Efficient, carbon-neutral hydrogenation using a palladium membrane reactor

Hydrogenation is a class of chemical manufacturing widely used for applications including fine chemicals, food, fertilizer, and fuels. Conventional thermochemical hydrogenation requires large amounts of hydrogen gas and heat derived from fossil fuel combustion to enable reaction. This process is highly carbon intensive. In this thesis, I present the electrocatalytic palladium membrane reactor (ePMR) as a technology that can reduce this carbon footprint by producing hydrogenated chemicals using water and renewable electricity. In this architecture, reactive hydrogen atoms are produced from water electrolysis on one side of a palladium membrane. These hydrogen atoms are then transported through the membrane to react with an unsaturated bond of a substrate on the other side. This technology eliminates the use of hydrogen gas and fossil fuels, and operates under ambient temperatures and pressures. In this thesis, I first demonstrate the utility of the ePMR to pair two organic reactions. Electrochemical synthesis generally forms a useful product at one electrode and a waste product at the other electrode. The palladium membrane acts as a physical barrier between the two electrodes, enabling optimized reaction conditions of two reactions simultaneously. I also investigate the effect of catalyst surface area, applied current, and electrolyte on reaction selectivity in the ePMR. I then focus on reducing the palladium content in an ePMR through a supported palladium membrane design. I show that a thin layer of palladium (<2 μm) deposited onto a porous support can enable a >20-fold reduction in palladium content compared to palladium foil membranes (25 μm) often used in the ePMR. The supported membrane design enables faster 1-hexyne hydrogenation rates than palladium foil and provides a strategy for designing cost-effective and potentially scalable membranes. Finally, I show that furfural (an important biomass derivative) can be hydrogenated into higher value products, furfuryl alcohol and tetrahydrofurfuryl alcohol at selectivities >84%. I also compare the ePMR to conventional electrochemical hydrogenation reactors. I find that furfural hydrogenation in the ePMR proceeds at higher selectivity, suppresses side product formation, and lowers operating voltages. This work presents an opportunity to decarbonize a >350,000 ton year-1 hydrogenation industry.