Palladium

• 1. Introduction

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  Palladium, the silvery-white metal with atomic number 46, carries a name born from astronomical discovery. When the English chemist William Hyde Wollaston jotted notes about a new noble metal in his lab book in July 1802, he was reaching for a name that captured a kind of cosmic newness. He found it in the asteroid Pallas, which had been discovered just two months earlier and was itself named after an epithet of the Greek goddess Athena. That chain of naming stretches from ancient myth to a laboratory in London to the periodic table, and it hints at something unusual about this element. Palladium is not merely a chemical curiosity. It sits at the center of some of the most consequential industrial processes on earth, and it has been the subject of geopolitical panic, billion-dollar corporate losses, and one of the most controversial scientific claims of the twentieth century. How does a metal discovered in crude platinum ore from South America become a linchpin of global automobile manufacturing? And what does it mean that the world's supply of this metal is concentrated in just a handful of places, some of them politically volatile?

• 2. A Contested Discovery

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  Wollaston did not announce his discovery through a formal paper in the scientific press. Instead, he purified a quantity of the new metal and offered it for sale, without naming himself as the discoverer, in a small shop in Soho in April 1803. That anonymous commercial debut provoked Richard Chenevix, who declared publicly that palladium was no new element at all but merely an alloy of platinum and mercury. Wollaston's response was characteristically indirect. He anonymously offered a reward of twenty pounds for twenty grains of synthetic palladium alloy, daring anyone to reproduce Chenevix's claim. Nobody collected. Chenevix nevertheless received the Copley Medal in 1803 after publishing his experiments, a recognition that must have stung Wollaston. It was not until 1804 that Wollaston published his discovery of a related metal, rhodium, and mentioned some of his palladium work. Full credit came only in 1805, when he finally disclosed in print that he was the discoverer of palladium. The method Wollaston used to isolate it reveals how close platinum and palladium are in nature. He dissolved crude platinum ore in aqua regia, neutralized the solution with sodium hydroxide, and precipitated platinum out using ammonium chloride. Then he added mercuric cyanide to form palladium cyanide, which he heated to extract the pure metal. That process of subtraction by subtraction left palladium as the residue of a residue.

• 3. The Lightest of the Platinum Metals

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  Palladium belongs to a family of six elements known collectively as the platinum group metals: platinum, rhodium, ruthenium, iridium, and osmium share the group with it. Among all six, palladium holds a particular distinction. It has the lowest melting point and is the least dense member of the family. It is soft and ductile when annealed but becomes significantly stronger and harder when cold-worked. It dissolves slowly in concentrated nitric acid and in hot concentrated sulfuric acid, and when finely ground it will dissolve in hydrochloric acid. At room temperature it does not react with oxygen and therefore does not tarnish in air. Heat palladium to 800 degrees Celsius, however, and a surface layer of palladium oxide begins to form. That behavior under heat matters in jewellery making, where temperatures above 400 degrees Celsius can cause discoloration through oxidation, making the metal more brittle. Its electronic structure is just as unusual. Palladium sits in group 10 of the periodic table, but its outermost electrons behave differently from what standard rules would predict. Rather than occupying the 5s orbital as the Madelung rule would suggest, they fill the 4d orbitals instead, because a completely filled 4d shell is energetically favorable. This makes palladium the heaviest element in period 5 with only one incomplete electron shell.

• 4. The Catalytic Converter Dependence

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  More than half of the world's supply of palladium flows into a single application: the catalytic converter fitted to automobile exhaust systems. These devices convert as much as 90 percent of the harmful gases in exhaust, including hydrocarbons, carbon monoxide, and nitrogen dioxide, into nitrogen, carbon dioxide, and water vapor. That transformation depends on palladium's properties as a catalyst. When finely divided, as in the form palladium on carbon, it accelerates heterogeneous processes including hydrogenation, dehydrogenation, and petroleum cracking. In 2010, the Nobel Prize in Chemistry recognized the significance of palladium's catalytic role when it was awarded to Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki for palladium-catalyzed cross-couplings in organic synthesis. Those reactions are widely practiced for the synthesis of fine chemicals. The coupling reactions named after these researchers and others, including the Suzuki, Stille, Sonogashira, and Kumada couplings, all depend on palladium compounds as catalysts or precatalysts. By 2017, global palladium sales of roughly 8.84 million troy ounces saw 86 percent directed into automotive catalytic converters. That concentration of demand in one sector creates enormous vulnerability. Catalytic converters are also targets for thieves, precisely because they contain palladium and other rare metals.

