Abstract
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•High selectivity to C9 alkyl guaiacols (51%) was obtained using Pd-Al2O3/activated biochar.•Pd0 catalyzes hydrogenation of Cα=Cβ and Al catalyzes dehydroxylation of Cγ−OH.•4-Propyl guaiacol was obtained at 38% selectivity at 240 °C, 3 MPa H2, and 3 h.•Coniferyl alcohol was used as a model compound to probe surface reaction chemistry.•Propyl guaiacol formation mechanism is elucidated using DFT calculations.
The conversion of biomass-derived lignin to valuable monomeric phenols at high selectivity is of paramount importance for sustainable biorefineries. In this study, a novel Pd-Al2O3 supported on activated biochar catalyst is developed for lignin hydrogenolysis. The catalyst characterization revealed that the (111) planes of both of Pd0 and Al2O3 were exposed to the surface. The maximum lignin conversion of 70.4% along with high liquid yield (∼57 wt%) was obtained at 240 °C, 3 h and 3 MPa H2 pressure. The total monomeric phenols yield in the liquid was 51.6 wt%, out of which C9 monomeric guaiacols constituted ∼ 30.0 wt% with 38.0% selectivity to 4-propyl guaiacol. Using the reaction intermediate, coniferyl alcohol, chemoselective hydrogenation of Cα=Cβ is proved to occur over the Pd site, while dehydroxylation of Cγ–OH is shown to occur over the alumina site. An impressive carbon atom economy of 60% was achieved for the production of monomeric phenols.