Impact of dopants on catalysts containing Ce1-xMxO2-3 (M = Fe, Sb or Bi) in NH3-SCR of NOx-A multiple spectroscopic approach

Ce1-xMxO2-3 solid solutions (M = Fe3+, Bi3+, Sb3+; x = 0.01, 0.03, 0.05) with and without VOy surface species were characterized by standard techniques and tested in low-temperature NH3-SCR of NOx. In situ DRIFTS and EPR measurements at elevated temperature in the presence of different feed components allowed to identify active sites and structure-reactivity relationships. Catalytic activity of V-free supports follows the order CeSb > CeFe > CeO2 > CeBi and correlates with the formation of Ce-O surface species which promote initial NO oxidation. VOy/Ce1-xMxO2-3 catalysts are more active than corresponding V-free supports, yet the order of NOx conversion (VSbCe > VCe > VFeCe > VBiCe) is governed by the efficiency of the V5+/V4+ redox shuttle which is faster in VOy/Ce1-xSbxO2-3 than in VOy/CeO2 but lower when M = Fe and Bi. Activity of V-free supports is raised by increasing Bronsted acidity after treatment with H2O/SO2 containing feed while no positive effect was observed for VOy/Ce1-xMxO2-3, since the redox properties of VOy dominate over the impact of surface acidity. (c) 2021 Elsevier Inc. All rights reserved.