Catalytic transfer hydrogenolysis of lignin α-O-4 model compound 4-(benzyloxy)phenol and lignin over Pt/HNbWO6/CNTs catalyst

Abstract

Cleavage of C–O bonds in aryl ether through the catalytic transfer hydrogenolysis (CTH) is an encouraging method for the valorization of lignin into fine chemicals and liquid fuels. In this contribution, the CTH of typical lignin α-O-4 model compound 4-(benzyloxy)phenol (BOP) and lignin extracted from ash wood have been explored over 0.45 wt% Pt/HNbWO6/CNTs catalyst. The effect of solvents was elaborated and the highest catalytic activity was achieved in the CTH of BOP using isopropanol as the solvent (98.1%). This was because isopropanol can provide more hydrogen atoms to promote CTH reaction due to the weakest interaction between isopropanol and BOP among all H-donor solvents. The favorable results obtained in the model compound study inspired us to afford Pt/HNbWO6/CNTs catalyst in the CTH of lignin. The relative oxygen content of lignin was sharply decreased after the CTH process, and the higher heating value (HHV) significantly increased from 21.4 MJ/kg to 30.8 MJ/kg. GPC, FT-IR, GC-MS, and 2D-NMR results revealed that lignin was successfully depolymerized into small molecule compounds over Pt/HNbWO6/CNTs catalyst through the CTH process. Thereinto, phenolic compounds were the major components in the liquid products in which most of them were monophenols. The results obtained in this work shed light on that Pt/HNbWO6/CNTs was a favorable catalyst in the depolymerization of lignin into valuable phenolic compounds via the CTH method.