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

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 H2O and SO2 in the feed. The activity studies showed that the support (Al2O3, TiO2, ZrO2)
of Pt catalysts significantly affects the extent of the oxidation reaction, in addition to the metal content
and calcination temperature over Co/Al2O3 catalyst. The highest activity was measured over 5 %
Co/Al2O3 calcined at 450 °C, while Pt/ and Rh/Al2O3 catalysts exhibited significant activity (absence of
SO2). The presence of 200 ppm SO2 inhibited irreversibly the NO oxidation mainly over Co/ and
Rh/alumina. In the presence of 10 % H2O in the feed the activity of all catalysts weakly decreased,
reversibly. FT-IR studies, over fresh Rh/Al2O3, showed the formation of Rh-NO+, Al-NO2 and Al-NO3
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
SO2.