Mn-Doped Maghemite (γ-Fe₂O₃) from Metal–Organic Framework Accompanying Redox Reaction in a Bimetallic System: The Structural Phase Transitions and Catalytic Activity toward NOx Removal

摘要

Mn-doped maghemite (γ-Fe_(2)O_(3)) particles were generated from a binary metal (Fe,Mn)-based metal–organic framework (MOF) via thermal decomposition under air. The X-ray photoelectron spectroscopy analysis revealed that the synthesis of Fe/Mn-MOF accompanied the reduction of the metal ions. The existence of Mn ions in this synthetic process leads to thermally stable maghemite particles under air. A temperature-induced structural phase transition from γ-Fe_(2)O_(3) to α-Fe_(2)O_(3) was observed through a mixed phase with another structure. Mn-doped γ-Fe_(2)O_(3) and α-Fe_(2)O_(3) exhibit superparamagnetic behavior. The sample annealed at 600 °C showed a mixed magnetic hysteresis loop indicating the existence of an intermediate structural phase between γ-Fe_(2)O_(3) and α-Fe_(2)O_(3) during the phase conversion from FeMn-MOF. The constructed Mn-doped iron oxides are active toward reducing nitric oxide with NH_(3). The NO conversion is 97% over Mn-doped γ-Fe_(2)O_(3) calcined at 320 °C.