Catalyst System for Use in Exhaust Gas Purification Apparatus for Automobiles, Exhaust Gas Purification Apparatus Using the Catalyst System, and Exhaust Gas Purification Method

摘要

This invention provides a catalyst system for use in an exhaust gas purification apparatus for automobiles, which, in contact of an exhaust gas discharged from an internal combustion engine in an automobile with a catalyst, can realize an excellent purification capability for nitrogen oxides even in the case where the concentration of hydrocarbons is varied, and an exhaust gas purification apparatus using the catalyst system, and an exhaust gas purification method. The catalyst system comprises two or more exhaust gas purification catalysts including a first catalyst supported on an inorganic structure carrier and a second catalyst different from the first catalyst. The catalyst system is characterized in that the first catalyst, when placed in an exhaust gas flow passage, is supported on the inorganic structure carrier in its part located on the upstream side while the second catalyst, when placed in an exhaust gas flow passage, is supported on the inorganic structure carrier in its part located on the downstream side and contains a cerium-zirconium-based composite oxide (A) having a pyrochlore phase in its crystal structure.