Relationships between Adsorption Amount of Surface Sulfate and NH₃-SCR Performance over CeO₂

Abstract

Sulfation is an effective means to improve the reactive performances of pure CeO2 for selective catalytic reduction of NO by NH3 (NH3-SCR). Herein, CeO2 is sulfated by SO2 + O2 at 150 °C and the amount of sulfate is controlled by sulfation time, and the influence of sulfate amount on the catalytic performances of CeO2 has been studied. Catalytic tests show that both NO conversion and N2 selectivity of sulfated CeO2 are enhanced with increasing sulfate amount. However, catalytic performances nearly keep unchanged when the sulfate amount is over 60% of saturated adsorption. Studies demonstrate that only surface sulfate species existed when CeO2 is sulfated at 150 °C, and the amount of surface sulfate increases with increasing sulfation time. Then, a corresponding model is proposed to explain the relationships between the adsorption amount of surface sulfate and catalytic performances. More surface sulfate can produce more Brönsted acid sites to improve the activity of sulfated CeO2. Moreover, adsorbed sulfate can hinder the formation of surface active oxygen species, resulting in better N2 selectivity. The NH3-SCR reaction can mainly proceed by the Eley–Rideal mechanism over the sulfated CeO2.