Process for the reduction of nitrogen oxides and sulphur oxides in the exhaust gas from internal combustion engine

Method for reducing amounts oxides of nitrogen and sulphur in exhaust gas from a lean burn internal combustion engine, the method comprising the steps of:

• passing the exhaust gas together with an adjusted amount of ammonia through a catalyst system comprising one or more catalysts being active in the reaction of nitrogen oxides to nitrogen, the ammonia is introduced into the exhaust as such or is formed after introduction into the exhaust gas prior to passage of the exhaust gas through the catalyst system;
• passing the thus treated exhaust gas through turbine in a turbocharger;
• and
• removing sulphur trioxide and/or ammonium sulphur compounds being present in the exhaust from the turbocharger in a down stream exhaust gas treatment step,
• wherein the exhaust gas is passed through the catalyst system at a temperature above condensation temperature of ammonium sulphur compounds formed by reaction with ammonia in the exhaust gas and wherein the amount of ammonia in the exhaust gas is adjusted to result in an amount of less than 2 ppm by volume or more than 10 ppm by volume after passage through the catalyst system.