Pd doped mesoporous biochar catalysts for the selective hydrogenation of alkynes to alkenes.

Hornsby, Karl

Abstract

The quest to develop Pd doped, sustainable catalysts for the selective hydrogenation of phenylacetylene resulted in the synthesis of two families of materials. Derived from lignocellulosic biomass residues, specifically barley straw, bulk and mesoporous biochars were created and characterised (TGA, CHN, N2 physisorption, PXRD, FTIR, SEM/EDX and HRTEM). Bulk biochars were produced after pyrolysis across a range of temperatures (500, 600, 700 and 800 °C) of leached barley straw, resulting in a carbon support material with low surface area but customisable Lewis acidity. Mesoporous biochars were produced following an elegant pre and post-treatment approach by using sacrificial KOH to generate a porous network. Using this method, biochars were created with an available surface area up to 1436.81 m2 g-1 (ABC-1), and a pore size as small as ~4 nm. Individually, the materials were all impregnated with a nominal loading of 1 wt% Pd which generated dispersed nanoparticles. The Pd nanoparticles were of similar size across all materials (averaging ~6.2 nm), within error and proved to be a minimum requirement for the catalytic transformation of phenylacetylene. By investigating the role of reaction temperature and how the structure (physical and chemical) of a biochar catalyst support can direct hydrogenation reactions, it was found that for a bulk biochar, by increasing pyrolysis temperature a hydrogen driven cascade reaction occurred. This meant that induced chemical functionality of the support led to the desired product, styrene, being consumed to ethylbenzene. For the case of mesoporous supports, by dispersing Pd sites across the material, it is believed that styrene re-adsorption was not favoured as the selectivity towards ethylbenzene was substantially lower than all bulk support testing. Additionally, when following normalised initial rates by factoring in the total Pd content of the catalyst, it was found that the mesoporous catalysts were superior across the board in terms of reaction rate and product selectivity.

Citation

Hornsby, K. Pd doped mesoporous biochar catalysts for the selective hydrogenation of alkynes to alkenes. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4866518

• Thesis Type: Thesis
• Deposit Date: Oct 15, 2024
• Publicly Available Date: Oct 29, 2024
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4866518
• Additional Information: School of Natural Sciences; University of Hull
• Award Date: Jul 10, 2024