In this work we explore the Mars-van Krevelen mechanism of oxidation reactions on Yttria-stabilized zirconia (YSZ). We propose that high temperature reduction of YSZ and subsequent re-oxidation by molecular oxygen are important steps in the generation of active oxygen species required for oxidation reactions, which explain the experimentally observed catalytic activity of YSZ. We also compare the oxidation of formaldehyde to formate with formaldehyde decomposition to synthesis gas. YSZ, commonly used as a support for metal particles for methane reforming and catalytic partial oxidation of methane (CPOM), has been shown to be active for CPOM in it’s own right1. CPOM on YSZ has been shown to proceed via a Mars-van Krevelen mechanism, with surface vacancies providing sites for oxygen activation, with exclusively lattice oxygen contained in oxidation products. Formaldehyde is proposed as a major reaction intermediate and water stabilizes formaldehyde with respect to oxidation to formate, increasing product selectivity to syngas2. In previous work we have developed a larger YSZ surface slab model, providing a more detailed representation of the YSZ surface, and shown that water will dissociate to fill oxygen vacancies present in the stoichiometric YSZ surface3. Here we find that molecular oxygen binds strongly to oxygen vacancies on reduced YSZ surfaces, resulting in a reduced surface oxygen species. We show that formaldehyde will physisorb to YSZ and nucleophilic attack by surface lattice oxygen results in a chemisorbed intermediate species both stoichiometric and reduced YSZ surfaces. However, the presence of the reduced oxygen species is required for further oxidation to formate (figure 1), reflecting experimental evidence of formate being a major stable surface species. References [1] Zhu, J. J; et al. J. Catal. 2004, 255, 388-397. [2] Zhu, J. J; et al. Catal. Today, 2006, 117, 163-167. [3] Chaopradith, D. T; Scanlon, D. O; Catlow, C. R. A, J. Phys. Chem. C, 2015, 119 (39) 22526-22533.

Oxidation reactions on yttria-stabilized zirconia: Redox chemistry on an irreducible oxide

251st National Meeting (2016)

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