Dual-Path Mechanism for Catalytic Oxidation of Hydrogen on Platinum Surfaces

The catalytic formation of water from adsorbed hydrogen and oxygen atoms on Pt(111) was studied with scanning tunneling microscopy and high resolution electron energy loss spectroscopy. The known complexity of this reaction is explained by the strongly temperature dependent lifetime of the product ${\mathrm{H}}_2\mathrm{O}$ molecules on the surface. Below the desorption temperature water reacts with unreacted O adatoms to ${\mathrm{OH}}_{\mathrm{ad}}$, leading to an autocatalytic process; at higher temperatures sequential addition of H adatoms to ${\mathrm{O}}_{\mathrm{ad}}$ with normal kinetics takes place.