Effect of the Al Siting on the Structure of Co(II) and Cu(II) Cationic Sites in Ferrierite. A Periodic DFT Molecular Dynamics and FTIR Study

Abstract

Periodic DFT molecular dynamics and FTIR spectroscopy were used to investigate the cationic sites of ferrierite exchanged with Co(II) and Cu(II) and their complexes with NO. Particular attention was paid to the effect of the Al siting in six-membered rings forming the cationic sites on the structure of these sites and the corresponding binding energies of Me(II) (Me = Co and Cu). Our calculations show that both the cations upon binding to cationic sites induce a rearrangement of the local structure of the zeolite framework. The rearrangement is significant for the α and β-2 sites while it is minor for the β-1 site. Comparison of the observed and theoretical NO stretching frequencies of ferrierite Co(II) and Cu(II) complexes with a NO molecule permitted the assignment of IR bands to the individual types of cationic sites. For NO-Co-ferrierite, the IR bands found at 1956, 1941, and 1935 cm–1 can be assigned to NO-Co complexes with Co(II) located in the α, β-1, and β-2 sites, respectively. Similarly for NO-C...