Effect of oxygen on reduction of NO with carbon monoxide over NiO and Cr2O3

Cr₂O₃ is found to be a less active catalyst than NiO in reduction of nitrogen oxides. Introduction of molecular oxygen into the NO–CO mixture decreases the conversion of NO_x on both catalysts. On NiO it is due to competition between O₂ and nitrogen oxides for CO. On Cr₂O₃ it is caused by the complete suppression of this reaction.

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Cr₂O₃ , NiO. NO CO NO_x ; NiO CO , Cr₂O₃- .