  With 1.85 billion tons produced per year, steel is the most important
material class in terms of volume and environmental impact. While steel is a
sustainability enabler, for instance through lightweight design, magnetic
devices, and efficient turbines, its primary production is not. For 3000 years,
iron has been reduced from ores using carbon. Today 2.1 tons CO2 are produced
per ton of steel, causing 30% of the global CO2 emissions in the manufacturing
sector, which translates to 6.5% of the global CO2 emissions. These numbers
qualify iron- and steel-making as the largest single industrial greenhouse gas
emission source. The envisaged future industrial route to mitigate these CO2
emissions targets green hydrogen as a reductant. Although this reaction has
been studied for decades, its kinetics is not well understood, particularly
during the wustite reduction step which is dramatically slower than the
hematite reduction. Many rate-limiting factors of this reaction are set by the
micro- and nanostructure as well as the local chemistry of the ores. Their
quantification allows knowledge-driven ore preparation and process optimization
to make the hydrogen-based reduction of iron ores commercially viable, enabling
the required massive CO2 mitigation to ease global warming. Here, we report on
a multi-scale structure and composition analysis of iron reduced from hematite
with pure H2, reaching down to near-atomic scale.
