# US 7,745,371 B2 · Exhaust gas purifying catalyst, metal oxide particle and production process thereof

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- Number: US 7,745,371 B2
- Document ID: US7745371B2
- Status: Granted
- Kind: B2
- Application number: 10/588,603
- Filed: 2005-03-08
- Published: 2007-08-02
- Granted: 2010-06-29
- Earliest claimed: 2004-03-09
- Assignees: Toyota Jidosha Kabushiki Kaisha
- Inventors: Takeshi Hirabayashi; Oji Kuno; Masahide Miura
- Web page: https://patentgrep.com/patent/US7745371B2

## CPC

- B01J 23/10: of rare earths
- B01D 53/945: {characterised by a specific catalyst}
- B01J 23/63: with rare earths or actinides
- B01J 37/0211: {using a colloidal suspension}
- B01J 37/0244: {Coatings comprising several layers}
- B01D 2255/102: Platinum group metals
- B01D 2255/206: Rare earth metals
- B01J 35/397: {Egg shell like}
- Y02T 10/12: Improving ICE efficiencies
- B01J: CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28)
- Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION

## Abstract

In order to provide an exhaust gas purifying catalyst having improved heat resistance and OSC, a metal oxide particle, and a production process of the metal oxide particle, a metal oxide particle having a core (1) where the total molar number of alumina and silica is larger than the molar number of ceria, and a surface layer (2) where the molar number of ceria is larger than the total molar number of alumina and silica is provided. Further, an exhaust gas purifying catalyst comprising the metal oxide particle and a noble metal supported on the metal oxide particle; and a production process of the metal oxide particle are provided.

## Claims

### Claim 1

A process for producing a metal oxide particle having a core where the total molar number of alumina and silica is larger than the molar number of ceria, and a surface layer where the molar number of ceria is larger than the total molar number of alumina and silica, said process comprising:
preparing a solution containing a ceria sol and a sol of at least either one of alumina and silica, wherein the isoelectric point of the ceria sol differs more than 3.5 from that of said at least one of alumina and silica sol,
adjusting the pH of said solution to be closer to the isoelectric point of the sol of at least either one of alumina and silica than to the isoelectric point of the ceria sol, and to fall within and ±2.0 of the isoelectric point of alumina and/or silica sol, and
aggregating the sol from said solution to produce an aggregate.

### Claim 2 (depends on 1)

The process according to claim 1, wherein the molar ratio of (Al+Si):Ce in the metal oxide particle is from 1:0.5 to 0.5:1.

### Claim 3 (depends on 1)

The process according to claim 1, wherein the pH of said solution is adjusted to be closer to the isoelectric point of the sol of at least either one of alumina and silica than to the isoelectric point of the ceria sol, and to fall within ±0.5 of the isoelectric point of alumina and/or silica sol.

### Claim 4 (depends on 1)

A process for producing an exhaust gas purifying catalyst, wherein the process comprises producing a metal oxide particle by the process according to claim 1, and then loading a noble metal on said metal oxide particle.