An exhaust-gas purification unit for purifying the exhaust gas from an internal combustion engine which is preferably operated in lean-burn mode, in particular a diesel engine used in motor vehicles, has a particulate filter and a SCR catalytic converter arranged in the exhaust pipe in succession in the direction of flow, and a reducing-agent supply. Ammonia can be added to the exhaust gas from the internal combustion engine on the entry side of the SCR catalytic converter by the reducing-agent supply. The exhaust-gas purification unit includes a hydrogen-generating unit for enriching the exhaust gas from the internal combustion engine with the hydrogen which it generates.