The influence of the framework on adsorption properties of ethylene/H-ZSM-5 system: an ONIOM study

The applicability and reliability of the two-layer ONIOM2 (Our-own-N-layered Integrated molecular Orbital + molecular Mechanics) approaches have been carried out on different aluminosilicate clusters representing H-ZSM-5 zeolitic catalysts containing up to 46 tetrahedrally coordinated tetravalent atoms and their interaction with ethylene. When carefully calibrated, by using the experimental observation, the ONIOM2(B3LYP/6-311++G(d,p):HF/3-21G) scheme, in which an inner part of the system containing the active site is treated at the B3LYP/6-311++G(d,p) level, and the rest-using the HF/3-21G-has been found to provide reliable information for calculating the effects of the extended zeolite framework on the structural and energetic properties of the C2H4/H-ZSM-5 system. The predicted adsorption energy for this ONIOM2 scheme is -9.14 kcal/mol, which corresponds well with the experimental estimate of -9 kcal/mol. (C) 2003 Elsevier Science B.V. All rights reserved.