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Developing below 150 °C highly activity and broad reaction window catalysts has been challenging by using Fe-based catalysts for NH 3 -SCR. The octahedral Fe3+ (Fe3+ Oh) sites exist in hematite (α-Fe 2 O 3) and maghemite (γ-Fe 2 O 3) are inactive for NH 3 -SCR due to the redox circle of Fe2+→Fe3+ reliance on the distribution of iron sites in crystal structure. Here we modified the α-Fe 2 O 3 crystal structure by substituting part inactive Fe3+ Oh sites with catalytically active Mn3+ Oh sites, which promoted the formation of γ-Fe 2 O 3 to generate the active tetrahedral Fe3+ (Fe3+ Td) sites and enhanced the magnetism of the Fe 1−y Mn y O x. The strong Fe-O-Mn interaction established by crystal coordinative configurations not only boosted the formation of NO 2 but also facilitated the Brønsted acid circle. Surprisingly, the Fe 0.85 Mn 0.15 O x exhibited the superior low temperature NH 3 -SCR activity, with NO x conversion above 100% at 100–275 °C under a GHSV of 60000 h−1. [Display omitted] • Fe 0.85 Mn 0.15 O x exhibited superior low temperature SCR activity and broad window. • Mn modified α-Fe 2 O 3 generate active tetrahedral Fe3+ and enhanced the magnetism. • The strong Fe-O-Mn interaction established by crystal coordinative configuration. • The interaction facilitated the redox circle and acid circle for NH 3 -SCR. [ABSTRACT FROM AUTHOR]