ABSTRACT
The “well-established” dogma of gold inactivity was broken by Haruta’s reports in the late 1980s (Haruta et al. 1987; 1989), showing that gold, when adequately prepared in the form of nanometer-sized particles, exhibits enormous catalytic activity in oxidation processes. It is one of the most pronounced illustrations of the influence of nanostructure on catalytic properties. In particular, a very high catalytic activity of gold loaded on some metal oxides in low temperature CO oxidation has been demonstrated. For some applications, gold properties are much superior to those of the platinum group metals because the bonding strength of adsorbates on Au defective sites is moderate and still weaker than that on Pd and Pt (Scirè and Liotta 2012). Since the first of Haruta’s works, the area of catalysis with the use of gold nanoparticles has experienced continuous growth. The beginning of the 21st century was a ‘golden’ time which brought a huge number of publications devoted to different methods of gold catalysts preparation, different supports for gold loading and different oxidation processes in which gold catalysts were tested. The knowledge on the gold catalysts has been greatly expanded and brought new insight into the effect of various properties of gold particles, apart from their size, on the effectiveness of reactions catalyzed by gold species. Depending on the reaction 255type, metallic gold, cationic gold or negatively charged gold particles have been proposed as active centres. The formation of different gold species strongly depends on the nature of the support. The chemical composition of the support determines the chemical interaction with gold which in turn influences the gold electronic state. Moreover, the support has been reported to participate in the control of the amount of gold anchored to the surface as well as the size and the shape of gold particles (Scirè and Liotta 2012). If reducible metal oxides are applied as supports, the anion vacancies can be easily created and have been suggested as the sites of oxygen adsorption and activation. In general, the performance of the supported gold catalysts is highly dependent on the nature of the support, the size of gold crystallites and the electronic state of gold species.
