Iron Vacancies Dictate Magnetite’s Properties

Magnetite (Fe₃O₄) is an inexpensive abundant material with surface properties that make it useful in heterogeneous catalysis, biotechnology, and other areas. The oxide has an unexplained knack, for example, for pinning individual, catalytically active precious-metal atoms on its surface and holding them in place even at high temperature. Researchers trying to understand the basis of that property, which could lead to exceptionally well dispersed catalysts, nearly always focus on the way oxygen vacancies in Fe₃O₄’s surface shape its electronic properties. But according to a team that includes Vienna University of Technology’s Gareth S. Parkinson and Ulrike Diebold, oxygen vacancies aren’t the key players. Rather, Fe₃O₄’s properties are governed by missing iron atoms in the subsurface layer (Science 2014, DOI: 10.1126/science.1260556). On the basis of experimental and computational analyses, the team concludes that in response to chemical reaction conditions, iron oxide shuffles iron ions. Precious-metal atoms latch onto the surface directly above the lattice positions where the metal ions are missing. Because these vacancies are spaced at regular intervals, the precious-metal atoms also remain well spaced and do not diffuse and form clusters.