Common Pathways in Ethanolysis of Kraft Lignin to Platform Chemicals over Molybdenum-Based Catalysts

One-pot complete catalytic ethanolysis of Kraft lignin into C6-C10 chemicals, that is, aliphatic alcohols, esters, phenols, benzyl alcohols, and arenes, is achieved with a batch reactor over a number of supported molybdenum-based catalysts at 553 K in pure ethanol under autogenous pressure of 10.6 MPa. Metallic molybdenum, its carbide, and nitride all show remarkable activity, with the carbide and metallic catalysts giving the higher overall yields: 1640 and 1390 mg/g lignin, respectively. The major phases composing the catalysts are well-preserved after the reaction; however, the detection of Mo(V) species verifies the partial oxidation of molybdenum, which leads to the formation of the dissociative Mo species, such as molybdenum V ethoxide, in the fluid phase. Through the product analysis and catalyst characterization, the common route of lignin conversion to value added chemicals over the Mo-based catalyst is presented in detail. Kraft lignin is first fragmented into segments with m/z similar to 700-1400 via a noncatalytic ethanolysis process. Meanwhile, the main active Mo(V) species dissociate from the solid catalyst into the fluid due to the interaction of ethanol. Then mainly the dissociative species catalyze, with the participation of the radicals, the further degradation of the segments into small molecules.