Interfacial confinement effect induced by pre-sulfurization for promoting SO2 tolerance of MnFe-TOS catalyst in low temperature NH3-SCR reaction

Abstract

SO2 poisoning still is an unresolved problem for NH3-SCR catalysts, especially under low temperature conditions. Herein, a two-pronged approach has been applied on MnFe-TOS for promoting SO2 tolerance at low temperature in NH3-SCR process. Pre-sulfurization via inserting SO42- into TiO2 lattice perturbed the local electronic environment to supplement rich surface acid sites, promoting the rapid adsorption of NH3 at reaction temperature. Active −NH2 and NH4+ could be quickly consumed by NO/nitrites via both L-H and E-R reaction pathway and resulted in high N2 selectivity. The strong interaction of Mn–O–Fe induced by interfacial confinement effect regulated redox ability and inhibited the adsorption/oxidation of SO2, which was benefited to NO activation on MnFe-TOS. At the same time, the (NH4)2SO4 generated during the NH3-SCR process was prone to dissociation into NH4+ and SO42-, where NH4+ continued to participate in the SCR reaction, while SO42- bonded to Fe, as a functional protective site, allowing the Mn site to be protected. DFT calculations have provide convincing evidence at the molecular level to demonstrate how pre-sulfurization induced lattice distortion and affected chemical adsorption characteristics of catalytic active centers (Mn–O–Fe–S). Consequently, the MnFe-TOS exhibited excellent resistance to SO2 at low temperature, and the N2 selectivity has been improved during a wide temperature window. This study provides a new approach for designing efficient and stable NH3-SCR catalysts.