Interactions of formic acid, formaldehyde, and methanol with germania surfaces

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Abstract
Infrared studies of the interaction of, respectively, formic acid, formaldehyde, and methanol with hydroxylated germania gel surfaces were made. Formic acid was dissociatively adsorbed to give covalently bonded formate species and new surface hydroxyl groups. Monomeric formic acid could not be observed. Degassing the treated sample at 246° removed most of the surface formate and the perturbing effects on the surface hydroxyls were also decreased. Two adsorbed species were observed when germania was exposed to high pressures (~10 Torr) of formaldehyde at room temperature. One species was very weakly bonded; it was removed by degassing at room temperature and its structure is tentatively taken as formaldehyde hydrogen-bonded to the surface hydroxyl groups. The other species had a spectrum very similar to polyoxymethylene, and it is proposed that it was in fact a surface polymer formed through the catalytic effect of the surface hydroxyl groups. Methanol was dissociatively adsorbed on germania surfaces. A species attributed to surface methoxide was formed and the concentration of the surface hydroxyl groups increased. Also, small concentrations of two other species were observed which gave absorptions at 2195 and 1727 cm−1, respectively. The band at 2195 cm−1 is assigned to a Ge—H species formed, possibly, at non-stoichiometric portions of the surface, while the latter species is tentatively ascribed to a surface formate species.

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