CC and CH bond activation of 1,2-propanedioxy by atomic oxygen on Ag(110): Effects of CO-adsorbed oxygen on reaction mechanism

Abstract

The stability of adsorbed 1,2-propanedioxy OCH(CH 3)CH 2O, generated via OH bond activation of 1,2-propanediol by oxygen adatoms on Ag(110), has been shown to be sensitive to the relative concentrations of 1,2-propanedioxy and O (a). When the concentration of O (a) is sufficiently large, OCH(CH 3)CH 2O (a) is formed via OH bond activation upon the adsorption of 1,2-propanediol at 175 K. CH bond activation, nucleophilic attack by O (a) and CC bond scission subsequently occur to yield formaldehyde, water, formate and acetate by 275 K. Acetol CH 3C(O)CH 2OH evolves at 335 K, driven from the surface either by the onset of the conversion of CH 3COO (a) to HCOO (a) and CO 2(g) or by through-surface interactions. CO 2(g), H 2O (g), acetol, lactaldehyde CH 3CH(OH)CHO and 1,2-propanediol evolve at 360 K. Production of pyruvaldehyde CH 3C(O)CHO, acetol, and lactaldehyde occurs at 415 K and is accompanied by the evolution of additional CO 2(g) and H 2)O (g) due to formate decomposition in the presence of O (a)(OH (a)). No H 2(g) evolves. Residual acetate decomposes to yield CO 2(g), CH 3COOH (g), and CH 2CO (g) in the absence of O (a) near 580–620 K. The evolution of H 2CO (g) and H 2)O (g) at 275 K and the production of acetol at 335 K suggest that initial CH bond activation occurs preferentially at the central carbon of 1,2-propanedioxy. The production of lactaldehyde at both 360 and 415 K and pyruvaldehyde at 415 K indicates that with heating subsequent CH bond activation occurs at carbon-1. Furthermore, these results demonstrate that OH and CH bond activation and CC bond scission are characteristic oxidation mechanisms for diols on oxygen-activated Ag(110).