More than you ever wanted to know about Catalytic Converters

I have seen a few posts about catalytic converters so I thought I would post what I know about them.

First, recycling catalytic converters is hard work, just like any other type of scrapping. It's not something you are going to get rich on fast, but you can make a very good living scraping them if you know what you are doing.

I am going to start with the different types of catalytic converters, and try to cover most of the information pertaining to the different types.

Oxidation catalysts

Oxidation catalysts convert carbon monoxide and hydrocarbons to carbon dioxide and water, but have but have almost no affect on nitrogen oxides. The early versions of catalysts in the USA, installed in the mid-seventies, were oxidation catalysts, containing Pt and/or Pd but no Rh.

Here is a picture of an oxidation catalyst



Three-way catalysts

This is the most common type of catalyst found on gasoline engines. The term ‘three-way’ means that it uses three different methods to reduce emissions (oxidation of CO into CO2, oxidation of HC into CO2 and H2O, reduction of NOx into N2, CO2 and H2O). Three-way catalysts operate in a closed-loop system including a oxygen sensor to regulate the air-fuel ratio.

The original three-way catalyst used the combination of Pt and Rh, typically in a 5:1 ratio, Newer three-way converters use different formulas, including Pt/Pd/Rh, Pd/Rh, Pd only, etc.

Here is a picture of a typical Three-Way Catalyst, notice the three different honeycomb structures, this is how you can tell it's a three way, three different catalytic honeycombs that each do a different function:





NOx adsorber catalysts is designed to adsorb NOx while operating in lean-burn condition. At regular intervals, the engine will be switched for a short time to rich conditions, which release the NOx (allowing the adsorber to regenerate) and reduce it to N2.

The adsorber function of such a catalyst is typically taken care of by particular rare earth oxides in the washcoat formulation, which allow storage of NO2 under lean engine operation conditions. The precious metal content of such an adsorber brick is not affected.

Umicore was the first catalyst manufacturer to supply the NOx adsorber catalyst technology for vehicles.

Here is a picture of a NOx adsorber, this one for a Cummings:



Diesel Particulate Filters (DPF)

Diesel Particulate Matter (often abbreviated as Diesel PM) refers to small solid particles, some of very small size, resulting from the burning of diesel fuel. These particles not only contain soot, but also hydrocarbons, ashes and sulphuric acid (resulting from the fuel’s sulphur). Although a diesel catalyst destroys most of the organic fraction of particulate matter, it does not affect the number of particles, so health issues related to ultra-fine particulates remain unresolved.

A diesel particulate filter (DPF) will act as a filter for these small particles. Ceramic wall flow filters (or traps) contain channels which are one-ended only, forcing the off-gas to find its way through the porous walls between the channels. PM will be stopped by this solid medium. On regular intervals, the filter has to be regenerated. Since most of the PM is carbon, the carbon needs to burn with air. This is initiated by lowering the temperature at which the carbon reacts with air: by using a variety of techniques such as a fuel additive (e.g. the EOLYS® from Rhodia) or through the presence of a precious metal in the diesel particulate filter (such as Pt; these DPFs are then called catalysed DPFs) or through electrical heating of the trap on or off the vehicle

HINT: Not all Diesel Particle Filters contain precious metals.

Here is a picture of a Diesel Particle Filter:



Diesel oxidation catalysts

A diesel engine always runs ‘lean’, i.e. with excess air. Therefore, a diesel catalyst operates as an oxidation catalyst only. Oxidation catalysts achieve significant reductions in CO, HC and destroy the organic fraction of the particulate matter (as it does the typical diesel smell). Diesel oxidation catalysts used to contain Pt only. In 2004 however, Umicore announced the development of diesel catalysts, whereby Pd has substituted some of the Pt.

HINT: Diesel oxidation catalysts contain no Rh. A large portion of diesel catalysts in a mixed load will have an adverse effect on the Rh assay\

Here is a picture of a Diesel oxidation catalysts:



Selective Catalytic Reduction (SCR)

This technique, originally developed for stationary emission control from power plants, is aimed at reducing NOx (by conversion to nitrogen) in heavy-duty and light-duty diesel engines, by using ammonia or ammonia precursors as reductants in combination with excess oxygen.

HINT: SCR units never contain precious metals.

Here is a picture of a Selective Catalytic Reduction, this one is actually mine and scrubs far more than just NOx:



NOx adsorber for diesel engines

Particular washcoat formulations will allow for accumulation and storage of NOx during a particular period of time under which the engine operates under lean-burn / excess air conditions. Then, for a short period of time, either through the injection of excess hydrocarbons / fuel (for common-rail diesel engines) or excess fuel conditions (for lean-burn gasoline engines), the stored NOx will be reduced and, as such, eliminated.
Other

Emission control catalysts are not only found on cars and trucks, but also on 2-wheelers and 3-wheelers as well as pollution abatement systems for stationary source emission control (engines and turbines for heat or power generation, off-gas in certain process industries, lawnmowers and other utilities, etc).

Here is a diagram of a NOx adsorber for diesel engines:



HINT: Most of the above usually contain precious metals and are therefore worthwhile to be recycled. Also, I have recently seen a few assays where the catalytic material also contained Ruthenium, if you are assaying and having the catalytic material processed yourself, this might be something to look for, it makes the value of the material worth more.

SOURCE: http://www.autocatalyst-recycling.um...yticConverter/

This is a document that describes the approximate values contained in each type of catalytic converter, with pictures.

