Abstract: The invention concerns a system (20) used to reduce pollutant emissions in the form of hydrocarbons, carbon monoxides and nitric oxides from internal combustion engines, in particular from ships' engines or stationary engines. The catalyst housing (40) is covered by a gas-insulation hood (24) which is open upstream for the waste gas (18) to be decontaminated and is closed downstream. The gas-insulation hood (24) comprises a water cooler (28) which at least in some cases rests on the exterior thereof. The gas-insulation hood (24) preferably takes the form of a baffle silencer of known type of construction.