Adsorbed Hydrogens and Reduction of Olefins on Platinum in Acid Solution

Platinum electrodes subjected to anodic activation reveal three kinds of adsorbed hydrogen (I, II, and III). These adsorbed hydrogens are interchangeable with each other. The adsorbed hydrogen I (ionization peak at ca. 40 mV, rhe) is the most reactive and responsible for the hydrogen evolution reaction. When C 2 –C 4 olefins are reduced by H 2 , the adsorption layer on Pt drastically changes depending on the composition of olefin and H 2 in the gas phase. At relatively low pressure of H 2 (region H), II (ca. 140 mV) takes part in the hydrogenation, whereas III (ca. 290 mV) gradually changes to II. Isotopic study proves that the hydrogenation in region H proceeds by the two Horiuti‐Polanyi type reaction paths, which is common among the olefins studied. The electroreduction gave the same results, where the discharge of H + is always taken to be in equilibrium.