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

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 C-O and C C 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 C-O model bonds was found: beta-O-4>alpha-O-4 >> 4-O-5, the 4-O-5 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. alpha-1 model C-C bonds were also cleaved by hydrogenolysis, but beta-1 model C-C bonds were not. The cleavage of C-O and C-C 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. (C) 2017 Elsevier B.V. All rights reserved.