Tailoring valence state of V in V-Mo atomically dispersed ensemble enables exceptional NH4HSO4 poisoning resistance for NH3-SCR reaction

Abstract

Although V2O5/WO3/TiO2 catalyst has been commercially used for selective catalytic reduction of NOx with NH3 (NH3–SCR), it suffers from activity loss due to ammonium bisulfate (ABS) poisoning at low temperatures below ABS dew point (≤280 °C). Here, we demonstrate that V2O5/MoO3/TiO2 catalyst with H2 pretreatment (designated V2O5/MoO3/TiO2_H2) exhibits high activity and excellently stable NH3–SCR performance at 180–230 °C under SO2 and H2O poisoning conditions. Nevertheless, commercial V2O5/WO3/TiO2 catalyst is quickly deactivated under identical conditions after reaction for 25 h due to formation of liquid–like ABS. Electronic structure investigations show that H2 pretreatment decreases oxidation states of V species of the V2O5/MoO3/TiO2_H2 catalyst, and reduced V species suppress the SO2–to–SO3 oxidation rate. The suppression of SO2–to–SO3 oxidation rate contributes to lower formation rate of ABS on catalyst surface. MoO3/TiO2 with ABS decomposition ability different from those of conventional or bulk material was synthesized on the basis of our previous efforts, and used as a fundamental building block in V2O5/MoO3/TiO2_H2. Control experiments show that the MoO3/TiO2 building block in V2O5/MoO3/TiO2_H2 has excellent ability to decompose ABS. Difficulty of ABS formation and rapid decomposition rate of ABS offer a net result in terms of improved ABS resistance and high activity for V2O5/MoO3/TiO2_H2 catalyst.