(560hp) Coupling the Magnetic and Catalytic Properties of Fe3O4 Via Shape-Controlled Routes and Cr Doping

Authors: 
Dorman, J. A., Louisiana State University
da Silva Moura, N., Louisiana State University
Watson, B., Louisiana State University
Simonson, H., Louisiana State University
Darapaneni, P., Louisiana State University
Dooley, K. M., Louisiana State University
Iron catalysts play a vital role in the leading chemicals industry, favoring the production of ammonia, hydrogen, and liquid hydrocarbons through the Haber-Bosch, Water-Gas Shift, and Fischer-Tropsch processes, respectively. These catalysts are benefited by an increase in surface area, which can be achieved through reduced dimensionality. To produce efficient catalysts, thermal decomposition routes capable of controlling size and shape of nanoparticles have been reported, enabling fine tuning of the catalytic properties of a given material. Consequently, for iron oxide (Fe3O4) nanoparticles, for example, structural control also enables improved magnetic properties. In the context of catalysis, Fe3O4 is a promising material due to its ability to generate localized heat by the conversion of electromagnetic radiation into heat, as seen in magnetic hyperthermia. Therefore, combining the properties of iron catalysts with synthetic control and doping have the potential to make an impact in the chemicals industry.

In this work, thermal decomposition is used to produce monodisperse, spherical, cubic and octahedral shaped, Fe(3-x)CrxO4 nanoparticles as a strategy to improve the activity of the iron oxide (Fe3O4) host nanoparticles via Cr+3 doping, while maintaining the magnetic properties of the host lattice. Cr+3 replaces Fe+3 in the octahedral sites of Fe3O4 inverse spinel structure at low doping concentrations (x < 15 mol%), and tetrahedral and octahedral sites are substituted at higher concentrations. Low doping concentration improves activity and redox performance due to coupling of the Fe+3/Fe+2 with Cr+2/Cr+3, and regeneration of Fe+2 on the surface. To confirm this regeneration effect and the site occupancy of Cr in Fe3O4, L-edge X-ray Absorption Spectra of Fe and Cr is collected as well as X-ray Photoelectron Spectroscopy (XPS), to determine the formation of oxygen vacancies and to probe the valence state of Cr and Fe. In addition, Cr doping changes the pore structure from mesopores to micropores, thereby increasing the surface area, demonstrated through BET measurements. Finally, magnetic properties are characterized via Superconducting Quantum Interference Device (SQUID) measurements to show how the saturation magnetization, and coercivity are preserved. Induction heating is characterized by determining the Specific Loss Power of these materials under various magnetic field strength.