title: Insight into magnetite's redox catalysis from observing surface morphology during oxidation.
abstract: We study how the (100) surface of magnetite undergoes oxidation by monitoring its morphology during exposure to oxygen at ~650 °C. Low-energy electron microscopy reveals that magnetite's surface steps advance continuously. This growth of Fe3O4 crystal occurs by the formation of bulk Fe vacancies. Using Raman spectroscopy, we identify the sinks for these vacancies, inclusions of α-Fe2O3 (hematite). Since the surface remains magnetite during oxidation, it continues to dissociate oxygen readily. At steady state, over one-quarter of impinging oxygen molecules undergo dissociative adsorption and eventual incorporation into magnetite. From the independence of growth rate on local step density, we deduce that the first step of oxidation, dissociative oxygen adsorption, occurs uniformly over magnetite's terraces, not preferentially at its surface steps. Since we directly observe new magnetite forming when it incorporates oxygen, we suggest that catalytic redox cycles on magnetite involve growing and etching crystal.
authors.affiliation: Sandia National Laboratories, Livermore, California 94550, USA.
authors.forename: Shu
authors.initials: S
authors.lastname: Nie
authors.forename: Elena
authors.initials: E
authors.lastname: Starodub
authors.forename: Matteo
authors.initials: M
authors.lastname: Monti
authors.forename: David A
authors.initials: DA
authors.lastname: Siegel
authors.forename: Lucía
authors.initials: L
authors.lastname: Vergara
authors.forename: Farid
authors.initials: F
authors.lastname: El Gabaly
authors.forename: Norman C
authors.initials: NC
authors.lastname: Bartelt
authors.forename: Juan
authors.initials: J
authors.lastname: de la Figuera
authors.forename: Kevin F
authors.initials: KF
authors.lastname: McCarty
mesh_terms: D002384:Catalysis; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D010084:Oxidation-Reduction; D013059:Spectrum Analysis, Raman; D013499:Surface Properties
chemical_list: D052203:Ferrosoferric Oxide