Porous material process of producing the porous material, catalyst for purifying exhaust gas comprising the porous material, method of purifying exhaust gas
Disclosed are a porous material comprising particles without substantial fibrous structure and having pores, the pores having a mean pore diameter in a meson-pore region, sharp pore size distribution, and at least a part of the pores being connected three-dimensionally to form a three-dimensional network structure with random passages, the porous material preferably being of alumina and having a spongy structure or the porous material preferably being an aggregate of particles having an aspect ratio of 3 or less; a process of producing the porous material which includes a step of aging a system capable of becoming an oxide on thermal decomposition; a catalyst for exhaust gas purification having excellent NO x removal performance, high resistance against sulfur poisoning, and satisfactory high-temperature durability which comprises the porous material as a carrier having supported thereon a noble metal and an NO x storage component; and a method of exhaust gas purification using the catalyst.
1. A porous material, comprising:
particles without substantial fibrous structure;
wherein said porous material has pores;
wherein the pores have a mean pore diameter in a meso-pore region; and
wherein at least a part of the pores are connected three-dimensionally to form a three-dimensional network structure with random passages.
2. The porous material according to claim 1 , wherein said mean pore diameter is in a range of from 2 to 100 nm.
3. The porous material according to claim 1 , wherein said particles are alumina; and
wherein said three-dimensional network structure has a spongy structure.
4. A process for producing the porous material according to claim 1 , comprising:
(1) preparing a system capable of becoming an oxide on thermal decomposition;
(2) aging said system at or above room temperature for a prescribed time to form a precursor; and
(3) calcining the precursor to form the porous material according to claim 1
wherein said aging is carried out in saturated vapor or nearly saturated vapor for a prescribed period of time to form a precursor.
5. The porous material according to claim 1 , wherein said porous material is amorphous and the pores exist on a surface and in an inside of said porous material.
6. The porous material according to claim 5 , wherein a volume of the pores within 5 nm of the mean pore diameter occupies 70% or more of a total meso-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
7. The porous material according to claim 5 , wherein a volume of the pores within 5 nm of the mean pore diameter occupies 80% or more of a total meso-pore volume; or
wherein the volume of the pores within 3 nm of the mean pore diameter occupies 70% or more of the total meso-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
8. The porous material according to claim 5 , wherein a volume of the pores within 3 nm of the mean pore diameter occupies 90% or more of a total mew-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
9. The porous material according to claim 1 , wherein the particles have an aspect ratio of 3 or smaller and aggregate together to form pores among the particles.
10. The porous material according to claim 9 , wherein the particles are crystalline oxides which are connected three-dimensionally to form pores among the particles.
11. The porous material according to claim 10 , which comprises at least one of a crystalline oxide or a crystalline complex oxide selected from the group consisting of alumina, zirconia, titania, magnesia, iron oxide, and ceria.
12. The porous material according to claim 10 , wherein said porous material is an alumina porous material; and
wherein a volume of the pores within 5 nm of the mean pore diameter occupies 70% or more of a total meso-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
13. The porous material according to claim 10 , wherein said porous material is an alumina porous material; and
wherein a volume of the pores within 5 nm of the mean pore diameter occupies 80% or more of a total meso-pore volume; or
wherein a volume of the pores within 3 nun of the mean pore diameter occupies 70% or more of a total meso-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
14. The porous material according to claim 10 , wherein said porous material is an alumina porous material; and
wherein a volume of the pores within 3 nm of the mean pore diameter occupies 90% or more of a total meso-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
15. The porous material according to claim 10 , wherein said porous material is a zirconia porous material; and
wherein a volume of the pores within 5 nm of the mean pore diameter occupies 40% or more of a total meso-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
16. The porous material according to claim 10 , wherein said porous material is a titania porous material; and
wherein a volume of the pores within 5 nm of the mean pore diameter occupies 50% or more of a total meso-pore volume; or
wherein a volume of the pores within 3 nm of the mean pore diameter occupies 40% or more of a total meso-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
17. The porous material according to claim 10 , wherein said porous material is a magnesia porous material; and
wherein a volume of the pores within 5 nm of the mean pore diameter occupies 80% or more of a total meso-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
18. The porous material according to claim 10 , wherein said porous material is a ceria porous material; and
wherein a volume of the pores within 5 nm of the mean pore diameter occupies 70% or more of a total meso-pore volume; or
wherein a volume of the pores within 3 nm of the mean pore diameter occupies 55% or more of a total meso-pore volume; and
wherein said total meso-pore volume is the volume of pores whose diameter is in a range of 2 to 100 nm.
19. A catalyst for purifying exhaust gases, comprising:
a carrier; and
a noble metal supported on said carrier;
wherein at least a part of said carrier comprises the porous material according to claims 5 or 10 .
20. A catalyst for purifying exhaust gases, comprising:
a carrier;
an NOX storage component comprising at least one member selected from the group consisting of an alkali metal, an alkaline earth metal, and a rare earth element, wherein said NOX storage component is supported on said carrier; and
a noble metal supported on said carrier, in which at least a part of said carrier comprises the porous material according to claim 5 or 10 .