Selective Deoxygenation of Lignin-Derived Phenols and Dimeric Ethers with Protic Ionic Liquids

Hydrodeoxygenation (HDO) of lignin-derived phenols and dimeric ethers to biofuels has great significance for advanced utilization of renewable lignocelluloses and the future biobased economy. Herein, we find that the deoxygenation process during the lignin-derived model compound HDO process could efficiently be catalyzed by low-cost protic ionic liquids under mild conditions. 2-Hydroxy-N-(2-hydroxyethyl)-N-methylethanaminium trifluoromethanesulfonate ([BHEM]­CF₃SO₃) shows the highest catalytic activity for the deoxygenation reaction during the lignin-derived compound HDO process with Rh/C as the hydrogenation catalyst. The conversion of phenol is 100% under 4 MPa H₂ at 130 °C for 6 h, and the yield of cyclohexane is 93.3%. Furthermore, the catalytic system with [BHEM]­CF₃SO₃ as the deoxygenation catalyst and Rh/C as the hydrogenation catalyst demonstrates efficient catalytic activity for various lignin-derived phenols and dimeric ethers with ≥99.0% conversion and >90.0% selectivity. The catalytic system is reused five times for HDO of phenol to test its stability.