Temperature-programmed desorption studies of the interactions of OD and CO with Pt(111)

Abstract

Temperature-programmed desorption (TPD) measurements were made to probe the interactions of hydroxyl radicals (OD) with Pt(111). A pure, intense molecular beam of OD was prepared by filtering the effluent from a supersonic corona discharge D2O/He source through an electrostatic hexapole. The hexapole selectively transmitted only OD radicals in the |JΩM〉=|323232〉 rotational state and eliminated any D2O, oxygen or hydrogen atoms, or other contaminants from the beam. Experiments were carried out by dosing the surface with OD at a surface temperature of TS=275K. Oxide states formed were characterized by desorption temperatures of TS=700, 735, and 790K. The 735K feature is believed to correspond to a near-surface oxide (PtOx) as seen previously in O3/Pt(111) studies. CO titration experiments revealed three CO2 desorption features: dominant features at TS=340K and TS=440K, the latter being perhaps due to oxidation via the PtOx. Another set of experiments were carried out by dosing OD at a surface temperature of TS=150K. Major D2O desorption features were observed at TS=210K corresponding to the decomposition of an OD-intermediate layer and at TS=170K corresponding to molecular water desorption. The O2 TPD spectra showed the same three features observed at the higher dosing temperature, however, in substantially different ratios. CO oxidation experiments also revealed new behavior. Five CO2 desorption features were detected: the dominant features near TS≈300K and at TS≈440K, a smaller feature at TS=650K, and two minor features at TS≈185 and 230K. Others have seen the latter two features previously in O2/CO Pt(111) studies.