Adsorption of aromatic hydrocarbon onto H-ZSM-5 zeolite investigated by ONIOM study

The ONIOM (Our-own-N-layer Integrated molecular Orbital + molecular Mechanics) approach utilizing two-layer ONIOM2 schemes-ONIOM2(MP2/6-31G(d,p):HF/3-21), ONIOM2(B3LYP/6-31G(d,p):HF/3-21), ONIOM2(B3LYP/6-31G(d,p):UFF), and ONIOM2(HF/3-21:UFF)-have been used to investigate adsorption properties of benzene in zeolites. The active site has been modeled with different cluster sizes up to 46 tetrahedra. Our results predict that benzene is favorably located in the intersection of straight and sinusoidal channels, which is supported by the recent power neutron and synchrotron X-ray diffraction techniques. The predicted adsorption energy for the ONIOM2(MP2/6-31G(d,p):HF/3-21) scheme is - 13.75 kcal/mol, which corresponds well with the experimental estimate of - 14.0 kcal/mol. (C) 2003 Elsevier B.V. All rights reserved.