The selective cleavage of C-O bonds present in phenolic and furanic species is essential to improve yields to valuable products from renewable biomass streams. One of the most challenging transformations is the selective cleavage of phenolic C-O bonds to yield aromatic hydrocarbons. While is known that the combination of metals such as Ru with a reducible support, such as TiO<sub>2</sub>, exhibit enhanced yields to deoxygenated products, the exact nature of the active site is subject to debate. Here we present a detailed investigation into the active sites responsible for the conversion of phenolic species to deoxygenated products. We illustrate that the initial conversion of methoxy groups present in species such as anisole or guaiacol is facilitated by defects on the oxide support induced by the metal nanoparticle, rather than unique sites present at the perimeter. Net rates of methoxy group conversion exhibit a strong dependence of the support polymorph. The cleavage of the strong OH bond on phenol or cresol, however, is facilitated by sites located at the metal-support interface. We demonstrate this by varying the support phase, metal loading, and deposition technique in order to quantify reaction rates over each prospective type of site. Results from kinetic fittings of experimental data are compared with DFT calculations, and a mechanism of selective deoxygenation at interfacial sites is presented with a barrier that is significantly lower than that over the metal surface. We further illustrate how the introduction of water molecules can result in a new pathway at interfacial sites via an adsorbed water molecule in a perimeter defect site. The resulting proton-assisted C-O cleavage significantly reduces the overall barrier of the C-O cleavage step by an additional 40 kJ/mol when compared with the traditional interfacial active site. We further show that the relative importance of reactions over interfacial active sites when compared to the various sites on the metal surface vary with water coverage. Finally, the behavior of phenolic C-O cleavage is contrasted with furanic species, where interfacial sites also facilitate selective C-O cleavage but co-fed water can lead to an alternative reaction pathway.

Influence of co-adsorbates on metal-reducible oxide interfacial sites for selective C-O cleavage reactions

254th National Meeting (2017)

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