Process for producing metal oxide particle and exhaust gas purifying catalyst
First Claim
1. A process for producing a metal oxide particle comprising a core part and a surface layer differing in the composition, the process comprising:
- providing a sol containing at least a population of first colloid particles and a population of second 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 first colloid particles than to the isoelectric point of said population of second colloid particles, thereby aggregating said population of first colloid particles, adjusting the pH of said sol to be closer to the isoelectric point of said population of second colloid particles than to the isoelectric point of said population of first colloid particles, thereby aggregating said population of second colloid particles onto said population of first colloid particles aggregated, and drying and firing the obtained aggregate.
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Abstract
The present invention provides an exhaust gas purifying catalyst and a process for producing a metal oxide particle comprising multiple species of metal oxides and capable of satisfactorily exerting the properties of respective metal oxides. A process of the present invention comprises providing a sol containing at least a population of first colloid particles and a population of second colloid particles differing in the isoelectric point with each other; adjusting the pH of the sol to be closer to the isoelectric point of the population of first colloid particles than to the isoelectric point of the population of second colloid particles, thereby aggregating the population of first colloid particles; adjusting the pH of the sol, thereby aggregating the population of second colloid particles onto the population of first colloid particles aggregated; and drying and firing the obtained aggregate.
49 Citations
11 Claims
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1. A process for producing a metal oxide particle comprising a core part and a surface layer differing in the composition, the process comprising:
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providing a sol containing at least a population of first colloid particles and a population of second 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 first colloid particles than to the isoelectric point of said population of second colloid particles, thereby aggregating said population of first colloid particles, adjusting the pH of said sol to be closer to the isoelectric point of said population of second colloid particles than to the isoelectric point of said population of first colloid particles, thereby aggregating said population of second colloid particles onto said population of first colloid particles aggregated, and drying and firing the obtained aggregate. - View Dependent Claims (2, 3, 4, 5)
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6. An exhaust gas purifying catalyst for internal combustion engine, comprising a particulate support and a noble metal supported thereon,
wherein the particulate support comprises a core part and a surface layer, the molar fraction of the zirconium constituting the zirconia in the core part being higher than the molar fraction of the zirconium constituting the zirconia in the surface layer, and the molar fraction of the cerium constituting the ceria in the surface layer being higher than the molar fraction of the cerium constituting the ceria in the core part; -
wherein said core part and said surface layer each comprises a plurality of primary particles;
wherein the composition of the boundary between said core part and said surface layer is gradually changing; and
wherein the content of ceria in the particulate support being 40 to 65 mol % or less. - View Dependent Claims (7, 8, 9, 10, 11)
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Specification