Desorption study of NO and O2 on Cu-ZSM-5

A detailed temperature-programmed desorption (TPD) study on NO and O₂ saturated Cu-ZSM-5 at different temperatures (300–723 K) has been performed. In the temperature range 373–723 K, the evolution of O₂ and NO₂ accompanying the desorption of NO from NO saturated Cu-ZSM-5 suggested the formation of nitrite/nitrate species. The amount of O₂ absorbed was very much lower than that of NO. The desorption profile of O₂ after contacting Cu-ZSM-5 with O₂ at 623 K showed a low temperature peak (369K) confirming the spontaneous ability of O₂ desorption from copper zeolite. Moreover, successive saturation cycles of NO followed by O₂ and vice versa have been performed at various temperatures (298–623 K) to understand the modifications which the adsorption sites undergo when the two molecules NO and O₂ are available together for adsorption on the catalyst sites. After each saturation cycle, a TPD profile was recorded following the evolution of NO, O₂ and other NO_x species. The competitive adsorption experiments revealed that, at 623 K, NO was not able to successfully compete with O₂ for the adsorption sites, therefore the adsorption of NO at 623 K on O₂ saturated catalyst was not completely restored. On the basis of the experimental work, an overall adsorption reaction scheme of NO on Cu-ZSM-5 was proposed