Types of Catalytic Converters | Complete Guide

What is a Catalytic Converter?

A catalytic converter is an important component of a vehicle’s exhaust system. It is designed to reduce harmful emissions produced by the engine, converting them into less harmful substances before they are released into the atmosphere. The primary purpose of a catalytic converter is to minimise the impact of vehicle emissions on the environment.

Catalytic converters are typically made of a stainless steel shell that contains a ceramic or metallic substrate coated with catalysts. These catalysts facilitate the chemical reactions that occur within the converter, transforming harmful gases into less harmful ones.

How do Catalytic Converters Work?

In order for a catalytic converter to function, it must undergo a number of internal chemical reactions. As the exhaust gases interact with the catalysts on the substrate, these reactions take place as they flow through the converter.

 

There are three basic types of chemical reactions that are involved in the operation of a catalytic converter: oxidation, reduction, and acid-base reactions.

The catalysts within the converter enable the transformation of unburned hydrocarbons (HC) and carbon monoxide (CO) into carbon dioxide (CO2) and water (H2O), respectively, throughout the oxidation processes. By implementing this technique, the vehicle’s emissions of hazardous gases can be significantly reduced.

 

A catalyst’s role in a reduction reaction is to facilitate the transformation of nitrogen oxides (NOx) into nitrogen gas and oxygen gas. Nitrogen oxides are a known contributor to air pollution and smog formation; this helps to minimise their levels.

 

Conversion of nitrogen oxides to nitrogen and oxygen and carbon dioxide to carbon monoxide and oxygen are two examples of the acid-base processes that take place in the catalytic converter. The vehicle’s emissions of dangerous gases are further reduced by these processes.

 

Catalysts play an essential part in every conversion. Chemical reactions can be facilitated by compounds called catalysts, which do not themselves undergo combustion. As a result, the reactions can take place at lower temperatures since the activation energy is reduced. The catalytic converter can begin its effective operation immediately upon engine start, regardless of temperature, therefore this is crucial.

Different Types of Catalytic Converters

There are several different types of catalytic converters, each designed to meet specific emission control requirements and work with different types of engines. The most common types of catalytic converters include three-way catalytic converters, oxidation catalytic converters, diesel particulate filters (DPFs), and selective catalytic reduction (SCR) systems.

Three-Way Catalytic Converters

 

Three-way catalytic converters are the most commonly used type of catalytic converter in gasoline-powered vehicles. They are designed to simultaneously reduce the levels of carbon monoxide, unburned hydrocarbons, and nitrogen oxides in the exhaust gases.

Three-way catalytic converters contain two separate catalysts: a reduction catalyst and an oxidation catalyst. The reduction catalyst helps to convert nitrogen oxides into nitrogen and oxygen, while the oxidation catalyst facilitates the conversion of carbon monoxide and unburned hydrocarbons into carbon dioxide and water.

The design of three-way catalytic converters allows for the simultaneous reduction of multiple pollutants, making them highly efficient in reducing emissions.

Oxidation Catalytic Converters

Oxidation catalytic converters, also known as two-way catalytic converters, are commonly used in diesel-powered vehicles and some gasoline-powered vehicles. They are designed to primarily reduce the levels of carbon monoxide and unburned hydrocarbons in the exhaust gases.

Oxidation catalytic converters contain a single catalyst, which facilitates the conversion of carbon monoxide and unburned hydrocarbons into carbon dioxide and water. However, they are less effective in reducing nitrogen oxides compared to three-way catalytic converters.

Diesel Particulate Filters (DPFs)

Diesel particulate filters (DPFs) are specifically designed for diesel-powered vehicles. They are used to trap and remove particulate matter, such as soot, from the exhaust gases.

DPFs work by physically trapping the particulate matter in a porous filter. Over time, the trapped particles accumulate and form a layer known as the “soot cake.” To prevent the filter from becoming clogged, the soot cake needs to be periodically burned off, a process known as regeneration.

Regeneration can occur passively or actively. Passive regeneration occurs when the exhaust gases reach a high enough temperature to burn off the trapped soot. Active regeneration, on the other hand, involves the use of additional heat sources, such as fuel injectors, to raise the temperature of the exhaust gases and facilitate the burning off of the soot.

Selective Catalytic Reduction (SCR) Systems

Selective catalytic reduction (SCR) systems are primarily used in diesel-powered vehicles to reduce nitrogen oxide emissions. They work by injecting a urea-based solution, known as Diesel Exhaust Fluid (DEF) or AdBlue, into the exhaust gases.

When the DEF comes into contact with the exhaust gases, it undergoes a chemical reaction that converts nitrogen oxides into nitrogen and water vapour. This reaction takes place in the SCR catalyst, which is typically made of a ceramic material coated with catalysts.

SCR systems are highly effective in reducing nitrogen oxide emissions and are commonly used in heavy-duty diesel vehicles, such as trucks and buses.

Frequently Asked Questions 

How many types of catalytic converters are there?

There are several types of catalytic converters, including three-way catalytic converters, oxidation catalytic converters, diesel particulate filters (DPFs), and selective catalytic reduction (SCR) systems. Each type is designed to meet specific emission control requirements and work with different types of engines.

Are there 3 catalytic converters?

No, there are not three catalytic converters in a vehicle. However, some vehicles may have multiple catalytic converters depending on their design and engine configuration. For example, some vehicles may have two catalytic converters, one located in the exhaust manifold and another further downstream in the exhaust system.

What is a 3-way catalytic converter?

A three-way catalytic converter is a type of catalytic converter commonly used in gasoline-powered vehicles. It is designed to simultaneously reduce the levels of carbon monoxide, unburned hydrocarbons, and nitrogen oxides in the exhaust gases. Three-way catalytic converters contain two separate catalysts: a reduction catalyst and an oxidation catalyst.

What is a 2-way catalytic converter?

A two-way catalytic converter, also known as an oxidation catalytic converter, is a type of catalytic converter commonly used in diesel-powered vehicles and some gasoline-powered vehicles. It is primarily designed to reduce the levels of carbon monoxide and unburned hydrocarbons in the exhaust gases. Unlike three-way catalytic converters, two-way catalytic converters do not effectively reduce nitrogen oxide emissions.

Why are catalytic converters stolen?

Catalytic converters are often targeted by thieves because they contain valuable metals, such as platinum, palladium, and rhodium. These metals have a high market value and can be extracted from the catalytic converter for resale. The theft of catalytic converters has become a significant issue in recent years, with many vehicles being targeted for their valuable converter components.