The catalytic converter is a steel box-shaped element that connects to the car’s exhaust pipe and reduces harmful gas emissions. The catalytic converter renders harmful unburned Hydrocarbons (HC), Carbon Monoxide (CO), Nitrous Oxides (NOx) in the exhaust gas harmless by chemical reaction. Catalytic convertors are used in both diesel and gasoline engines.
The platinum group metals in catalytic converters perform the conversion process. Platinum, Palladium and Rhodium. A typical catalytic converter is mainly made of a porous metallic or ceramic carrier coated with PGM metals.
The catalytic carrier is surrounded by fibrous material and enclosed in a shell made of stainless-steel plate. The PGM layer is put on a ceramic carrier (Al2O3 with e.g., CeO2 -wash coat), which is honeycomb, meaning a dense network of square holes. This type of structure increases the active surface, which is the contact area of the exhaust gases flowing through the channels and the catalytic substances (Pt, Pd, Rh).
Reducing light dimming, reducing back pressure, etc. certain areas, a metallic carrier is chosen instead of ceramics. Ceramic substrate converters cover approximately 95% of the total market.
Because metal heats up much faster than ceramic, metal catalysts quickly reach “operating temperature” and quickly purify exhaust gases. They are also more resistant to damage from thermal shock and high temperature (determined by their resistance to 1300 °C). The advantage of metal-supported catalysts is their better thermal conductivity, which is achieved due to the high platinum content.
Metallic carrier catalytic converters – MSC (Metal Substrate Converters) were originally designed for sports and racing cars. This is partly a cost issue. When Ceramic carriers are produced in large quantities, it is not expensive. Metallics are cheaper in small production. Both of them are designed to provide a high surface area. Metallic foil monoliths are made of FeCrAl.
Ceramic or metallic carriers are the most important factor in catalytic, which are widely used not only in automobiles but also in all industries. The table below shows the advantages of ceramic and metallic carriers.
|Very High Specific Surface,
|Ease Of Heat Transfer,
|High Corrosion Resistance,
|Small Hydraulic Resistances,
|High Adhesion Of Active Substances,
|High Mechanical Strength,
|High Melting Temperature,
|All Visible Dust Density,
|Ease Of Styling.
|Smaller Susceptibility To Mechanical Damage.
The table below shows the difference between the two catalytic converters.
|Part of Catalysts
|Washcoat (with PGM)
The table below shows the efficiency of the gases converted in the ceramic and metallic converter.