Selective lignin depolymerization via transfer hydrogenolysis using Pd/hydrotalcite catalysts: model compounds to...

Area of Science:

• Chemical Engineering
• Green Chemistry
• Catalysis

Background:

• Lignin valorization is crucial for biorefineries.
• Catalytic transfer hydrogenolysis (CTH) offers a sustainable alternative to traditional lignin processing.
• Mild reaction conditions and renewable hydrogen donors are economically advantageous.

Purpose of the Study:

• To demonstrate efficient catalytic transfer hydrogenolysis and decarbonylation of lignin model compounds.
• To evaluate transition metal-modified Pd hydrotalcite catalysts using ethanol as a hydrogen donor.
• To apply the developed catalytic system for whole biomass delignification.

Main Methods:

• Synthesis and characterization of transition metal-modified Pd hydrotalcite catalysts.
• Testing catalysts with various lignin model compounds (α-O-4, β-O-4, 4-O-5 linkages) under CTH conditions.
• Utilizing ethanol as both hydrogen donor and solvent.
• Applying the optimized process to whole pine biomass.

Main Results:

• Quantitative conversion and high yields for α-O-4 and β-O-4 lignin model compounds.
• Successful delignification of whole pine biomass with a 97% yield.
• Achieved a 22% yield of phenolic monomers, with 64% selectivity for 4-(3-hydroxypropyl)-2-methoxyphenol.
• Demonstrated catalyst efficacy for cleaving aromatic ether bonds, though challenging for strong sp2 C-O bonds (4-O-5 linkage).

Conclusions:

• Pd hydrotalcite catalysts are effective for catalytic transfer hydrogenolysis of lignin model compounds under mild conditions.
• Ethanol serves as a viable and renewable hydrogen donor and solvent for lignin valorization.
• The developed CTH process shows significant potential for efficient biomass delignification and the production of valuable phenolic compounds.