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Schlagwörter:
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Zusammenfassung:
The catalytic oxidation of carbon monoxide is studied in situ by means of reaction-rate measurements on a macroscopic scale and photoelectron emission microscopy (PEEM) on a mesoscopic scale on a Pt(111) single-crystal surface partially modified by evaporated Cu. By using a special preparation technique it is possible to cover selectively certain parts of the Pt(111) surface with copper, thus enabling a simultaneous PEEM investigation of the behavior of each separate catalyst component as well as their mutual influence. The objective of the work is to investigate the possible influence of deposited copper on CO oxidation on Pt(111) and to compare the results with pure Pt(111). Cu-modified regions preferentially form oxygen adsorption layers under the reaction conditions. The well-documented behavior of CO oxidation on Pt(111) is modified by the presence of the Cu domains. This modification concerns the transition between the CO-covered and oxygen-covered state of the Pt surface. The macroscopic effect of the modification by Cu is to shift the whole hysteresis in the reaction rate to higher CO pressures. On the mesoscopic scale the nucleation of oxygen islands at the beginning of the phase transition takes place on Cu-modified areas. On a Pt(111) sample on which submonolayer quantities of copper were uniformly deposited, the propagation velocity of the reaction/diffusion front of a growing oxygen island increases with the amount of deposited Cu. These experiments demonstrate the possibility of creating special geometric adsorbate patterns during CO oxidation on the Pt(111) surface, and of modifying the velocity of propagation of the reaction/diffusion front.
