A general method for studying reactive surface species, CT-SKAn: Charge-transfer spectrokinetic analysis

A spectrokinetic methodology was developed to determine reactive surface species by combining operando ultraviolet–visible spectroscopy and charge transfer kinetic models. The methodology consisted of three general steps: 1) concomitant measurement of reaction rates and charge transfer via ultraviolet–visible spectroscopy; 2) development of rate expressions from kinetic models involving the adsorbed species of interest. These rate expressions relate reaction rates, charge transfer, and partial pressures of gas phase species; and 3) evaluation of the goodness of fit of the rate expressions to the experimental data. The species whose rate expressions show the best fit are the more likely reactive surface species for the studied reaction. An example is presented for the determination of reactive oxygen species during ethanol oxidation over Au/TiO₂. The charge transfer spectrokinetic analysis showed that surface hydroperoxyl, hydroxyl, and atomic oxygen species were reactive surface intermediates, whereas surface molecular oxygen was not.