Effect of water on NO adsorption over Cu-ZSM-5 based catalysts

The adsorption of NO has been investigated in the temperature range 50–150 °C on Cu-ZSM-5 and La-Cu-ZSM-5 also in the presence of water and O2 in a continuous flow reactor. TPD experiments have been performed after each adsorption test monitoring all desorbed NOx species. Water has been found to displace NO from copper sites strongly reducing its adsorption except for nitrate-like species which are partially preserved also in the presence of water. O2 addition, although decreasing NO adsorption, limits the negative effect of water. Lanthanum co-exchange results in improving the NO adsorption capacity of the zeolite both in the absence and in the presence of water.

Both water and oxygen depress NO adsorption on Cu-ZSM-5 at low temperature. Water almost totally displaces NO pre-adsorbed on copper sites but in the presence of oxygen the oxidation of NO to NO2, that partially occurs, promotes the formation of nitrate-like species which are not removed by water. Lanthanum co-exchange improves the copper adsorption capacity both in the absence and in the presence of water and O2.Figure optionsDownload high-quality image (136 K)Download as PowerPoint slideHighlights
► Both water and oxygen depress NO adsorption on Cu-ZSM-5 at low temperature.
► Water and NO compete for the same copper sites.
► Water displaces NO adsorbed on copper sites except for nitrate-like species.
► La co-exchange improves the adsorption also in the presence of water and O2.