Gold nanopartIcles
Due to its largely nonreactive nature gold has long been considered a “noble” metal, undergoing few of the reactions of its transition metal counterparts. This assumption of considering gold catalytically inert changed, however, in the late 90s after the seminal contribution of Haruta, who reported that gold nanoparticles are extremely active in promoting the low - temperature, aerobic oxidation of CO to CO2 (Fig 1) [1] . Moreover, Haruta and co-workers showed that the catalytic activity of gold appears for particles in the nanometric size range, there being a direct relationship between activity and particle diameter [2]. Since this breakthrough, research has been aimed at determining the reaction types that can be efficiently catalyzed by nanometric gold particles, increasing the catalytic activity of gold by stabilizing nanoparticles against agglomeration, understanding the role of the solid support in the catalytic activity and also demonstrating the similarities and distinctive properties of gold catalysis with respect to catalysis by other noble metals.

Fig 1: Schematic illustration of one of the coadsorption and catalytic combustion cycles.

The importance of gold nanoparticles in catalysis derives in part from the wealth of information and reliable experimental procedures to form these nanoparticles in different sizes and, even different shapes [3].

1- Haruta, M., T. Kobayashi, et al. (1987). "Novel Gold Catalysts for the Oxidation of Carbon Monoxide at a Temperature far Below 0 °C " Chemistry Letters 16: 405-40

2- Haruta, M. (1997). "Size- and support-dependency in the catalysis of gold " Catalysis Today ( 36 ): 153-166.

3- Astruc, M.-C. D. a. D. ( 2004). "Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties, and Applications toward Biology, Catalysis, and Nanotechnology." Chem. Rev. 293-346 104: 293-346