InterPore2026

Tuning Zeolite Catalysts using Organic Additives: Molecular Modelling Studies

20 May 2026, 15:35

1h 30m

Poster Presentation (MS09) Pore-Scale Physics and Modeling Poster

Speaker

Matthew Robinson (Cardiff University)

Description

Zeolites are commonly used as industrial acid catalysts, with capability to be fine-tuned for a given process. Typically, zeolites are fine-tuned through substitution of other elements into the framework, but it has been shown that some zeolite catalysts can be tuned more flexibly by adding organic additives.[1] In the domain of renewable chemicals, protonated mordenite (H-MOR) has been identified as a strong candidate for catalysing the dehydration of ethanol to ethylene,[2] a potential green route from bio-ethanol to a highly-demanded feedstock chemical (>200 million metric tonnes of ethylene currently produced globally p.a.).[3] When catalysed by H-MOR, the reaction produces side products such as diethyl ether, which are thought to only originate from Brønsted Acid (BA) sites in the larger 12 membered ring (MR) and not the smaller 8MR side pocket (SP). Pyridine has been shown to selectively titrate BA sites in the 12MR,[4,5] particularly at industrially-relevant temperatures,[6] therefore this project aims to investigate the application of pyridine-based additives to tune the selectivity of the H-MOR-catalysed ethanol dehydration reaction.
Periodic DFT calculations were performed using the PBE exchange-correlation functional with the non-local many-body dispersion correction (MBD-NL) through the FHI-Aims software package[7] (all-electron, numerical atomic orbitals). Each of the 12 crystallographically-distinct combinations of Al position (T-site) and H+ position (neighbouring oxygen: O-site) were considered, with three representative highly-stable sites taken forward to investigate the different pore regions (12MR, 8MR SP (shallow), 8MR SP (deep)).
Static pyridine adsorption calculations (0 K) clearly showed the favourability of adsorption in the larger 12MR over the 8MR SP. However, some 8MR SP sites showed somewhat comparable favourability to the 12MR sites, aligning well with the previous literature suggesting that pyridine is only disfavoured in the 8MR SP at higher temperatures.[6] This was confirmed by calculating adsorption free energies at the industrial reaction temperature, which showed that pyridine adsorbs endergonically in the deep 8MR SP. In contrast, the data at the shallow 8MR SP went against the literature[6] and showed that pyridine exergonically adsorbs in that region. This was then validated by molecular dynamics, which showed that pyridine favourably remains in the shallow 8MR SP region, with metadynamics calculating a high barrier to diffusion out of the 8MR SP into the 12MR.
Whilst pyridine does not show desirable adsorption behaviour (exergonic in 12MR, endergonic in 8MR SP), it can be decorated with other functional groups, which can further enhance or diminish the additive’s adsorptive behaviour to the zeolite. The choice of tailor-made additives could open up wider applications and higher selectivities for zeolite-catalysed reactions. Adsorption free energies showed the effects of adding different groups to the pyridine ring, with 2- and 3-ethylpyridine performing particularly well. Comparison of adsorption free energies and fragmentation energies determined that the steric effects of substituents were more important than electronic effects.
Investigation into expanded applications is ongoing, with nudged elastic band and dimer calculations used to compare barriers of diffusion into the 8MR SP and dehydration of higher alcohols to determine the viability of production of higher alkenes.