Frequently asked questions
Q. What is a catalyst?
A. A catalyst helps substances react together but remains unchanged in the process. In an automobile catalytic converter, the catalyst helps the pollutants (unburned hydrocarbons, carbon monoxide, nitrogen oxides and volatile organic fraction of particulates) react with each other and other components of the exhaust gas to form non-toxic compounds (water, carbon dioxide and nitrogen).
Q. Do catalytic converters spoil the performance and driveability of cars and increase fuel consumption?
A. Modern catalytic converters do not reduce vehicle performance significantly under most driving conditions because they are designed with low backpressure as an integral part of the exhaust system. With the advances incorporated in today’s engines, they perform significantly better both in terms of power and fuel economy than their pre-catalyst ancestors.
Q. Is it true that catalytic converters don't work on a short journey such as the "school run" or a visit to the shops?
A. No. While catalytic converters do need a moderately hot exhaust to start working, it is a myth that catalytic converters do not work on short journeys. Emission control systems become operational as soon as the engine conditions permit. In fact modern catalytic converters fitted to passenger cars start working in a few seconds and Diesel Particulate Filters remove particulates under all conditions.
Q. What is the effect of sulfur-free fuel on exhaust emissions?
A. Exhaust emissions will be lower - particularly from catalyst-equipped cars. Sulfur in petrol and diesel fuel has a major negative impact on catalyst performance, especially for NOx catalysts and adsorbers. The effect of sulfur on catalyst performance becomes more critical as lower tailpipe emissions are targeted for the very low emission levels now required. Sulfur strongly competes against pollutants for "space" on the catalyst surface limiting the efficiency of catalyst systems to convert pollutants at any sulfur concentration - so the lower the sulfur levels in fuels the better the catalyst performance that can be obtained. The conversion of sulfur to a sulphate aerosol can cause net increases in diesel particulate emission.
Q. What are the differences in toxic emissions from diesel and petrol engines?
A. Because maximum power production from diesel engines is fuel and not air limited it is still the only engine that is "lean burn" across the full power/speed range. This brings real fuel and carbon dioxide emission savings - good for the global environment. But it challenges the catalyst chemist to control nitrogen oxide and particulate emissions at low exhaust temperatures with excess oxygen. In parallel to low sulfur diesel fuel introduction, Diesel Particulate Filters (DPF) are now fitted on passenger cars and Selective Catalytic Reduction (SCR) catalysts and NOx traps are being progressively introduced. This will help the diesel engine to reach the exhaust emission levels of the petrol engine.
Q. How can toxic particles from engines be avoided?
A. The best way is to use a particulate filter. These systems consist of a filter positioned in the exhaust line and designed to collect solid and liquid particulate matter (PM) emissions while allowing the exhaust gases to pass through the system. Increasing numbers of diesel cars, trucks and buses are now being fitted with Diesel Particulate Filters (DPF).
Q. Do all filters have the same efficiency?
A. No, based on engine technology and engine management, different filter technologies may be used to meet the prescribed emission standards.
It is possible with advanced filter technology (wall-flow filters) to almost completely eliminate the carbon particulates, including fine particulates of less than 100 nanometres (nm) diameter with an efficiency of >95% in mass and >99% in number. The removal of ultra-fine particles is very important since health experts believe that they are carried deep into the lungs and are thought to be the most dangerous size of PM.
Partial-flow filters operate with the bypass flow principle. The overall filtration efficiency of these partial-flow filters is 30-60% in mass depending on application and operating conditions.
Q. Doesn't the DPF become plugged with particulate material after a while?
A. Particulate filters retain all particles: soot, lube-oil ashes, engine wear products and, when applicable, Fuel Borne Catalyst (FBC) ashes. On-board catalytic soot burning allows automatic regeneration of the DPF's efficiency. Depending on the application, this can be done through passive regeneration (continuous oxidation of particulates by NO2), the use of a FBC which lowers the soot burning temperature, or, active engine control strategies periodically increasing the exhaust temperature. Any residual ash can be cleaned during maintenance if requested by the car manufacturer but most passenger car systems are now designed to last for the lifetime of the vehicle without maintenance.
Q. Is the catalyst helpful to health and the environment?
A. Yes, the average family car would emit 15 tons of the toxic and harmful polluting gases (carbon monoxide, hydrocarbons and nitrogen oxides), over a 10-year life, if catalytic converters were not fitted to all new cars to remove 98% of pollution as required by current regulations.
Q. Catalytic converters produce CO2. Is this adding to the greenhouse effect?
A. All the carbon contained in fossil fuels is ultimately converted to CO2 in the atmosphere. By accelerating that conversion, and removing other dangerous pollutants in the process, catalytic converters do not increase overall CO2 levels. The only way to reduce CO2 emissions is to burn less fossil fuel.
