Filter for treating a gas such as the exhaust gas stream from a diesel engine, which exhaust gas often conveys carbon particles into the atmosphere. The treating filter comprises a casing holding a plurality of serially arranged filter beds. The latter are comprised of monolith ceramic discs, and are maintained in spaced apart relationship by spacer rings to define a turbulation chamber between adjacent beds. Said beds are provided with an oxidation catalyst to promote incineration of the retained particles. The beds further serve to reinforce and support a non-rigid filtering media contained within the respective chambers.