Catalyst choice impacts aromatic monomer yields and selectivity in hydrogen-free reductive catalytic fractionation

Hydrogen-free reductive catalytic fractionation (RCF) is a promising method to extract and depolymerize lignin from native biomass without the use of external hydrogen gas. Here, we show that Pt/C and Pd/C achieve comparable monomer yields regardless of hydrogen pressure, whereas Ru/C and Ni/C show lower yields under H-2-free conditions. Ru/C and Ni/C primarily perform hydrodeoxygenation regardless of the hydrogen pressure, but Pt/C and Pd/C demonstrated the ability to form both ethyl products from dehydrogenation and propanol products through hydrogenation depending on the presence of external H-2. Adding water to the solvent increased HDO selectivity to propyl products for both Pt/C and Pd/C. Monomer yields from poplar RCF showed similar trends in yield and selectivity to reactions with the model compound coniferyl alcohol, suggesting that H-2-free RCF performance is dictated by the stabilization rate of reactive monomer intermediates.

Automated summary

Hydrogen-free reductive catalytic fractionation (RCF) is a promising method to extract and depolymerize lignin from native biomass. Pt/C and Pd/C achieve comparable monomer yields regardless of hydrogen pressure, while Ru/C and Ni/C show lower yields under H-2-free conditions. Pt/C and Pd/C can form ethyl and propanol products through dehydrogenation and hydrogenation reactions. Adding water increases the selectivity of propyl products. Similar trends in yield and selectivity are observed for poplar RCF and reactions with coniferyl alcohol, indicating the importance of stabilization rate of reactive monomer intermediates in H-2-free RCF.