Investigating Closed and Open Site Stability of Sn-, Ti-, Zr-, and Hf-Beta Zeolites: A Comprehensive Periodic DFT Study

This study presents a comprehensive periodic DFT analysis of Sn-, Ti-, Zr-, and Hf-doped Beta zeolites, materials known for their versatile catalytic properties in sustainable chemical processes. We focus on assessing the stability of closed versus open sites, which is crucial to monitor the nature of the active sites under relevant conditions for analysis and catalysis. Using first-principles thermodynamics, we find that closed sites are stable under low water pressure and high temperature but over stability (T, P) domains that depend on the nature of the metal and on its location in the framework. Our findings also offer novel insights into water adsorption in zeolites with respect to earlier proposals by favoring scenarios with undissociated H₂O. The evaluation of Lewis acidity, quantified by pyridine adsorption, shows various acidity levels across different T sites, with T6 (following the polymorph B terminology) showing the strongest and T9 showing the weakest Lewis acidity. Titanium (Ti) is identified as having the weakest Lewis acidity among the studied dopants. A subtle interplay between electrostatic field and bonding energy terms is shown to be correlated with this behavior. This study improves the molecular understanding of zeolite stability and catalytic behavior, providing valuable insights for the development of advanced catalysts in sustainable chemical processes.