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The zeolite Beta is considered as a promising additive for FCC catalyst in diesel oil production. In this article, it is shown that hierarchical zeolite Beta obtained by an optimized desilication procedure increases Diesel and propylene yields during gas-oil cracking reaction.The alkaline treatment of zeolite Beta (Si/Al = 22) by desilication with NaOH and NaOH&TBAOH was investigated. The catalytic performance improvement of desilicated zeolite Beta has been rationalized by deep characterization of the samples including X-ray diffraction, low temperature adsorption of nitrogen, solid-state 29 Si MAS NMR and IR studies of acidity. Finally, the catalytic performance of the zeolites Beta was evaluated in the cracking of n-decane, 1,3,5-tri-iso-propylbenzene and vacuum gas oil. It was found that desilication with NaOH&TBAOH ensures the more uniform intracrystalline mesoporosity with the formation of narrower mesopores, while preserving full crystallinity resulting in catalysts with the most appropriated acidity and then, with better catalytic performance.

The effect of Al for Si substitutions in the tetrahedral sites of the faujasite framework with low and high aluminium content on the properties of Brønsted sites is investigated by computational techniques. A combined quantum mechanics-interatomic potential functions approach (QM-Pot.) is applied which uses periodic boundary conditions and treats the whole zeolite structure. Both the Hartree-Fock and the density functional (B3LYP) methods are employed. Energies of deprotonation, O-H stretching harmonic frequencies, and 1 H NMR chemical shifts are calculated. In the first approximation, the acidity of Brønsted sites measured by the deprotonation energy is determined by the number of nearest neighbor Al atoms of the Si atom in the Al-O(H)-Si bridge, while the O-H stretching frequency and 1 H chemical shift depend on their crystallographic position. Beyond this, the 1 H NMR chemical shifts show a strong dependence on the overall lattice composition. There is no correlation between 1 H NMR chemical shifts and deprotonation energies; however, a linear relation between 1 H NMR chemical shifts and OH vibrational frequencies is supported.