Calculation of the properties of acid sites of the zeolite ZSM-5 using ONIOM method

The performance of the ONIOM method was tested in reproducing the properties of the acid sites of the zeolite ZSM-5. The acid sites in three crystallographic locations (A13-O19(H)-Si6, A16-O18(H)-Si9 and A17-O17(H)-Si4) have been modelled by three combinations of two-layer ONIOM method with varied size (two and eight T atoms) and calculation method (ab initio and DFT) used for the chemically important (active) part. The best correspondence with experimental data was achieved in case of A16-O18(H)-Si9 site calculated with ONIOM(B3LYP/6-311+G**:MNDO) method using eight T atoms in model system for the following properties: stretching vibrational frequencies, H-1 NMR chemical shifts of the bridged hydroxyl groups, vibrational frequency shifts and changes in H-1 NMR chemical shifts of the hydroxyl groups upon adsorption of CO. (C) 2002 Elsevier Science B.V. All rights reserved.