In this study, we investigate the hydrogenation reaction of levulinic acid to 4-hydroxypentanoic acid on ligand-modified Pt(111) using DFT. Modifying nanoparticle surfaces with ligands can have beneficial effects on the desired reaction such as improved selectivity or lower activation energies. The N3,N3-dimethyl-N2-(quinolin-2-yl)propane-1,2-diamine (AQ) ligand was selected to modify the surface, since it combines good surface adsorption properties with functional groups that can influence the reaction. The adsorption geometry of the AQ ligand was studied as well as the co-adsorption of a second AQ ligand for the possibility of self-assembly. We found that dissociated hydrogen from the Pt(111) surface can protonate the AQ ligand and discuss the role this plays on the mechanism of the hydrogenation reaction of levulinic acid (LA). By comparing the ligand-modified Pt(111) surface to the bare Pt(111) surface we show that the reaction changes from a step-wise to a concerted mechanism due to the influence of the ligand molecule. This demonstrates the effect that ligand-modified surfaces can have on catalyzing reactions and shows that desired reactions can be achieved by tuning the reaction environment.