Introduction to Gold Catalysts

A catalyst is a substance or material that accelerates the rate of a chemical reaction without itself being consumed by the reaction. Catalysts are an essential component of many different industrial processes used to produce chemicals, foodstuffs and other materials. Perhaps one of the first intentional uses of catalysis was in the fermentation of sugar to make alcohol. Another common every day application is the use of catalytic converters on cars for the control of exhaust emissions

 

Gold as a Catalyst

Gold had been overlooked by most researchers as a possible industrial catalyst until very recently. However, the following reactions have now been shown to be effectively catalysed by supported gold catalysts:

 

Gold on titanium dioxide support. Courtesy of AIST, Japan

 

The following reactions have now been shown to be effectively catalysed by supported gold catalysts:

• Carbon monoxide oxidation, including selective oxidation in a hydrogen stream
• Catalytic combustion of hydrocarbons
• Hydrochlorination of ethyne
• Hydrogen + oxygen reaction to give hydrogen peroxide
• Hydrogen sulphide and sulfur dioxide removal
• Oxidation of glucose to gluconic acid
• Oxidative decomposition of dioxins
• Oxidative removal of mercury
• Ozone decomposition
• Reduction of NOx with propene, carbon monoxide or hydrogen
• Selective oxidation, e.g. epoxidation of olefins
• Selective hydrogenation, e.g. of alkynes and dienes to mono-olefins
• Vinyl acetate synthesis from ethene, acetic acid and oxygen
• Water Gas Shift

The use of gold as a catalyst requires careful and unconventional preparation of the gold metal, centred on achieving a very small gold particle size.

 

Commercial Applications

Gold is set to take its place alongside the other precious metals (platinum group metals and silver) as a key catalyst in a range of industrial processes and uses. Gold alloy catalysts are already used in the commercial production of vinyl acetate monomer (VAM).

Project AuTEK in South Africa is one of the leading organisations seeking to commercialise important new catalytic applications for gold.