Q. What is retrofit?
A. Typically, retrofit involves the addition of an emissions control device to remove emissions from an existing vehicle. Retrofits can be very effective at reducing emissions of the legacy fleet, eliminating up to 90 percent of pollutants in some cases. Some examples of emissions control devices used for diesel retrofit include diesel oxidation catalysts, diesel particulate filters and selective catalytic reduction systems. More information on Heavy-duty Diesel retrofit in Europe can be found here.
Q. Are catalytic converters fragile? Do they need replacing frequently?
A. The modern catalytic converter is robust, one of the most reliable elements in the engine management system and corresponds to the lifetime of the car. Under Euro 4 emissions legislation, it is required that the emissions remain below the legal limits for at least 100 000 km. This will increase to 160 000km with the new Euro 5 legislation as of 2009.
Q. Is more pollution emitted in the mining and refining of precious metals than the pollution they remove from engine exhaust?
A. Researchers(1) have calculated that after the first 4 900 km of the vehicle's life there is a net benefit to the environment. This is based on the acidification potential of nitrogen oxides (NOx) emissions removed from exhausts by autocatalysts and the sulfur oxides (SOx) emitted in precious metal refining.
(1) Hagelücken, Hochfeld, Gediga, Autoabgaskatalysatoren, 2001.
Q. Are there enough precious metals for catalytic converters?
A. The precious metals, including platinum (Pt), have been recycled since long before this became a necessity to conserve our resources. From the onset of their use in cars, catalytic converters have been removed from end-of-life (EOL) vehicles and the platinum, palladium (Pd) and rhodium (Rh) recovered. In Europe, autocatalysts platinum recycled share increased from 5 to 10% between 1997 and 2007 whilst that for palladium went from essentially zero to 33% over the same period. On a worldwide basis, 21% of Pt, Pd and Rh demand for automotive catalyst was met by recovered precious metals in 2007(2). The share of recycled precious metals continues to grow as the first generation of cars equipped with catalysts are reaching the end of their useful lives. Although highly efficient refining processes are available and used to recover PGMs from autocatalysts with more than 95% yield, significant inefficiencies still exist in the end-of-life phase of cars. Especially old European cars are increasingly exported to developing countries where for various reasons no proper recycling takes place at the final end-of-life. In total this leads to considerable losses from the autocatalyst lifecycle, thus a more sound management of EOL-cars as well as to create a global recycling infrastructure is needed. The current leakages in the autocatalyst lifecycle are not a real threat from the reserve base, but better recycling rates would mitigate price volatility and environmental impact of the PGM supply.
(2) Johnson Matthey Platinum 2007 Interim Review
Q. How are used catalytic converters recycled?
A. Modern car dismantlers, scrap yards and workshops remove used catalytic converters from end-of-life vehicles according to the European End-of-Life Vehicle Directive which specifies minimum levels of recycling for scrapped vehicles. Specialist companies collect them and accumulate bigger lots at central warehouses. The converters are decanned; i.e. the ceramic or metallic catalyst is removed from the steel can by special cutting devices. The steel is sorted by quality and sold as secondary scrap to steel plants. The catalyst with the precious metals is delivered to precious metals refiners, specialised in the recovery of Platinum Group Metals (PGM) to generate high purity platinum, palladium and rhodium identical to newly extracted PGM from the mines.
Q. How are pollutants regulated worldwide?
A. European and American emission limits are used in other continents. For example, in India, passenger cars and commercial vehicles met Bharat stage I (equivalent to Euro 1) nation-wide in 2000 and Bharat stage II (equivalent to Euro 2) in 2005. In 11 Indian metropolitan areas, Bharat stage III (Euro 3) has to be met since 2005. This Bharat stage III is now planned nation-wide in 2010 except for 11 major cities where the tougher Bharat stage IV (Euro 4) limit will be required. For 2-3 wheelers, Bharat stage II norms are applicable from 2005 and Bharat stage III will come into force between 1st April 2008 and 1st April 2010.
In China, Euro 1-based legislation was introduced in 2000 (GB stage 1) followed by a Euro 2-type limits in 2003-2004 (GB stage 2), a Euro 3-type limits were introduced in 2007 (GB stage 3) and Euro 4 is planned for 2010 (GB stage 4). Specific emission limits are to be progressively introduced in big cities such as GB stage 4 in Beijing at the beginning of 2008.
Fuel quality standards enhancement is now required to move to more stringent legislation on emissions.
Q. If a catalytic converter is damaged in an accident how can one be sure that the replacement catalyst fitted on my vehicle is functioning as effectively as the original equipment?
A. A converter supplied from a franchised dealer for the car is the most reliable way to ensure this. New converters supplied by reputable, specialist exhaust suppliers should be produced in accordance with strict rules, developed by the European Commission, to ensure similar performance to the original equipment part. The use of second-hand converters, from for example a car involved in an accident, is not recommended. Even if the size of the converter fits the catalyst may have been developed for a different engine or poisoned or otherwise damaged in its former life.If you have other questions, please click here