Reductive catalytic fractionation (RCF) depolymerizes lignin into aromatic monomers. This study investigates how catalyst supports influence monomer yield and selectivity during H2-free RCF of softwood biomass using 1,3-dimethoxypropan-2-ol (DMP), a glycerol-derived hydrogen transfer solvent. A series of Pt nanoparticle catalysts were synthesized on supports with varying acidity, including inert (Pt/C), amphoteric (Pt/TiO2), and acidic (Pt/FAU > Pt/Al2O3 > Pt/ZrO2). Reactions at 200 °C for 7 h with 10 wt% catalyst gave monomer yields of 22.8 wt% (Pt/C), 18.6 wt% (Pt/TiO2), 21.4 wt% (Pt/Al2O3), 22.1 wt% (Pt/ZrO2), and 21.9 wt% (Pt/FAU). While yields were similar, monomer selectivity was governed by support acidity. Pt/C and Pt/ TiO2 favored monomers with saturated and unsaturated alkyl side chain such as 4-ethylguaiacol (0.09 – 0.10 mol/mol), 4-propylguaiacol (0.12 – 0.15 mol/mol), trans-isoeugenol (0.29 – 0.31 mol/mol), and eugenol (~0.10 mol/mol). Acidic supports favored monomers with oxygenated alkyl side chain such as coniferaldehyde (0.23 – 0.29 mol/mol), vanillin (0.18 – 0.24 mol/mol), and vanillic acid (0.04 – 0.06 mol/mol). Control experiments using bare supports confirmed that acidity directs selectivity, while Pt enhances yields through hydrogenolysis. Model studies identified coniferaldehyde as a key intermediate, and CuO oxidation quantified theoretical yields by tracking β-O-4 cleavage. MALDI-TOF analysis showed that Pt/C and Pt/TiO2 promoted dehydration and decarbonylation, whereas Pt/Al2O3, Pt/ZrO2, and Pt/FAU retained oxygenated side chain functionalities. 1H–13C HSQC NMR confirmed complete β-O-4 cleavage for all catalysts except Pt/TiO2, which showed residual linkages correlating with its lower yield. Native lignin linkages were fully hydrogenated post-RCF, with catalyst-dependent structural differences. This study demonstrates that catalyst support acidity strongly influences monomer selectivity and provides a pathway to control product distribution during catalytic lignin valorization.
