Shielding ceria based catalysts from SO2 poisoning in NH3-SCR reaction: Modification effect of acid metal oxides

Modifying CeO2 with acid sites is a common strategy for designing efficient catalysts for the selective catalytic reduction of NOx by NH3 (NH3-SCR of NOx). However, the effect of acid metal oxide modification on the SO2 resistance of CeO2 has not been well revealed. In this work, it was found that the SO2 resistance of CeO2 modified with several acid metal oxides (i.e., MoO3, WO3 and Nb2O5), followed an order of Mo/CeO2 ≥ W/CeO2 > Nb/CeO2. Further systematic characterizations revealed that Mo-OH and W-OH on CeO2 as Brønsted acid sites could better inhibit the SO2 adsorption and the sulfation of active sites than highly dispersed NbOx mainly as Lewis acid sites because NH4+ coordinated to Brønsted acid sites could help trap SO2 to form ammonium sulfates rather than metal sulfates. The findings in this work provided important guidance for the design of efficient catalysts with superior SO2 resistance performance.