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 °C. Further, Ni and Au segregate into an Au-NiO hybrid structure at 600 °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.