Modifying MgO with Carbon for Valorization of Lignin to Aromatics

We developed a Pd-doped catalyst where the support MgO was modified with carbon species via methanol thermal annealing, catalyzing the cleavage of β-O-4 lignin-type dimers and actual lignin into aromatics. Methanol as a carbon precursor was processed to a carbon species that was loaded with metallic palladium. The carbon species supported Pd on MgO surface changed the acid–base strength and affected the catalytic activity of C–O bond hydrolysis/hydrogenolysis. The β-O-4 linkage in dimer was effectively fractured over Pd/MgO-C, and catalyst’s strong acid facilitated aldehyde decarboxylation to alkyl aromatics while relatively weak acid and strong base were highly selective for stable aromatics (such as 1-methoxy-4-propylbenzene and 1-methoxy-4-(propenlyl) benzene). This allowed Pd/MgO-C-700 to be successfully applied to pine depolymerization, to give 24.6 wt % of aromatics; in addition, almost β-O-4 linkages were broken at 160 °C, and surprisingly, 77.2% of 2-methoxy-4-(propenlyl)phenols was obtained. The reaction pathways for lignin valorization are hypothesized over the Pd/MgO-C catalyst.