Ligand-capped metal nanoparticles exhibit promising properties as catalysts, because their large surface area to volume ratio allows for high catalytic activity, while their ligands dictate the immediate environment around the catalytic surface allowing for directed catalytic selectivity. Our research group has recently reported the effects of surface ligand density on the catalytic activity and selectivity of Pd nanoparticles (PdNPs) in chloroform. Overall, enhanced catalytic activity for the hydrogenation and/or isomerization of alkenes has been observed for PdNPs with a lower surface ligand density. This poster presents the investigation of catalytic activity and selectivity of PdNPs with different surface ligand density in different surrounding environments that change either the conformational structure of ligands or ligand-substrate interactions. First, colloidal Pd nanoparticles are synthesized using the reversed thiosulfate addition protocol, completing the nucleation-growth of PdNPs before the addition of alkyl thiosulfate ligand; this step is completed using tetraoctylammonium bromide (TOAB), in a way to control the size of PdNPs. Second, the catalytic activity and selectivity of PdNPs with different ligand density are investigated in various solvents. This study confirms the solvent-induced conformational change of surface ligands has a profound influence on the catalytic activity and selectivity of PdNPs. Third, the lipid-nanoparticle assemblies (LNAs) of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) lipids and PdNPs with different surface ligand density are prepared using a thin film hydration method. This process produces LNAs with a hydrophobic bilayer region where the hydrophobic PdNP catalysts reside. Fourth, the influence of liposome bilayer embedding on catalytic activity and colloidal stability of these PdNPs is studied. The presence of hydrophobic bilayer allows the facile diffusion of substrates and hydrogen gas molecules near the catalytic sites for the enhanced hydrogenation of alkenes in aqueous environments especially for PdNPs with a lower surface ligand density. The catalysis results of alkene hydrogenation are obtained using <sup>1</sup>H NMR and gas chromatography analyses.

Effects of surface ligand density and lipid encapsulation on the catalytic activity of hydrophobic Pd nanoparticles

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ACS Fall 2022

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