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

Abstract

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.

Hydrogenation of Lignin-Derived Phenolic Compound Eugenol over Ruthenium-Containing Nickel Hydrotalcite-Type Materials

“… − The resulting product distribution is in line with results from the literature . The noble metals in the presence of a hydrogen atmosphere are highly active for both hydrogenation and deoxygenation reactions . Unlike transition metal-based catalysts, the reaction of noble metal catalysts proceeds via simultaneous demethoxylation and aromatic ring saturation.…”

“…Ethylbenzene showed approximately 83% conversion compared to phenolic derivatives, which showed complete ring hydrogenation with 100% conversion. Furthermore, the present NiRu-HT0.2 catalyst selectively hydrogenated aromatic rings in comparison to the phenolic hydroxyl group, which is analogous to some of the recent literature. ,− …”

“…2 The noble metals in the presence of a hydrogen atmosphere are highly active for both hydrogenation and deoxygenation reactions. 39 Unlike transition metal-based catalysts, the reaction of noble metal catalysts proceeds via simultaneous demethoxylation and aromatic ring saturation. In general, ring hydrogenation requires high pressures and high temperatures; however, in the present study, the NiRu-0.2-HT catalyst facilitated simultaneous demethoxylation and aromatic ring hydrogenation under moderate reaction conditions (150 °C, 2.5 MPa).…”

Alternatives for Chemical and Biochemical Lignin Valorization: Hot Topics from a Bibliometric Analysis of the Research Published During the 2000–2016 Period

“…Systematical analysis of the thermodynamics of hydrogenolysis of typical functional groups found in lignin have been applied to identify the mildest operation conditions. As a result, the theoretical foundation for the feasibility of designing novel reactions was provided, which demonstrated that new green catalysts, like transition metal catalysts, will allow lignin hydrogenolysis near ideal mild conditions (room temperature, room pressure, and aqueous solvent) [291]. For further information about the state-of-the-art of selective lignin hydrogenolysis, a very interesting published perspective can be consulted in [292].…”

State of the Art and Perspectives in Catalytic Conversion Mechanism of Biomass to Bio-aromatics

“…Cellulose and hemicellulose can be converted into platform compounds such as alcohols, furfural, and furan compounds . These platform compounds can then be further converted into bio-aromatics through a series of reactions, such as deoxygenation, dehydrogenation, and cyclization. , Compared with cellulose and hemicellulose, lignin can be directly converted to bio-aromatics, which is regarded as a promising technology …”