DFT Study on the Stability and the Acid Strength of Brønsted Acid Sites in Zeolite β

Acid sites are studied computationally for zeolite β. Different deprotonated and protonated models are used. The issue of difference in the stability of acid sites is addressed. Separate and paired acid sites are created, and their stability and acidity are estimated. The sites in the 6-membered rings have a favorable position; however, the study does not exclude the diversity of sites in other positions. The zeolite module and model chemistry have an influence on the computational results. The influence of the mutual arrangement of two acid sites in a single model is studied. Hydrogen bonding influences the stability and acidity in this case. Four and six acid sites are created that possess hydrogen bonding in the same model. The distance and mutual orientation of the sites affect their stability. Thus, the dipole-dipole interactions, structure deformations, and inductive effect all play their roles in the chemistry of the acid sites. Both thermodynamics and chemical kinetics of the zeolite can influence Al locations in zeolites, and their influence should be concerted according to the linear relation of the free energies.