Abstract: A catalyst system for converting hydrocarbons, carbon monoxide and nitrogen oxides contained in exhaust gas generated by an internal combustion engine. The catalyst system comprises: first, second, and third catalyst bricks arranged in series in an exhaust gas passage of an internal combustion engine downstream of an exhaust gas manifold. The first brick has the smallest volume and is closely coupled to an exhaust gas manifold of the engine and the first catalyst brick is positioned adjacent to and spaced apart from the second catalyst brick by a predetermined distance of no more than 10 inches. Each catalyst brick individually comprises a substrate material coated with a metallic catalyst carried on a porous support, wherein the metallic catalyst provided on the first brick comprises palladium.