Aqueous-phase hydrogenation of various lignin-derived phenols to cycloketones as platform compounds over Br modified metal-acid mixed catalyst

The cycloketones were prepared efficiently via the selectively hydrogenation of aqueous phase lignin-derived single phenolic monomer and mixtures. The yield and selectivity of cycloketones was greatly improved over Br modified metal-acid mixed catalyst (PdH5@Br). First, the effect of side-chain functional structures on the aqueous-phase hydrogenation of phenols with Pd/C catalysis was investigated and it was found that the benzene ring with methyl group attached is more easily hydrogenated, and the phenolic hydroxyl side chain was more susceptible to form carbonyl than methoxy groups. A large number of enols existed, thus the catalyst acidity was adjusted by extra addition of HZSM-5, over which the yield of cycloketones from guaiacol was significantly boosted to 67.9 %. Subsequently, the electronic properties of catalyst were altered by adding Br over Pd catalyst, weakening the over-chemisorption of intermediate phenol, and the hydrogenating of phenol under PdH5 were enhanced, thus an increased yield of cycloketone of 18.4 % occurred. After the hydrotreating of guiaiacol for 2 h at 523 K and 2 MPa H2, the yield of cycloketone reached 80.4 % on PdH5@Br. The hydrotreating performance of PdH5@Br with lignin-derived phenolic monomer mixtures as the feedstock was also tested, and it presented great universality and stability. It provides an efficient catalyst system and promising technological ideas for biomass hydrotreating.