Tracking the redox reaction-induced reconstruction of NiAu nanoparticles via environmental scanning transmission electron microscopy

Atmosphere-related atom migration and phase reconstruction are an easy way for optimizing the catalytic activity of a bimetallic catalyst. Herein, the structure evolutions of NiAu nanoparticles under oxidative and reductive environments are investigated via combining identical location and in situ environmental scanning transmission electron microscopy. During oxidation, a NiO layer first forms and the redispersion of Ni and Au atoms yields a Ni@Au@NiO multi-shell structure at 350 degrees C. Further, Ni and Au segregate into an Au-NiO hybrid structure at 600 degrees C. During reduction, Au atoms disperse over the particle surface forming a NiAu alloy shell with scattered Au atoms/clusters. In situ observation further discloses that the reduction changes the local structural ordering from Ni3Au to NiAu alloy. Very interestingly, the reduced NiAu exhibits promoted activity over oxidized ones for the CO-NO reaction. Density functional theory calculations further reveal the structure-property relationships of CO, NO, and O adsorbates on NiAu alloy surfaces. This study is beneficial for understanding the atmosphere-related evolution behaviors of bimetallic systems, thereby inspiring the catalytic surface optimization.

Automated summary

This study investigates the structural evolution of NiAu nanoparticles under oxidative and reductive environments and reveals that the reduced NiAu exhibits promoted activity over oxidized ones for the CO-NO reaction.