Why would somebody steal your ‘cat’?

Catalytic converters have become a target for theft, thanks to their precious metals

Catalytic converters (also referred to as “cats”) have been widely used in vehicle production for more than 50 years. They’re designed to reduce the emissions produced by your car.

Most people probably don’t know their car has one, but they are quite valuable and there have been recent cases of criminals getting under cars and stealing them to sell for a healthy profit.

Why do vehicles need one?

Catalytic converters change harmful substances in a car’s exhaust gases into less harmful output like carbon dioxide and water vapour, through chemical reactions.

As part of normal vehicle fuel combustion, emissions are expelled from the exhaust; the main three are nitrogen gas, carbon dioxide and water vapour.

Other harmful emissions can be found in the exhaust, such as carbon monoxide — a poisonous gas that is colourless and odourless. Hydrocarbons or volatile Organic compounds (VOCs) are produced mostly from evaporated unburned fuel and nitrogen oxides. These are a contributor to smog and acid rain, which can cause irritation to human mucus membranes.

How do catalytic converters work?

In chemistry, a catalyst is a substance that causes or accelerates a chemical reaction without being affected itself. Catalysts participate in the reactions, but are neither reactants nor products of the reaction that they catalyse.

In the catalytic converter, there are two different types of catalyst at work: a reduction catalyst and an oxidation catalyst. Both consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. The idea is to create a structure that exposes the maximum surface area of catalyst to the exhaust stream, while also minimising the amount of catalyst required as the materials are very expensive. Some of the newest converters use gold mixed with the more traditional catalysts.

Types of catalytic converters

There are various types of catalytic converters. There’s a simple “twoway” oxidation catalytic converter which works to turn carbon monoxide into carbon dioxide and hydrocarbons — particles of unburnt fuel — to carbon dioxide and water.

The “three-way” catalytic converter fitted to modern cars does the same as the above while also reducing emissions of nitric oxide and nitrogen dioxide (together, more commonly known as NOx), a major cause of localised air pollution.

Different on a diesel

Many diesel vehicles have special catalytic converters to cope with the specific emissions from compression-ignition engines.

These diesel oxidation catalyst (DOC) units are routinely paired with additional exhaust treatment technologies such as exhaust gas recirculation (EGR), diesel particulate filters (DPF) to trap soot, and selective catalytic reduction (SCR), which uses injections of diesel exhaust fluid (DEF) like AdBlue urea solution to remove NOx.

Why would someone want to steal a catalytic converter? Catalytic converters are coated with precious metals to help with the catalyst generation. These metals can be quite lucrative for someone wanting to recycle them. For example, the spot price per ounce of platinum was recently more than $1500; palladium was more than $3700. Overseas, used complete converters are sold on the black market to take advantage of a supply shortage of new ones. The situation is similar to more than a decade ago, where criminals would strip copper wiring or pipes from houses to sell for scrap.

Why are some more valuable than others?

Hybrid cars like the Toyota Prius are potentially popular with thieves because they have two power sources — an electric motor and a petrol engine — so their catalytic converters are used less frequently to process pollutants. This means the metals inside them are less likely to have corroded, making them more valuable.

How do I stop theft?

● Park your car in a locked garage or a well-lit area in public view with the car close to a wall or fence to prevent the vehicle being jacked up

● Have a vehicle alarm installed with sensors that warn you if the vehicle gets jacked up

● Instal a home security camera system and/or signs warning of CCTV cameras in operation

● Get your car’s VIN number etched into the casing of your catalytic converter

● Ask a garage to weld the bolts on your catalytic converter, or use commercial anti-theft devices that will make it harder to remove.

If you suspect your exhaust system has been tampered with or stolen, the best giveaway is that when you start the car, your exhaust system will sound very loud (almost like a tractor) and you will most likely see a warning light in the dashboard. In this case we recommend that you visit aa.co. nz/repair to find your nearest AA Auto Centre or AA Approved Repairer.