A DFT study on Cu(I) coordination in Cu-ZSM-5: effects of the functional choice and tuning of the ONIOM approach

The coordination of Cu+ at the T1 and T7 positions of the M7 ring of Cu-ZSM-5, and the interaction of NO with coordinated Cu+ were investigated by means of DFT/ONIOM calculations. The B3LYP, BLYP, PBE1PBE, PBE, M06 and M062X functionals with the def2-TZVP (def2-QZVP for Cu) basis set were employed in the high-level part of ONIOM calculations, with the HF/3-21G, B3LYP/LANL2DZ, M06/LANL2DZ and M062X/LANL2DZ methods in the low-level part. The ability of suitable combinations of the above methods to reproduce (i) the crystallographic structure of purely siliceous ZSM-5, (ii) the tendency of Cu+ to be two- or fourfold-coordinated by framework oxygen atoms of Cu-ZSM-5 and (iii) the interaction energy and the N–O stretching frequency of adsorbed nitrogen oxide are discussed, showing that different results are obtained depending on the adopted computational approach. With reference to above properties, some considerations about the employment of the ONIOM approximations are also included