EPR study of the surface basicity of calcium oxide. 2: The interaction with alkanes

The present paper reports experimental evidence of the heterolytic dissociation of some saturated hydrocarbons (methane, ethane, propane, and cyclohexane) at the surface of high surface area CaO activated at high temperature. The reaction takes place at RT on particularly basic O2- sites at the surface of CaO. The reaction has been followed via EPR spectroscopy in two distinct ways. The former one consists of monitoring the formation of superoxide radical anions (O2-) which occurs when the hydrocarbon and molecular oxygen are coadsorbed at the surface via surface intermolecular electron transfer reaction. The latter one is based on ionization of the negative hydrocarbon fragment upon exposure to UV light with consequent formation of a surface trapped electron (a surface color center known as Fs(H)+) in which the electron is stabilized nearby an hydroxyl OH- group produced by the hydrocarbon splitting. This latter OH- group undergoes isotopic exchange transforming in OD- when contacted with D2 or CD4.