Absolute acidities and site specific properties of zeolite catalysts modelled by advanced computational chemistry technology

Hartree–Fock structure predictions are made for two crystallographically distinct Brønsted sites, O1H and O3H, of the zeolite catalyst H-faujasite. The structure optimisation adopted very large cluster models without symmetry (163 atoms; 2033 basis function) and applied the parallel TURBOMOLE code on a multi-processor compute server. The predicted acidity strength of the two sites, 1166±10 kJ/mol, is the same within chemical accuracy, but – in agreement with experiment – characteristic differences are found for the OH stretching frequencies (3617 and 3574 cm−1) and the 1H NMR chemical shifts (4.0 and 4.5 ppm).