Perovskite catalyst system for lean burn engines

Abstract

A catalyst system for use with an internal combustion engine to provide emissions reductions under lean and stoichiometric operating conditions. The catalyst system comprises a first catalyst comprised of a newly developed Perovskite-based formulation having an ABO 3 crystal structure designed to bring the precious metal and NO x trapping elements close together. The first catalyst acts primarily to maximize the reduction of emissions under lean operating conditions. The catalyst system also comprises a second catalyst comprised of precious metals which acts primarily to maximize the reduction of emissions under stoichiometric conditions.

1 . A catalyst for optimizing the storage of NO x  emissions under lean air/fuel ratios, comprising:
 a Perovskite-type ABO 3  crystal structure wherein the A cation sites are occupied by lanthanide ions and the B cation sites are occupied by cobalt ions, wherein from about 1 to up to 70% of the lanthanide A cation sites are substituted with a NO x  trapping metal selected from the group consisting of barium, magnesium and potassium to result in a charge balanced crystal structure that forms oxygen vacancies to promote NO x  storage, wherein from about 1 to up to 60% of the cobalt B cation sites are substituted with a metal selected from the group consisting of platinum, rhodium, iron, copper and manganese; and   wherein the substituted A sites and B sites are selected to ensure close proximity between the two at a molecular level to improve thermal stability and NO x  reducing capability.   
     
     
         2 . A method of reducing emissions from an exhaust gas stream comprising:
 providing a first catalyst for optimizing the storage of NO x  emissions under lean air/fuel ratios, comprising a Perovskite-type ABO 3  crystal structure wherein the A cation sites are occupied by lanthanide ions and the B cation sites are occupied by cobalt ions, wherein from about 1 to up to 70% of the lanthanide A cation sites are substituted with a NO x  trapping metal selected from the group consisting of barium, magnesium, strontium and potassium to result in a charge balanced crystal structure that forms oxygen vacancies to promote NO x  storage, wherein from about 1 to up to 60% of the cobalt B cation sites are substituted with a metal selected from the group consisting of platinum, rhodium, iron, copper and manganese; wherein the substituted A sites and B sites are selected to ensure close proximity between the two at a molecular level to improve thermal stability and NO x  reducing capability; and   providing a second catalyst for optimizing the reduction of hydrocarbon, NO x  and CO emissions under stoichiometric air/fuel ratios comprising a catalyst mixture PM-Rh wherein PM is a catalyst material selected from the group consisting of platinum, palladium and combinations thereof wherein the first and second catalysts are closely coupled, the first catalyst being placed in a forward position and the second catalyst being placed in a downstream position in the exhaust stream.