Infrared spectroscopy of MO(CH4)n (M = Ce, Y; n = 1-3) reveals two distinct adsorption configurations.

Investigation of the interactions of methane with metal oxides is crucial for elucidating absorption configurations at active sites of catalysts, which has proven to be a challenging experimental target due to the difficulty in size selection of neutral systems. In this work, the interactions of methane with rare earth metal oxides are studied by using size-specific infrared-vacuum ultraviolet spectroscopy and quantum chemical calculations. Two distinct configurations of methane adsorption are found in the MO(CH4)n (M = Ce, Y; n = 1-3) complexes. In the first configuration, the C and H atoms of methane are positioned between a Lewis acid-base pair (M2+-O2-); in the second configuration, one H atom of methane is oriented toward a Lewis basic oxygen anion (O2-). Such adsorption features of methane on cerium and yttrium monoxides are dominantly governed by electrostatic interactions. These findings provide key microscopic information for methane adsorption on metal oxides that are helpful for understanding the crucial initial steps in the catalytic cycles.