TPD study of the interaction of oxygen and NO with reduced Cu/ZSM-5

The adsorption and desorption of oxygen and NO over reduced 103% Cu/ZSM-5 were studied by means of TPD and TPD-FTIR. The oxygen TPD patterns with adsorption temperatures from -100 to 500 degrees C contained at least three desorption peaks which showed strong temperature dependence. The results of O-18(2)-TPD and kinetic oxygen desorption-adsorption experiments revealed that dissociative adsorption of oxygen starts above 200 degrees C. At lower temperature, oxygen adsorbs mainly in molecular form. The amount of oxygen adsorbed at low and higher temperatures correspond to the ratio of 0.15 O-2/Cu and 0.17 O/Cu, respectively. The results of NO TPD indicated that about 80% of the copper sites are active for NO adsorption. The adsorbed NO can be partially desorbed as NO below 300 degrees C. During the process of NO adsorption, some of the NO molecules react with ELO to form NO2 which can be desorbed around 400 degrees C. The co-adsorption of NO and oxygen suggested that oxygen and NO compete for the same part of copper sites. These results indicate that oxygen adsorption, NO decomposition and NO2 formation happen at the same type of copper site which is believed to be the copper center bonded with ELO.