Catalyst Basics: Platinum, palladium, and rhodium – key ingredients that make converters tick
By: Dr. Jeff Rieck
Senior Technology Manager, Johnson Matthey

Automotive exhaust contains three harmful pollutants, which are formed due to inefficiencies in the fuel combustion process…

Here’s how they work:

Automotive exhaust contains three harmful pollutants, which are formed due to inefficiencies in the fuel combustion process. Hydrocarbons (HC) and carbon monoxide (CO) are formed as a result of the incomplete combustion of gasoline. 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.

The Misleading Nature of the PO42O Code
By Ken Schafer Jr.
© Reproduced with permission from Undercar Digest. For subscription information call 800-274-7890 or visit www.mdpublications.com.

Upon the arrival of the Onboard Diagnostics II (OBD-II) system, I remember thinking to myself that this new system was going to be the greatest thing to happen to vehicles since I had started working on them.

Upon the arrival of the Onboard Diagnostics II (OBD-II) system, I remember thinking to myself that this new system was going to be the greatest thing to happen to vehicles since I had started working on them. Now all I needed to do was plug in a scan tool, since all vehicles would have the same data-link connector (DLC) much to my delight again, and the car would tell me what was wrong with it.

Sadly, it was only a few weeks later that I learned that this new system was still only a guideline and not a complete diagnosis. Throughout the years, after the start of OBD-II, it has become more and more accurate, but it still requires a bit of investigating after retrieval of the diagnostic trouble codes (DTCs). The P0420 code is no different.

Here is a scenario: A customer pulls into the shop and says, “My check-engine light is on.” I tell them that I will scan the vehicle and find out what the problem is. Once I hook the scan tool up and navigate through the setup menus and click on display codes, I see P0420. Then I click the display code data and the scan tool says “Converter efficiency below threshold.” I crane my head out of the driver’s seat and yell to the manager that the vehicle needs a converter. This may not be true, as further diagnosis is necessary.

From here on, I will try to explain some of the more-general steps I would take when diagnosing a converter with a scan tool. I will stay away from any finer points, as there are variances from manufacturer to manufacturer, but using these steps as a guideline should help to properly diagnose a catalytic converter.

Upon displaying the codes, first be sure that the P0420 is the only code present; if not, diagnosis of the other codes is necessary, as they may be causing the P0420 code. The reason for this is that the converter is the end result in the OBD-II diagnostic. Basically, if there is a problem with one of the sensors in the engine or exhaust, it can cause either too much or too little fuel to enter the engine.

Fig. 01 - Melted Catalyst
If the engine is getting too little fuel it causes a lean condition, which raises combustion temperatures and, in turn, raises exhaust temperatures. Since converters operate properly only between certain temperatures (900-1,400° F), extreme temperatures lower the efficiency of the catalyst and can trigger the P0420 DTC. At temperatures above 2,100° the catalyst will begin to melt down, permanently destroying the catalyst (see Figure 1).

Fig. 02 - Burned Catalyst
Too much fuel does two things. First, the excess fuel entering the exhaust can coat the catalyst, cooling it as well as protecting the precious metals (which cause the catalytic reaction). This will last until the second problem happens: A spark enters the converter and ignites the fuel, at which point it turns into a secondary combustion chamber, destroying the catalyst (see Figure 2).

Once all the other DTCs are fixed, clear the codes and start the engine. Warm the engine until the water temperature is stable. Then, increase engine speed for about three minutes, usually between 2,500 and 3,000 rpm; this will help the catalytic converter light off. After this, look at the wave forms between the front and rear O2 sensors. If the front O2 wave form is switching from high to low (rich to lean) and the rear is close to a straight line, the original converter should be OK. If the rear O2 sensor is mimicking the front one, the converter most likely took damage and may need to be replaced. A drive cycle may need to be completed and the converter monitor ready before you know whether the converter is good or bad. Follow the manufacturer guidelines for the correct drive cycle.

Once you have completed the drive cycle, or if when you first scan the vehicle the only code present is P0420, you should first look at the freeze-frame data. This will tell you the conditions that were present when the DTC was set (vehicle speed, engine speed, O2 readings and fuel trim, among others, but these four I have found most useful).

Looking at the fuel trim can tell you a lot without telling you too much. I know it sounds cryptic, but here’s an example: The only code is the P0420 but the fuel trim is high – usually above +8%, but this can vary, and one should consult a repair database for proper percentages. You already know that the engine is getting extra unmetered air into the intake and the ECM is compensating for this by dumping extra fuel into the intake. When this condition is present I look for any type of vacuum leak, intake leak or a dirty mass-air-flow (MAF) sensor that could be the cause of this problem.

