The invention relates to a device for reducing pollutant gas emissions by means of catalyst management in the combustion process, characterised in that it comprises: a hollow cylindrical body with a fuel inlet hole in one side of said cylindrical body and a fuel outlet hole in the other side of said cylindrical body; a perforated cylindrical separator inside said body; and a sheet formed by at least one magnetic element and which is situated between the perforated separator and the inner wall of the hollow cylindrical body, such that when the fuel flows inside the device, part of the components of the hydrocarbon magnetise.