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O: Oberflächenphysik

O 11: Grenzfl
äche fest-flüssig

O 11.3: Talk

Monday, March 24, 2003, 15:30–15:45, M\"UL/ELCH

The Role of Mono-Atomic Steps and of Step Decoration by Foreign Metals on Electrocatalysis — •Thomas Loeffler, Helmut Baltruschat, and Rainer Bussar — Universitaet Bonn, Abteilung Elektrochemie, Roemerstrasse 164, 53117 Bonn

The extent of hydrogenation of unsaturated hydrocarbons on Pt single crystal electrode surfaces was elucidated with the help of differential electrochemical mass spectrometry (DEMS). The hydrogenation of these substances takes place in a noteworthy extent at steps only. The relation of terrace width to the size of the molecules also plays a role: during adsorption, benzene and cyclohexene molecules find enough space on the (111) terraces of a Pt(332) crystal, which is about 5 Pt atoms large; during reductive desorption, however, they are completely hydrogenated to cyclohexane. A decoration of the steps with Cu suppresses hydrogenation, as expected. The ethene molecule can be hardly desorbed from a Pt(111) surface, whereas up to 70 The catalytic activity of the Pt(332) electrode lies in between that of the Pt(111) and the Pt(110) surface with regard to ethene hydrogenation. In order to gain a better knowledge about the different adsorbate states, we performed temperature-dependent DEMS experiments ranging from 0 to 50 degrees on single-crystal electrodes as well.

[1] U. Müller, H. Baltruschat, J. Phys. Chem. , B 2000, 104, 5762.