NH3-SCR performance and SO2 resistance comparison of CeO2 based catalysts with Fe/Mo additive surface decoration

Abstract Fe2O3 and/or MoO3 surface decorated CeO2 were designed and synthesized by in situ deposition and incipient wetness impregnation to adjust the SCR catalytic performance and SO2 resistance of CeO2. The addition of iron oxide slightly improved low temperature SCR activity of CeO2-Fe2O3, but resulted in a fast decline of NOx removal efficiency at higher temperatures, which was due to the enhanced NH3 oxidation by surface redox capacity improvement. Surface acidity instead of redox capacity was the main limiting factor for SCR activity of CeO2 and CeO2-Fe2O3. Meanwhile, the introduction of MoO3 increased NOx conversion of CeO2-MoO3 and CeO2-Fe2O3-MoO3 dramatically in a broad temperature range. The increase of catalysts surface acid sites promoted their SCR catalytic performance through Eley-Rideal mechanism. SO2 resistance test indicated the different surface characteristics for the four catalysts resulting from the composition disparity leaded to different deactivation behaviors at 250 °C. The deposition of ammonium sulfate species accounted for the main activity loss of CeO2 and CeO2-Fe2O3, while the sulfation of redox sites was main deactivation reason for CeO2-MoO3 and CeO2-Fe2O3-MoO3. The interaction between SO2 and CeO2/CeO2-Fe2O3 catalysts changed the surface active sites for SCR reaction essentially and MoO3 could inhibited surface sulfation and ammonium sulfate species deposition. The variation behavior of NOx conversion during SO2 resistance test depended on the reaction temperature. All four catalysts show the usability in the presence of SO2 when the reaction temperature is between 300 °C and 400 °C. Considering the complexity of preparation process, catalytic performance and SO2 durability, CeO2-MoO3 catalyst is a better choice for substituting the traditional V-Ti catalyst.