Synergistic effect in lean NO_x reduction by CH₄ over Co/Al₂O₃ and H-zeolite catalysts

In the reduction of NO by CH₄ in the presence of a large excess of oxygen, the conversion to N₂ over a physical mixture of Co/Al₂O₃ and H-zeolite catalysts was found to be twice as high as that expected if these components acted independently. This synergistic effect was observed with both H-ZSM-5 and H-USY. By comparing the activities of these catalysts for NO oxidation and CH₄ reduction of NO₂, it was concluded that the synergistic effect could be explained by the participation of Co ions and proton sites in the reaction. NO is oxidized to NO₂ over the Co ions, and NO₂ is reduced by CH₄ to N₂ over the proton sites.