You're probably thinking of the Catalytic converter, which is in the exhaust system and looks like a canister usually under the car around the front seats, but there are many systems imposed on vehicles to reduce emissions, such as an exhaust gas recirculation valve which takes some of the hot air from the exhaust and runs it through the engine again.
Catalytic converters.
carbon monoxide is a rich indicator, if you are producing too much, you have a fuel system problem.
Hydro carbons, oxides of nitrogen and carbon monoxide. HC, NOx, and CO
They reduce emissions of three harmful compounds found in car exhaust: Carbon monoxide, Nitrogen oxides, and Hydrocarbons.
Cars do not have anything in their exhaust to reduce carbon monoxide. A Catalytic Convertor in the Exhaust System is used to remove Carbon Monoxide from the exhaust gasses.
If you want to reduce your carbon footprint, you can reduce your emissions of CO2 (carbon dioxide) into the atmosphere.
By its self it does not reduce carbon emissions. What it does do is provide an alternative source of energy that does not create any more carbon emissions. Though, this will only become effective when solar energy is more cost effective than carbon based energy.
Recycle things such as plastic so as to reduce the use of plastic.
carbon offsets
catalyitic converters reduce pollution by converting carbon monoxide into carbon dioxide which is a less harmful gas
the Coke supplies carbon monoxide to reduce the ore in a blast furnace and supplies heat to melt the iron.
Government should decrees the taxes.