Catalyst for exhaust gas purification and process for production thereof

A catalyst for exhaust gas purification, comprising:

• a heat-resistant inorganic carrier;
• a first catalyst layer loaded on said carrier, said first catalyst layer comprising a catalyst composition containing at least one noble metal selected from the group consisting of Pt and Pd, and active alumina, said catalyst composition maintaining a specific surface area of not less than 50 m.sup.2 /g and a porosity of not less than 50% after the catalyst composition is held at 1,000.degree. C. for 20 hours in air;
• and
• a second catalyst layer loaded on said first catalyst layer, said second catalyst layer comprising a second catalyst composition containing active alumina and Rh loaded thereon, wherein said second catalyst composition maintains a specific surface area of not less than 50 m.sup.2 /g and a porosity of not less than 50% after the catalyst composition is held at 1,000.degree. C. for 20 hours in air.

A process for producing a catalyst for exhaust gas purification, comprising the steps of:

• hydrolyzing an aluminum salt or an aluminum alkoxide derivative to obtain an alumina precursor sol or gel;
• drying said sol or gel under a supercritical temperature and pressure to obtain an alumina porous material;
• firing the material at a temperature of not less than 500.degree. C. to obtain active alumina;
• adding at least one noble metal selected from the group consisting of Pt, Pd and Rh to said active alumina to obtain a catalyst composition;
• and
• forming a catalyst layer containing said catalyst composition on a heat-resistant inorganic carrier, wherein said catalyst composition maintains a specific surface area of not less than 50 m.sup.2 /g and a porosity of not less than 50% after the catalyst composition is held at 1,000.degree. C. for 20 hours in air.

The A process for producing a catalyst for exhaust gas purification, comprising the steps of:

• forming a noble-dispersed alumina precursor sol or gel by adding at least one noble metal selected form the group consisting of Pt, Pd and Rh to an aluminum salt or aluminum alkoxide derivative;
• drying said sol or gel under a supercritical temperature and pressure to obtain a noble metal-dispersed alumina porous material;
• firing the material at a temperature of not less than 500.degree. C. to obtain an noble metal-dispersed active alumina, thereby forming a catalyst composition;
• and
• forming a catalyst layer containing the catalyst composition on a heat-resistant inorganic carrier, wherein said catalyst composition maintains a specific surface area of not less than 50 m.sup.2 /g and a porosity of not less than 50% after the catalyst composition is held at 1,000.degree. C. for 20 hours in air.

A process for producing a catalyst for exhaust gas purification, comprising the steps of:

• forming an alumina-rare earth composite precursor sol or gel by adding a rare earth component to an aluminum salt or an aluminum alkoxide derivative;
• drying said sol or gel under a supercritical temperature and pressure to obtain an alumina rare-earth composite porous material;
• adding at least one noble metal selected from the group consisting of Pt, Pd and Rh to the material to obtain a catalyst composition;
• and
• forming a catalyst layer containing the catalyst composition on a heat-resistant inorganic carrier, wherein said catalyst composition maintains a specific surface area of not less than 50 m.sup.2 /g and a porosity of not less than 50% after the catalyst composition is held at 1,000.degree. C. for 20 hours in air.

A process for producing a catalyst for exhaust gas purification, comprising the steps of:

• forming an alumina-rare earth composite precursor sol or gel by adding a rare earth component to an aluminum salt or an aluminum alkoxide derivative;
• drying the sol or gel under a supercritical temperature and pressure to obtain an alumina-rare earth composite porous material;
• firing the material at a temperature of not less than 500.degree. C. to obtain an active alumina-rare earth composite;
• adding at least one noble metal from the group consisting of Pt, Pd and Rh to the composite to obtain a catalyst composition;
• and
• forming a catalyst layer containing the catalyst composition on a heat-resistant inorganic carrier, wherein said catalyst composition maintains a specific surface area of not less than 50 m.sup.2 /g and a porosity of not less than 50% after the catalyst composition is held at 1,000.degree. C. for 20 hours in air.

A process for producing a catalyst or exhaust gas purification, comprising the steps of:

• forming a noble metal-dispersed alumina-rare earth composite precursor sol or gel by adding a rare earth component and at least one noble metal selected from the group consisting of Pt, Pd and Rh to an aluminum salt or aluminum alkoxide;
• drying the sol or gel under a supercritical temperature and pressure to obtain a noble metal-dispersed alumina-rare earth composite porous material;
• firing the material at a temperature of not less than 500.degree. C. to obtain a catalyst composition;
• and
• forming a catalyst layer containing the catalyst composition on a heat-resistant inorganic carrier, wherein said catalyst composition maintains a specific surface area of not less than 50 m.sup.2 /g and a porosity of not less than 50% after the catalyst composition is held at 1,000.degree. C. for 20 hours in air.