Patent ID: 8695329

Claim:
A process for decreasing the amount of nitrogen oxides present in the lean exhaust gas from an internal combustion engine by selective catalytic reduction by means of ammonia, comprising: oxidizing a portion of nitrogen monoxide present in an exhaust gas to nitrogen dioxide over a precatalyst, the precatalyst containing at least one oxidation-active catalytic component, the gas has a target NO 2 /NO x ratio of from 0.3 to 0.7 prior to passing, together with ammonia, over the reduction catalyst; and regualting a temperature of the precatalyst independently of an operating state of the engine, by temperature-control device that selectively heats and cools the precatalyst, so that the target NO 2 /NO x ratio is achieved, wherein regulating the temperature of the precatalyst by the temperature-control device includes selectively heating and cooling the precatalyst such that the exhaust gas has a first NO 2 /NO x ratio prior to entering the particle filter, the first NO 2 /NO x ratio being a ratio that compensates for a reaction between the exhaust gas and soot loading of the particle filter such that the exhaust gas has the target NO 2 /NO x ratio upon interacting with an SCR-active catalytic coating of the reduction catalyst.