(6c) Predictive Multiscale Modeling of Liquid-Phase Alkene Epoxidation catalyzed By Titanium-Substituted Zeolites

Zeolites serve as versatile catalysts and adsorbents in a variety of industrial processes. Among these, alkene epoxidation catalyzed by transition metal-doped zeolites emerges as a promising alternative to current industrial technologies, which often involve organic peroxy compounds or chlorohydrins and generate a lot of waste.¹ Extensive research has focused on unraveling the intricate relationship between metal identity, solvation, and defect concentration, as these factors affect epoxidation catalysis by modulating enthalpies and entropies of formation of reaction intermediates and transition states. However, achieving atomic-level understanding of the underlying mechanisms remains a challenge. This is primarily due to the limitations of computational methods and protocols when applied to complex catalytic systems involving uncertain defect distributions, bicomponent liquid solvents, long-chain reactants, and confined porous environments.

In this study, we develop and apply a multiscale approach integrating density functional theory (DFT), microkinetic modeling (MKM), and grand canonical molecular dynamics (GCMD) simulations to obtain microscopic insights into both gas-phase and liquid-phase alkene epoxidation in Ti-substituted *BEA (Ti-BEA) zeolites. In the gas phase, we identify the OH-mediated reaction pathway associated with an open-site Ti site, which reproduces the experimental reaction orders and the apparent activation enthalpy within 10 kJ/mol. By combining ab initio gas-phase kinetics, GCMD-predicted solvent compositions in Ti-BEA pores, and the Born-Haber thermodynamic analysis,² we reproduce the liquid-phase experimental apparent activation enthalpy within 10 kJ/mol in both defected hydrophilic and defect-free hydrophobic Ti-BEA for a range of alkene reactants. Our results demonstrate the capability of state-of-the-art computational methods to make accurate and reliable predictions of liquid-phase reaction kinetics in a confined environment and reveal the physical origins of the observed alkene epoxidation reactivity trends.

(1) Bregante et al. J. Catal. 2017, 348, 75–89.

(2) Potts et al. ACS Catal. 2022, 12 (21), 13372–13393.