Regulating electronic state of δ-MnO2 through an organic-inorganic hybrid engineering for boosted low-temperature NOx elimination

Birnessite-type δ-MnO 2 is a promising candidate for low-temperature NH 3 -SCR reaction owning to its excellent redox properties. However, its performance is severely hampered by the excessive oxidation state of Mn species, which induces strong NH 3 chemisorption and subsequent over-oxidation to NO x . Herein, phenylalanine-functionalized δ-MnO 2 nanosheets (MnO x -Phe) were developed, leveraging Phe's coordinating –NH 2 group to modulate surface properties of Mn species. The optimal MnO x -Phe-0.1 catalyst achieves ∼90% NO x conversion at 75 °C with a broad temperature window from 75 to 210 °C (GHSV = 50,000 h −1 ), representing a reaction rate 4.8 to 8.2 times greater than that of pure δ-MnO 2 . Additionally, the catalyst exhibits remarkable resistance against SO 2 and H 2 O. Comprehensive characterizations and density functional theory calculations reveal that Phe modification shifts down the d -band center of δ-MnO 2 from −1.22 eV to −2.78 eV, and attenuates the oxidation state of Mn species. This unique configuration suppresses the over-oxidation of NH 3 and weakens the interaction between catalyst and poisons, while promoting the activation of NH 3 to *NH 2 with a lower energy barrier, thus driving a desired Eley-Rideal pathway and endowing strong tolerance against SO 2 and H 2 O at low temperatures. This work provides a novel organic-inorganic hybrid strategy for designing robust low-temperature NH 3 -SCR catalysts with superior activity and poison resistance.