Theoretical study of N2O decomposition mechanism over binuclear Cu-ZSM-5 zeolites

• Different active centers have a significant influence on catalytic behaviors.
• The NO splitting step controls catalytic cycle in binuclear center.
• Binuclear center in Cu-ZSM-5 is not suffered from O2 inhibition.
• The value of theoretical conversion rate is close to the experiment.
• Understanding catalytic behaviors are important for control active centers.

The mechanism of N2O decomposition over binuclear Cu-ZSM-5 zeolites is investigated using density functional theory (DFT). It is found that the activation energy of two N2O molecules dissociation are 47.19 and 63.89 kcal/mol, and the desorption energy of O2 from Cu2O2 is 14.70 kcal/mol. The DFT results show that the NO splitting step of N2O molecule controls the whole catalytic cycle, and the binuclear Cu-ZSM-5 has not suffered from O2 inhibition. Moreover, some experimental work reports O2 inhibition is not observed at high Cu loading, which is in agreement with the present calculation. These findings suggest that the catalytic behavior of binuclear Cu-ZSM-5 is different from that of mononuclear. Furthermore, the kinetic analysis confirms the rate-limiting step in the binuclear Cu-ZSM-5 system is the N2O dissociation step, and the rate constant indicates that high temperature could accelerate the N2O dissociation. These results could allow us to understand the structure of the active sites and reveal the active sites controlling catalytic activity. The DFT calculation results combined with the kinetic study would provide us a comprehensive understanding on the NOx decomposition mechanism over the Cu-ZSM-5 zeolites.

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