(45e) Bridging Simulations with Experiment: Predicting Solvent and Confinement Effects in Catalysis By Hydrophilic and Hydrophobic Zeolites

Surroundings of an active catalytic site influence adsorption, reaction, and activation free energies, thereby providing extra degrees of freedom for tuning the reaction kinetics. Synergetic effects of combinations of factors provide new opportunities for controlling reaction rates, breaking linear scaling relationships, and ultimately designing novel environmentally benign and energy-efficient catalytic processes. However, describing both the catalyst and its environment quantitatively from first principles in the multiscale modeling hierarchy poses a unique set of challenges due to the large quantities of atoms involved and poor scaling of computational methods with the system size.

To this end, we develop a protocol for describing both solvent and confinement effects of long-chain 1,2-epoxyalkanes (C₆-C₁₈) in both pristine hydrophobic and defected hydrophilic Ti-doped beta zeolite catalysts in the presence of water-acetonitrile solvent mixtures. The system is prototypical due to its complexity and due to the industrial relevance of both zeolites and the environmentally friendly synthesis of epoxides in liquid media. The multiscale method integrates grand-canonical molecular dynamics (GCMD) simulations, cross-validated against Gibbs ensemble Monte Carlo, the cluster-model state-of-the-art quantum mechanics/molecular mechanics to describe chemical bonding and polarization effects, as well as the stochastic protocol for defect generation in the material. Our method yields adsorption enthalpies and solvent uptakes in excellent agreement with both calorimetry and NMR experimental data. The method’s extension to describe solvation and confinement of transition states in zeolites is discussed, and implications for quantitative prediction of liquid-phase reaction kinetics in zeolites are addressed.