US Patent 7473665 Exhaust gas-purifying catalyst system

An exhaust gas-purifying catalyst system is provided with a plurality of catalyst layers including a first and a second catalyst layers, supported on a support structure. The first catalyst layer comes into contact with an exhaust gas stream firstly among the plurality of catalyst layers. The second catalyst layer is provided adjacent to the first catalyst layer. The first catalyst layer contains a first noble metal active component including rhodium, together with a powder of a barely soluble barium compound in an amount of 0.05 mol to 0.2 mol per volume in liter of the support structure. The second catalyst layer contains a second noble metal active component.