A Water-Promoted Mars-van Krevelen Reaction Dominates Low-Temperature CO Oxidation over Au-Fe 2 O 3 but Not over Au-TiO 2

We provide experimental evidence that is inconsistent with often proposed Langmuir-Hinshelwood (LH) mechanistic hypotheses for water-promoted CO oxidation over Au-Fe O . Passing CO and H O, but no O , over Au-γ-Fe O at 25 °C, we observe significant CO production, inconsistent with LH mechanistic hypotheses. Experiments with H O further show that previous LH mechanistic proposals cannot account for water-promoted CO oxidation over Au-γ-Fe O . Guided by density functional theory, we instead postulate a water-promoted Mars-van Krevelen (w-MvK) reaction. Our proposed w-MvK mechanism is consistent both with observed CO production in the absence of O and with CO oxidation in the presence of H O and O . In contrast, for Au-TiO , our data is consistent with previous LH mechanistic hypotheses.