(762f) Controlling Selectivity of Metal Catalysts By Using Self-Assembled Monolayers on the Oxide Support

Application of phosphonate-based self-assembled monolayers (SAMs) for chemoselective hydrogenation and hydrodeoxygenation has been investigated. Here, our approach was to control the near-surface environment of active metals via covalent attachment of organic ligands to the support. The SAMs were formed by immersing catalysts such as Pt/Al₂O₃ and Pd/Al₂O₃ into a phosphonate solution followed by annealing and washing. Control experiments indicated that SAMs were selectively formed on the support rather than the metal. Uncoated and SAM-coated catalysts were used in several reactions including the gas-phase hydrodeoxygenation of benzyl alcohol and furfuryl alcohol. Depending on the structure of the organic ligand tethered to the support, a significant improvement in selectivity towards desired products, toluene and methyl furan, respectively, could be observed. Importantly, the catalytic activity was not compromised by the SAMs, and in fact was increased for certain coatings. Diffuse infrared Fourier transform spectroscopy conducted after CO adsorption showed no apparent change in the site distribution after coating with the SAMs. These results indicate that the performance of supported metal catalysts can be significantly altered via attachment or organic ligands to the support, complementing prior work in which SAMs have been directly attached to the metal.