Diffusion and Relaxometry Studies in Mesoporous Systems using Nuclear Magnetic Resonance

The role of diffusion plays a crucial part in catalytic reactions by facilitating the transport of reactants to the catalysts' active sites. Numerous chemical processes involve species with branches, such as the hydroisomerisation of fuels, Low-Density Polyethylene (LDPE) production, and the separation of branched and linear species. Despite the significance of branched species in various daily product-producing chemical processes, more studies are needed on the impact of branching on diffusion. Therefore, in this thesis, the effect of branching on diffusion has been examined using Pulsed Field Gradient (PFG) NMR. This includes a diffusion study of binary mixtures consisting of *n*-dodecane and one of octane isomers. It has shown that linear octane diffuses distinctively faster than branched octane isomers, indicating physical restriction to diffusion due to branches. Moreover, the change in diffusion coefficients and diffusion mechanisms with varying degrees of branching and confinement levels have been studied. It has shown that the decrease in the diffusion coefficients with increasing degrees of branching depends on the confinement level. At the highest degree of branching of 80%, diffusion coefficients decreased by 15% in bulk liquid, while they decreased by 51% in a pore size of 6.9 nm. However, the types of diffusion mechanisms did not vary significantly with the degree of branching. In addition to the diffusion studies, a magnetic resonance technique, named the 𝑇₁ to 𝑁 technique, was developed to determine the carbon number distributions of linear hydrocarbon mixtures *in situ* using NMR relaxometry. The carbon number distributions of alkane mixtures were determined with the highest sum of the residuals of ± 0.03. Also, the average carbon numbers from the distributions had a maximum deviation of ± 0.4 carbon number. Also, the proposed 𝑇₁ to 𝑁 technique has been tested at elevated temperatures ranging from 140 to 200 °C. Furthermore, this technique has been applied to study operando Fischer-Trospch process.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Lee, Yeo Jin

Advisor dc:contributor.advisor

• Sederman, Andrew

• Diffusion NMR
• NMR
• Porous media
• Relaxometry NMR

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/0ca942d5-421a-4ce4-9c13-8947b4acb14a/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.112764

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/374865