Heterogeneous Catalysis by Gold

Gold can be deposited as nanoparticles (NPs) with diameters of 2–5 nm and clusters with diameters less than 2 nm on a variety of materials such as oxides, carbides, and sulfides of transition metals, carbons, and organic polymers. Such supported gold NPs and clusters exhibit surprisingly high catalytic activities for many reactions, with both gas- and liquid-phase reactants, in particular, at temperatures below 573 K. Until now, more than 10 techniques have been developed for depositing gold as NPs and clusters. The atomic scale structures of supported NPs and clusters have been extensively and intensively investigated with a high-resolution transmission electron microscopy. The mechanisms of catalysis by supported gold NPs have recently been elucidated by using real powder catalysts and model single-crystal catalysts for the low-temperature oxidation of CO. Another simple reaction that has recently been investigated is dihydrogen dissociation, for which gold NP catalysts are still poorly active. Both of these reactions have been demonstrated to take place at perimeter interfaces around the gold NPs. This result means that there is a great chance for gold to exhibit high catalytic activity for hydrogenation reactions by an appropriate choice of metal oxide supports and by minimizing the diameters of gold particles. The catalytic nature of gold clusters has also been investigated theoretically in relation to the effect of cluster size and the influence of organic ligands and polymers. The catalytic performance of gold NPs and clusters has been explored extensively for reactions of both gases and liquids. Supported gold catalysts are useful for air cleaning at room temperature, and they are valuable for green production of bulk and fine chemicals. Supported gold clusters are expected to open new doors for simple chemistry for the selective manufacture of needed products. Size and structure specificity are expected to present opportunities for selective conversions. It is recommended that researchers explore the magic numbers and structures of gold and suitable support materials for selected target reactions.