Novel bifunctional catalytic systems for the SCR of NOx using hydrocarbons as reductants: Step one, NO oxidation

Abstract

The oxidation of NO over Co-, Pt-and Rh-based catalysts was studied by combined catalytic activity and FT-IR studies. The activity of Co-, Pt-and Rh-based catalysts was measured in the presence and absence of H 2 O and SO 2 in the feed. The activity studies showed that the support (Al 2 O 3 , TiO 2 , ZrO 2 ) of Pt catalysts significantly affects the extent of the oxidation reaction, in addition to the metal content and calcination temperature over Co/Al 2 O 3 catalyst. The highest activity was measured over 5 % Co/Al 2 O 3 calcined at 450 °C, while Pt/ and Rh/Al 2 O 3 catalysts exhibited significant activity (absence of SO 2 ). The presence of 200 ppm SO 2 inhibited irreversibly the NO oxidation mainly over Co/ and Rh/alumina. In the presence of 10 % H 2 O in the feed the activity of all catalysts weakly decreased, reversibly. FT-IR studies, over fresh Rh/Al 2 O 3 , showed the formation of Rh-NO + , Al-NO 2 and Al-NO 3 species, while over presulfated catalyst only the Rh-NO + species was detected. Activity and FT-IR studies were used to propose a mechanism for the NO oxidation, in the presence and in the absence of SO 2 .