University of Science and Technology

Recently, Professor Zeng Jie of the University of Science and Technology of China, in collaboration with Li Zhenyu, has made new progress in the study of the catalytic mechanism of dicrystalline metal nanocrystals. The researchers successfully prepared Au75Pd25 icosahedron and octahedron, although the two alloys exposed the same crystal plane, but the Au75Pd25 icosahedral structure with twin structure catalytic activity and selectivity in cyclohexane oxidation reaction is significantly higher than the single crystal Octahedron of structure. Through in-depth theoretical calculations, the researchers found that the outstanding performance of twin-crystals stems from the enhancement of the surface strain energy induced by the twin structure and the increase of the anion concentration on the active metal surface. The results were published in the "Nano Express" on May 18th. The co-first authors of the thesis were doctoral students Wang Liangbing and Zhao Songyu.

The catalyst used in the cyclohexane oxidation reaction has a significant bottleneck in the improvement of catalytic performance, manifested in enhancing the activity of molecular oxygen as an oxidant and increasing the selectivity towards the target product cyclohexanone. Due to its unique twin structure and the synergistic effect of the alloy, the twin-crystal alloy nanocrystals perform well in the catalytic cyclohexane oxidation reaction. However, the reaction mechanism of the twin structure in the catalytic reaction still lacks in-depth exploration.

To this end, Zeng Jie's research group synthesized Au75Pd25 icosahedron and octahedron separately by adjusting the amount of iodide ion added based on the theory of oxidative etching. The two kinds of alloy nanocrystals expose the same crystal surface, the icosahedron has a twin structure, and the octahedron is a single crystal. Therefore, they are suitable for studying the different behaviors and reaction mechanisms of twins and single crystals in catalytic reactions. In the cyclohexane oxidation reaction, the instantaneous yield of the icosahedron reached 15 106 h−1, three times that of the octahedron, and the selectivity of the icosahedron to cyclohexanone was as high as 84.3%. To explain this phenomenon, researchers combined first-principles calculations and spectral techniques. Studies have shown that the twin structure in the icosahedron causes the surface of the crystal to swell and accumulates a high concentration of negative charges on the surface, both of which promote the enhancement of the icosahedral catalytic activity. The research results provide a new experimental basis and theoretical basis for applying the twin structure to the molecular oxygen oxidation reaction.

The study was funded by the Ministry of Science and Youth's "973" program, the National Natural Science Foundation, and the National Youth 1000-person Program.