• 5. Geopolitics of Supply

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  Russia's company Norilsk Nickel ranks first among global palladium producers, accounting for 39 percent of world production. The most important commercial sources are the Norilsk-Talnakh deposits in Siberia and the nickel-copper deposits found in the Sudbury Basin in Ontario. The Bushveld Igneous Complex in South Africa, the Stillwater Complex in Montana, and the Lac des Iles complex in Ontario make up most of the rest. That geographic concentration has produced genuine crises. In the run-up to the year 2000, Russia's palladium exports to the global market were repeatedly delayed and disrupted; for political reasons, the export quota was not granted on time. The resulting market panic drove the price to an all-time high, at that point, of 1,340 dollars per troy ounce in January 2001. The Ford Motor Company, fearing that automobile production would be disrupted, stockpiled the metal heavily. When prices fell in early 2001, Ford lost nearly one billion US dollars on that position. World demand for palladium had grown from 100 tonnes in 1990 to nearly 300 tonnes in 2000. Russia's annexation of Crimea in 2014 revived supply fears, pushing prices to their highest since 2001 and above 900 dollars per ounce in September of that year. By January 2019, palladium futures climbed past 1,344 dollars per ounce. Palladium reached 2,024.64 dollars per troy ounce on the 6th of January 2020, and the price rose above 3,000 dollars per troy ounce in both May 2021 and March 2022. The all-time high of 2,981.40 dollars per troy ounce was recorded on the 3rd of May 2021. A later surplus was caused by the Russian government selling Soviet-era stockpiles at a rate of roughly 1.6 to 2 million troy ounces a year, though the total size of that stockpile remains a state secret.

• 6. Hydrogen, Cold Fusion, and Medicine

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  Palladium has a uniquely high capacity to absorb hydrogen at room temperature, forming palladium hydride. It does not lose its ductility until the hydrogen-to-palladium ratio approaches 1. This property made palladium a key component in the controversial cold fusion experiments of the late 1980s, and it has also attracted sustained interest as a possible basis for hydrogen fuel storage, though palladium's expense has so far made that application impractical. Hydrogen diffuses easily through heated palladium, and membrane reactors with palladium membranes are used in the production of high-purity hydrogen. There is a medical dimension to the element as well. Palladium is used in small amounts, about 0.5 percent, in some dental amalgam alloys, where it decreases corrosion and increases metallic lustre. It is also used in pacemakers. Historically, palladium chloride was prescribed as a tuberculosis treatment at a rate of 0.065 grams per day, roughly one milligram per kilogram of body weight. That treatment carried many negative side-effects and was eventually replaced by more effective drugs. More recently, in 2017, effective catalytic activity of palladium nanoparticles was demonstrated in mammals as a tool for treating disease.

• 7. Jewellery and the Investment Market

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  Palladium has been used as a precious metal in jewellery since 1939, introduced as an alternative to platinum in the alloys called white gold. Its natural white color means it does not require rhodium plating, unlike some other white gold alloys. Being much less dense than platinum, palladium can be beaten into leaf as thin as 100 nanometers. When platinum became a strategic resource during World War II, jewellery bands were commonly made from palladium instead. The casting difficulty that had limited its wider use was eventually resolved, and by the time gold and platinum prices rose steeply in early 2004, China began fabricating palladium jewellery at significant volume, consuming 37 tonnes in 2005. As the relative price of platinum shifted again, demand fell to 17.4 tonnes by 2009. In January 2010, hallmarks for palladium were introduced by assay offices in the United Kingdom, with hallmarking becoming mandatory for all jewellery advertising pure or alloyed palladium. Articles can be marked as 500, 950, or 999 parts of palladium per thousand of the alloy. Palladium also carries ISO currency codes XPD and 964, making it one of only four metals, alongside gold, silver, and platinum, to hold such codes. WisdomTree Physical Palladium, listed on the London Stock Exchange as PHPD, was the world's first palladium exchange-traded fund. Available bullion coins include the Canadian Palladium Maple Leaf, the Chinese Panda, and the American Palladium Eagle, though liquidity in direct palladium bullion remains lower than for the other three precious metals.