Deep oxidation of chlorobenzene on the Pt(1Â 1Â 1) surface

The reaction between chlorobenzene and coadsorbed oxygen has been characterized on the Pt(1 1 1) surface using temperature programmed reaction spectroscopy (TPRS). Desorption of weakly bound molecular chlorobenzene is observed from the atomic oxygen saturated surface at 212 K. Coadsorbed chlorobenzene and oxygen react to form H2O over the range 200-445 K, CO2 at 417 K, and CO at 455 K. After the coadsorbed oxygen is depleted, HCl is observed at 440 K, and the remaining H2 from chlorobenzene desorbs over the range 555-770 K. During chlorobenzene oxidation a chlorophenyl like intermediate is believed to form in the 250 to 270 K region based on the observed yield of H2O and the absence of skeletal oxidation products in this temperature range. This intermediate is further oxidized with increasing temperature until the surface oxygen is depleted. Compared to chlorobenzene adsorbed alone, molecular desorption increases in the presence of coadsorbed atomic oxygen indicating that the low temperature reactivity of the surface is decreased by adsorbed atomic oxygen. Water formation is observed above 200 K indicating that oxydehydrogenation is dominant at low temperature. No hydrogen is available for reaction until all the adsorbed oxygen is depleted. The first hydrogenated product observed is HCl which is formed at 440 K in the temperature range where oxygen is depleted. Benzene formation is not observed in the presence of coadsorbed oxygen because of hydrogen depletion by oxidation. With excess coadsorbed oxygen, skeletal oxidation results in large CO2 yields near 400 K. No CO partial oxidation product is observed until oxygen depletion begins near 430 K with excess chlorobenzene. These reactivity results indicate that dechlorination of the adsorbate/surface system is substantially inhibited by the presence of oxygen, since the favored low temperature dechlorination pathway is HCl formation.