Marked effect of In, Pb and Ce addition upon the reduction of NO by CO over SiO2 supported Pd catalysts

Addition effect of In, Pb and Ce on the NO–CO reaction over SiO2 supported Pd catalysts was studied, using a closed gas circulation system as well as an in situ infrared spectroscopy. Formation of intermetallic compounds was observed in the cases of Pd–In/SiO2 and Pd–Pb/SiO2 catalysts, which caused the drastic enhancement of the reaction rate of N2O formation. The infrared analyses revealed the weakening of adsorption strength of CO on Pd metal by the formation of intermetallic compounds, which is the main reason for the enhancement of the reaction rate. In the case of Pd–Ce/SiO2 catalysts, SMSI-like interaction between Pd and CeO2 would be important for the enhancement effect.