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

Abstract

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.