If the fuel trim is low – usually below -8%, but this can vary the same as a high fuel trim – you know that the engine is getting extra unmetered fuel into the intake and the ECM is compensating by leaning out the fuel mixture. This is usually caused by either a stuck fuel injector or a bad fuel-pressure regulator.

Once the problem has been identified the repairs should be made, and after the warm-up process has been performed the vehicle should be tested to ensure that no other codes arise.

If the fuel trim looks within range it is time to look at the O2 values. The front O2 sensor should be switching from rich (over 600mV) to lean (under 300mV) and the rear O2 sensor, or converter monitor, should be a nice, smooth line with minimal variance in mV. When looking at the values of the O2 sensors pay particular attention to the switching rate of the sensors and be sure that neither the front nor rear sensor drops out or spikes for extended amounts of time. If either a slow switching rate or spike/drop-out happens, but the O2 then recovers and appears to be operating normally, the O2 sensor may be starting to deteriorate – or as a lot of people say, “It has become lazy” and may need to be replaced.

Fig. 03 - Contaminated Catalyst
If you determine that the O2 sensor is lazy, remove it and check it for any type of contamination, usually by oil or antifreeze; if they are present, check the catalyst to ensure that it is not contaminated or poisoned (see Figure 3). If so, converter replacement will be necessary but not until the engine is repaired and the poisoning agent is no longer entering the exhaust, for this will lead to premature converter failure. If none of the above conditions are present and the engine is at operating temperature look at the front and rear O2 sensors. If the rear O2 sensor is mimicking the front one, the converter will most likely need to be replaced; there are only a few other easy things to look at.

Fig. 04 - Damaged Converter Body
After reviewing all the data and determining that there are no outside conditions causing the P0420 DTC, it is time to raise the vehicle and inspect the converter. I first look for any impact marks on the converter (see Figure 4) that may have resulted from road damage. If there are no marks on the converter I then inspect the body of the converter to see whether it is discolored, indicating that the converter has been overheated. If I see this, I usually consult the customer to find out whether they have had any other repairs to the engine that I am not aware of. This way I can ensure that a new converter will not suffer the same fate as the one that is on the vehicle. In most cases they would tell me that they have had other repairs done in the recent past and I would proceed with replacing the converter. If they tell me that they have not, I inform them that additional diagnosis may be needed. This is when I settle down and look over technical service bulletins (TSBs) and the diagnostic flow chart for the specific application; I will not go into these as they vary so much from application to application.

Fig. 06 - Waveform Comparison
The last thing I do, after replacing the converter with an approved quality aftermarket converter like those from Eastern Catalytic, is hook up my scan tool again and clear the codes, warm up the engine again, and watch the O2 sensors to see that the new converter lights off. Once I see this and the rear O2 sensor has a nice, smooth line (see Figure 6)5, I can release the vehicle with confidence that the problem has been fixed.

Ken Schafer Jr. is Emission Certification Manager at Eastern Catalytic

Why Converters Fail

Most catalytic converters fail due to engine related problems. Replacing the catalytic converter without fixing the cause of the failure may lead to another ruined converter...

O2 Sensors: FYI
(Reprinted with permission from Babcox’s Tomorrow’s Technician Magazine — May 2007, http://www.babcox.com)

How many oxygen sensors are on today’s engines?

ANSWER:

It depends on the model year and type of engine. On most four- and straight six-cylinder engines, there is usually a single oxygen sensor mounted in the exhaust manifold. On V6, V8 and V10 engines, there are usually two oxygen sensors, one in each exhaust manifold. This allows the computer to monitor the air/fuel mixture from each bank of cylinders. When displayed on a scan tool, the right and left oxygen sensors are typically labeled “Bank 1, Sensor 1” and “Bank 2, Sensor 1.”

On later-model vehicles with OBD II (some 1993 and ‘94 models, and all 1995-and-newer models), one or two additional oxygen sensors are also mounted in or behind the catalytic converter to monitor converter efficiency. These are referred to as the “downstream” O2 sensors, and there will be one for each converter if the engine has dual exhausts with separate converters.

On a scan tool, the downstream sensor on a four- or straight six-cylinder engine with single exhaust is typically labeled “Bank 1, Sensor 2.” On a V6, V8 or V10 engine, the downstream O2 sensor might be labeled “Bank 1 or Bank 2, Sensor 2.” If a V6, V8 or V10 engine has dual exhausts with dual converters, the downstream O2 sensors would be labeled “Bank 1, Sensor 2” and Bank 2, Sensor 2.” Or, the downstream oxygen sensor might be labeled Bank 1, Sensor 3 if the engine has two upstream oxygen sensors in the exhaust manifold (some do to more accurately monitor emissions). It’s important to know how the O2 sensors are identified because a diagnostic trouble code that indicates a faulty O2 sensor requires that sensor to be replaced. Bank 1 is usually the front bank of cylinders on a transverse mounted V6 engine. But on a longitudinal V6, V8 or V10, it could be either the right or left bank. It may therefore be necessary to refer to the vehicle service literature to determine how the cylinder banks and oxygen sensors are labeled.

