Industry organisation the World Platinum Investment Council (WPIC) has summarised the 100-year history of platinum woven gauze catalysts and highlighted the relevance of platinum as an efficient industrial material owing to its ductility; its resistance to corrosion, oxidation and temperature; and the ability to recycle these woven catalysts.
Modern uses can involve ammonia and air that are routed over platinum alloy gauzes heated to 900 °C, producing nitrogen oxide that bonds with water to create nitric acid. This chemical reaction requires round-knitted gauzes of up to 6 m in diameter.
Gauze catalysts are recycled at the end of their useful life. The individual components, such as platinum and rhodium, are carefully separated and the purified precious metals are then turned back into wires and used to make new gauzes.
Very little platinum by weight is lost in the production of nitric acid. While a new plant may be equipped with over a ton of platinum gauze catalysts, only a few per cent of this needs to be replaced when the gauze is periodically recycled, the WPIC pointed out.
Meanwhile, platinum catalysts were first used to make nitric acid from ammonia in the early twentieth century in a chemical reaction known as the Ostwald process, after the pioneering work of Nobel Prize-winning chemist Wilhelm Ostwald in 1901.
Fifteen years later, global science and chemicals company Johnson Matthey made a further breakthrough in platinum catalyst technology, selling the first woven gauze catalyst to the UK Munitions Inventions Department in 1916 to make nitric acid for explosives following the outbreak of the First World War.
The technology continued to evolve and gauzes made from platinum-rhodium alloys were first introduced in the 1930s to increase gauze strength, reduce platinum losses and increase conversion efficiency. In the 1990s, knitting technology allowed a diverse range of structures and alloys to be used, improving performance and reducing manufacturing time.
"In addition to its catalytic properties, platinum’s mechanical properties make it especially suited to being woven into a gauze, because it is ductile and can be easily pulled into long, thin wires. Its resistance to corrosion, oxidation and temperature are also important attributes. Gauzes made from platinum are instrumental to a range of industrial processes," the WPIC noted.