A Computational Study on Stabilization Trends of the Adsorption Complexes of C1-C4 Primary Alcohols on Modified Acidic Zeolites

The adsorption complexes and the binding energies of a series of aliphatic alcohols on Ti and P-modified acidic zeolites have been studied computationally employing combined Quantum Mechanics/Molecular Mechanics (QM/MM) methods suited for large-scale calculation. The investigation has been carried out using an extended 84T cluster model with one hydroxyl Brønsted acidic site. This cluster model has been studied employing the hybrid (QM/MM) B3LYP/6‑31+G(d,p):UFF method and its counterpart B3LYP‑D3/6‑31+G(d,p):UFF level of theory accounting for dispersion forces. The use of the B3LYP-D3 technique has led to a considerable improvement in the B3LYP results, underlining the critical role of the long-range dispersion forces. The modification exhibits higher deprotonation energies and a decreasing acidic character.The modified clusters show a considerable reduction of the order of 3 to 4 kcal/mol in adsorption energy for all alcohol molecules, especially emphasized in the Ti-modification in comparison to that of Al-zeolite.