Multiscale studies of framework structure, composition and defect influences on small molecule behaviour in zeolites

Zeolites are microporous silica-based solids with a highly modifiable structure. Their defining characteristic is that they contain pores of molecular dimensions. This feature has led to their widespread use in a range of applications such as catalysis (in the cracking and transformation of hydrocarbons in the fossil fuel industry), molecular sieving and water purification. They also have potential for further use in drug delivery systems and the agrochemical industry. All these processes require small molecules to enter the zeolite framework, diffuse through the pore system to an active site, where it can undergo a reaction, and to eventually diffuse out of the system. This means that the movement of molecules confined within the zeolite structure is of great interest as it can define their use. It can also guide which post-synthetic treatments may be applied to the zeolite to optimise its structure, and composition, and subsequent application. One of the most important factors affecting molecular behaviour within zeolites are the interactions with structural features and defects (such as cations, Bronsted acid sites, silanol nests and extra-framework aluminium). Currently, there is a significant research gap in gaining an accurate understanding of the effect of these features which will have high impact on the industrial applications of zeolites.

Research question: This research aims to quantify and understand the effects of structural features on small molecule diffusion within zeolites on multiple scales - meaning that both experimental and theoretical techniques will be employed. A large combination of different structure types (i.e. variations in pore size and geometry), structural features (i.e. different counter ions, silanol nests, acid sites) and compositions (i.e. silicon to aluminium ratios) need to be investigated and in many different combinations to fully understand the effects of these variables and how they can interplay with each other.

Objectives:
Measure the effect structural features and defects on the diffusivity of small molecules (such as water, short chain hydrocarbons, ammonia). Initially, starting with water in zeolites containing Bronsted acid sites and silanol nest defects.
Determine the effect of different cations (such as sodium, potassium, calcium) being incorporated in the zeolites.
Investigate how framework topology, alongside other factors, can alter the molecular behaviour. Initially starting with industrially relevant structure types - such as ZSM-5 and FAU (Zeolite Y) - but with the potential to move further afield.
Model these systems computationally via quantum mechanical calculations based on density functional theory alongside experimental techniques such as vibrational spectroscopy to investigate the molecular-scale behaviour.
Investigate the nanoscale behaviour via simulation with classical molecular dynamics paired with quasielastic neutron scattering experiments.
Together, the multiscale-multifaceted approach will allow the production of novel ideas and insights into how small molecules behave upon confinement within zeolites with varied compositions and defects present.

There are multiple reasons why this research is appropriate for funding from the EPSRC. Firstly, the fundamental nature of the project, coming from a "bottom-up" approach keeps the UK globally competitive in research. On top of this, the nature of the study provides a long-term impact in terms of the understanding within zeolite science. And finally, it's impact on industry and therefore the economy due to the wide-ranging industrial applications - particularly catalysis - of these materials.

Relevant EPSRC research areas:
Computational and theoretical chemistry
Catalysis
Fossil Fuel power generation