QUESTION:
I was wondering – how does a downstream O2 sensor monitor converter efficiency?

ANSWER:

A downstream oxygen sensor in or behind the catalytic converter works exactly the same as an “upstream” O2 sensor in the exhaust manifold. The sensor produces a voltage that changes when the amount of unburned oxygen in the exhaust changes. If the O2 sensor is a traditional zirconia type sensor, the voltage output drops to about 0.2 volts when the fuel mixture is lean (more oxygen in the exhaust). When the fuel mixture is rich (less oxygen in the exhaust), the sensor’s output jumps up to a high of about 0.9 volts. The high or low voltage signal tells the PCM the fuel mixture is rich or lean.

On some newer vehicles, a new type of “wideband” oxygen sensor is used. Instead of producing a high or low-voltage signal, the signal changes in direct proportion to the amount of oxygen in the exhaust. This provides a more precise measurement for better fuel control. These sensors are also called “air/fuel ratio sensors” because they tell the PCM the exact air/fuel ratio, not just a rich or lean indication like a conventional O2 sensor.

The OBD II system monitors converter efficiency by comparing the upstream and downstream oxygen sensor signals. If the converter is doing its job and is reducing the pollutants in the exhaust, the downstream oxygen sensor should show little activity (few lean-to-rich transitions, which are also called “crosscounts”). The sensor’s voltage reading should also be fairly steady (not changing up or down), and average 0.45 volts or higher.

If the signal from the downstream oxygen sensor starts to mirror that from the upstream oxygen sensor(s), it means converter efficiency has dropped off and the converter isn’t cleaning up the pollutants in the exhaust. The threshold for setting a diagnostic trouble code (DTC) and turning on the Malfunction Indicator Lamp (MIL) is when emissions are estimated to exceed federal limits by 1.5 times.

If converter efficiency has declined to the point where the vehicle may be exceeding the pollution limit, the PCM will turn on the Malfunction Indicator Lamp (MIL) and set a diagnostic trouble code. At that point, additional diagnosis may be needed to confirm the failing converter. If the upstream and downstream O2 sensors are functioning properly and show a drop off in converter efficiency, the converter must be replaced to restore emissions compliance. The vehicle will not pass an OBD II emissions test if there are any converter codes in the PCM.

 

QUESTION:
I would like to know, what’s the difference between a “heated” and “unheated” oxygen sensor?

ANSWER:

Heated oxygen sensors have an internal heater circuit that brings the sensor up to operating temperature more quickly than an unheated sensor. An oxygen sensor must be hot (about 600 to 650 degrees) before it will generate a voltage signal. The hot exhaust from the engine will provide enough heat to bring an O2 sensor up to operating temperature, but it may take several minutes depending on ambient temperature, engine load and speed. During this time, the fuel feedback control system remains in “open loop” and does not use the O2 sensor signal to adjust the fuel mixture. This typically results in a rich fuel mixture, wasted fuel and higher emissions.

By adding an internal heater circuit to the oxygen sensor, voltage can be routed through the heater as soon as the engine starts to warm up the sensor. The heater element is a resistor that glows red hot when current passes through it. The heater will bring the sensor up to operating temperature within 20 to 60 seconds depending on the sensor, and also keep the oxygen sensor hot even when the engine is idling for a long period of time.

Heated O2 sensors typically have two, three or four wires (the extra wires are for the heater circuit). Note: Replacement O2 sensors must have the same number of wires as the original, and have the same internal resistance.

The OBD II system also monitors the heater circuit and will set a trouble code if the heater circuit inside the O2 sensor is defective. The heater is part of the sensor and cannot be replaced separately, so if the heater circuit is open or shorted and the problem is not in the external wiring or sensor connector, the O2 sensor must be replaced.

What is a Troy Ounce?

The troy system of weight is named after the city of Troyes in France, and was widely used in Europe during the Middle Ages. It fell into disuse when other systems began to be preferred, continuing to be used only in the highly specialized fields of precious metals, gems and medicines, up to the nineteenth century...

The troy ounce is the unit of weight traditionally used for precious metals such as platinum.

1 troy ounce = 0.0311 kilograms
32.1507 troy oz = 1 kilogram

The troy ounce (troy oz) differs from the more common ounce (oz) used in the U.K. and U.S.A., being slightly heavier, with 1 troy oz = 1.097 oz.

