EVIDENCE FOR THE OXIDATION OF CO BY MOLECULAR-OXYGEN ADSORBED ON AG(110)

The oxidation of CO with molecularly adsorbed oxygen has been investig ated on the Ag(110) surface by means of the surface titration techniqu e. By directly measuring the CO, production rate with a mass spectrome ter, substantial reaction has been observed upon the admission of CO v ia a molecular beam onto an O-2 layer well below the dissociation temp erature of molecular oxygen, which is strong evidence for O-2 particip ating in the primary step. The data at 100 K clearly exhibit an induct ion period as a characteristic of the reaction, indicating a Langmuir- Hinshelwood mechanism. The effect of thermal dissociation of adsorbed molecular oxygen is apparent in the titration curves. The influence of external parameters such as substrate temperature, pre-coverage and m agnitude of the CO flux, has been studied by systematic variation and the results have been used to set up a model system of reaction equati ons which include the temporary formation of an intermediate complex o f CO and O-2. The numerical solution of the corresponding system of ra te equations has been fitted to the experimental data with the rate co nstants acting as fit parameters. Both the activation energy and the f requency factor for the reaction steps could be calculated from the re sulting values.