DFT Study of the Lewis Acidities and Relative Hydrothermal Stabilities of BEC and BEA Zeolites Substituted with Ti, Sn, and Ge

Metal-substituted beta-zeolites have proven to be effective catalysts for various important reactions involving the transformation of biomass-derived molecules. In this study, a combination of quantum mechanical calculations and integrated quantum mechanics–molecular mechanics along with a polarizable continuum model were used to determine the preferred substitution site of Sn, Ti, and Ge metals in zeolite beta (BEA) and in the polymorphism C of zeolite beta (BEC), as well as the Lewis acidity and the hydrothermal stability of the metal-substituted zeolites. Our results demonstrate (1) the most favorable substitution of Ti, Ge, and Sn in BEC is in the T1 site; (2) Ti-BEC has Lewis acidity similar to that of Sn-BEA; (3) the hydrolysis of Ge-BEC is energetically favorable when the Ge/Si ratio is 1/13; and (4) Ti-substituted zeolites show the highest hydrothermal stability of the zeolites studied.