Study Of The Effect Of SO₂on The Activity Of Ag/Al₂O₃Catalysts With C₃H₆as Reductant For NO_x Reduction

The sulfur dioxide as a result of exhaust gas from diesel engines is a serious problem. However, conclusive information on the effects of SO2on Ag/Al2O3catalysts which can reduce NOx emissions from diesel engines effectively is not in consensus due to the different results reported in the literatures. In this paper, we mainly study the effect of SO2on the activity of Ag/Al2O3catalysts with C3H6as reductant for NOx reduction in lean conditions.The gamma alumina support and silver nitrate as the precursor of Ag were chosen to prepare Ag/Al2O3catalysts using an incipient wetness impregnation technique. Besides, the selective catalytic reduction over Ag2SO4/Al2O3, AgCl/Al2O3, Ag/H2SO4/Al2O3and sulfated Ag/Al2O3catalysts was studied in order to understand the effect of SO2on the catalytic performance futher. The catalytic test was measured by passing a mixture of450ppm NO,900ppm C3H6,7%O2,0-80ppm SO2and the balance of argon gas operating at a space velocity of30000h-1and total flow=500cm3/min at the temperature of between from200℃to600℃.TPD and in situ DRIFTS were used to study the effect of SO2on the activity of catalysts. Results showed that the effect of SO2on the activity of HC-SCR over catalysts was dependent on the variability in the loading of silver and the concentration of SO2. A surface aluminium sulfate and a sulfate associated with the silver phase could be produced on the surface of Ag and Al2O3in the presence of SO2. The silver sulfate could promote the formation of the enolic species and organo-nitrite, which lead to a corresponding increase in the SCR activity. The formation of a surface aluminium sulfate could suppress the formation of the enolic species and adsorption of NO3-, consequently suppressed the SCR activity. For the low Ag loading, the formation of aluminium sulfate played a leading role, which lead to a corresponding decrease in the SCR activity after highly concentrated SO2exposure. For the high Ag loading, the increase in activity was attributed to the sulfation of enough silver species in the presence of SO2.