Abstract: SO2 shows a significant promoting effect on the activity of Sn0.5Ti0.5O2 solid solution catalyst for NO reduction with CO at 350 ℃. The mechanism of the promotion was studied by transient techniques combined with reaction test, XRD, XPS and TPD methods. The XPS analysis proves the existence of surface sulfur species, which was formed during the COSO2 or COSO2NO reaction. It was suggested that the surface sulfur weakened the N－O bond and promoted its split hence promoted NO reduction. Therefore, surface S is one of the more importance active site for NO reduction in the SO2NOCO reaction. The mechanism of SO2 promoted NO reduction by CO was proposed.

Key words: DeSO_x, DeNO_x, Sn_0.5Ti_0.5O₂, Catalyst, Rutile, Reaction mechanism