Embodiments of the invention pertain to a catalyst, which may be used in a catalytic converter for treating a gas stream containing pollutants. In an embodiment, the catalyst comprises a substrate having a plurality of axially enclosed channels defined by the porous wall elements extending between an inlet end and an outlet end. Washcoat particles are disposed substantially within the pores of the walls, and the surfaces of the wall elements have a porous, rough texture after coating with the washcoat and substantially no fillets formed on the channels.