Hydrothermal conversion of lignin model compound eugenol

• Eugenol is hydrogenated in water/ethanol mixtures over Pd/C.
• Ethanol serves as H-donor solvent.
• Eugenol isomerization followed by CC hydrogenation.
• Phenol and methoxy groups no dot react.
• Langmuir–Hinshelwood mechanism.

The hydrothermal conversion of eugenol over a Pt/C catalyst at temperatures between 250 and 300 °C in a water/ethanol mixture in the absence of gaseous H2 was investigated using various catalysts. Under these conditions, the CC double bond of the propenyl chain is hydrogenated, but the hydroxyl and methoxy groups of eugenol do not react. The reaction can be described by a two-step process. The first step is the isomerization of the double bond on the alkyl chain of eugenol. The second step is the hydrogenation of this double bond, hydrogen being supplied by ethanol, which is converted into acetaldehyde. The kinetics of the two-step process can be adequately described by a Langmuir–Hinshelwood mechanism with all components in quasi-adsorption equilibrium on a single site (Pts) and the surface steps as rate-determining.

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