The transition towards carbon-neutral energy systems has identified the iron/iron-oxide cycle as a promising solution for long-duration energy storage and transport, due to iron's abundance, high energy density, and recyclability. However, the industrial viability of this technology relies on the efficient regeneration of iron oxides using green hydrogen in fluidized bed reactors. A key challenge lies in optimizing this reduction process, which is strongly influenced by the physical and chemical variability of the iron ore powders. ?? ??This thesis investigates the influence of particle size distribution, morphology, and chemical composition on the fluidization behaviour and hydrogen reduction of iron-oxide powders. A multi-technique approach was applied, combining detailed particle characterization (using TGA, BET, XRD, SEM/EDS and ICP-OES analyses) with cold-bed tests and high-temperature reduction experiments at 500 and 600 °C.