The effect of H-2 addition and silver loading on the SO2 tolerance and de-NOx performance of Ag/Al2O3 for the C3H8-SCR reaction was investigated by catalytic testing combined with various characterization results. SO2 tolerance is improved by H-2 cofeeding as well as an increase in Ag loading of Ag/Al2O3. In situ IR results shows that the reaction of sulfates on Ag-containing sites with H-2 results in the desorption of SO2 or migration of the sulfates to alumina surface. TPD/TRP results show that sulfate desorption in He or in H-2 occurs at lower temperature for the higher loading sample. Combined with UV-vis and in situ IR results, these findings suggest that the higher SO2 tolerance of high loading catalyst for the H-2-C3H8-SCR reaction is caused by the higher rate of sulfate reduction that is more advantageous over partially reduced silversites than over Ag+ sites. (c) 2006 Elsevier Inc. All rights reserved.