Patent attributes
Exhaust gas aftertreatment system for internal combustion engines operated with a lean mixture, wherein nitrogen oxides are reduced by an SCR catalyst, and particulates are removed by a particle separator or filter. A thermolysis catalyst is located near the engine in the exhaust gas split stream downstream of the supply point of the reducing agent. At temperatures above 135° C., this thermolysis catalyst vaporizes the water component of the aqueous urea solution. It contains a catalyst material that is thermally stable at exhaust gas temperatures occurring near the engine and preferentially reacts with the urea to form isocyanic acid. A hydrolysis catalyst is located in the exhaust gas stream downstream of the return of the split stream into the main stream of exhaust gas. The hydrolysis catalyst converts the isocyanic acid formed during thermolysis to ammonia and carbon dioxide using water vapor formed in the thermolysis catalyst.
