High-Throughput Transition-State Searches in Zeolite Nanopores

Abstract

Zeolites are important for industrial catalytic processes involving organic molecules. Understanding molecular reaction mechanisms within the confined nanoporous environment can guide the selection of pore topologies, material compositions, and process conditions to maximize activity and selectivity. However, experimental mechanistic studies are time- and resource-intensive, and traditional molecular simulations rely heavily on expert intuition and hand manipulation of chemical structures, resulting in poor scalability. Here, we present an automated computational pipeline for locating transition states (TS) in nanopores and exploring reaction energy landscapes of complex organic transformations in pores. Starting from the molecular structure of potential reactant and products, the Pore Transition State finder (PoTS) locates gas-phase transition states using DFT, docks them in favorable orientations near active sites in nanopores, and leverages the gas-phase reaction mode to seed condensed-phase DFT calculations using the dimer method. The approach sidesteps tedious manipulations, increases the success rate of TS searches, and eliminates the need for long path-following calculations. This work presents the largest ensemble of zeolite-confined transition states computed at the DFT level to date, enabling rigorous analysis of mechanistic trends across frameworks, reactions, and reactant types. We demonstrate the applicability of PoTS by analyzing 644 individual reaction steps for transalkylation of diethylbenzene in BOG, IWV, UTL and FAU zeolites, and in skeletal isomerization of 162 individual reaction steps in BEA, FER, FAU, MFI and MOR zeolites finding good experimental agreement in both cases. Lastly, we propose a path to address the limitations we observe regarding unsuccessful TS searches and insufficient theory in other reactions, like alkene cracking.