Unraveling the complexity of oxygen reactions on Pt surfaces

Abstract

Platinum (Pt) is a key material in automotive catalytic converters used to clean up the exhaust of the combustion engine. Pt particles in a ceramic matrix serve as an oxidation catalyst to eliminate toxic carbon monoxide (CO) and unburned hydrocarbons (CxHy) from the engine’s exhaust gases. For this process to work, air is added to the hot exhaust gas before it comes into contact with the catalyst surface where the oxygen molecules from the air stick and dissociate into oxygen atoms. The oxygen atoms adsorbed on the catalyst surface then react with CO and hydrocarbons and convert them into CO2 and H2O, which are released through the tailpipe into the atmosphere. This and other applications of Pt catalysts in the chemical industry have motived extensive studies of oxygen adsorption on Pt surfaces, which have showed that O2 sticking and dissociation on a Pt surface is far from a simple direct dissociation process first described by Langmuir 100 y ago (1, 2). In PNAS, Cao et al. (3) shed new light on the adsorption of oxygen by measuring O2 sticking on a specially prepared (curved) single Pt crystal and by using a beam of rotationally aligned O2 molecules incident on stepped single-crystal Pt surfaces (Fig. 1).\n\n\n\nFig. 1. \nSchematic representation of a curved platinum single crystal exposing a variable step density as function of position on the surface. The magnetic hexapole filter is used to align the rotation of incident O2 molecules either in helicopter (H) or cartwheel (C) orientation.\n\n\n\nPrevious experiments have shown that O2 chemisorption on Pt is rather complex, proceeding via multiple channels occurring on both the step and terrace … \n\n[↵][1]1To whom correspondence may be addressed. Email: rainer.beck{at}epfl.ch.\n\n [1]: #xref-corresp-1-1