Synergistic Effects of Gold–Palladium Nanoalloys and Reducible Supports on the Catalytic Reduction of 4-Nitrophenol

Abstract

Herein we report on the catalytic activity of mesoporous nickel, iron, cerium, cobalt, and manganese oxides prepared using KIT-6 as a hard template via evaporation-assisted precipitation. The mesoporous metal oxides (MMOs) were characterized and used as heterogeneous catalysts in the reduction of 4-nitrophenol (4-Nip) by sodium borohydride (BH4 –). Furthermore, polyamidoamide (PAMAM) dendrimers were used to synthesize gold–palladium nanoalloy particles. The size of AuPd/PAMAM was found to be 3.5 ± 0.8 nm in diameter before being immobilized on the aforementioned mesoporous metal oxides and used as catalysts in the reduction of 4-Nip. Prior to catalytic evaluation, the reduction profiles of the mesoporous metal oxides were investigated by hydrogen-temperature-programmed reduction (H2-TPR) and showed that mesoporous metal oxides can be easily reduced at lower temperatures and that the immobilization of gold–palladium nanoalloy particles lowers their reduction temperatures. Mesoporous cobalt and manganese oxides showed catalytic activity toward 4-Nip reduction, and the activity was enhanced after immobilization of the gold–palladium nanoalloys. Isolation of nanoparticles activity was achieved by immobilization of the gold–palladium nanoalloys on the inert silica support. From this we postulated an electron relay mechanism for the reduction of 4-nitrophenol. With the use of power rate law we showed that 4-Nip reduction follows pseudo-first-order kinetics.

Enhanced Selective Production of Carbonyl Products for Aerobic Oxidation of Benzylic Alcohols over Mesoporous Fe2O3 Supported Gold Nanoparticles

“…average pore diameter. From the pore size distribution analysis of Au/meso-Fe2O3, the pore size distribution of the catalyst was still uniform, which is in agreement with the XRD results [20,27]. The Au/meso-Fe2O3 catalyst still exhibits typical type IV isotherms with a mesoporous structure [30,31].…”

“…Additionally, the aerobic oxidation activities of Au/meso-Fe 2 O 3 for benzylic alcohol are much higher than those of Au/bulk-Fe 2 O 3 [18,19]. The mesostructures of the catalysts improved the oxidative performance by providing a high distribution of gold active sites [20], and the mesopores could enable the efficient transport of reactants and products to the catalytic sites [21,22].…”

Synthesis of Au-Pd Bimetallic Nanoflowers for Catalytic Reduction of 4-Nitrophenol

“…The enhanced catalytic activity for 4-NP reduction of Au-Pd NFs (Au 1 Pd 1 core), compared to Au-Pd NFs (Au core), could be attributed to more exposed reactive surfaces of Pd according to CV curves ( Figure 3 ). Pd by alloying with gold could be favorable to the surface adsorption of the nitrophenol reactant and the reducing agent on the catalyst to follow the Langmuir-Hinshelwood mechanism, and the modification of electronic property of nanoalloys [ 36 , 37 ]. To better understand the synergistic effect in 4-NP reduction by Au-Pd alloy, computational calculation about the binding energy between the reactants adsorbed on the surface of the nanoalloy and the electron transfer effect between Pd and Au atoms is in progress.…”

Kinetic investigation for the catalytic reduction of nitrophenol using ionic liquid stabilized gold nanoparticles

“…For example, Au 25 clusters, gold-palladium nanoalloys, gold nanowires and Au@Fe 3 O 4 yolk-shell nanostructures, have been used as effective catalysts for the reduction of 4-nitrophenol. [29][30][31] Many reports indicate that the NPs used for the reduction of 4-nitrophenol follow two mechanisms: (1) Langmuir-Hinshelwood (L-H) mechanism and (2) Eley-Rideal (E-R) mechanism. [32][33][34][35] Several research groups have analyzed the kinetics of the reduction reaction by varying the concentration of 4-nitrophenol and NaBH 4 for determining the reaction mechanism.…”