Despite its importance, catalysis is not a particularly well understood or appreciated branch of science and technology. The production of almost all industrial chemicals rely on catalysts, and many aspects of ‘green chemistry’ (i.e. chemical products and processes that reduce or eliminate the use or impact of hazardous substances) would not be possible without them. Simply put, they are critical to ensuring a safer, cleaner world in the 21st century.
Metals make excellent catalysts because they are chemically ‘pliable.’ They can interact with the starting materials and solvents within the reaction while being relatively stable to heat and pressure. This gives them longevity: a fundamental characteristic of an efficient catalyst.
Precious metals such as platinum, palladium and silver are commonly used in chemical catalysis. Many already know that catalytic convertors in cars contain relatively significant quantities of platinum and palladium. The reason is simple; these metals are capable of removing large amounts of the pollutants generated by diesel and petrol engines over the course of a vehicle’s life. The converters are relatively costly as a consequence of the precious metals, but can operate efficiently for many years in the harsh environment of a car’s exhaust system. In 40 years of R&D, only precious metals have been shown to be capable of delivering these results.
Gold also can be as effective a catalyst as platinum or palladium. During the Second World War, DuPont chemists in the USA discovered that small quantities of gold added to certain chemical reactions both sped them up and improved the quality of the end product. Fast forward almost 70 years and one company, Johnson Matthey (JM), is now bringing such a gold catalyst to market.
The specific reaction in question is Vinyl Chloride Monomer (VCM). VCM is the precursor to Poly Vinyl Chloride (PVC), the world’s third most widely produced synthetic polymer (or plastic), which is used in construction materials from pipes to siding. It’s an important material which can be synthesised a number of ways. One of the most common involves the use of a mercury-based catalyst which, given the considerable quantity of VCM produced on a yearly basis, represents one of the largest single uses of mercury in the world. This breakthrough – utilising a gold-based catalyst – provides an opportunity for VCM producers to remove mercury from their process in a cost-effective manner.
JM has commissioned a plant in Shanghai to produce the catalyst (called Pricat MFC), and is working alongside some of the world’s leading VCM manufacturers to drive adoption. For more general information on this work, visit the JM sustainability website here, or technical detail is available in a recently published research article here.