Metal-Metal Interactions of Ternary Spinel for Efficient NH_3 Selective Catalytic Reduction of NO_x at a Low Temperature

摘要

Low-temperature selective catalytic reduction (SCR) is an economical and feasible technology to effectively reduce NC% emissions from combustion sources. However, low-temperature SCR still suffers from low activity and SO2 H2O poisoning of catalysts. Here, a strategy to promote SCR activity and anti-poisoning ability was proposed through enhancing the metal-metal interaction. Ternary ferrite spinel material (CuMnFeO4) with a stronger metal-metal interaction was synthesized through incorporating Mn cations into the tetrahedral sites of CuFe2O4 spinel. CuMnFeO4 spinel mainly exists in an amorphous form and shows good SCR performance and SO2/H2O anti-poisoning ability in the temperature window of 200-350 degrees C. Density functional theory calculations were used to investigate the atomic-level reaction mechanism of NO reduction. Theoretical results indicate that NO and NH3 adsorptions over the CuMnFeO4 catalyst are controlled by the chemisorption mechanism. The interaction between reactants (NO and NH3) and the CuMnFeO4 surface is closely associated with the orbital hybridization of N and Fe atoms. The SCR reaction of NO with NH3 over the CuMnFeO4 catalyst is governed by a six-step process (NO - NO* - H2NNO* - HNHNO* - HNNOH*- N-2* - N-2), in which the first H-transfer reaction (H2NNO* HNHNO*) presents the highest activation energy barrier of 230.84 kJ/mol and is the rate-determining step of the NH3-SCR reaction. Finally, a SCR cycle reaction scheme was proposed to understand the reaction process of NO reduction over CuMnFeO4 spinel.