Exploiting H-transfer reactions with RANEY® Ni for upgrade of phenolic and aromatic biorefinery feeds under unusual, low-severity conditions

This paper focuses on the fundamental chemical aspects of hydrogen transfer reactions with RANEY® Ni and propan-2-ol. It aims at novel process options for defunctionalization and hydrodeoxygenation of phenolic and aromatic biorefinery feeds under low-severity conditions. A series of 32 model substrates were explored, providing a comprehensive description of the reactivity of RANEY® Ni toward transfer hydrogenation and transfer hydrogenolysis. In addition, the aspects related to the catalyst stability were addressed in detail. With regard to the processing of a model-substrate mixture, important features of the chemoselectivity of RANEY® Ni were also revealed. Herein, we also demonstrate that hydrogen transfer reactions could hold the key to the upgrade of bio-oil under unusual, low-severity conditions. Indeed, bio-oil was easily upgraded to cyclohexanols and less functionalized alkylphenols, with RANEY® Ni and propan-2-ol, at 120 °C. Full saturation of bio-oil to cyclic alcohols, cyclohexane-1,2-diols and other products with reduced oxygen content was achieved at 160 °C under autogenous pressure. RANEY® Ni efficiently catalyzes the hydrodeoxygenation of phenolics, aromatics and bio-oil using propan-2-ol - as H-donor and solvent - under unprecedented, low-severity conditions.