Process for reducing NO2 from combustion system exhaust

A method for reducing an amount of NO2 in an exhaust gas mixture of an internal combustion engine, the exhaust gas mixture having a mixture of carbon monoxide, hydrocarbons, and NO2, the NO2 being present in a first NO2 concentration, the method consisting of:

• contacting a first portion of the exhaust gas mixture with a first catalyst, the first catalyst including platinum in an amount from about 0.1 to 300 g/cubic foot, the exhaust mixture being a diesel exhaust, the first catalyst including a first precious metal, the first portion of the exhaust gas mixture being converted into a first oxidized exhaust mixture comprising NO2 in a second NO2 concentration, the second NO2 concentration being greater than the first NO2 concentration;
• passing a second portion of the exhaust gas mixture through a bypass;
• combining the second portion of the exhaust gas mixture with the first oxidized exhaust mixture at a position downstream of the first catalyst to produce a combined exhaust gas mixture;
• and
• contacting the combined exhaust gas mixture with a second catalyst positioned downstream of the first catalyst such that NO2 is consumed in oxidizing the carbon monoxide and hydrocarbons from the second portion, the second catalyst including palladium in an amount from about 2 to 300 g/cubic foot, the second catalyst including palladium, the second catalyst converting the combined exhaust gas mixture to a second combined exhaust gas mixture, the second combined exhaust gas mixture having NO2 present in a third NO2 concentration, the third NO2 concentration being less than the second NO2 concentration such that a portion of the NO2 in the first oxidized exhaust mixture is converted to NO, a diameter and the positioning of the bypass determining an amount of unreacted gas and associated reductants delivered to the second catalyst.