Collaborative Research: SusChEM: Designing Catalytic Interfaces to Promote Selective Lignin Depolymerization

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Lignin is one of the three major components of woody and grassy plant cell walls, and its chemical make-up is not only carbon-rich but also resembles many petroleum-based chemical precursors. This project addresses challenges presented by the catalytic deconstruction of lignin into its constituent units in an effort to generate renewable and low-cost aromatic chemicals. Specifically, the aims are to understand how the catalyst interacts with portions of lignin that are susceptible to cleavage. The catalyst contains copper nanoparticles dispersed on a porous solid support, and in supercritical methanol (sc-MeOH) it catalyzes the cleavage of solid lignin to energy-rich organic liquids without forming char. Two key problems are movement of the bulky, poorly soluble polymer and access to the internal surfaces of the catalyst. By tuning the reaction conditions and the properties of the catalytic material, the interactions of the catalyst with lignin will be optimized to enhance depolymerization and enable economical production of renewable aromatic chemicals. The goal is to develop innovative, sustainable, and scalable conversion processes that generate platform renewable chemicals from lignin economically using porous solid catalysts made with Earth-abundant materials. This project will test two overarching hypotheses: 1) that lignin absorption into a porous catalyst and its adsorption onto catalyst surfaces induce conformational changes that increase interactions between the lignin and the catalyst; and 2) that porous catalysts with appropriate internal structure and composition maximize interactions of the key aryl ether linkages with catalytically active sites. The research will involve: 1) ordered mesoporous catalysts with controlled and systematically varied pore architecture and surface functionality (i.e., hydrophobicity); 2) lignin dimer and oligomer model systems that have controlled and systematically varied chain length, proportion of linkages that are aryl ethers, and spacers between aryl ether linkages, and 3) in-situ assessment of adsorption modes and reaction kinetics. The plan to achieve these objectives and test these hypotheses involves synthesizing both lignin model systems and templated mesoporous catalysts with controlled and systematically varied structures and compositions to probe solvent-lignin, solvent-catalyst, and lignin-catalyst interactions; and using advanced spectroscopic methods, to probe interfacial interactions between lignin and catalyst to understand how they promote selective lignin depolymerization by hydrogenolysis of aryl ether linkages. The research team will collaborate with the Institute for School Partnership to develop outreach and education activities for underrepresented and underprivileged eighth grade students in the St. Louis community. Specifically, the outreach efforts will include an annual Researcher for a Day program for local underrepresented minority students through a campus visit, a campus tour, and lab demonstrations. A similar activity will be offered through the SciTrek outreach program at UC Santa Barbara.