Uncovering gold’s secrets

An international group of scientists led by researchers at Cardiff University has unlocked the secret of a gold-based catalyst that is used in the manufacturing of polyvinyl chloride (PVC), the world's third-most widely used plastic.

PVC has become an indispensable part of modern life. Its applications include construction pipes, credit cards, window and door frames, plumbing equipment, and electrical cable insulation.

Led by Professor Graham Hutchings, Director of the Cardiff Catalysis Institute, the Cardiff University team have pioneered research into gold catalysts in recent years, and made the landmark discovery that gold is a remarkable catalyst for the production of vinyl chloride – the main ingredient of PVC. They found that gold offers an alternative to the environmentally harmful and toxic mercury catalyst that was traditionally used in industry.

Gold catalyst in production

As a result of the team’s pioneering work, the gold catalyst has now been commercialised by leading chemicals company Johnson Matthey and is currently in production at a purpose built reactor in Shanghai, China.

Current estimates suggest that 20 million tonnes of vinyl chloride could be manufactured each year using the gold catalyst.

In a new paper published in the leading international journal Science, the team, which also includes researchers from Lehigh University, Southampton University, University College London and Johnson Matthey, found that gold needs to be ionized in order to convert acetylene, a gas derived from coal, to the VCM molecules that can be subsequently linked to form PVC.

An ionized gold atom means that it is missing some of its electrons.

The team also determined that the gold needs to be atomically dispersed, where the atoms are separated on the carbon support and are not touching each other.

The team hope that these findings will help to design and optimize gold-based catalyst systems for use in other important reactions, such as the water-gas-shift reaction, which generates hydrogen that could potentially be used a green fuel.

Professor Graham Hutchings said: “It’s fantastic to see that the original predication I made in the early 80s has been fully validated. I predicted that gold cations would be the best catalyst and in this paper we show these are indeed the active catalyst.”