S. Varshney, R. Bar-Ziv, D. Meyerstein, T. Zidki
Keywords: catalysis, kinetics, 4-nitrophenol reduction, nanoparticles
Summary:Metallic nanoparticles (NPs) in catalysis have gained a massive interest as catalysts and been a subject of wide research [1-2]. Herein, we present a comprehensive kinetic study of two competitive reduction reactions: hydrogen evolution reaction (HER), and the reduction of 4-nitrophenol to 4-aminophenol. The investigated catalysts were Ag, Au, Pt metallic and Au-Pt, Ag-Pt bimetallic alloy NPs that were synthesized in aqueous suspensions without using any added stabilizer and the reducing agent was NaBH4. Owing to synergism between the metals in the alloy NPs, those have shown superior catalytic performance compared to other reported metallic and bimetallic NPs. Ag-Pt (9:1) NPs display them both as a low-cost and highly efficient reduction catalyst with an apparent rate constant of 59 × 10-3 s-1 and an extremely high activity parameter value of 13,600 s-1g-1. This high activity parameter value is being reported for the first time. Kinetics studies of hydrogen evolution on various metallic and bimetallic NPs were also conducted in order to follow the competition and the reduction mechanism of the fastest Ag-Pt catalyst where the reducing species role among the hydrogen, hydride, and electron was examined. High-resolution transmission electron microscopy (HR-TEM) and X-Ray powder diffraction (XRD) studies show that the silver-rich Ag-Pt alloy NPs have a spherical linked shape and confirm the structure of an alloy with the size of ~4.0 nm. REFERENCES 1. Herves, P., Perez-Lorenzo, M., Liz-Marzan, L. M., Dzubiella, J., Lu, Y., & Ballauff, M. (2012). Catalysis by metallic nanoparticles in aqueous solution: model reactions. Chemical Society Reviews, 41(17), 5577-5587. 2. Singh, A. K., & Xu, Q. (2013). Synergistic catalysis over bimetallic alloy nanoparticles. ChemCatChem, 5(3), 652-676.