Lean selective catalytic reduction of NO₂ by methane over Co‐zeolites

Abstract

The reaction of NO₂, CH₄ and O₂ was studied using low levels of methane compared to NO₂ and O₂ over protonic and cobalt‐exchanged ferrierite, ZSM‐5 and mordenite zeolites. Results suggest that two reaction pathways at low and high temperatures may be involved in the lean selective catalytic reduction (SCR) of NO₂ by methane. At low temperatures, the reduction of NO₂ to NO and N₂ might be the initial reaction step. It is likely that NO₂ or its adsorbed precursors initiate the reaction of methane at low temperatures. At high temperatures, the oxidation of NO and combustion of methane with oxygen might be involved. No appreciable differences were observed in the reduction of NO₂ over Co‐zeolites as compared to known results of NO reduction over these materials. However, enhanced N₂ formation rate was observed on H‐zeolites starting from NO₂ instead of data reported for NO. Furthermore, it appears that the active sites for SCR are both acid and metal sites.