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

Abstract

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-d2 on 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 [2+2] 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 ν(O−C−O) stretching mode near 1500...