Enhancing Stability\nof Surface Au under Oxidizing\nConditions through Reduced Bulk Au Content

Contrary to the common assumption that a higher bulk\ncontent of\nprecious metals facilitates the preservation of more surface noble\nmetal by serving as a reservoir for surface enrichment, we demonstrate\nthat a lower bulk content of Au results in a more stable arrangement\nof Au atoms at the surface of Cu–Au nanoparticles when exposed\nto an O<sub>2</sub> atmosphere. Using ambient pressure X-ray photoelectron\nspectroscopy, we investigate the surface segregation and oxidation\nbehavior of Cu–Au nanoparticles across various compositions.\nOur results reveal that in Au-rich nanoparticles exposed to an H<sub>2</sub> atmosphere, surface segregation prompts the formation of\na continuous Au-enriched shell, which subsequently oxidizes into a\ncomplete CuO<sub><i>x</i></sub> shell upon transitioning\nto an O<sub>2</sub> atmosphere. Conversely, in Au-poor nanoparticles\nduring H<sub>2</sub> treatment, segregation results in the emergence\nof Au clusters embedded within the surface layer, persisting upon\nexposure to O<sub>2</sub>. This unexpected phenomenon shows that reducing\nthe bulk content of precious metals can enhance the surface stability\nof noble atoms under oxidizing conditions, as further demonstrated\nby comparing the catalytic performance of Cu–Au nanoparticles\nwith varying Au bulk contents in CO oxidation.