Molecular Oxygen Network as a Template for Adsorption of Ammonia on Pt(111)

Abstract

Low-temperature scanning tunneling microscopy (STM) was used to observe a mixed NH₃–O₂ overlayer on Pt(111). At adsorption temperatures below 50 K, the chemisorbed O₂ molecules form an ordered network at high coverages. The STM images reveal that this network features a distributed set of holes corresponding to on-top sites of the Pt lattice that are surrounded by two or three O₂ molecules. Different hole–hole distances are observed with 0.73 nm most common. These holes in the O₂ network act as preferential adsorption sites for the ammonia molecules leading to the formation of an NH₃–O₂ complex that serves as a precursor to ammonia oxydehydrogenation