Catalytic Gold Nano‐Particles

Abstract

Although gold is the most inert of all metallic elements, it has interesting properties as a heterogeneous catalyst. There are a number of curious aspects to catalysis by gold that are currently attracting academic investigation, while the observation that gold-based catalysts are active at room temperature and below is driving considerable industrial interest. However, much is still not understood about these catalysts and, for example, apparently similar preparation techniques result in activities of hugely varying magnitude. In the present paper we assess the known phenomenology of heterogeneous catalysis by gold, with particular reference to the material properties of the individual nano-particles of catalyst and the many disagreements in the literature. Even the structure of the nano-particles is uncertain, with claims being made for truncated octahedra, cub-octahedra, icosahedra, various kinds of decahedra, and amorphous structures. As far as uncertainty concerning the mechanism of catalysis is concerned, we show that the situation has not yet been resolved, with evidence that catalysis can proceed even in the absence of either a discrete particulate morphology or an oxide support. One possibility is that more than one mechanism applies. Alternatively, the explanation may be that the activity of gold as a catalyst is determined only by the availability of surface gold atoms with low coordination numbers and an associated electron density suitable for whatever reaction is being catalysed. In this case, the role of the oxide support and of gold particle size and structure is indirect, and they would serve mainly to modulate the specific surface area of the gold, and the electronic configuration of its surface atoms.