On the mechanism of selective catalytic reduction of NO by propylene over Cu-Al-MCM-41

The selective catalytic reduction of NO by propene in the presence of excess oxygen over Cu-Al-MCM-41 catalyst has been studied by a number of catalytic techniques to characterize the structural, chemisorptive and reactive properties. The characterization using XRD and NMR revealed that the structure of Cu-Al-MCM-41 remained unchanged after the reaction. The active sites related to the reduction of NO and the reaction mechanism were explored based on the data of H2 temperature programmed reduction (TPR), NO temperature programmed desorption (TPD), X-ray spectrometry (XPS) and in situ FT-IR. The results showed that a redox of Cu ions in Cu-Al-MCM-41 between monovalent and divalent states happened during the selective catalytic reduction of NO, and the reduction seemed to proceed via the intermediate of organic nitro compounds produced by the reaction of propylene adspecies and NO2. In addition, the presence of oxygen is essential to the formation of NO2 intermediate and to the cycle of active center between Cu2+ and Cu+. However, it also caused the deep oxidation of propylene, leading to the depletion in reducing agent at higher temperature.