Catalytic diesel engine emission control. - studies on model reactions over a europt-1 (Pt/SiO₂) catalyst

Catalytic oxidation of NO to NO₂in the presence of SO₂over a standard Pt/SiO₂catalyst (EUROPT-1) was studied. The gas phase reactions between NO, SO₂and O₂were found to be insignificant under the experimental conditions concerned. The Pt/SiO₂catalyst was observed to be very active in catalyzing the reactions of both NO+O₂to NO₂and SO₂+O₂to SO₃In the presence of SO₂the catalytic activity for NO oxidation dropped dramatically, and in contrast, the presence of NO promoted SO₂oxidation. Formation of a complex surface species of the type (NO)_x(SO₂)_yattached on Pt, was observed when both NO and SO₂were present in the gas phase. It is proposed that this species reacts towards SO₃rather than NO₂and is responsible for the mutual effect between NO and SO₂Deactivation of the catalyst was also observed during activity test. It is believed that the deactivation was mainly due to the built-up of non-active nitrogen- and sulphur-compounds on the catalyst surface and the sintering of Pt particles under the reaction environment. This has been confirmed by XPS, TPR and H₂chemisorption measurements.