Catalytic Decomposition of Lignin Model Compounds to Aromatics over Acidic Catalysts

Recent progress on the catalytic decomposition of lignin model compounds to aromatics was reported in this review. Cesium-exchanged heteropolyacid catalysts (CsxH3.0−xPW12O40), palladium catalysts supported on cesium-exchanged heteropolyacid (Pd/CsxH3.0−xPW12O40), and palladium catalysts supported on various activated carbon aerogels (ACAs) (Pd/ACA-SO3H (X), Pd/XCs2.5H0.5PW12O40/ACA, Pd/CsxH3.0−xPW12O40/ACA, and Pd/Cs2.5H0.5PW12O40/ACA-SO3H) were prepared, and they were employed for the decomposition of C–O bond in lignin to aromatics. Phenethyl phenyl ether, benzyl phenyl ether, and 4-phenoxyphenol were used as dimeric lignin model compounds representing for β-O-4, α-O-4, and 4-O-5 bonds in lignin, respectively. It was observed that CsxH3.0−xPW12O40 and Pd/CsxH3.0−xPW12O40 were highly active for the decomposition of phenethyl phenyl ether and benzyl phenyl ether to aromatics. However, these catalysts showed very low catalytic performance in the decomposition of 4-phenoxyphenol. Palladium catalysts supported on various ACAs (Pd/ACA-SO3H (X), Pd/XCs2.5H0.5PW12O40/ACA, Pd/CsxH3.0−xPW12O40/ACA, and Pd/XCs2.5H0.5PW12O40/ACA-SO3H) were efficient for the decomposition of 4-phenoxyphenol to aromatics. Acidity of the catalysts played a key role in determining the catalytic performance in the decomposition of 4-phenoxyphenol to aromatics.