Mechanism of Acetone Oxidation on Ag{111}-p(4 × 4)−O

The decomposition of acetone over preoxidized Ag{111} has been studied using reflection absorption infrared spectroscopy. Propane-2,2-diyldioxy and acetone enolate are formed through O-induced nucleophilic addition and H abstraction at 180 K. Further oxidation occurs rapidly above 220 K via acetone enolate to yield metallacyclic intermediates that break down into ketene and methylenedioxy, which deprotonate to produce stable ketenylidene and formate, respectively. The measured vibrational frequencies of several surface-bound ketenylidene isotopomers have been successfully fit to a modified valence force field analysis. Although ketenylidene and CO adsorbed on a metal surface both exhibit strong absorption features due to ν op (CCO) and ν(CO), respectively, at ∼2000 cm -1 in their vibrational spectra, it is shown that they may still be readily distinguished by selective 13 C or 18 O substitution of their carbonyl atoms only, since this results in pairs of absorption bands that possess frequencies of the opposite order (ν op (C 13 CO) < ν op (CC 18 O) and ν(C 18 O) < ν( 13 CO)). A reaction mechanism has been proposed that accounts for the fact that ketenylidene retains the acetone carbonyl group while formate is wholly derived from the acetone methyl group.