NO REDUCTION BY H-2 OVER PROMOTED PT CATALYSTS

The activity and selectivity of a 5 wt.-% Pt/SiO2 catalyst, a Pt/CoOx/ SiO2 catalyst with 3 wt.-% Co3O4 and a Pt/MnOx/SiO2 catalyst with 25 w t.-% MnO2 for NO/H-2 reactions were compared with a commercial PtRh/Al 2O3 catalyst, with 0.4 wt.-% Pt and 0.08 wt.-% Rh. Activity and select ivity measurements have been performed under stoichiometric (for N-2 p roduction) and reducing conditions. The activity, expressed in tempera tures of 50% NO conversion, does not significantly change upon the add ition of the metal oxides after a reductive pretreatment. The selectiv ity to N-2, N2O or NH3, however, is affected by the addition of cobalt or manganese oxide, compared to Pt/SiO2. After a reductive pretreatme nt, the Pt/CoOx/SiO2 catalyst shows a better selectivity to N-2 than P tRh/Al2O3, while the latter catalyst is more selective to N-2 after an oxidative pretreatment. Pt/MnOx/SiO2 produces a considerable amount o f N2O, even at a reducing gas mixture. In general, the addition of Co3 O4 or MnO2 to Pt/SiO2 leads to more N2O production at stoichiometric g as mixtures.