Graham J. Hutchings, Mathias Brust and Hubert Schmidbaur introduce the newly discovered allure of gold

Gold is a metal with high monetary value that is now finding new uses in chemistry

Gold is a material that has fascinated humankind since it was first discovered. It is the most noble of metals; it does not tarnish on exposure to the atmosphere and retains its beautiful lustre 

undiminished for millennia. It has been the inspiration for great artworks and also the cause of great conflicts. It is also a metal with high monetary value and, in these current times of high energy costs, gold has increased in value dramatically. Hence, from the perspective of the monetary, art and historical communities, gold is an important metal, something that has high value and is readily traded. Gold was also the fascination of alchemists as they tried, in vain, to make gold from base metals. However, for mainstream chemists, until recently, gold has presented very little fascination. Its chemical inertness in a bulk state convinced chemists that few, if any, exciting chemistries awaited deeper investigation. Hence, the real wonders of gold chemistry have only recently been discovered and the observation that gold, when sub-divided to the nanoscale, can be exceptionally active as a catalyst, has spurred a great number of discoveries. In tandem with catalysis discoveries, there have been enormous developments in the fabrication and uses of gold nanoparticles that are underpinned by the growing field of structural and theoretical advances that are being made in gold chemistry. Gold now fascinates material scientists, catalysis, surface and synthetic chemists and theoreticians in great numbers. From a catalysis viewpoint, gold has become the hot topic and now gold is the catalyst of choice for many reactions. Indeed, the observation that it can catalyse the oxidation of carbon monoxide at temperatures as low as minus 76 degrees Celsius has fascinated many researchers in the recent past.

In terms of application, gold catalysts are starting to show efficacy in selective oxidation and hydrogenation, often showing activities far higher than other previously tried catalysts. Of course, there still remains a fascination with carbon monoxide oxidation, since this is expected to find applications in fuel cells for removal of the last traces of carbon monoxide impurities in the hydrogen fuel, something that gold can readily achieve without oxidizing the valuable hydrogen. A key discovery has been the discovery that gold-palladium alloys can act as efficient catalysts for the direct formation of hydrogen peroxide by hydrogenation of oxygen, which we anticipate will find commercial application.

Although the field of gold chemistry and catalysis has been significantly advanced in recent years, many key challenges remain. In the case of gold chemistry, we now need to gain precise control in the preparation strategies of the particle shape. Most effort has gone into controlling particle size, but controlling shape will be more challenging. In the field of catalysis, the remaining main challenge concerns the nature of the active site for supported gold nanoparticles. This has proved to be a highly controversial topic and a number of key debates concern the electronic nature of the active species. It is most likely that different gold species will be active for the myriad of reactions that gold can catalyse. However, as yet the active site for most reactions remains an area of intense activity.

Read more in 'Gold-an introductory perspective' in issue 9 of Chemical Society Reviews.