Promotion effect of bulk sulfates over CeO2 for selective catalytic reduction of NO by NH3 at high temperatures

Abstract

Understanding the influence of sulfates over catalysts for selective catalytic reduction of NO with NH3 (NH3-SCR) is crucial due to the universal presence of SO2 in exhaust gas. Depending on the degree of sulfation, there mainly exist surface and bulk sulfates and NH3-SCR activity is generally considered to suffer more from bulk sulfates. Herein, the unique function of bulk sulfates over CeO2 in promoting high-temperature SCR reaction is revealed. Notably, compared with CeO2 dominated with surface sulfates (S-CeO2–4h) and commercial V2O5-WO3/TiO2, CeO2 with bulk sulfates (S-CeO2–72h) exhibits admirable NO conversion at the temperature range of 400–550 °C. Bulk sulfates provide more Brønsted acid sites with stronger strength for NH3 adsorption. Moreover, the oxidation ability of CeO2 is significantly inhibited due to electron-withdrawing effect from bulk sulfates, which alleviates NH3 oxidation at high temperatures. More NH3 adsorption with high stability and limited NH3 oxidation capacity ensure the excellent catalytic performance for S-CeO2–72h in high-temperature denitration. This work provides new insight of bulk sulfates in promoting SCR activity and open a new avenue to design deNOx catalysts employed at high temperatures.