Density Functional Theory Calculation on the Dissociation Mechanism of Nitric Oxide Catalyzed by Cu₄ Cluster in ZSM-5 (Cu₄-ZSM-5) and Bimetal Cu₃Fe in ZSM-5 (Cu₃Fe-ZSM-5)

Zeolite-based catalysts have been investigated as a well-known catalyst in a selectively catalytic reduction (SCR), in the conversion of NO to N₂ molecule. Here we have performed periodic DFT calculations to simulate pure metal, Cu₄, and bimetal Cu₃Fe clusters, on the ZSM-5 by introducing a single Al atom in the unit cell of ZSM-5 (Si/Al ratio=95). The calculated results show that the most stable structures of both Cu₄ and Cu₃Fe clusters in ZSM-5 are both T_d configuration. In addition, the NO bond length would be elongated from 1.15 Å to 1.25∼1.30 Å in the adsorption of NO on metal-cluster stabilized zeolites (both Cu₄-ZSM-5 and Cu₃Fe-ZSM-5), being longer than the counterparts on single-metal anchored zeolites. Furthermore, the calculated NO bond cleavage barrier on Cu₃Fe-ZSM-5 was lower than its counterparts on Cu₄-ZSM-5. To understand the electronic properties, we performed the calculation of Bader charge analysis and local densities of states, and the result was explicable.