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Abstract

Application of temperature-variable scanning tunneling microscopy (STM) for investigations of heterogeneous catalyzed reactions is demonstrated. By atomic resolution insight into the microscopic processes of the reactions was obtained. New results are presented on the oxidation reactions of carbon monoxide and hydrogen on Pt(111).
   CO+O:
   Kinetic parameters were determined by in situ following the reaction between preadsorbed oxygen atoms with CO (237-274 K). In this way it was able to verify the macroscopic kinetics on the basis of experimental information about the atomic scale. During the reaction a phase separation into a pure CO- and a mixed O-CO-phase was observed. The reaction preferentially takes place at the phase boundaries. Monte Carlo simulations reproduced the experimental observations.
   H+O:
   It was demonstrated that the mechanism of the water forming reaction changes qualitatively at the water desorption temperature Tdes (170 K). Below this temperature water acts as an autocatalytic species by reacting with oxygen to a hydroxyl intermediate (OH). The autocatalytic mechanism became manifest by observation of reaction fronts, the motion of which was followed with STM. With increasing temperature the residence time of water on the surface and the influence on the reaction decreases until above Tdes consecutive addition of hydrogen to oxygen applies.