An internal combustion engine of a motor vehicle has an adsorption catalyst which may be loaded with nitrogen oxides and unloaded. During the unloading, the exhaust-gas stream through the adsorption catalyst may be decreased by a control unit or an add-on device, using a valve. During the unloading, a fuel/air mixture may be added to the exhaust-gas stream reaching the adsorption catalyst, by the control unit or the add-on device, using an atomizer. Upon switching over from the unloading to the loading of the adsorption catalyst, the addition of the fuel/air mixture to the exhaust-gas stream is initially stopped by the control unit or the add-on device. The decreasing of the exhaust-gas stream is then ended after a predefined flushing time.