OXIDATIVE CLEAVAGE OF PROPENE ON IR(111) - DOUBLE-BOND SCISSION DURING THE FORMATION OF ACETATE

High-resolution electron energy-loss spectroscopy (HREELS) and tempera ture-programmed reactive desorption (TPRD) techniques have been used t o examine the interaction of coadsorbed propene (propylene) and oxygen on the Ir(111) surface. At less than 80 K, propene adsorbs onto oxyge n-precovered Ir(111) in a pi-bound state. Acetate and eta(2)(C,O)-acet one as well as gaseous acetone, water and dihydrogen are produced by 2 95 K during the oxidation of this species. Isotopic labeling experimen ts suggest that acetate and eta(2)(C,O)-acetone are produced in parall el to or in competition with one another rather than from each other, and that pi-allyl (CH2CHCH2) is not a precursor to either species. In contrast, exposing the bare Tr(111) surface to propylene at less than 80 K results in adsorbed propylene, which is more strongly rehybridize d than that on the oxygen-precovered Ir(111) surface. This propylene, nominally referred to as di-sigma-bound propylene, could also be oxidi zed to acetate and eta(2)(C,O)-acetone. Possible mechanisms for the ox idation of pi-bound propene are developed, and comparisons/contrasts a re made between the interaction of propene and oxygen on Ir(111) and t he interaction of 2-methylpropene (isobutylene) and oxygen on this sur face. (C) 1998 Published by Elsevier Science B.V.