Mechanistic insight to alcohol reactions on Pd-Au bimetallic catalysts

This dissertation focuses on the use of precious metals in ultra-high vacuum to get a better mechanistic understanding of industrially-relevant processes. Ethanol (EtOH) is an excellent candidate as an alternative energy source because the infrastructure is already constructed to effectively distribute it as a liquid and because processes are continuously improving to make EtOH from non-edible biomass. Therefore, we explored the dehydrogenation, decomposition, and oxidation of EtOH on a Pd-Au alloy surface in ultra-high vacuum using quadrupole mass spectrometry, Auger electron spectroscopy, and reflection-absorption infrared spectroscopy coupled with support from theoretical calculations. With growing interest in a hydrogen fuel economy, dehydrogenation from EtOH can serve as an alternative to produce H₂. With molecular beam experiments and DFT calculations, we correlated mechanistic differences of EtOH dehydrogenation with changes in the Pd ensemble size on the Au(111) substrate. Next, we investigated the decomposition of EtOH and observed preferential C-C bond breakage over that of the C-O on our Pd-Au catalysts. A major hindrance to direct ethanol fuel cells is incomplete dehydrogenation, oftentimes yielding acetaldehyde as an unwanted byproduct. Therefore, gaining insight on how EtOH decomposes is beneficial to designing better catalysts. Additionally, we investigated the oxidative self-esterification of ethanol to produce ethyl acetate. Here, we observed how the presence of oxygen and hydroxyl group enables facile EtOH dehydrogenation to acetaldehyde, enabling cross-coupling to form an ester. In whole, the compilation of my work is an example of how mechanistic understanding in controlled environments can lead to better catalytic design for real-world applications.