SURFACE OXYGEN SPECIES AND THEIR REACTIVITIES IN THE MILD OXIDATION OF ETHYLENE ON CERIUM OXIDE STUDIED BY FT-IR SPECTROSCOPY

Surface oxidation of ethylene on cerium oxide was studied at mild temperatures (293-473 K) by using in situ FT-IR spectroscopy, and isotopic technique. Ethylene oxidation took place even at around 330 K on a well outgassed cerium oxide independent of the presence of gaseous O2. At mild temperatures, the surface adsorbed product was mainly formate species. Adsorbed superoxide (O2-) species was definitely observed at temperatures up to 373 K when gaseous oxygen was present. However isotopic experiment confirmed that the superoxide was not the active form of oxygen due to the mild oxidation of ethylene. The principal oxygen species participating in the mild oxidation of ethylene was surface lattice oxygen which is supposed to be in O--like form created by an outgassing at high temperatures. The mild oxidation of ethylene could be also initiated by surface peroxide (O2(2-)) and O- species which were formed via the adsorption of O2 on a partially reduced cerium oxide.