(691a) A DFT Study to Gain Mechanistic Insights into Selective Hydrogenation Using Self-Assembled Mono-Layers

Self-assembled monolayers (SAMs) can be used to enhance selectivity in various reactions by altering the availability of certain active sites or interacting with surface reaction species. We use density functional theory (DFT) to investigate the adsorption behavior of alkane-thiolates over Pd step and terrace surfaces. We also investigate reaction pathways for various hydrogenation reactions on SAM coated/uncoated surfaces, and compare results with experimental reactivity data. DFT calculations indicate that, at lower coverages, small chain alkane-thiolates prefer to adsorb on under-coordinated step sites. Due to stronger van der Waals interaction in longer chain thiolates, at higher coverage, long chain alkane-thiolates form highly ordered self-assembled structures on the terrace sites. This leaves the step sites open for catalytic reaction, selectively facilitating specific reaction paths. One example of such a selective path is the hydrogenation of furfural to furfuryl alcohol. On an uncoated Pd surface, the furan ring in furfural adsorbs lying flat on the terrace sites, facilitating decarbonylation to form furan. However, on SAM coated Pd catalysts, the furfural to furan pathways are hindered due to the SAM occupying the terrace sites. This forces the furan ring in furfural to attach upright on the step sites via the carbonyl oxygen, facilitating the conversion pathway to furfuryl alcohol. DFT results examining alkene hydrogenation/isomerization as well as initial studies of SAM coating on nanoparticles using a reactive force field will be discussed.