Unraveling the Unexpected Offset Effects of Cd and SO2 Deactivation over CeO2-WO3/TiO2 Catalysts for NOx Reduction

It is challenging for selective catalytic reduction (SCR) of NOx by NH3 due to the co-existence of heavy metal and SO2 in the flue gas. The thorough probe into deactivation mechanisms is imperative but still lacking. This study unravels unexpected offset effects of Cd and SO2 deactivation over CeO2-WO3/TiO2 catalysts, potential candidates for commercial SCR catalysts. Cd and SO2 co-poisoned catalysts demonstrated higher activity for NOx reduction than Cd poisoned one but lower than SO2 poisoned one. Compared to SO2, Cd had more severe effects on acidic and redox properties, distinctly decreasing the SCR activity. After sulfation of Cd poisoned catalysts, SO42- preferentially bonded with the surface CdO and released CeO2 active sites poisoned by CdO, thus reserving the highly active CeO2-WO3 sites and maintaining a high activity. The sulfation of Cd poisoned catalysts also provided more strong acidic sites, and the synergistic effects between the formed cerium sulfate and CeO2 contributed to the high-temperature SCR performance. This work sheds light on deactivation mechanism of heavy metals and SO2 over CeO2-WO3/TiO2 catalysts and provides innovative pathway for inventing high-performance SCR catalysts, which have great resistance to heavy metal and SO2 simultaneously. It is favorable to academic and practical applications in the future.