Interaction between H2O and Preadsorbed D on the Stepped Pt(553) Surface

We have studied the interaction of Pt(553) with varying coverages of preadsorbed D and H2O and compare results to those from the similar Pt(533) surface. We have used temperature programmed desorption spectroscopy in combination with isotopic labeling to monitor H-D exchange. Similar to results for Pt(533), on Pt(553) small amounts of D weaken the H2O-metal bonding at steps. Larger D coverages also weaken the stability of the water overlayer at the (111) terraces. However, in contrast to Pt(533), water wets the Pt(553) surface at all D-coverages and the surface does not become hydrophobic. We attribute the difference in the long-range ordering of water to the difference in bond energy of deuterium to (100) and (110) step sites. This also affects HOD formation by H-D exchange. The exchange increases with H2O and D-ad coverage, although less than proportional. Availability of bare Pt sites for both adsorbates is key to obtaining high reactivity.