This is by no means a definitive document, the values may be different than what you see. This is because sometimes some of the material is blown out, or the catalytic converter was made in a different year and the standards changed. Regardless, this document can give you a good idea of what catalytic converter has in PGM content, virgin. Please keep in mind this pertains to European cats, catalytic converters in the US will be different.

https://dl.dropbox.com/u/56505223/Re...Converters.pdf

Here is the American version of this catalog, or as best as I am able to provide at this time. I have another document somewhere and will post when I find it. This also has other information pertaining to scrapping cars, and how to sell on ebay, all very good information.

https://dl.dropbox.com/u/56505223/Re...gm-content.pdf

Here are some pictures and diagrams on catalytic converters that might be of some interest.

This is honeycomb material still in the can:



This is catalytic honeycomb removed from a can, but not well used, you can tell by the color it's light brown instead of grey or dark grey:



Here is an example of the ceramic honeycomb before it's coated with the catalytic metals:



Here is some well used catalytic material before ball milling and incineration:



Here is a mock up side cut of a catalytic converter that contains beads:



Here is a close up of catalytic bead material:

https://dl.dropbox.com/u/56505223/Ca...verters/12.jpg

This is a two stage catalytic converter, notice only two honeycomb bricks:



This is a three stage catalytic converter:



This is your basic exhaust setup:

Some pointers when scrapping cats

Make sure that both ends are cut off so the scrap yard can see the honeycomb inside

If possible, identify what car each cat came off of, this helps in pricing

It's best not to decan the catalytic material, you will get more money with the catalytic converter intact, also remember that the can is made out of stainless steel, you should be getting paid on that as well

Most refineries that purchase catalytic material do not process themselves, they pass it along to another refiner that specializes in this type of material.

It's better to sell to an end refiner, rather than a scrap yard. If possible it's even better to represent your own material, you will make a far better profit doing so

Another way you can sell your catalytic converters is by decanning and selling the beads or honeycomb on ebay. This makes it cheap to ship. You may or may not make more money this way. If you learn about catalytic converters, you can even separate out the different types of bricks that contain different types of PGMs, and post this in your action. For example, in a three way converter, some of the honeycomb contains more platinum, some contains some rhodium. Knowing this and posting in your auction may make your auction more attractive to buyers. This is one of the only times I would even think about decanning.

The other time you may want to decann is if you live far away from anyone who buys this type of material and you need to ship it. Decanning might be a better way to ship if the cost of shipping is more than the amount you will loose because the refiner cannot tell what type of converter your catalytic material came out of.

As I think of more tips I'll post them here, I hope if other members have tips they will also post here.

Scott

If you decide to have your converters processed by a refiner, this is an example of how it would be done, and the methods used to do so:

decanning of ceramic converters

The decanning of (ceramic) catalytic converters, containing ceramic honeycomb bricks, involves opening the converter in order to separate the ceramic brick (or broken brick) from the steel can. This type of operation is mostly done by some form of hydraulic shear. Alternative processes include a plasma burner or a disc saw, but the latter two processes are usually limited to small quantities.

shredding of metallic converters

The shredding of (metallic) catalytic converters, containing a metallic substrate (rolled up corrugated foil), itself coated with a thin layer of metal oxides (washcoat), is achieved by passing it through one or more different types of shredders, zerdirators, hammer mills, followed by separation of various fractions of steel scrap (such as can-fraction, foil-fraction) from the precious metal containing fraction (washcoat)..

weighing and sampling of ceramic honeycomb or washcoat

Making sure that material is accurately weighed and sampled - thereby providing correct weights, moisture content and representative samples for assaying - is one of the most important steps in an assay-based transaction. The sample must be a good, homogenous, representative example of your material.

Representative samples should be assayed by both the refiner's lab and by a lab you choose. Assays from both labs can then be exchanged and compared, leading to settlement by splitting the difference or, if this is too large, relying on assays by a third party, or umpire assay.

Each recycling lot shipped to a refiner should be settled with you based on the agreements and contract agreed upon beforehand. These contracts should consider the values from recovering the (precious) metals on the one hand and the efforts needed to do this (including off-gas and waste water treatment) on the other. You should receive detailed documentation, which states the weights and quality of materials received.

needs to be a sticky, excellent post

Originally Posted by zito

Thanks for all this information! A question I have is on the document that lists the PM content of converters. Are those values expressed in ounces? That's what I'm guessing it is, but would like to confirm. Also, I believe that's a European document, either with some American cats added, or perhaps those are American cats also used in European models. In any case, is there a difference between EPA and European emission standards, and if there is a difference, do you know how it would affect the converters and values shown? Thanks again.

Good questions.

It is a European document, I am looking for the American counterpart, I have it somewhere I just need to locate it. The numbers are relative to new cats, how much they contain when they are installed, new. This will not account for cats that have been "blown out" or any other material that has been lost while in use. Also keep in mind that usually only about 70% of the total PGMs are extracted. This is due to the fact that the precious metals are coated onto alumina silicates that have a honeycomb structure themselves. This makes it difficult to remove unless very dangerous methods are used. The big refiners, like BASF and Johnston Matthey, use what is called submersible arc furnaces to break the alumina silicates so that they can extract more, but even they are not getting the total amount. This document is only to express potential values, not to base what you sell your cats for, in other words it can be used as a guide, but these values will not exist in a used cat, and not all of the values are recoverable.

The values are expressed thus,

The red brackets are in cm, this is to easily identify the cat

The larger number in grams, like in picture one for example, 230g is the weight of the honeycomb, virgin

The metals are expressed in ounces, you are correct.

***** Updated the original post above with a link to another document I had on American Catalytic Converters *****

AWESOME set of Posts! Much thanks. Far more than I ever knew about Cats. Thank you for taking the time to put all of this together.. AND share it with us!!