Tailoring the Electronic Ru-Al2O3 Interaction to Regulate Reaction Barriers for Selective Hydrogenolysis of Aromatic Ether

Aromatics are desirable products from the depolymerization/valorization of lignin; however, it is still challenging to achieve selective hydrogenolysis of the C-O bond with the preservation of aromatic rings. In this work, the electronic Ru-Al2O3 interaction was tailored by controlling the sizes of supported Ru nanoparticles to regulate the profiles of energy barriers for selective hydrogenolysis of diphenyl ether (DPE, modeling compound of lignin). Complementary characterizations and kinetic studies demonstrate that a stronger electronic metal-support interaction (EMSI) occurs between smaller Ru nanoparticles and Al2O3, leading to a more electron-deficient Ru domain. This tailored electronic structure dramatically increases the barrier of an undesired secondary reaction (i.e., ring hydrogenation), outstripping that of DPE hydrogenolysis for the production of aromatics. In addition, although the latter barrier also increases over smaller and more electron-deficient Ru, the much more abundant active site compensates for the increased barrier and enhanced the apparent reactivity. The catalyst bearing the smallest Ru particle displays the highest activity and selectivity under the tested conditions. This work provides an approach to control selectivity in hydrotreatment by regulating the energy barriers along the reaction pathway.