Biomass Depolymerization projects
Catalytic Carbon-Oxygen Bond Cleavage For Upgrading Lignin
EBI chemists are working to find alternatives to the enzymes that serve as nature’s catalysts in lignin deconstruction. This project conducts studies to develop transition-metal catalysts for this purpose. They have identified nickel catalysts that selectively remove groups containing oxygen atoms from lignin model compounds in precise places without destroying the entire molecule. The less oxygen lignin has, the better it will work as a fuel. The group is working to translate those fundamental studies to the catalytic cleavage of lignin itself.
We are developing new catalytic reactions for lignin degradation under mild reductive atmosphere. Previously, we disclosed a heterogeneous nickel(0) catalyst supported on activated carbon, which is a robust system that leads to the hydrogenolysis of C-O bonds in aryl- and benzyl ethers without reduction of the arene moieties at one atmosphere of H2. The new Ni/C catalyst operates at lower catalyst loading than our prior published nanoparticulate nickel species derived from Ni(TMEDA)(CH2TMS)2. We discovered Beta-O-4 linkage cleavage catalyzed by commercially available Pd/C catalysts under reagentless conditions; the method is also applicable for fragmentation of various organosolv lignin samples with minimal implementation of H2 as the reducing agent.
We are seeking new catalytic reactions for the reductive or redox-neutral cleavage of aromatic and aliphatic C-O bonds in lignin. Previously, we published the first catalytic hydrogenolysis of aryl ethers C-O bonds without hydrogenation of the arene and later the first heterogeneous catalyst for the same reaction without hydrogenation. During the past year, we have shown that basic conditions trigger this selectivity with heterogeneous catalysts and have identified inexpensive, stable supported catalysts for such transformations. We have also identified conditions for reagentless cleavage of the aliphatic C-O bonds of model lignin compounds by the combination of dehydrogenation and hydrogenolysis catalyzed by heterogeneous catalysts.
Our EBI research focuses on the discovery of catalytic methods for the cleavage of the carbon-oxygen bonds in the bio-polymer lignin. These methods have the potential to transform lignin into small molecules for the production of fuels and fine chemicals. We recently discovered a nickel nanoparticle that catalyzes the hydrogenolysis of diaryl ethers and benzyl aryl ethers, which are important structural sub-units of the lignin bio-polymer. The products of these reactions are arenes and phenols, which are common commodity chemicals. This nickel catalyst is uniquely active at low temperatures (120-180 ºC) and low pressures (15 psi) of hydrogen, and it forms only aromatic products.
The high selectivity of this nickel catalyst for the formation of aromatic products implies that only one equivalent of hydrogen is consumed during the catalytic reactions. Most metal catalysts for hydrogenolysis that cleave the carbon-oxygen bonds within diaryl ethers also add hydrogen to the arenes to form less desirable cycloalkanes and waste hydrogen. However, the high activity and selectivity of our nanoparticulate nickel catalyst requires the addition of a relatively expensive alkoxide base. Thus, we are currently seeking additives that create similar nickel catalysts but are more practical for commercial lignin valorization.
The EBI group discovered new catalysts that break ether bonds of the kind found in lignin. The high selectivity of the new system, which cleaves the recalcitrant aromatic C-O bonds, provides a significant advance toward conversion of lignin to liquid arene feedstocks. Researchers also discovered that the bio-derived solvent methyl formate can be used to convert sugars into furans with fuel-like properties. Methyl formate helps remove some of the OH groups, a big barrier to converting lignocellulose to fuels, and caps the others as methoxy groups, which are ideal components of automotive fuels.
Published in 2012
Production of Hybrid Diesel Fuel Precursors from Carbohydrates and Petrochemicals Using Formic Acid as a Reactive Solvent, Xiaoyuan Zhou, Thomas Rauchfuss, ChemSusChem, Vol. 332DOI: 10.1002/cssc.201200718.
A Heterogeneous Nickel Catalyst for the Hydrogenolysis of Aryl Ethers Without Arene Hydrogenation, A. G. Sergeev, J. D. Webb, J. F. Hartwig, Journal of the American Chemical Society 134, 20226–20229.
Published in 2011
Selective, Nickel-Catalyzed Hydrogenolysis of Aryl Ethers, Alexey Sergeev, John Hartwig, Science, Vol. 332(6028), pp. 439-443, April 22, 2011.
Published in 2010
Catalytic C-O Bond Cleavage of 2-Aryloxy-1-arylethanols and Its Application to the Depolymerization of Lignin-Related Polymers, Jason Nichols, Lee Bishop, Robert Bergman, Jonathan Ellman, Journal of the American Chemical Society, 132(36), pp. 12554-12555, August 23, 2010.