Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 21: Adsorption an Oberfl
ächen II
O 21.3: Vortrag
Dienstag, 25. März 2003, 15:30–15:45, HSZ/03
Coadsorption of CO and H2 on Pd(111): A combined SFG, TDS and LEED study — •Matthias Morkel, Günther Rupprechter, and H.-J. Freund — Fritz-Haber-Institut der MPG, Abt. Chemische Physik, Faradayweg 4-6, 14195 Berlin
Sum Frequency Generation (SFG) vibrational spectroscopy was carried out in conjunction with thermal desorption spectroscopy (TDS), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) to investigate the coadsorption of CO and H2 on Pd(111), a combination of particular interest in methanol synthesis and decomposition. In order to study intermolecular interactions, the gases were dosed sequentially or applied as mixtures at different temperatures.
It will be shown that preadsorbed CO was able to impede dissociative adsorption of hydrogen for CO-coverages of 0.55 ML and higher. On the other hand, preadsorbed hydrogen caused strong site-blocking effects for CO at 100K, while CO was able to replace hydrogen at 150K. A very different adsorption behavior was observed when CO/H2 mixtures were exposed at low temperatures.
Due to its 2nd order non-linear optical nature, SFG spectroscopy further allows to acquire vibrational spectra of adsorbed species even up to atmospheric gas pressure. SFG spectra of CO-H2 mixtures acquired in the mbar range up to 550 K allowed to draw conclusions on the adsorption geometry of CO during catalytic reaction conditions.
Corresponding results on Al2O3-supported Pd-nanoparticles and studies of methanol decomposition will also be discussed.