Metal oxide particle, production process thereof and exhaust gas purifying catalyst
AssigneeToyota Jidosha Kabushiki Kaisha
InventorMasahide Miura
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Abstract
The present invention provides a metal oxide having a combination of multiple properties useful in the production of an exhaust gas purifying catalyst, a production process thereof, and an exhaust gas purifying catalyst for purifying the components in an exhaust gas. The metal oxide particle of the present invention comprises a core part 1 relatively rich in a ceria-zirconia solid solution and a surface layer 2 relatively rich in a second metal oxide such as ceria or zirconia.
Claims6
An exhaust gas purifying catalyst comprising platinum supported on a metal oxide particle comprising a core part and a surface layer, wherein:
- a molar fraction of cerium and zirconium constituting a ceria-zirconia solid solution in the core part to all the metals in the core part is higher than a molar fraction of the cerium and zirconium constituting a ceria-zirconia solid solution in the surface layer to all the metals in the surface layer;
- and
- a molar fraction of cerium constituting ceria in the surface layer to all the metals in the surface layer is higher than a molar fraction of the cerium constituting the ceria in the core part to all the metals in the core part,
- wherein said core part and said surface layer each comprises a plurality of primary particles, and the primary particles constituting said core part are particles of ceria-zirconia solid solution.
A process for producing an exhaust gas purifying catalyst, the method comprising:
- producing metal oxide particles including:
- providing a sol containing at least a population of ceria-zirconia solid solution colloid particles and a population of ceria colloid particles differing in the isoelectric point with each other,
- adjusting the pH of said sol to be closer to the isoelectric point of said population of ceria-zirconia solid solution colloid particles than to the isoelectric point of said population of ceria colloid particles, thereby aggregating said population of ceria-zirconia solid solution colloid particles,
- adjusting the pH of said sol to be closer to the isoelectric point of said population of ceria colloid particles than to the isoelectric point of said population of ceria-zirconia solid solution colloid particles, thereby aggregating said population of ceria colloid particles onto said population of ceria-zirconia solid colloid particles aggregated, and
- drying and firing the obtained aggregate;
- and
- loading platinum on said metal oxide particles:
- wherein:
- the metal oxide particle comprises a core part and a surface layer;
- a molar fraction of cerium and zirconium constituting a ceria-zirconia solid solution in the core part to all the metals in the core part is higher than a molar fraction of the cerium and zirconium constituting a ceria-zirconia solid solution in the surface layer to all the metals in the surface layer;
- and
- a molar fraction of cerium constituting ceria in the surface layer to all the metals in the surface layer is higher than a molar fraction of the cerium constituting the ceria in the core part to all the metals in the core part;
- wherein said core part and said surface layer each comprises a plurality of primary particles, and the primary particles constituting said core part are particles of ceria-zirconia solid solution.
Dependencies are inferred from the claim text.