A filtering device for diesel engines is based on metal foams. In order to achieve high filtration efficiency with low pressure drop using deep bed filtration metal foams, a radial flow concept is used based on a “porosity gradient”. The foams can also be coated with catalytically active material to enhance soot oxidation (regeneration), as well as reduction of other exhaust gas pollutants (CO, hydrocarbons, nitrogen oxides). This may be accomplished by using non-uniform amounts of catalytic materials within the filter depending on the targeted application. An additional secondary filter segment may be placed within the metal support of the main filter segment. The metallic diaphragms at the entrance and exit of the external shell are designed in such a way as to allow the flow to be divided between the main and the secondary filter segments according to the respective flow resistances.