Quantum Chemistry Analysis of Reaction Thermodynamics for Hydrogenation and Hydrogenolysis of Aromatic Biomass Model Compounds

Designing effective and selective reactions at sustainable or mild conditions is key for the valorization or refinery of lignin biomass using H₂ reduction methods. However, it remains unclear what are the feasible mildest conditions for the reductive valorization of lignin, at which transformations can be designed. Here, we aim to exploit this critically important question using quantum chemistry calculations to systematically analyze the thermodynamics of hydrogenation and hydrogenolysis of typical functional groups found in lignin based on a set of aromatic model compounds. Our results show that it is thermodynamically feasible to break ether linkages and remove oxygen content in the model compounds even at room temperature, room pressure, and in aqueous solvent (i.e., the global mildest conditions). Interestingly, the potential influence on the thermodynamics by reaction variables is ranked in the order of temperature > H₂ pressure > solvent dielectric constant; a strategically chosen solvent may enable increased selectivity for hydrogenolysis over hydrogenation. Our predicted reaction thermodynamics is consistent with our experimental findings of probed reaction pathways. This work may inspire researchers to pursue the design of “ultimate” green biomass conversion processes closer to the global mildest conditions.