Metal-organic framework catalysis in the Guerbet upgrading of ethanol

The catalytic upgrading of bioethanol to 1-butanol and higher alcohols through the Guerbet reaction is a candidate chain-extension step in Alcohol-to-Jet routes to sustainable aviation fuel (SAF). It requires a solid in which metal sites for dehydrogenation and hydrogenation operate next to Lewis acid sites for aldol condensation. This thesis deals only with that catalytic step. The environmental benefits attributed in the literature to the wider ATJ pathway are not evaluated here: no life-cycle assessment was performed and no finished fuel was produced. Au, Pd and Au–Pd nanoparticles (0.1–6.0 wt.%) were deposited on a defect-engineered UiO-66(Zr) framework by wet impregnation followed by NaBH4 reduction. The materials were characterised by XRD, TGA, N2 sorption, UV–Vis DRS, CO-DRIFTS, XPS and STEM–EDX, and tested in a continuous fixed-bed reactor at 250 °C, 4.1 bar of ethanol and 500 mmol·g−1·h−1. The rates were checked for external and internal mass-transfer limitations before the kinetic analysis. Three findings stand out. (i) The reduction conditions set the nanoparticle size: reducing K2PdCl4 with two equivalents of NaBH4 in water gave 4.5 nm Pd particles, against about 20 nm with aspartic acid, and an ethanol conversion rate nearly four times higher than the non-optimised preparation; the same protocol gave 3.7 nm Au particles. (ii) Au is an active phase on its own: 1.0Au and 1.0Pd converted ethanol at the same rate (40 ± 3 mmol·g−1·h−1) with about 80% of the converted ethanol following the dehydrogenation route, and over 2.0Au the apparent activation energies were 79.2 and 99.9 kJ·mol−1 for dehydrogenation and dehydration, with the best 1-butanol selectivity at 250 °C. (iii) Alloying helps at low metal loading: 0.5Pd0.3Au gave the highest 1-butanol formation rate of the bimetallic series, its Au 4f7/2 binding energy shifted by −0.58 eV relative to 1.0Au, and its particles (3.0 ± 0.8 nm) were smaller than those of 2.0Au (3.7 ± 1.2 nm).