William DeSisto, William Gramlich, Mark Haggerty, M. Clayton Wheeler
The transition from non-renewable fossil fuel chemical feedstocks to bio-renewable chemical feedstocks will be vital for the health of the environment. The current processing and use of fossil fuels produced by the petroleum industry release greenhouse gasses like carbon dioxide into the air causing heat to get trapped in the atmosphere. If greenhouse gas emissions continue at the rate they are now it is expected to cause polar ice caps to melt, ocean levels to rise, and climate all over the globe to change. By switching to bio-renewable feedstocks, the level of greenhouse gasses emitted would drastically decrease because processing renewable resources is nearly carbon neutral, meaning there would be no additional carbon dioxide output than what was already present in the plants and trees from which the renewable resources were sourced from.
Some of the major challenges surrounding conversion of bio-renewable resources are finding efficient ways to mass produce the chemical building blocks, prevention of catalyst deactivation due to biogenic impurities like sulfur containing amino acids and selective conversion of compounds containing α,β-unsaturated aldehydes to their respective unsaturated alcohols. Some of the way’s researchers have been trying to overcome these challenges have been by synthesizing heterogeneous catalysts using new approaches to get them to perform more selectively. One possible method is synthesizing multi-metal catalysts. Multi-metal catalysts have been proven to increase catalytic activity as well as increase reaction rate, making them of interest for the conversion of biomass. Another possible method is by introducing a polymer microenvironment to the surface of the catalyst to act as a “solid solvent”. This microenvironment has been proven to decrease catalyst deactivation due to biogenic impurities as well as restrict access to the catalyst’s active sites causing a shift in catalyst selectivity.
The goal of this research was to determine if introducing a polystyrene polymer microenvironment present above the surface of carbon supported palladium and platinum catalysts would increase the selectivity of the cinnamaldehyde hydrogenation to the reduction of the C=O double bond and away from the reduction of the C=C double bond. This study is important because it is desirable to find an effective way to reduce α,βunsaturated aldehydes, and if this method is successful with this reaction, it could be possible to apply it to other widely available bio-based compounds.
Incipient wetness impregnation was used to apply the polymer to the catalyst pores. The hydrogenation reactions performed with the commercial catalyst indicated that the Pd/C catalyst preferred the more thermodynamically favored reduction of the alkene whereas the Pt/C catalyst had some selectivity towards both the alkene and the unsaturated aldehyde. Addition of the polymer microenvironment to the Pd/C catalyst didn’t appear to have any effect on the selectivity of the reaction. This could be due to the reactions running at 100% conversion, making it impossible to know the extent of the reaction. Conversely, our observations could be due to inadequate cross-linking of the polymer causing it to be flushed out by the dioxane solvent. One of the reactions run with the polymerized Pt/C catalyst showed a significant increase in the selectivity towards the unsaturated alcohol, suggesting that this method may be a way to efficiently complete this conversion.
Logan, Madeline, "Selectivity of the Catalytic Hydrogenation of Cinnamaldehyde Using a Polymer Cross-Linked Catalyst" (2020). Honors College. 605.