Site-specific catalytic activity of model platinum surfaces in different electrolytic environments as monitored by the CO oxidation reaction

[Display omitted] •CO oxidation on terraces of (111) planes was sensitive to the nature of the anions.•CO catalytic activity of surface steps was not inhibited by different anions.•Contrasting effects of pH on the catalytic activity of different Pt sites. Stepped Pt surfaces having different width (111) terraces interrupted by (110) or (100) monoatomic steps were employed to evaluate the catalytic activity toward CO oxidation at Pt specific sites in HClO4, H2SO4, and H3PO4 solutions, as well as in phosphate buffer and alkaline solution. The catalytic activity at the (111) terraces was sensitive to the nature of the anions derived from the electrolyte dissociation, while no effect on activity was detected at the monoatomic steps. A change in solution pH, passing from acid to alkaline solutions, had contrasting effects on catalytic activity at the (111) terraces and the step sites, with the catalytic activity of the (111) terraces improving, while activity at the step sites deteriorated. During the CO adlayer oxidation, the release of surface sites occurred preferentially from the (111) terraces of the Pt(s)−[(n−1)(111)×(110)] surfaces, while from Pt(s)−[(n)(111)×(100)] surfaces, (111) terrace and (100) step sites were released simultaneously.