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Asian lignin was directly depolymerized to phenol-rich oil fraction (lignin-oil) over Pt/C, Pd/C, Ru/C, and Ni/C under supercritical alcohols. Ethanol and Pt/C (E-Pt) proved to be an excellent combination for producing large amounts of lignin-oil (77.4 wt%) with the smallest amount of char (3.7 wt%). Lignin-oil mainly consisting of monomeric phenols and higher molecular phenolic was subjected to several chemical analyses. Elemental analysis indicated that hydrodeoxygenation and hydrogenation primarily occur during lignin depolymerization. 1 H-/2D-HSQC-NMR and GPC analysis revealed that the M w of lignin-oil remarkably lower than that of Asian lignin, which is clear evidence of β-O-4 and β-β bond cleavages. The top four main monomeric phenols in lignin-oil were 4-ethylphenol, guaiacol, 4-ethylguaiacol, and syringol, for which the sum was mostly produced in E-Pt (41.8 mg/g of lignin) with the highest selectivity (38.3%). With increasing catalyst dosage, we observed that excessive catalyst caused side reactions to hinder the production of monomeric phenols.

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