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This review focuses on the reduction of iron oxides using hydrogen as a reducing agent. Due to increasing requirements from environmental issues, a change of process concepts in the iron and steel industry is necessary within the next few years. Currently, crude steel production is mainly based on fossil fuels, and emitting of the climate‐relevant gas carbon dioxide is integral. One opportunity to avoid or reduce greenhouse gas emissions is substituting hydrogen for carbon as an energy source and reducing agent. Hydrogen, produced via renewable energies, allows carbon‐free reduction and avoids forming harmful greenhouse gases during the reduction process. The thermodynamic and kinetic behaviors of reduction with hydrogen are summarized and discussed in this review. The effects of influencing parameters, such as temperature, type of iron oxide, grain size, etc. are shown and compared with the reduction behavior of iron oxides with carbon monoxide. Different methods to describe the kinetics of the reduction progress and the role of the apparent activation energy are shown and proofed regarding their plausibility.
Spreitzer et al. (2019) studied this question.