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Diffusion and Relaxometry Studies in Mesoporous Systems using Nuclear Magnetic Resonance https://doi.org/10.17863/CAM.112764 Lee, Yeo Jin Sederman, Andrew 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. University of Cambridge 2024-05-20 Thesis Doctoral Doctor of Philosophy (PhD) eng Shell https://www.repository.cam.ac.uk/handle/1810/374865 embargo 2025-10-23 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/3ff83a34-2d40-4f79-ab4e-5d86ebe850fc/download d06d5c5200071668fa46ac2795ce4545 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/0ca942d5-421a-4ce4-9c13-8947b4acb14a/download 87eda9de84448d1f82354d60eee3eb5f https://www.rioxx.net/licenses/all-rights-reserved/ Diffusion NMR NMR Porous media Relaxometry NMR