(723f) Exploring Influences of Catalyst Supports on Hydrogen-Free Reductive Fractionation of Lignins in Glycerol-Derived Solvents

Lignin is the most abundant natural source of phenolics, and accounts for about 15 to 30 wt% of lignocellulosic biomass. The thermocatalytic decomposition of lignin yields compounds of societal importance. For example, aromatic compounds derived from lignin can be used as feedstocks for the production of high value products such as fine chemicals, pharmaceutical ingredients, and sustainable aviation fuels. Recent research efforts have been directed towards ameliorating the selective lignin reductive catalytic fractionation (RCF) process by eliminating its use of high-pressure molecular hydrogen (10 - 50 bar) and volatile solvents. This is key regarding commercialization goals.

In the present investigation, we evaluate the efficacy of glycerol-derived compounds (GDCs) as tractable solvents for catalytic transfer hydrogenolysis (CTH) of lignins. We demonstrate that glycerol diethers boast excellent solvent and hydrogen transfer abilities. These green solvents from glycerol byproduct of the biodiesel industry were leveraged to efficiently fractionate and depolymerize lignin component of lodgepole pine in the presence of commercially procured Pt/C and Ru/C catalysts. Respective aromatic monomer yields and delignification up to 25 wt% (based on 28.9% initial lignin content) and 91% were achieved. With insights already garnered from spectroscopic, spectrometric, and reaction parameters variation studies, we now aim to elucidate the role of catalysts supports with regards to selectivity for individual monomers, and overall yield of aromatic monomers. The current research endeavors to illuminate the functions of metal and acid sites, while comprehending the effects of reaction conditions on the intricate pathways of the reaction. To this end, a suite of metal-oxide and zeolite catalyst supports have been synthesized and evaluated for CTH. We demonstrate interrelationships between CTH of lignin intermediates and surface Lewis and Brønsted acidity of catalysts, and hydrogen-abstraction capability of metals. Overall, the present study advances low-pressure lignin deconstruction to valuable products by advancing insights on the role of catalyst supports during CTH.