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 for the reduction of nitric oxide by a reducing agent which does not contain 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 order: Pt/ZSM-5 > Rh/ZSM-5 > Co/ZSM-5 > Cu/ZSM-5. Between the above catalysts Co/ZSM-5 was the most selective to nitrogen with a formation of ammonia 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 hydrogen, methane and ethane as the reducing agent has been made. In all cases 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 species in the reaction mechanism.