NO reduction by H 2 over promoted Pt catalysts

Abstract

The activity and selectivity of a 5 wt.-% Pt/SiO 2 catalyst, a Pt/CoO x/SiO 2 catalyst with 3 wt.-% Co 3O 4 and a Pt/MnO x/SiO 2 catalyst with 25 wt.-% MnO 2 for NO/H 2 reactions were compared with a commercial PtRh/Al 2O 3 catalyst, with 0.4 wt.-% Pt and 0.08 wt.-% Rh. Activity and selectivity measurements have been performed under stoichiometric (for N 2 production) and reducing conditions. The activity, expressed in temperatures of 50% NO conversion, does not significantly change upon the addition of the metal oxides after a reductive pretreatment. The selectivity to N 2, N 2O or NH 3, however, is affected by the addition of cobalt or manganese oxide, compared to Pt/SiO 2. After a reductive pretreatment, the Pt/CoO x/SiO 2 catalyst shows a better selectivity to N 2 than PtRh/Al 2O 3, while the latter catalyst is more selective to N 2 after an oxidative pretreatment. Pt/MnO x/SiO 2 produces a considerable amount of N 2O, even at a reducing gas mixture. In general, the addition of Co 3O 4 or MnO 2 to Pt/SiO 2 leads to more N 2O production at stoichiometric gas mixtures.