Improvement of Nb Doping on SO2 Resistance of VOx/CeO2 Catalyst for the Selective Catalytic Reduction of NOx with NH3

The influence of sulfation treatment on Nb-VOx/CeO2 and VOx/CeO2 catalysts for the selective catalytic reduction (SCR) of NOx with NH3 was fully investigated. The Nb VOx/CeO2 catalyst showed higher catalytic activity and stronger resistance to SO2 than VOx/CeO2. The formation of sulfates, small specific surface area, and reduction in the number of active sites were all responsible for the low catalytic activity over VOx/CeO2 after sulfation under SCR conditions. On the contrary, Nb VOx/CeO2 adsorbed much more nitrate than sulfate when sulfated under SCR conditions and showed much higher NH3-SCR activity than VOx/CeO2 after the same treatment. After sulfation by SO2 + O-2 only, instead of sulfation under SCR conditions, both of the samples exhibited decreased NH3-SCR activity, mainly due to the formation of sulfates and the blockage of the Langmuir-inshelwood reaction pathway.