Exhaust gas treatment is based on metal foams using catalytic coatings. A catalytic converter for diesel and gasoline engines includes oxidation catalysts, 3-way catalysts, de-NOx catalysts, NH3 slip catalysts. Foam high surface areas and high mixing rates enhance catalytic performance. Particulate filtration in both diesel and direct injection gasoline engines uses deep bed filtration. A multiple-pass radial flow uses more than one foam segments, separated by a diaphragm. Filtration, pressure drop and catalytic performance are enhanced using variable foam porosities in axial and radial flow directions and non-uniform catalyst coatings. More than one catalytic functionalities may be incorporated in a single shell. Secondary foam segments are placed within main foam segments. Diaphragms at the entrance and exit of the external shell allow the flow to be divided between the main and the secondary foam segments according to the respective flow resistances.