Rhodium in catalytic converters and other uses

Uses for Rhodium

Rhodium is used to make electrical contacts, as jewelry and in catalytic converters, but is most frequently used as an alloying agent in other materials, such as platinum and palladium. These alloys are used to make such things as furnace coils, electrodes for aircraft spark plugs and laboratory crucibles.

History of Rhodium

Rhodium was discovered by William Hyde Wollaston, an English chemist, in 1803 shortly after his discovery of the element palladium. He obtained rhodium from a sample of platinum ore that was obtained from South America. After removing the platinum and palladium from the sample, he was left with a dark red powder. The powder turned out to be sodium rhodium chloride (Na3RhCl6·12H2O). Wollaston obtained rhodium from the powder by treating it with hydrogen gas (H2). Rhodium tends to occur along with deposits of platinum and is primarily obtained as a byproduct of mining and refining platinum. Rhodium is also obtained as a byproduct of the nickel mining operation. Rhodium, together with rutheniumpalladiumosmiumiridium, and platinum form a group of elements referred to as the platinum group metals (PGM). It is lustrous and silvery white in colour. Rhodium has a higher melting point and lower density than platinum. It has a high reflectance and is hard and durable. Upon heating it turns to oxide when red and at higher temperatures turns back to its element. Rhodium is unaffected by air and water up to 600 C. It is insoluble in most acids, including aqua regia, but is dissolved in hot concentrated sulfuric acid and it is attacked by molten alkalis.

 

Applications     

Most metal (85%) goes into catalytic converters for cars. The major use of the metal is in alloys with platinum and iridium. Which gives improved high-temperature strength and oxidation resistance. These alloys are used in furnace winding’s, pen nibs, phonograph needles, high-temperature thermocouple and resistance wires, electrodes for aircraft spark plugs, bearings and electrical contacts.  The metal itself is used to plate jewelry and the reflectors of searchlights, due to its brilliance and resistance to tarnish. It is also a highly useful catalyst in a number of industrial processes.

 

Health effects of rhodium

Rhodium compounds are encountered relatively rarely by most people. There are almost no reported cases of human being affected by this element in any way. All rhodium compounds should be regarded as highly toxic and as carcinogenic. Compounds of rhodium stain the skin very strongly. Flammable. Dust explosion possible if in powder or granular form, mixed with air. Reacts with oxygen di-fluoride causing fire hazard. Routes of exposure: The substance can be absorbed into the body by inhalation of its aerosol. Inhalation risk: Evaporation at 20°C is negligible; a harmful concentration of airborne particles can, however, be reached quickly when dispersed. Health effects of exposure to the substance have not been investigated. Insufficient data are available on the effect of this substance on human health, therefore utmost care must be taken.

 

Environmental effects of rhodium

Do not allow the material to be released into the environment without the proper governmental permits. Rhodium is too rare for the amount of it in soils or natural waters to be assessed. So its effect on the environment can be assumed to be nil. Tests on plants have shown that it is the least toxic member of the platinum group of metals. To find out more about the pricing of Rhodium for extraction and recycling purposes.

Palladium in catalytic converters

What are the primary uses and applications for palladium?

Palladium in catalytic converters. The manufacture of catalytic converters continues to be the primary use for palladium, with its consumption accounting for approximately 66% of forecast global demand in 2015 (CPM Group Platinum Group Metals Yearbook, 2015). Other major sources include: electronics (14%), dental (8%), jewellery (5%), petrochemical refining (5%) and a range of other, minor industrial applications (2%).

What are the common properties of PGMs?

Palladium is one of the six platinum group metals (PGMs), consisting of: platinum, palladium, osmium, ruthenium, iridium and rhodium. Of the six, palladium has the lowest melting point and is the least dense. PGMs are known for their:

  • Strength and durability

  • Strong catalytic properties

  • Resistance to oxidation and corrosion

  • Conductivity and ductility

  • High melting point

  • Geological scarcity (much rarer than gold)

PGMs are most commonly used for technological advances in the fields of autocatalysts, power generation, alternative fuel sources, transportation, electronics and healthcare. Growing and anticipated future applications for palladium include fuel cells, hydrogen gas generation from natural gas, nano technology and super-capacity hard drives.

 

 

How do the different engine types impact the use of palladium in catalytic converters?

  • Petrol engines: use more than 90% palladium in catalytic converters.

  • Diesel engines: historically used platinum due to technical requirements, however now use approximately 30% palladium, with a scope to increase to 50% due to the introduction of low sulphur diesel fuel.

  • Hybrids & other new power forms: expected to account for <1% of global cars sales in 2015 with a recent decline in popularity noted in the 2015 sale figures for most hybrid vehicle manufacturers.  Expected to have a neutral impact on PGM use as petrol hybrids tend to use as much palladium as normal petrol engines.

  • Electric: forecast to account for <1% of global car sales in 2015; have no requirement for catalytic converters therefore would have a negative impact on PGM use. Given their current challenges (lack of infrastructure to recharge, high costs, long charging periods and short driving range) and the recent decline in global oil prices, electric vehicles are not expected to be major threats to fabrication demand in the next decade.

