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 coexistence of heavy metal and SO2 in the flue gas. A 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-copoisoned catalysts demonstrated higher activity for NOx reduction than a Cd-poisoned catalyst but lower than that for an SO2-poisoned catalyst. In comparison 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 the deactivation mechanism of heavy metals and SO2 over CeO2-WO3/TiO2 catalysts and provides an innovative pathway for inventing high-performance SCR catalysts, which have great resistance to heavy metals and SO2 simultaneously. This will be favorable to academic and practical applications in the future.