The conversion of biomass to chemicals or fuels requires catalytic reductions of C-O bonds. The aromatic C-O bonds in aryl ethers are some of the strongest and least reactive C-O bonds and are one class of the C-O bonds in the lignin portion of lignocellulosic biomass. One potential renewable source of arenes are the aryl ethers contained in lignin, but methods to cleave the C-O bonds of this material are required to meet this goal.
In one set of studies, we discovered nickel complexes and nanostructured nickel materials that catalyze the hydrogenolysis of C-O bonds. These reactions occur with just one atmosphere of hydrogen at milder temperatures than required for prior catalysts. Most important, these reactions are the first reductions of the C-O bonds in aryl ethers that occur without concomitant reduction of the arene. Studies to improve the activity of the catalysts, to understand the origin of the high selectivity, to identify the nickel species that cleaves the C-O bond within the catalytic cycle, and to reduce additional classes of C-O bonds are the subject of current studies in our laboratory.
In a second set of studies we discovered conditions to use heterogeneous palladium catalysts for the breakdown of lignin by the reagentless cleavage of the b-O-4 linkages. These reactions generate hydrogen by the dehydrogenation of alcohols and use this hydrogen to cleave the C–O bonds in the b-O-4 linkages.