(58f) Operando Solid-State NMR Study of Hydrogenolysis of Lignin Ether Linkages

Lignin is the most abundant and readily available feedstocks for bio-derived aromatics. Under mostly reductive conditions, transition metals like Ni and Pd catalyze the hydrogenolysis of lignin ether linkages in the liquid phase. However, the conversion chemistry is lack of molecular understanding especially at the solid-liquid interface, mostly owing to the demanding reaction conditions including high temperature/pressure. Customized high temperature/pressure solid-state NMR rotors were adapted, allowing operando solid-state NMR measurements of conversion of lignin catalyzed with supported metal catalysts. For example, benzylphenylether (BPE) as the a-O-4 model compound was studied with supported Ni catalysts at 120-225 °C. Kinetic and mechanistic study was performed with selective isotope labeling (¹³C, ²H) of both reactants and solvent. The pressure of 50 bar H₂ allows the simultaneous study of the further hydrogenation of phenol to cyclohexanol while toluene showed much higher stability with almost no conversion to methylcyclohexane. When no extra hydrogen gas is charged in the rotor, solvent 2-proponal can also serve as the hydrogen source and Ni can catalyze the transfer hydrogenation reaction with acetone formed and detected in situ.