Selective catalytic reduction type catalyst, and exhaust gas purification equipment and purifying process of exhaust gas using the same

• US 20080286184A1
• Filed: 05/05/2008
• Published: 11/20/2008
• Est. Priority Date: 05/09/2007
• Status: Active Grant

• Current Assignee: N.E. Chemcat Corporation
• Original Assignee: N.E. Chemcat Corporation
• Inventors: Kanno, Yasuharu, Ando, Ryuji, Nagata, Makoto, Hihara, Takashi
• Granted Patent: US 7,906,449 B2
• Time in Patent Office: Days
• US Class Current: 423/213.5
• CPC Class Codes: B01D 2251/2062 Ammonia
• CPC Class Codes: B01D 2251/2067 Urea
• CPC Class Codes: B01D 2255/1021 Platinum
• CPC Class Codes: B01D 2255/1023 Palladium
• CPC Class Codes: B01D 2255/1025 Rhodium
• CPC Class Codes: B01D 2255/206 Rare earth metals
• CPC Class Codes: B01D 2255/20707 Titanium
• CPC Class Codes: B01D 2255/20715 Zirconium
• CPC Class Codes: B01D 2255/20738 Iron
• CPC Class Codes: B01D 2255/20776 Tungsten
• CPC Class Codes: B01D 2255/2092 Aluminium
• CPC Class Codes: B01D 2255/30 Silica
• CPC Class Codes: B01D 2255/502 Beta zeolites
• CPC Class Codes: B01D 2255/504 ZSM 5 zeolites
• CPC Class Codes: B01D 2255/9022 Two layers
• CPC Class Codes: B01D 2255/9027 More than three layers
• CPC Class Codes: B01D 2255/91 NOx-storage component incorporated in the catalyst
• CPC Class Codes: B01D 2258/012 Diesel engines and lean burn gasoline engines
• CPC Class Codes: B01D 53/9413 Processes characterised by a specific catalyst
• CPC Class Codes: B01D 53/9436 Ammonia
• CPC Class Codes: B01D 53/9468 : in different layers
• CPC Class Codes: B01D 53/9477 : with catalysts positioned on separate bricks, e.g. exhaust systems
• CPC Class Codes: B01J 21/06 : Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
• CPC Class Codes: B01J 21/063 : Titanium; Oxides or hydroxides thereof
• CPC Class Codes: B01J 23/42 : Platinum
• CPC Class Codes: B01J 23/63 : with rare earths or actinides
• CPC Class Codes: B01J 29/46 : Iron group metals or copper
• CPC Class Codes: B01J 29/7615 : Zeolite Beta
• CPC Class Codes: B01J 37/0244 : Coatings comprising several layers
• CPC Class Codes: B01J 37/0246 : Coatings comprising a zeolite
• CPC Class Codes: B01J 37/0248 : Coatings comprising impregnated particles

Abstract

The present invention relates to a technology to purify nitrogen oxides contained in exhaust gas exhausted from lean combustion engines such as diesel engine with ammonia and a selective catalytic reduction type catalyst, and an object of the present invention is to provide a selective catalytic reduction type catalyst which can effectively purify nitrogen oxides even at a low temperature as well as inhibit leak of ammonia, and an exhaust gas purification equipment and a purifying process of exhaust gas using the same.

The present invention is a selective catalytic reduction type catalyst for purifying nitrogen oxides in exhaust gas exhausted from lean combustion engines using ammonia or urea as a reducing agent, it is provided with a selective catalytic reduction type catalyst, characterized in that said catalyst comprises a lower-layer catalyst layer (A) having an oxidative function for nitrogen monoxide (NO) in exhaust gas and an upper-layer catalyst layer (B) having an adsorbing function for ammonia on the surface of a monolithic structure type carrier (C), and that the lower-layer catalyst layer (A) comprises a noble metal component (i), an inorganic base material constituent (ii) and zeolite (iii), and the upper-layer catalyst layer (B) comprises substantially none of component (i) but the component (iii).

Claims

1. A selective catalytic reduction type catalyst for purifying nitrogen oxides in exhaust gas exhausted from lean combustion engines using ammonia or urea as a reducing agent, characterized in that the catalyst comprises a lower-layer catalyst layer (A) having an oxidative function for nitrogen monoxide (NO) in exhaust gas and an upper-layer catalyst layer (B) having an adsorbing function for ammonia on the surface of a monolithic structure type carrier (C), and that the lower-layer catalyst layer (A) comprises the following components of (i), (ii) and (iii), on the other hand, the upper-layer catalyst layer (B) comprises substantially none of the following component (i) but the component (iii):

(i) one or more kinds of noble metals selected from platinum, palladium and rhodium;

(ii) one or more kinds of oxides selected from alumina, titania, silica, zirconia, tungsten oxide, transition metal oxides, rare earth oxides, or composite oxide thereof, and

(iii) zeolite.

