Supported Heterogeneous Gold Nanoparticles As a Catalyst for the 4-Nitrophenol Hydrogenation Reaction

Abstract

Bulk gold cannot oxidize in air and is known for its minimal reactive ability with many chemical reagents. Because of this, bulk gold is known to be chemically inert, and this low activity is due to the particle sizes.1 However, gold nanoparticles (AuNPs) are the most highly active of catalyst due to the lack of a stable oxide (unlike most elements).2–4 As the Fermi potential of metal nanoparticles becomes more negative, they exhibit a substantial decrease in potential. The result of this unique property allows them to behave as catalysts in electron transfer processes, such as hydrogenation reactions. Electrical, optical, and catalytic properties are frequently seen in small nanomaterials and gold nanoparticle catalysts show excellent potential for the selective oxidation or hydrogenation of organic substrates.1,5 It is believed that gold nanoparticles will be key building blocks for many disciplines in the 21st century. For example, their individual particle size behaviors, and the electronic, magnetic and optical properties (quantum size effect), show great promises to the catalysis, nanotechnology, and biological field.2–4 Four different sizes of nanoparticles were synthesized and then suspended on four different economically favorable supports. The catalytic properties were investigated in this study with the reduction of 4-nitrophenol, a common hydrogenation reaction. Kinetics of the catalysis was monitored with UV-Vis spectrophotometry and samples were characterized with both transmission electron microscopy (TEM) and X-ray fluorescence (XRF). It was found that all reactions followed first order kinetics. Activated carbon did not behave as a catalytic surface, but was found to absorb the nitrophenol for all nanoparticle sizes. Glass wool and the largest AuNP (53.5nm) proved to be the best support by providing the fastest rate constants. This heterogeneous catalyst was also found to be recyclable. REFERENCES 1) Abdel-Fattah, T. M. & Wixtrom, A. Catalytic reduction of 4-nitrophenol using gold nanoparticles supported on carbon nanotubes. ECS J. Solid State Sci. Technol. 3, M18–M20 (2014). 2) Seoudi, R. & Said, D. A. Studies on the Effect of the Capping Materials on the Spherical Gold Nanoparticles Catalytic Activity. World J. Nano Sci. Eng. 01, 51–61 (2011). 3) Daniel, M.-C. & Astruc, D. Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology. Chem. Rev. 104, 293–346 (2004). 4) Heddle, J. Gold Nanoparticle-Biological Molecule Interactions and Catalysis. Catalysts 3, 683–708 (2013). 5) Huang, J. et al. Ag Dendrite-Based Au/Ag Bimetallic Nanostructures with Strongly Enhanced Catalytic Activity. Langmuir 25, 11890–11896 (2009).