Efficient conversion of Kraft lignin to guaiacol and 4-alkyl guaiacols over Fe-Fe3C/C based catalyst under supercritical ethanol

Abstract

One-pot lignin catalytic depolymerization (LDP) under supercritical ethanol was an effective strategy for converting lignin into value-added aromatic monomers. However, complex substructure and linkages in lignin limited the development of gaining high selectivity aromatic monomers. In this study, carbon supported Fe-Fe3C/C based catalysts prepared using high temperature reducing method were employed as LDP catalysts. GC–MS and 1H−13C 2D HSQC NMR results of lignin oil display that the optimum Fe-C-700 catalyst can converted lignin into lignin oil consisting of guaiacol and 4-alkyl guaiacols with an 86 wt% of selectivity at a 48 wt% of conversion rate. The XRD, Raman, HRTEM, TEM-EDS mapping, and the XPS characterization results of Fe-Fe3C/C catalysts show that the graphitized and amorphous carbon encapsulates iron carbide nanocrystal and metal iron nanoclusters. The NH3-TPD and CO2– TPD profiles revealed a system of strong acid-base sites on Fe-Fe3C/C catalysts which means acid sites are responsible for C-O bonds breaking and base sites are responsible for cleavage of C–C bonds. Metal Fe (0) was considered to be a key factor to activate the hydrogen source in order to promote the hydrogenation process.