Low-temperature selective catalytic reduction of NOx with NH3 over Ce-modified (Co, Mn)3O4 hollow porous microspheres

Abstract

• Ce x -(Co, Mn) 3 O 4 de-NO x catalysts were synthesized by hydrothermal-calcination. • Modification with CeO x improved the low-temperature NO x removal activity. • Mn-Co-Ce mixed oxides exhibited the morphology of hollow and porous microsphere. • The interaction between metal cations produced higher atomic content of Mn 4+ and Co 3+ . CeO x -(Co, Mn) 3 O 4 catalysts with various Ce: Mn ratios were synthesized via the hydrothermal-calcination and then used for the selective catalytic reduction (SCR) of NO x by NH 3 . The modification of (Co, Mn) 3 O 4 by CeO x extended its operating temperature window and boosted its low-temperature catalytic activity. The optimum Ce-Co-Mn mixed-oxide catalyst converted over 98% NO x at 175–275 °C and displayed high N 2 selectivity, good thermal stability, and resistance against H 2 O and SO 2 . The characterization results showed that the hollow and porous microspheres supplied the catalyst with a high specific surface area and many exposed Lewis acid sites that adsorbed and activated the reactants. The uniform distribution of Mn, Co, and Ce species exerted a synergetic effect (Ce 4+ + Mn 3+ ↔ Mn 4+ + Ce 3+ , Ce 4+ + Co 2+ ↔ Co 3+ + Ce 3+ ) that improved the redox properties of the catalyst. A promising candidate for low-temperature SCR was obtained over Ce-modified (Co, Mn) 3 O 4 mixed-oxide catalyst.