REACTIONS OF PI-ALLYL WITH ATOMIC OXYGEN AND HYDROXYL ON AG(110)

The oxidation of the adsorbed pi-ally] (eta3-C3H5), prepared on atomic oxygen- and hydroxyl-covered Ag(110) by dissociation of allyl chloride (C3H5Cl), is investigated with temperature-programmed desorption and high-resolution electron energy loss spectroscopy. Allyl chloride adsorbs molecularly on oxygen-covered Ag(110) at 110 K. Upon heating to 180 K, some allyl chloride dissociates to form pi-allyl and atomic chlorine, and the remainder desorbs molecularly. The pi-allyl undergoes combustion to form hydroxyl or carbonate until all of the free oxygen is consumed by 200 K. Migratory insertion of hydroxyl into excess pi-allyl commences near 220 and finishes by 250 K, forming adsorbed allyl alcohol (C3H5OH), which reacts either with excess hydroxyl near 240 K to form allyl alkoxy (eta1(O)-C3H5O) and water, or with pi-allyl at 250 K to form allyl alkoxy and propylene (C3H6). The allyl alkoxy evolves acrolein (C3H4O) by beta-hydrogen elimination near 285 K, and propylene is evolved concurrently as the hydrogen released by this reaction rapidly scavenges pi-allyl. Finally, the remaining pi-allyl dimerizes to form 1,5-hexadiene (C6H10), which desorbs at 315 K. The gross observations of reaction pathways and temperatures are used to evaluate important aspects of the thermochemistry of these reactions.