Probing the Lignin Disassembly Pathways with Modified Catalysts Based on Cu-Doped Porous Metal Oxides

Abstract

Described are the selectivities observed for reactions of lignin model compounds with modifications of the copper-doped porous metal oxide (CuPMO) system previously shown to be a catalyst for lignin disassembly in supercritical methanol (Matson et al., J. Amer. Chem. Soc. 2011, 133, 14090–14097). The models studied are benzyl phenyl ether, 2-phenylethyl phenyl ether, diphenyl ether, biphenyl, and 2,3-dihydrobenzofuran, which are respective mimetics of the α-O-4, β-O-4, 4-O-5, 5-5, and β-5 linkages characteristic of lignin. Also, briefly investigated as a substrate is poplar organosolv lignin. The catalyst modifications included added samarium­(III) (both homogeneous and heterogeneous) or formic acid. The highest activity for the hydrogenolysis of aryl ether linkages was noted for catalysts with Sm­(III) incorporated into the solid matrix of the PMO structure. In contrast, simply adding Sm3+ salts to the solution suppressed the hydrogenolysis activity. Added formic acid suppressed aryl ether hydrogenolysis, presumably by neutralizing base sites on the PMO surface but at the same time improved the selectivity toward aromatic products. Acetic acid induced similar reactivity changes. While these materials were variously successful in catalyzing the hydrogenolysis of the different ethers, there was very little activity toward the cleavage of the 5-5 and β-5 C-C bonds that represent a small, but significant, percentage of the linkages between monolignol units in lignins.

Breaking the Limit of Lignin Monomer Production via Cleavage of Interunit Carbon–Carbon Linkages

“…Therefore, biphenyl is selected for in-depth investigation as a model compound for C-C cleavage. 7,40 To closely monitor the intermediates, the reaction was conducted at a reduced temperature of 280 o C (Figure 3). Initially, phenylcyclohexane (4) was found to accumulate rapidly to 73% within 1h, and then gradually converted to benzene (1) and cyclohexane (2) as the reaction proceeded.…”

Evaluating lignin valorization via pyrolysis and vapor-phase hydrodeoxygenation for production of aromatics and alkenes

“…The use of CuPMO catalyst in supercritical methanol (sc-MeOH) for hydrogenolysis of α-O-4 and β-O-4 aryl ether linkages and depolymerization of lignin and other biomass components has been extensively studied. 21,[58][59][60][61][62][63] These studies showed that the reactive intermediates formed during lignin solvolysis were stabilized and further depolymerized and altered through hydrogenation, hydrodeoxygenation, and methylation reactions in the presence of sc-MeOH and the CuPMO catalyst, preventing repolymerization into char and leading to essentially no char formation. 21,61,62 Consequently, most of the ether bonds in the lignin structure were cleaved before pyrolysis, which would reduce the formation of reactive species that could potentially repolymerize and form char.…”

State-of-the-art catalytic hydrogenolysis of lignin for the production of aromatic chemicals

“…55 After 4h of reaction at 250 o C in water, 22 wt % yield of hydrocarbon products could be obtained from the depolymerization of the recovered insoluble lignin ( Table 1 entry 13). Recently, Wang et al 75 designed a new catalytic system (Ru-Cu/HY) for converting lignin to biofuels. Ru-Cu/HY was better than the combined catalyst of Ru/Al 2 O 3 and HY zeolite, giving yield of 32 wt % hydrocarbon products at same reaction conditions (Table 1 entry 14).…”