Reduction of micron-sized iron oxide particles with high initial porosity in a fluidized bed reactor using hydrogen: Morphology and phase analysis

The aim of this study is to investigate the reduction behavior of Fe2O3 particles with initially high porosity in a fluidized bed reactor using hydrogen. The powder used is characterized by a large specific surface area and a highly porous initial morphology. The generic Fe2O3 powder exhibits a particle structure similar to those typically observed after multiple oxidation/reduction cycles.
The reduction behavior of these Fe2O3 particles was studied at temperatures ranging from 500°C to 700°C with reduction times of 30 min to 120 min. Physisorption measurements using the Brunauer-Emmett-Teller (BET) method were performed to assess changes in specific surface area before and after reduction. Scanning electron microscopy (SEM) was employed to examine morphological transformations both at the surface and within the particle surface areas by visualizing cross-sections, as well as particle agglomeration. Statistical analysis of the cross-sectional SEM micrographs was performed to determine the pore size growth during the reduction process. Thermogravimetric analysis (TGA) was used together with calorimetry to monitor the reduction degree. ... mehrAdditionally, Mössbauer spectroscopy (MS) and X-ray diffraction (XRD) were used to analyze the contributions of residual oxides after reduction.
The reduction of highly porous Fe2O3 in a fluidized bed exhibits temperature- and time-dependent behavior, with the formation of bimodal pore size distributions, a decrease in specific surface area, and reduction degrees exceeding 90 % after 120 min, reaching up to 99.5 % at 700°C, confirmed through TGA, calorimetry, XRD, and MS, which also revealed minor residual oxides and nano-structured domains at lower temperatures.