Abstract

We have studied the adsorption of methanol on the (1 1 0) and (1 1 1) surfaces of bulk ceria (CeO2) single crystals using infrared reflection–absorption spectroscopy (IRRAS). To assign the experimentally observed features, density functional theory (DFT) has been applied. For ceria (1 1 0), only a single intense band at 1108 cm−1 is observed, which is assigned to a monodentate methoxy species.

For the fully oxidized ceria (1 1 1) surface, a more complex spectrum has been obtained: the small band at 1108 cm−1 is attributed to methanol adsorption at a small amount of (1 1 0) facets exposed at step edges in the (1 1 1) surface. The strong bands at 1085 and 1060 cm−1 are assigned to a methanol monolayer that consists of H-bonded methoxide as well as molecularly adsorbed methanol species.

These assignments are derived from molecular dynamics simulations for several adsorption structures with low and high methanol coverage. Surface defects were also considered. Our results reveal that a simple relation between the redshift in the methoxy CO stretching mode and the number of cerium cations coordinated to the methoxide oxygen atom (as often used in previous work) does not apply.

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