The enhanced SCR performance and SO2 resistance of Mn/TiO2 catalyst by the modification with Nb: A mechanistic study

Abstract The bad resistance to SO2 was still the primary defect of Mn/TiO2 catalyst for selective catalytic reduction of NOx with NH3. To address that, a series of MnNb/TiO2 catalyst samples with different Nb/Mn molar ratio were prepared by sol-gel method and used in NH3-SCR reaction. Experimental results indicated that the MnNb/TiO2-0.12 catalyst exhibited outstanding SCR activity and SO2 resistance. The introduction of Nb into Mn/TiO2 catalyst could promote the formation of more Mn4+ and chemisorbed oxygen species on its surface, along with the generation of more NO2. In addition, the doping of Nb on Mn/TiO2 catalyst could remarkably intensify its surface acidity. All these factors were conducive to improving the SCR performance of MnNb/TiO2-0.12 catalyst. The results of DRIFT study revealed that the NH3-SCR reaction over MnNb/TiO2-0.12 catalyst took place through both Eley–Rideal and Langmuir-Hinshelwood pathways, in which Eley–Rideal pathway was predominant. In the presence of SO2, it seemed that the NH3-SCR reaction over Mn/TiO2 and MnNb/TiO2-0.12 mainly happened between adsorbed NO2 and gaseous NH3 (Eley–Rideal mechanism), thus the formation of more NO2 over MnNb/TiO2-0.12 catalyst should mainly account for its super SO2 tolerance.