A periodic DFT study of the synergistic mechanisms between extra-framework aluminum species and Brønsted acid sites in HY zeolites

A series of model probes with different sizes and polarity, such as ammonia, pyridine and thiophene, have been used to insight into the influence mechanisms of EFAl species on the properties of Bronsted acid sites in HY zeolites by periodic DFT calculation. EFAl species enhance the intrinsic strength of BAS in HY zeolites similar to the generally accepted results. However, the presence of EFAl species induce significant deviation of correlation between the adsorption energies of the probe molecules and the changes in intrinsic acidity characterized by DPE. These results demonstrate that EFAl species exert the additional forces (dispersion forces) on the probe molecules adsorbed on the BAS. In this work, a principal finding is using weaker polarity and right fit size molecule (that of thiophene in this work) as a probe can reveal the synergistic mechanisms between the EFAL species and the BAS.