What are the current trends in palladium consumption for jewellery?

China remains the largest consumer of platinum and palladium jewellery. Palladium jewellery was introduced to China in 2004 in the form of Pd950 (95% palladium) and in 2005 in the higher purity Pd990 (almost pure palladium) opening up a brand new market. Its lower cost compared to platinum, has made palladium more accessible to more consumers.  Most Chinese manufacturers now have the technical ability to work with palladium and combined with low palladium lease rates, benefit from the greater margins from the metal.  Recent price-driven declines in palladium (and platinum) demand for jewellery in China and globally have been more than offset by increased demand in the auto catalyst manufacturing sector (see CPM Group Platinum Group Metals Yearbook, 2015).

What is the impact of the palladium ETFs?

Palladium exchange traded funds (ETFs), which have only been around since 2007, have significantly contributed to the increased investor interest in palladium. These ETFs are now trading in Zurich, London, Japan, Johannesburg and New York. Global ETFs’ holdings recently peaked at approximately 3 million ounces of palladium in physical form although recent outflows have reduced this amount to approximately 2.4 million ounces.  Looking ahead and assuming a balance between industrial demand and primary and scrap/secondary supply, major changes in global ETF holdings are likely to play an increased role in determining palladium prices in the future.

Catalytic Converter Basics: Key ingredients that make catalytic converters tick.

It takes a precise combination of precious metals to help make catalytic converters an effective method for emission control.

Here’s how they work:

Vehicle exhausts contain three harmful pollutants, which are formed due to inefficiencies in the fuel combustion process.

Ceramic substrates are coated with a washcoat containing precious metal catalysts prior to installation into the converter can.

Hydrocarbons (HC) and carbon monoxide (CO) are formed as a result of the incomplete combustion of petrol. Oxides of nitrogen (NOx) are created from the burning of the nitrogen present in the intake air at the high temperatures and pressures encountered in the

cylinders during ignition. HC and NOx are major contributors to smog formation, and CO reduces the ability of the blood to pick up and transport oxygen through the body. As a result, catalytic converters were developed as an after-treatment to reduce these harmful emissions. Platinum, palladium, and rhodium have historically been the key active components used in these catalytic converters.

These precious metals are unique in their ability to facilitate the reactions of HC and CO with oxygen to produce water and carbon dioxide and to promote the reaction of CO with NOx to convert the NOx to harmless nitrogen gas. With the combination of a properly tuned engine and a properly designed catalytic converter, it is theoretically possible to have complete removal of these pollutants. The precious metals are typically dispersed in a washcoat, which is then coated on a flow-through ceramic or metallic substrate which supports them in the exhaust stream. The washcoat contains various components and additives to promote the activity and durability of the precious metals. Exhaust gasses pass through the catalytic converter substrate, which is coated with a washcoat containing platinum (Pt), palladium (Pd), or rhodium (Rh). Hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx) in the exhuast are converted to carbon dioxide .(CO2), nitrogen gas (NOx) and water vapor (H2O).

These three precious metals each have their own unique properties that come into play in determining which ones must be used for a particular application. Platinum is a very good oxidation catalyst and has good resistance to poisons such as sulfur, phosphorus, or lead, which may be 
present in the exhaust. Two drawbacks to platinum are its low activity for the conversion of NOx and its high price relative to palladium. In addition, platinum is sensitive to the high temperatures which may occur in the catalytic converter during high engine loads. Palladium, which is currently the cheapest of the three metals, has excellent activity for the oxidation of hydrocarbons as well as very good thermal durability. In addition, with a well-designed washcoat, palladium can have very good activity for the removal of NOx. Drawbacks to palladium include its sensitivity to poisons. Rhodium, currently the most expensive of the three, has by far the highest activity for the removal of NOx from the exhaust. In addition, it has significant activity for the oxidation of HC and CO and very good resistance to the poisons present in the exhaust stream. Its primary drawback is its high cost. Most catalytic converters today consist of some combination of palladium and rhodium. With current precious metal prices, this gives a good trade-off between cost and performance. While efforts continue to find cheaper alternatives to the precious metals, the tightening aftermarket and OEM emission standards make it likely that they will remain the key components of catalytic converters in the future.

Platinum in a catalytic converter?

 Platinum amounts differ in catalytic converters significantly, depending on the year the catalytic converter has been made and of course the type of vehicle it is used in. Small cars for instance will have less, than say larger vehicles such as trucks for example. Catalytic converters are composed of elements which are essentially alike. However there is a broad variant in the metallic makeup and consistency. Catalytic converter size and constitution is reliant on engine displacement and the type of fuel that vehicle uses. Differing market prices of platinum extraction on catalytic converter recycling with the inclusion of supply and demand fluctuating over the years. Has impacted the quantity of platinum used in the manufacturing of  catalytic converters over the years. Catalytic converters are part of the vehicles exhaust system and are used in internal combustion engines. Whether these are fueled by petrol or diesel. The platinum in the catalytic converter’s purpose is to speed up the chemical reaction used to convert damaging car emissions into less detrimental substances.