AN INVESTIGATION OF THE MECHANISM OF THE SELECTIVE CATALYTIC REDUCTION OF NO ON VARIOUS METAL ZSM-5 CATALYSTS - REACTIONS OF H2/NO MIXTURES/

Several metal/ZSM-5 catalysts (Pt, Rh, Co and Cu/ZSM-5) were studied f or the reduction of nitric oxide by a reducing agent which does not co ntain carbon, such as H-2, in the absence of oxygen. It has been found that these catalysts are very active towards the above reaction with H-2 even at relatively low temperatures, with a reactivity in the orde r: Pt/ZSM-5 > Rh/ZSM-5 > Co/ZSM-5 > Cu/ZSM-5. Between the above cataly sts Co/ZSM-5 was the most selective to nitrogen with a formation of am monia much lower than that observed on Pt/ZSM-5, Rh/ZSM-5 and Cu/ZSM-5 even at higher hydrogen partial pressures. A comparison between hydro gen, methane and ethane as the reducing agent has been made. In all ca ses the catalytic activity is higher using hydrogen rather than ethane or methane, the latter being the least active reductant. All data are consistent with a simple redox mechanism of NO reduction, and exclude the participation of carbonaceous deposits or carbon-containing speci es in the reaction mechanism.