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 ₂ O ₃ . Passing CO and H ₂ O, but no O ₂ , over Au-γ-Fe ₂ O ₃ at 25 °C, we observe significant CO ₂ production, inconsistent with LH mechanistic hypotheses. Experiments with H ₂ ¹⁸ O further show that previous LH mechanistic proposals cannot account for water-promoted CO oxidation over Au-γ-Fe ₂ O ₃ . 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 ₂ production in the absence of O ₂ and with CO oxidation in the presence of H ₂ ¹⁸ O and ¹⁶ O ₂ . In contrast, for Au-TiO ₂ , our data is consistent with previous LH mechanistic hypotheses.
Competing Interests: The authors declare no competing financial interest.
(© 2024 The Authors. Published by American Chemical Society.)