Catalytic Converter

A catalytic converter "cat" is a device used to reduce the toxicity of emissions from an internal combustion engine. A catalytic converter works by using a catalyst to stimulate a chemical reaction in which toxic by-products of combustion are converted to less-toxic substances. This typically results in 90% conversion of carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful gases.

Diesel Particulate Filter

A diesel particulate filter, sometimes called a DPF, is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. Wall-flow diesel particulate filters usually remove 85% or more of the soot, and can at times (heavily loaded condition) attain soot removal efficiencies of close to 100%. A diesel-powered vehicle equipped with a functioning filter will emit no visible smoke from its exhaust pipe.
 
In addition to collecting the particulate, a method must exist to clean the filter. Some filters are single-use (disposable), while others are designed to burn off the accumulated particulate, either through the use of a catalyst (passive), or through an active technology, such as a fuel burner which heats the filter to soot combustion temperatures. This is known as "filter regeneration".