What are the precious metals in a catalytic converter

A catalytic converter is a device used to convert toxic vehicle emissions to less harmful substances by way of catalyzed, or accelerated, chemical reactions. Most present-day vehicles that run on gasoline, including automobiles, trucks, buses, trains, motorcycles, and planes, have exhaust systems employing a catalytic converter.

The catalyst component of a catalytic converter is usually platinum (Pt), along with palladium (Pd), and rhodium (Rh). All three of these platinum group metals, or PGMs, are extremely rare but have a broad range of applications in addition to catalytic converters. Platinum, for example, is used in laboratory and dental equipment, electrical contacts and electrodes, and jewelry, while palladium plays a key role in fuel cell technology. With numerous applications and limited supply, these valuable metals are an attractive target for recovery and reuse from spent catalytic converters.  In 2010, the total value of Pt, Pd, and Rh reclaimed from the recycling of spent catalytic converters was $3 billion.

Determining the recovery value of the PGMs in a catalytic converter begins with knowing the composition and ratios of the metals used.  Automotive catalyst material is made either of a ceramic substrate, mostly cordierite coated with a precious metal containing a wash coat, or of a metallic substrate with an aluminum oxide wash coat also containing precious metals.  The average concentration and the ratio of Pt and Rh were more or less constant 20 years ago, so a simple weighting was sufficient to arrive at a good estimation of the precious metal content. However, the price of these three elements has fluctuated strongly over the last 20 years, depending on the supply, demand, and speculation. These variations, as well as the tightening of emission legislation, have had a direct correlation on the composition of the catalysts, which themselves have had a strong influence on demand.

Currently, the composition, which depends on the engine displacement and the type of fuel used, varies dramatically. The formulation can consist of only Pt, or various ratios of Pt-Pd-Rh, Pt-Rh, and Pd-Rh. Most of today’s recycled catalytic converters come from cars manufactured, on average, 10 to 15 years ago. The recoverable amounts of Pt, Pd, and Rh in each can range from 1-2 grams for a small car to 12-15 grams for a big truck in the US.

The corresponding value in recoverable PGMs ranges from $25 to a few hundred dollars per vehicle. Moreover, the trade of ground-up material sold as catalysts can be very dangerous because of possible alterations, which can mean inclusion of lead or spent nickel-cadmium batteries.

To avoid considerable financial losses, companies need to quickly and accurately determine the contents of Pt, Pd, and Rh in spent catalytic converters at the collector’s site or in the refineries. But there is no technique for analyzing non-homogeneous materials like catalytic converters directly without sample preparation. Therefore, the collected catalysts with ceramic substrate undergo a “de-canning” operation, which is the extraction of the honeycomb-structured ceramic material from the steel case. All of the ceramic is then sorted crushed, milled, and mostly blended with other catalysts. In contrast, converters with a metallic substrate are first shredded or milled, and then the metallic parts are separated using magnets and winnowing from the wash coat powder containing precious metals. Because of this enrichment, the PGM content of these wash coat samples is usually much higher than that for milled ceramics. In both cases, the materials are pulverized to a maximum 250µm and loaded into sample cups or sample bags for analysis, and then analyzed using x-ray fluorescence (XRF) technology.

A recent study evaluated x-ray fluorescence (XRF) analysis as compared to lab assays for achieving this objective. To see the results, including the correlation curves, repeatability data, methodology, and comments, read  Automotive Catalytic Converters application summary.

Truth be told, the answer is in fact, in the question itself. Catalytic converters are valuable because they contain three precious earth metals: Platinum, Palladium, and Rhodium. All three belong to Platinum Group Metals (PGMs) and contain similar chemical properties and physical attributes.

There are six elements that comprise Platinum Group Metals and all six elements are most valued for their wide range of applications within automotive, medical, electronic, and industrial fields. So why are converters loaded with metals within the group?

Emission pollutants from gasoline vehicles are damaging to air, soil, and water. The catalytic converter’s function is to create a chemical reaction that changes these emissions into less harmful gasses and reduce pollution. Platinum, palladium, and rhodium are the precious metals used within a converter acting as the catalyst to transform emissions such as carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful off gasses.

Platinum and Palladium are traded as a commodities in global stock markets, there are multiple purchasers of these metals, therefore, prices fluctuate according to supply, demand, and are speculated on. In addition to catalytic converter manufacturing, platinum and palladium have a wide range of end uses within medical tools and applications, electrical manufacturing as well as jewelry fabrication to name a few. In other words, end buyers of these two metals emerge from a multitude of industries.

Rhodium is much more focused with its application in the automotive and industrial market. 80% of all Rhodium is used in automotive sector while the remainder is used in industrial applications for reducing harmful fossil fuel emissions.  Rhodium is one of the rarer of the rare earth metals and as such is not bought and sold on open world market exchanges. Buyers and sellers of Rhodium are directly acting with each other, meaning transactions between end users of the metals and those responsible for production are where prices are determined. These prices are often reported in ranges, actual sale prices are subject to the sellers price offer.

As a catalytic converter contains all three metals, the value of any one unit can fluctuate every minute according to the metal market and the supply, demand and speculation that influences platinum, palladium, and rhodium prices.

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