A research team led by Prof. Qiang Fu and Prof. Xinhe Bao from Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences in collaboration with Prof. Bing Yang from DICP and Prof. Yi Gao from Shanghai Institute of Applied Physics of the Chinese Academy of Sciences reported an oxygen adsorption-induced dispersion of metallic Ag nanoclusters in a typical oxidative atmosphere. The results were published in Nature Communication 2021, 12, 1406 (https://www.nature.com/articles/s41467-021-21552-2).
Oxidative dispersion has been widely used in regeneration of sintered metal catalysts and fabrication of single atom catalysts. The consensus on the oxidative dispersion process includes the formation of mobile metal oxide species from large metal particles and capture of these species on the support surface. This oxidation-induced dispersion mechanism remains to be solidified by in situ electron microscopic and/or spectroscopic characterizations.
With the help of in situ imaging methods including environmental scanning electron microscopy (ESEM) and newly developed near-ambient pressure photoemission electron microscopy (NAP-PEEM), researchers found that micron-scale Ag nanowires can be dispersed into subnanometer clusters under oxygen atmosphere. Ex situ experiments indicated that Ag nanowires were converted to AgOx nanoclusters. In contrast, in situ near-ambient pressure photoelectron spectroscopy (NAP-XPS) directly demonstrated a transitional state of metallic Ag nanoclusters during dispersion at high temperature while the oxide formation occurred during cooling process. The dynamic dispersion of Ag nanowires during CO oxidation was further demonstrated. Based on the experimental and theory calculation results, chemisorption of oxygen from O2 atmosphere was proved as the essential driving force for the dispersion of metallic Ag nanoclusters. This work provides a new understanding for the role of O2 atmosphere played in oxidative dispersion, which is of great significance in predicting and controlling the dynamic dispersion/redispersion of supported metal catalysts under reaction conditions.
This work was financially supported by the National Natural Science Foundation of China, the Strategic Priority Research Program (B) of the Chinese Academy of Sciences, the Ministry of Science and Technology of China, and DNL Cooperation Fund. (Text/image by Rongtan Li).