 

The troy system of weight is named after the city of Troyes in France, and was widely used in Europe during the Middle Ages. It fell into disuse when other systems began to be preferred, continuing to be used only in the highly specialised fields of precious metals, gems and medicines, up to the nineteenth century. Today it is only for the trading of precious metals and gemstones.

A History of Platinum

Although the modern history of platinum only begins in the 18th century, platinum has been found in objects dating from 700 BC, in particular the famous Casket of Thebes (see image). This little box is decorated with hieroglyphics in gold, silver and an alloy of the platinum group metals...

Early Occurrences

Although the modern history of platinum only begins in the 18th century, platinum has been found in objects dating from 700 BC, in particular the famous Casket of Thebes (see image). This little box is decorated with hieroglyphics in gold, silver and an alloy of the platinum group metals.

For the Spanish Conquistadors of the 16th century, platinum was a nuisance. While panning for gold in New Granada they were puzzled by some white metal nuggets which were mixed with the nuggets of gold and which were difficult to separate. The Spanish called this metal Platina, a diminutive of Plata, the Spanish word for silver. Some thought that the platinum was a sort of unripe gold, so that for many years it had no value except as a means of counterfeiting.

Scientific Developments

In the 18th century platinum was a tough challenge to European scientists trying to understand and use the metal. Their difficulties came from the very properties which make platinum suitable for so many applications, such as its high melting point and its great resistance to corrosion. The problems were compounded by the other metals of the platinum group, which were present in raw platinum in varying quantities.

In 1751, a Swedish researcher named Sheffer succeeded in melting platinum by adding arsenic to it. He also recognized platinum as a new element. In 1782, Lavoisier achieved the first true melting of platinum using oxygen, which had recently been discovered; even so, it was another 25 years before commercial quantities of platinum could be produced by this method. During this period, platinum was used for the decoration of porcelain as well as for making laboratory ware and ornaments.

In the 19th century scientific and technological progress gathered pace. During 1802, Wollaston and Tennant developed refining of platinum and discovered palladium, followed in 1804 by rhodium, iridium and osmium. Meanwhile Wollaston perfected a method of producing malleable platinum. Grove studied the catalytic properties of platinum and in 1842 devised the very first fuel cell using platinum electrodes.

There are other metals within the platinum ore, the Platinum Group Metals or PGM’s are Platinum, Palladium, and Rhodium.

In England, Percival Norton Johnson began work on refining the platinum group metals. He took as his apprentice in 1838 George Matthey, and this collaboration gave birth to the partnership of Johnson and Matthey in 1851. The two men perfected the techniques of separation and refining of platinum group metals and the melting and casting of pure and homogeneous ingots. Matthey went on to create the standard metre in platinum and iridium, at the request of the French Academy of Science, in 1879.

Growth in Supplies

Until 1820 Colombia was the only known source of platinum. As production began to decline, deposits were by chance discovered in the Ural mountains of Russia. These became the principal source of platinum for the next 100 years.

In Canada in 1888, platinum was discovered in the nickel-copper ores of Ontario. Between the end of the First World War and the 1950s, Canada was the world’s major source of supply. In 1924 a farmer in the Transvaal province of South Africa discovered several nuggets of platinum in a riverbed. Following this up, the geologist Hans Merensky discovered two deposits each of around 100 kilometers in length. These became known as the Bushveld Igneous Complex and its mines today provide three quarters of the world’s platinum output.

The Last 50 Years

Platinum mine production has grown continuously since the Second World War in response to the development of new applications. One of the principal new uses of platinum was in the petroleum industry, where platinum catalysts were introduced to increase the octane rating of gasoline and to manufacture important primary feedstocks for the growing plastics industry.

During the 1960s, demand for platinum in jewelry experienced a spectacular rise in Japan, appealing to the Japanese public by virtue of its purity, color, prestige and value. Platinum jewelry later succeeded in penetrating other markets – in Germany in the 1970s, Switzerland and Italy in the 1980s and the United Kingdom, the USA and China – today the world’s biggest single market for platinum jewelry – in the 1990s.

In 1974, with its new regulations on air quality, the United States inaugurated the era of the autocatalyst, a technology which uses platinum group metals to convert the noxious gases in vehicle exhausts into harmless substances. Use of autocatalysts has spread worldwide and since its introduction has prevented over 12 billion tonnes of pollution from entering the earth’s atmosphere.

During the 1980s the rapid increase in the value of precious metals, including platinum, gave rise to the production of a variety of bars and coins, many of them collectable items, to meet demand for platinum as a physical investment product.