Reactivity of lignin model compounds through hydrogen transfer catalysis in ethanol/water mixtures

- Hydrothermal conversion of eight lignin model compounds in water/ethanol mixture.
- H-transfer hydrogenolysis with ethanol as H-donor.
- Reactivity order of CO bonds: βO4 > αO4 >> 4O5.
- α1 model CC bonds are cleaved but β1 are not.

The conversion of lignin into useful bio-based chemicals and fuels requires a fundamental understanding of the reaction mechanisms involved in the cleavage of the specific chemical bonds that constitute its polymeric structure. The catalytic conversion of eight lignin model compounds emulating various CO and CC bond of lignin was explored in a batch reactor with a Pt/C catalyst in ethanol/water mixtures, using ethanol as both H-donor and solvent. The order of reactivity for hydrogenolysis of CO model bonds was found: βO4 > αO4 >> 4O5, the 4O5 bond exhibiting a very low reactivity. Phenolic hydroxyl and methoxyl groups were unreactive, whereas aliphatic hydroxyl groups could be eliminated by dehydration, leading to an overall partial deoxygenation. α-1 model CC bonds were also cleaved by hydrogenolysis, but β-1 model CC bonds were not. The cleavage of CO and CC bonds obtained by H-transfer catalysis in water-ethanol mixtures was very selective, intermediate products were sometimes detected before full reaction completion but no decomposition or degradation products.

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