Catalytic Converter Steel

Applications
Catalytic Converter Steel

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HISTORY

Catalytic Converter Steel

The word catalysis emanates from the Greek words; cata-, meaning down, and lysein, meaning to split or break. Interestingly, the Chinese word ”tsoo mei”, which is used for catalyst, also means ”marriage breaker”. A catalyst is defined as a substance, which increases the rate at which a chemical reaction approaches equilibrium, without being consumed in the process. The phenomenon occurring when a catalyst acts is termed catalysis. It was first used by Berzelius, who in 1836 used it to describe a variety of diverse observations concerning the effects of trace substances on reaction rates. One example included was the effect of platinum on the reaction of hydrogen and oxygen.

In catalytic air pollution control, all processes use solid heterogeneous catalysts through which gaseous reactants pass. The primary effect of a catalyst on a chemical reaction is, as stated above, to increase its rate. The use of catalysts in the automotive exhaust gas treatment has been of utmost success. No other method has demonstrated such a feasibility in decreasing unburned hydrocarbons, carbon monoxide and nitrogen oxides from SI-engines. However, the catalytic treatment has been possible only due to significant engine modifications and a powerful engine management control together with lead-free gasoline.

Already in 1927, Kettering proposed the carbon monoxide catalyst, since automotive exhausts were considered as noisy, dangerous and smelly. General motors tested the very first catalysts 1959. In 1964, the first emission standards were introduced in California and in the seventies the catalyst development accelerated even more, which led to that Volvo as the very first car manufacturer could introduce the three-way catalytic converter.

On the 1:st of January 1996, petrol engine vehicles equipped with catalytic converters and registered after 1 August 1995 became subject to the new cat emissions test. The new test procedure includes tests on the emission levels of CO and HC. A 1997 legislation will also require the majority of diesel cars to be equipped with converters.

CONSTRUCTION REQUIREMENTS

The material of the substrate and the construction of the catalyst are subjected to great mechanical, thermal and chemical strain. The construction should meet the stringent requirements such as

Large effective area
Light weight
Small size
Good thermal conductivity
High mechanical strength
Low back pressure

ADVANTAGES

A metal-based monolith offers many advantages in comparison with a ceramic one, for instance

Better thermal conductivity
Shorter light off time
Less risk of overheating
Less back pressure
Larger effective area
Greater catalytic capacity
Smaller and more flexible design
Thinner walls
Higher mechanical strength
Better resistance to thermal shock

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