What is the name of the device fitted to car exhausts to reduce pollution?

Catalytic Converter

The Catalytic Converter (commonly known as a Cat) is a device fitted in the exhaust system of your car that effectively reduces the harmful exhaust gases entering the atmosphere.

Catalytic Converters have been fitted to almost all petrol cars after 1994 in the UK. Cats are also now fitted to many diesel cars. Cats are fitted to reduce the pollution in the atmosphere. The Cat works quietly and, with no moving parts, you would not be aware of it being there.

The Cat works by filtering the exhaust gases through an internal honeycomb section known as a Monolith or a Catalyst. This Monolith (made of either Ceramic or Metal) is coated with precious metals such as Platinum, Palladium and Rhodium that act as a filter for the harmful gases.

Once these gases flow through the Monolith they are largely converted in a chemical reaction into non-harmful emissions such as water and carbon dioxide.

The Cat that converts these three gases below and this is known as a 'three way Catalytic Converter'.

http://www.ukcar.com/features/tech/others/Catalytic-Convertor/index.htm

Black Box Device:

CO2 Emission Reduction Technology
SINGLE SOLUTION: A single solution to further reduce CO2 emissions from cars does exist. Climate Cleanups "Black Box Device" is simply and easily fitted to the existing car exhaust pipe. No modifications of any component are required.

https://www.environmental-expert.com/news/cheap-co2-emission-reduction-technology-25668