Ce in car cats for oxygen storage

Introduction

Ce is the most common rare earth element and usually seen as non-critical (3), but has also been classed as “near critical” in the short term by the US Department of Energy due to its importance to clean energy technologies in combination with projected supply risks (7) (citing (8)). Its abundance is similar to that of copper (5). However, it is still one of the eight rare earth elements of highest economic interest (alongside lanthanum, neodymium, praseodymium, samarium, dysprosium, europium and terbium) (5) Common applications include lens polishes, petroleum refining, metal alloys and automotive catalysts (6, 7).

Ce used in automotive catalysts

Automotive catalysts convert toxic exhaust fumes into less harmful fumes. Hydrocarbons (CmHn) carbon monoxide (CO) and nitrous oxides  (NOx)are converted into CO2; H2O and N2 via redox reactions (2).

In order for the process to work efficiently, a certain operating temperature, a large surface area and a certain level of oxygen are necessary. In the first few minutes of the engine warm-up phase, the operating temperatures are still too low for the process to work well, which results in most emissions being released in this phase (1). The required surface area is often achieved by a honeycomb structure made from ceramic or stainless steel and coated with aluminum oxide, rare earth oxides and platinum group metals which act as catalysts (2). Three-way catalysts use ceria compounds for oxygen storage (4). The compounds act as a buffer by absorbing and releasing oxygen, thereby helping to generate the required stoichiometric conditions for the redox transformations to work (4). The cerium is oxidized “by default”, but capable of absorbing further oxygen in an oxygen-rich atmosphere, thereby helping to increase the efficiency of the nitrogen oxide reduction process (2). The stored oxygen is released again when needed, which again helps the oxidation of carbon monoxide to work more efficiently (2). The process is supported by sensors which measure the oxygen content and the air-to-fuel ratio is adjusted accordingly (10, 4). It may be interesting to mention that it has been suggested to utilize the oxygen buffer capacity of cerium oxides in medical applications, too. Scientists at Rice University found that the use of cerium oxide as an antioxidant aimed at damaging reactive oxygen species could help treat traumatic brain injuries, cardiac arrest and Alzheimer’s patients and help with radiation-induced side effects suffered by cancer patients (9).

Furthermore, organic cerium compounds added to diesel fuel help promote soot combustion and thereby help avoid the clogging of diesel particulate filters (4).

The conversion efficiency rates of cats (for hydrocarbons, carbon monoxide and nitrogen oxides) lie at around 98% (10). The use of rare earths in automotive catalyst applications has helped to improve their performance greatly and may help further enhance the exhaust fume control and fuel efficiency in future (4).

Cat recycling activities

Monoliths (the previously described honeycomb structures in automotive catalysts) are recycled, which is primarily due to the fact that they contain platinum group metals. BASF, Umicore and Johnson Matthey, for example, refine precious metals from cats (11, 12, 13). Used cats provide a valuable recycling stock at 75-250 $ per piece (2010 figures) (2). Existing commercial-scale recycling processes do not currently recover cerium compounds, which are disposed of with the slag (2). However, proactive research on the recovery of cerium compounds from cats is being undertaken to prepare for potential future cerium supply shortages and/or price increases, and 70% recovery rates have been achieved in small scale experiments (2).

References

1)    GSF & Flugs (2004): Katalysatoren in Kraftfahrzeugen – Freund oder Feind für Umwelt und Gesundheit?

2)    Bleiwas, D.I., USGS (2013):  Potential for recovery of cerium contained in automotive catalytic converters; Open-File Report 2013–1037; U.S. Department of the Interior, U.S. Geological Survey.

3)    Hatch, G. P. (TMR, LCC) (2011): Critical Rare Earths Global supply & demand projections and the leading contenders for new sources of supply.

4)    Shinjoh, H. (2006): Rare earth metals for automotive exhaust catalysts, Journal of Alloys and Compounds 408–412, 1061–1064

5)    Massari, S.; Ruberti, M. (2013): Rare earth elements as critical raw materials: Focus on international markets and future strategies, Resources Policy 38, 36–43

6)    Hayes-Labruto, L,  Schillebeeck, S.; Workman, M., Shah, N. (2013): Contrasting perspectives on China’s rare earths policies: Reframing the debate through a stakeholder lens, Energy Policy 63, 55–68

7)    Weber, R.J., Reisman, D.J. (2012):  Rare Earth Elements: A Review of Production, Processing, Recycling, and Associated Environmental Issues

8)    US Department of Energy (2011): Critical Materials Strategy – Summary

9)    Phys.org (2013): Scientists create a super antioxidant: Common catalyst cerium oxide opens door to nanochemistry for medicine Oct 15, 2013 http://phys.org/news/2013-10-scientists-super-antioxidant-common-catalyst.html, accessed 09th April 2014

10) BASF (2014): How Catalytic Converters Work http://www.catalysts.basf.com/p02/USWeb-Internet/catalysts/en/content/microsites/catalysts/prods-inds/mobile-emissions/how-it-works , accessed 09th April 2014

11) BASF (2014): Autocatalyst Recycling http://www.catalysts.basf.com/p02/USWeb-Internet/catalysts/en/content/microsites/catalysts/prods-inds/prec-metal-svcs/autocat-recycling?mid=0, accessed 16th April 2014

12) Johnson Matthey (2014): Refining and Precious Metal Management Services http://matthey.com/whatwedo/productsandtechnologies/refiningandmanagement, accessed 23rd April 2014

13) Umicore (2014): Excellence in Recyclinghttp://www.preciousmetals.umicore.com/PMR/; accessed 23rd April 2014

Europium (Eu) used in TVs and lamps

Introduction: Europium
Although Europium is one of the light rare earth elements (USGS definition) which tend to be more abundant than the heavy rare earths, it is one of the most expensive rare earth elements and has been classed as one of the critical rare earths(2). Shortages have been predicted with a high degree of probability (3). Due to the high prices of europium and terbium, lighting and display systems constitute one of the most economically relevant rare earth applications (4).

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How dangerous are strong neodymium magnets?

Dear Reader,

All of us use the magnets in a daily life, but do we really pay an attention on that? When you switch a cell phone to vibrate mode, the fast movement and corresponding sound that you hear in a consequence is caused by a miniature Nd magnet inside the phone. If you are a teenager or huge fan of high-tech or addicted from music, I am almost sure that you have the most modern headphones ever, but did you know that this great sound quality as well as a full spectrum of bass is improved by Nd magnets? Yes, this is one of their applications as well. Regarding very popular since a while term ECO, users of hybrid and electric vehicles should know that their cars often use high-strength Nd magnets to power the vehicles’ DC motor. Moreover, wind turbine generators depend on NdFeB magnets in order to produce electricity. Besides these we can find Nd magnets in office supplies, jewelry, toys, machines, tool, etc.. They are simply around us! But do we really know how to use them properly? Do we really know what are they capable of? Do we take into account that they may be dangerous?

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