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Catalysis by Gold: Imaging and Local Chemical Probing of the CO Oxidation under in-situ conditions

par Visart de Bocarmé, Thierry ;Bar, Thomas ;Chau, Thoi-Dai ;Kreuzer, Hans Juergen;Kruse, Norbert
Référence International Congress on Catalysis (13: 2004-07-10->15: Paris)
Publication Non publié, 2004-07-13

Communication à un colloque

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Résumé :

The CO oxidation over Au crystal surfaces was studied under in-situ conditions at pressures below 10-3 mbar in the absence of a support material using video-FIM (Field Ion Microscopy). Chemical waves were observed to move across the catalyst surface. Local chemical probing (~300 surface sites) by short field pulses allowed to monitor the chemical surface composition during wave propagation. Partial positive charges at step sites due to the application of imaging fields of several V/nm cause the sticking probability of oxygen molecules to increase by many orders of magnitude. This ensures the presence of significant oxygen surface coverages to perform either titration or co-adsorption experiments with CO gas. In both cases chemical fronts were observed and associated with the formation of CO2. The mass spectra change substantially while waves move across the probe-hole: they contain only oxygen ions first and become dominated by Au carbonyls (AuCOn+ and Au(CO)2n+) later on. The results suggest CO oxidation over pure Au to involve only step sites.