| The adsorption of acrolein and propionaldehyde on the polar, Cu+ -terminated Cu2O(100) surface was investigated using X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). The major reaction products observed for both aldehydes were nonselective oxidation products (CO,CO2, and H2O). Propene and acrolein were also detected as minor reaction products during propionaldehyde thermal desorption. Additionally, propene and propionaldehyde were detected as minor products during the reaction of acrolein with preadsorbedhydrogen. The coincident desorption of the propionaldehyde, acrolein, and propene from either acrolein and peradsorbed hydrogen or propionaldehyde adsorption suggests that a common surface intermediate is involved in these minor side reactions. A reaction pathway involving a surface enolate intermediate (CH2CH=CHO-) is proposed to explain the side reactions to C3 products. The surface intermediate is believed to be formed from propionaldehyde via a Lewis acid catalyzed reaction similar to Bronsted calalyzed keto-enol tautomerization in solution. A process similar to solution-phase (1,4) addition is postulated to give rise to the enolate intermediate during the reaction of preadsorbed hydrogen and alpha,beta unsaturated acrolein. The enolate-mediated reactions to C3 compounds generate only a minor ammount of the total reaction products. As with the reaction of other oxygenates over Cu2O(100), the nonselective oxidation pathway involves deoxygenation of the adsorbate, subsequent dehydrogenation of hydrocarbon fragments, and the burn-off of surface carbon with lattice oxygen. |