Different copper species as active sites for NH3-SCR reaction over Cu-SAPO-34 catalyst and reaction pathways: A periodic DFT study

Cu-SAPO-34 SCR catalyst has drawn much attention because of its high NH3-SCR activity and N-2 selectivity. Different copper species as active sites for SCR reaction in Cu-SAPO-34 catalyst were studied by DFT calculations , primarily focusing on copper sites in six-membered rings (6 MR) and eight-membered rings (8 MR). The relative energies of various Cu species were calculated and organized as phase diagrams to investigate the stabilities of Cu species. The diagrams show that Cu-2(+) can exist in 6 MR, and [Cu-O-Cu](2+) tends to form in 8 MR.The DFT results show that the adsorption energies for NH3 on Cu+ and Cu2+ in 8 MR are the highest and but NH3 can hardly dissociate in 8 MR, which indicate isolated Cu ions located in 8 MR will hinder the NH3-SCR reaction. However, the additional Cu ion and O atom in 8 MR effectively reduces the dissociation energy barrier. These results indicate that isolated Cu2+ is the active site in 6 MR, and [Cu-O-Cu](2+) is the active site in 8 MR. Besides, the NH3 dissociation on Cu2+ and [Cu-O-Cu](2+) are the key steps for the reactions in 6 MR and 8 MR.