| abstract |
Exhaust gases from internal combustion engines are purified by catalytic treatment. The systems have an initial catalyst, preferably in a separate vessel near the engine, and a subsequently-in-line catalyst. Preferably, the catalysts are of the honeycomb-type. The exhaust gases and an excess of oxygen, with or without a supplemental fuel, are passed through the initial catalyst during the start-up of the engine to insure that the exhaust gases are purified more or less as soon as the engine begins operation. In order to reduce the amount of nitrogen oxides in the exhaust gas after start-up, an excess of extraneous fuel is fed to the initial catalyst to reduce nitrogen oxides to nitrogen. The subsequently-in-line catalyst serves to reduce the carbon monoxide and hydrocarbon contents of the exhaust gases. |