HYDROGENATION OF 1,3-BUTADIENE AND THE ADSORBED HYDROGENS ON A PLATINUM-ELECTRODE

Hydrogenation of 1,3-butadiene on a Pt electrode in M H2So4 was studied both on open circuit and under potentiostatic polarization to examine the reactivity of the adsorbed hydrogens. Results in region-H (PH/PB < 20 on open circuit, ø > 80 mV/rhe in the electroreduction) show that the most stable hydrogen is inactive and interchanges to the secondly stable hydrogen during the hydrogenation. The latter adsorbed hydrogen, Hqø, is always in equilibrium with H+ and e- by Hø ⇄ H+ + e- and reacts with adsorbed diene, giving butenes and n-butane. The rate of the interchange is three orders of magnitude smaller than the hydrogenation rate. Among the surface elementary steps, the second addition of hydrogen atom seems to be slowest. Difference in hydrogen source, ie H2 molecule or proton and electron, has no effect on the reaction mechanism. © 1979.