Carbon-Oxygen Coupling in the Reaction of Formaldehyde on Ge(100)-2×1

Although catalytic properties are usually ascribed to transition metals and their oxides, the present work identifies a catalytic carbon-oxygen coupling reaction on a group-IV (100)-2×1 semiconductor surface. The reactions of formaldehyde and formaldehyde-d2on Ge(100)-2×1 were investigated with multiple internal reflection infrared (MIR-IR) spectroscopy, temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. Formic acid was also studied for comparison. Infrared data indicate that formaldehyde adsorbs in a dative-bonded state and also forms a minority C-H dissociation product. In addition, theory predicts that a CO 22 cycloaddition product may form, although the infrared spectra are inconclusive as to its presence. Time-dependent and annealing infrared studies suggest that the dative-bonded species undergoes a subsequent coupling reaction with a nearby surface adduct, resulting in a bidentate formate group as evidenced by an intense (O-C-O) stretching mode near 1500 cm-1. The desorption of CO2during TPD experiments confirms the carbon-oxygen coupling reaction.