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.

Gold had been overlooked by most researchers as a possible industrial catalyst until very recently. However, there is now a growing excitement about the potential gold may hold for catalysing industrial reactions, stimulated by the early work of Graham Hutchings at Cardiff University and researcher Masatake Haruta from AIST in Japan.

Examples of applications where a gold based catalyst is being used, developed or considered for use include the following :

Vinyl acetate monomer (VAM) production

There is a need for VAM for large scale uses in emulsion-based paints, wallpaper paste and wood glue.There are a number of well-established commercial processes for the manufacture of vinyl acetate monomer from ethene, acetic acid and oxygen using gold-palladium catalysts. The presence of gold leads to a three fold increase in space time yield compared with use of palladium alone.

The chemical technologies for these processes were developed in the 1960s, and have been operated commercially since the 1970s and today VAM is produced with high efficiency and yield in many plants around the world.  Worldwide VAM capacity is currently ca 5 million metric tonnes per year, and is expanding. VAM catalyst consumption is several hundred tonnes per annum.

Methyl glycolate pilot plant

Recently a liquid-phase air-oxidation process has been developed by Nippon Shokubai in Japan for the one-step direct production of methyl glycolate from ethylene glycol and methanol using a gold catalyst. Methyl glycolate is used as a solvent for semi conductor manufacturing processes, as a building block for cosmetics and as a cleaner for boilers and metals.

A pilot plant demonstration, with a capacity of tons per month, successfully showed that this can be run as a clean and simple continuous process with the product obtained in high purity.  The catalyst used for this reaction, as given in the associated published paper, was based on gold.

Conversion of glucose to gluconic acid

Gluconic acid is an important food and beverage additive, and it is also used as a cleansing agent and is made on the 60,000 tonnes per annum scale. Work at the Federal Agricultural Research Centre, Braunschweig, Germany has demonstrated that the oxidation of glucose to gluconic acid can be been maintained at high efficiencies using a stirred tank reactor for up to 110 days, with gold catalysts. Südzucker have filed a patent covering use of gold catalysts for this conversion.

 A list of scientific reviews on gold catalysis can be found here .

Catalysts

A Feature article in ChemComm by Prof Graham Hutchings describing nano gold catalysts for chemical synthesis.
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