Tungsten-Based Bimetallic Catalysts for Selective Cleavage of Lignin C−O Bonds

Graphical Chop up the wood : Tungsten-based bimetallic catalysts exhibit high activity and selectivity in the hydrogenolysis of typical model compounds of the α-O-4 linkage in lignin and deconstruction of lignin feedstock for the production of aromatic chemicals. High yields of C−O cleavage products are obtained without destroying the aromatic rings. Tungsten-based bimetallic catalysts M–W/AC (M=Ru, Pt, and Pd; AC=activated carbon) exhibited high activity and selectivity in the hydrogenolysis of typical α-O-4 model compounds and deconstruction of lignin feedstock for the production of aromatic chemicals. Synergy effect was observed between tungsten and noble-metal species, which on the one hand modulated the hydrogenolysis activity of tungsten and improved the activity of catalyst, and on the other hand suppressed overhydrogenation that avoided the formation of cycloalkanes. The conversion of α-O-4 model compounds with different substituents showed that electronic effects play an important role in stabilizing the reaction intermediates, and the electron-donating methoxy group on the aromatic ring accelerated the hydrogenolysis efficiency. Solvent effect was another factor that determined hydrogenolysis efficiency; dipolar aprotic solvents such as n -hexane provided the high yields of target aromatics. In the conversion of realistic lignins, the bimetallic catalyst showed excellent activity not only in α-O-4 cleavage but also in the hydrogenolysis of other major linkages such as β-O-4 and β−β between aromatic units, so that a high yield of liquid oil was obtained from lignin.