Journal article
α‑Fe2O3 Nanoparticles as Oxygen Carriers for Chemical Looping Combustion: An Integrated Materials Characterization Approach to Understanding Oxygen Carrier Performance, Reduction Mechanism, and Particle Size Effects
Energy & fuels, Vol.32(7), pp.7959-7970
07/19/2018
DOI: 10.1021/acs.energyfuels.8b01539
Abstract
Through continuous flow reactor experiments, materials characterization, and theoretical calculations, we provide new insights into the reduction of hematite (α-Fe2O3) nanoparticles by methane (CH4) during chemical looping combustion (CLC). Across CLC-relevant temperatures (500–800 °C) and gas flow rates (2.5–250 h–1), decreasing α-Fe2O3 particle size (from 350 to 3 nm) increased the duration over which CH4 was completely converted to CO2 (i.e., 100% yield). We attribute this size-dependent performance trend to the greater availability of lattice oxygen atoms in the near-surface region of smaller particles with higher surface area-to-volume ratios. All particle sizes then exhibited a relatively rapid rate of reactivity loss that was size- and temperature-independent, reflecting a greater role for magnetite (Fe3O4), the primary α-Fe2O3 reduction product, in CH4 oxidation. Bulk (X-ray diffraction, XRD) and surface (X-ray photoelectron spectroscopy, XPS) analysis revealed that oxygen carrier reduction proceeds via a two-stage solid-state mechanism; α-Fe2O3 reduction to Fe3O4 followed the unreacted shrinking core model (USCM) while subsequent reduction of Fe3O4 to wüstite (FeO) and FeO to iron metal (Fe) followed the nucleation and nuclei growth model (NNGM). Atomistic thermodynamics modeling based on density functional theory supports that reduction initiates via the USCM, as partially reduced α-Fe2O3 surfaces exhibited a wide range of stability relative to bulk Fe3O4. Reduction and reoxidation cycling experiments were also performed to explore more practical aspects related to the long-term performance of unsupported α-Fe2O3 nanoparticles as oxygen carriers for CLC.
Details
- Title: Subtitle
- α‑Fe2O3 Nanoparticles as Oxygen Carriers for Chemical Looping Combustion: An Integrated Materials Characterization Approach to Understanding Oxygen Carrier Performance, Reduction Mechanism, and Particle Size Effects
- Creators
- Hayder A Alalwan - Middle Technical UniversitySara E Mason - University of IowaVicki H Grassian - Departments of Chemistry and Biochemistry, Nanoengineering, and Scripps Institution of OceanographyDavid M Cwiertny - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Energy & fuels, Vol.32(7), pp.7959-7970
- Publisher
- American Chemical Society
- DOI
- 10.1021/acs.energyfuels.8b01539
- ISSN
- 0887-0624
- eISSN
- 1520-5029
- Grant note
- DOI: 10.13039/100007523, name: Division of Advanced Cyberinfrastructure, award: ACI-1548562; DOI: 10.13039/100000146, name: Division of Chemical, Bioengineering, Environmental, and Transport Systems, award: CBET-1509432; DOI: 10.13039/501100009928, name: Higher Committee for Education Development in Iraq
- Language
- English
- Date published
- 07/19/2018
- Academic Unit
- Chemistry; Occupational and Environmental Health; Center for Health Effects of Environmental Contamination; Chemical and Biochemical Engineering; Civil and Environmental Engineering; Public Policy Center (Archive)
- Record Identifier
- 9983985954502771
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