Catalytic evaluation of dendrimer-templated Pd nanoparticles in the reduction of 4-nitrophenol using Langmuir-Hinshelwood kinetics

This study aimed to produce well-defined palladium nanoparticles using a dendrimer template technique and investigate their catalytic behavior through intensive kinetic evaluation using 4-nitrophenol (4-Nip) reduction as a model reaction. Three dendrimers, generation 4, 5, and 6 hydroxyl terminated poly(amidoamine) dendrimers, G4-OH, G5-OH, and G6-OH were used as templates, while metal to dendrimer ratios of 40, 80, and 160 were used for the G4-OH, G5-OH, and G6-OH dendrimers, respectively. The average diameters obtained for dendrimer-templated G4-OH(Pd₄₀), G5-OH(Pd₈₀), and G6-OH(Pd₁₆₀) nanoparticles were 2.35 ± 0.58 nm, 2.02 ± 0.45 nm, and 2.21 ± 0.31 nm, respectively. Kinetic evaluation of the 4-Nip reduction catalyzed by the Pd nanoparticles was performed under various experimental conditions, such as various concentrations of the catalysts, 4-Nip, NaBH₄, and various temperatures. The highest catalytic activity was obtained by using G6-OH(Pd₁₆₀) catalyst. The adsorption equilibrium constants of 4-Nip (K_Nip) and borohydride (KB_H4-) obtained by data fitting to the Langmuir-Hinshelwood equation as well as the activation parameters such as enthalpy of activation (ΔH^‡), entropy of activation (ΔS^‡), and activation energy (E_A) obtained by Eyring and Arrhenius equations are reported.