Solvated Metal Atoms in the Preparation of Supported Gold Catalysts

Several reviews appeared in the last years to emphasize the unique properties showed by gold metal, when particle size falls in nanometers range. Au nanoparticles (NPs) have found uses in ceramics, medicine, and other areas. Among them the most exciting and growing field of application is undoubtedly catalysis. Historically, gold was regarded to be catalytically inert, since the discoveries made by Haruta and Hutchings. in the late 1980s: surprisingly, they demonstrated simultaneously and independently that supported gold nanoparticles are the best catalyst for low-temperature CO oxidation and ethyne chlorination to vinylchloride. In recent years, it has been shown that gold becomes active for many novel reactions of synthetic interest when stabilized in the form of nanoparticles deposited on several organic and inorganic supports. Supported Au NPs have found numerous applications as unique catalysts in aerobic oxidative processes, reduction of organic compounds, C-C coupling reactions, etc. Moreover, the ability of gold to coordinate with triple bonds has no parallel with other transition metals. Upon coordination and formation of the corresponding adduct, the alkyne becomes activated and more reactive towards nucleophiles such as alcohols, amines and hydrosilanes. It was clearly evidenced that particle size play a crucial role in determining catalytic activity of supported gold particles in CO oxidation, as well as in others reactions. On the other hands, it has been also demonstrated that the superficial oxidation state of the metal, the nature of the support, the Au-support interface and the particle morphology may strongly affect catalytic performance of AuNPs. All these findings have increased the efforts made by scientist to investigate how the different preparation methods can affects the above mentioned factors. In this chapter we intend to provide a synapsis of the synthesis of supported gold catalysts by the metal vapor synthesis (MVS) approach. In particular, the contribution includes the work undertaken till date in our and other research groups pointing out the key factors to control the size of Au nanoparticles by this synthetic method.