Experimental and First-Principles Evidence for Interfacial Activity of Ru/TiO2 for the Direct Conversion of m-Cresol to Toluene

The selective cleavage of C-O bonds in phenolic species is perhaps the most difficult transformation required for converting biomass-derived monomers to aromatic fuels and chemicals. Metals supported on reducible oxides, such as Ru/TiO2, have demonstrated considerable promise for a variety of selective C-O cleavage reactions, but the active site has been subject of a great deal of speculation. This paper employs a combination of theory and experiments to investigate the nature of the active site for the selective transformation of m-cresol to toluene. Through variation of metal loading, particle size and support phase, we show that sites responsible for direct C-O cleavage of m-cresol lie at the perimeter of the metal particle. The activation barrier for C-O cleavage is reduced from 1.4 eV on the Ru surface to 0.7 eV at an interfacial site. The introduction of water facilitates a further reduction to 0.3 eV via a proton-assisted C-O cleavage. These results answer a long-standing question regarding the nature of these important active sites, with broad implications for biomass upgrading.