The Interaction between H2O and Preadsorbed O on the Stepped Pt(533) Surface

We have investigated coadsorption of H2O and O-ad on the stepped Pt(533) surface using temperature-programmed desorption in combination with isotope exchange. Water desorption from both bare and oxygen precovered Pt(533) gives rise to three easily identifiable peaks in the TPD spectrum between 140-210 K. Only in coadsorption experiments does a desorption feature at similar to 270 K appear, which we ascribe to recombinative desorption of OHad on step sites lithe surface is saturated with O-ad, we also observe a broadening of the desorption peak at 188 K, indicative of OH formation on terrace sites. Oddly, the magnitude of the isotope exchange hardly varies with O-ad precoverage. Detailed analysis of the results suggest a strong bias for OHterrace formation over OHstep formation. This is likely related to the extent to which OHad can be incorporated into a larger hydrogen bonded network. In spite of the observation that OHstep is more strongly bound than OHterrace, the overall exchange on the Pt(533) surface is much lower than on P(111).