Exhaust Catalyst

The catalytic converter for cleaning up exhaust gas was invented by Eugene Houdry (1956), probably best known for inventing a process for cracking crude oil.

Two-Way Catalyst

Three-Way Catalyst

Acoustics

A catalytic converter is known to have two distinct acoustic effects:

Reactive Effect Acoustic wave reflections caused by cross-sectional area changes within the catalyst can and the catalyst brick.

Resistive Effect Acoustic wave dissipation caused by viscous losses. The resistive effect is frequency-dependent, that is, the catalytic converter acoustic transmission loss due to the resistive effect would increase with increasing frequency. It emanates from the multi-tubular brick of catalyst material. Other engine exhaust system components have resistive elements, such as the absorptive packing in a muffler.

Diesel Oxidation Catalyst

Catalyst promoting oxidation processes in diesel exhaust. Usually designed to reduce emissions of the organic fraction of diesel particulates, gas-phase hydrocarbons, and carbon monoxide.

Geometric Surface Area

The total channel surface area per unit of substrate volume.

Intumescent Mat

Ceramic fibre mat which irreversibly expands after exposure to high temperature. Usually contains vermiculite. Intumescent mats are used in the canning of catalytic converters and diesel filters to hold the ceramic substrate inside the steel canister.

Lean NOx Catalyst

Catalyst designed to reduce nitrogen oxides from diesel or spark-ignited engine exhaust gases under net oxidizing conditions (in the presence of excessive amounts of oxygen).

Open Frontal Area

Total substrate cross-section area which is available for the flow of gas. Often expressed as a percentage of the total substrate cross-section (sometimes called the substrate void fraction).

Oxygen Storage Capacity

A capacity of the catalyst washcoat to store oxygen at lean and to release it at rich condition. Typically provided by cerium oxide, which oscillates between an oxidized and reduced state, depending on the exhaust gas chemistry. The oxygen storage capacity is an important component of three-way catalysts, used to extend the catalyst window.

Selective Catalytic Reduction

Used to describe the catalytic reduction of NOx in diesel exhaust or flue gases by nitrogen containing compounds, such as ammonia or urea.

Historical Notes

  1. 1836 the phrase catalysed processes was coined by Jons Jakob Berzelius.
  2. 1956 catalytic converter for cleaning up exhaust gas was invented by Eugene Houdry.
  3. 1973 first production catalytic converter developed by John J. Mooney and Carl D. Keith at the Engelhard Corporation.
  4. 1981 three-way catalytic converters used in vehicle emission control systems.

See also: Aftertreatment, Catalyst, Closed-Loop Fuel Control, Exhaust, Exhaust Gas Oxygen, Exhaust Gases, Oxygen Sensor.

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Subjects: Noise & Vibration