Characterisation of dynamic catalytic surfaces for small molecule reduction using grazing incidence techniques

Research into heterogeneous catalysis focuses on elucidating the nature and reactivity of surfaces, as well as understanding the influence of properties such as particle size, surface area, morphology (such as preferred crystal growth planes), dispersion, and metal-support interactions (MSI). The work featured in this thesis contains the results from the study of two model planar catalytic systems of industrial interest. Due to minimal amounts of ‘active material’ on planar substrates, surface-sensitive X-ray techniques are essential for their characterisation, therefore this study employs synchrotron radiation, namely Grazing Incidence X-ray Diffraction (GIXD) and X-ray Reflectivity (XRR), to examine 2D models in situ including Cobalt catalysts during reduction-oxidation-reduction (ROR) cycles and Fischer-Tropsch Synthesis (FTS), as well as thin film supported Palladium catalysts during acetylene hydrogenation under operando conditions. GIXD data reveals support-dependent variation in Cobalt’s reducibility and polymorph formation, with all samples forming more Co face-centred cubic (FCC) than hexagonal close-packed (HCP) polymorphs. A Scherrer analysis of FTS catalyst regeneration shows that on TiO2 and α-Al2O3 supports, larger Co nanoparticles re-oxidise while smaller ones remain metallic, suggesting that a strong MSI is not the sole influence on structural evolution. The ROR cycle’s importance is stressed as the results confirm ‘active’ Cobalt can be freed from TiOx encapsulation phenomena. Thin film Pd-catalysts were studied to determine the presence of PdZn and PdC during acetylene hydrogenation. Analysis of GIXD, XRR, and online mass spectrometry data revealed that favourable acetylene conversion on Pd/ZnO/Si catalyst requires active Pd, PdC0.05, and β-PdZn with ZnO, with catalytic stability depending on early-stage β-PdZn formation and a high Pd:ZnO ratio. Studies using a redesigned high pressure reactor on Pd/SiO2 catalysts showed PdC0.05 as the most active and selective phase for ethylene at both ambient pressure and but particularly at 5 bar and at 90°C.