2. The selective catalytic reduction type catalyst according to claim 1, characterized in that the component (i) in the lower-layer catalyst layer (A) comprises platinum as a noble metal component, and content thereof per unit volume of the monolithic type carrier (C) is 0.05 to 3 g/L.

3. The selective catalytic reduction type catalyst according to claim 1, characterized in that content of the component (ii) in the lower-layer catalyst layer (A) per unit volume of the monolithic type carrier (C) is 5 to 80 g/L.

4. The selective catalytic reduction type catalyst according to claim 1, characterized in that the component (iii) in the lower-layer catalyst layer (A) or the upper-layer catalyst layer (B) comprises β

-type zeolite and/or MFI-type zeolite.

5. The selective catalytic reduction type catalyst according to claim 1, characterized in that the component (iii) in the lower-layer catalyst layer (A) or the upper-layer catalyst layer (B) comprises at least one kind of iron component or cerium component.

6. The selective catalytic reduction type catalyst according to claim 1, characterized in that content of the component (iii) in the lower-layer catalyst layer (A) per unit volume of the monolithic type carrier (C) is 5 to 80 g/L.

7. The selective catalytic reduction type catalyst according to claim 1, characterized in that the lower-layer catalyst layer (A) or the upper-layer catalyst layer (B) further comprises the following component (iv) as a catalytic promoter component:

(iv) one or more kinds of oxides selected from rare earth oxides, transition metal oxides, tin oxide, or composite oxides thereof.

8. The selective catalytic reduction type catalyst according to claim 1, characterized in that thicknesses of the lower-layer catalyst layer (A) and the upper-layer catalyst layer (B) are each substantially in a range from 5 to 200 μ

m.

9. The selective catalytic reduction type catalyst according to claim 1, characterized in that the lower-layer catalyst layer (A) is coated on the monolithic structure type carrier (C), and directly thereon the upper-layer catalyst layer (B) is coated so as to be a top layer where directly contacts with the aforementioned exhaust gas flow.

10. The selective catalytic reduction type catalyst according to claim 1, characterized in that content of the component (iii) in the upper-layer catalyst layer (B) per unit volume of the monolithic type carrier (C) is 10 to 160 g/L.

11. An exhaust gas purification catalyst equipment formed by arranging an oxidation catalyst (DOC) having an oxidative function for nitrogen monoxide and hydrocarbon and a selective catalytic reduction type catalyst (SROC) having an oxidative function layer according to claim 1 in the subsequent stage thereof, in a flow path of exhaust gas, characterized in that a spraying means to supply an urea aqueous solution or an aqueous ammonia solution is arranged in the downstream of the aforementioned oxidation catalyst and in the upstream of aforementioned selective catalytic reduction type catalyst.

12. The exhaust gas purification catalyst equipment according to claim 11, characterized in that a selective catalytic reduction (SCR) catalyst having substantially no oxidative function layer is further arranged in the upstream of the aforementioned selective catalytic reduction type catalyst (SROC) having an oxidative function layer and in the downstream of the aforementioned spraying means.

13. A purifying process of exhaust gas, characterized by comprising, using the exhaust gas purification catalyst equipment according to claim 11;

passing exhaust gas exhausted from lean combustion engines through the aforementioned oxidation catalyst (DOC) to convert nitrogen monoxide in exhaust gas to nitrogen dioxide;

subsequently supplying by spraying an urea aqueous solution or an ammonia component thereto;

then passing the exhaust gas through the aforementioned selective catalytic reduction type catalyst (SROC) to reduce and purify nitrogen oxides in exhaust gas.

14. A purifying process of exhaust gas, characterized by comprising, using the exhaust gas purification catalyst equipment according to claim 12;

passing exhaust gas exhausted from lean combustion engines through the aforementioned oxidation catalyst (DOC) to convert nitrogen monoxide in exhaust gas to nitrogen dioxide;

subsequently supplying by spraying an urea aqueous solution or an ammonia component thereto;

then passing the exhaust gas through the aforementioned selective catalytic reduction catalyst (SCR) to reduce nitrogen oxides in the exhaust gas;

further passing the exhaust gas through the aforementioned selective catalytic reduction type catalyst (SROC) to oxidize and purify surplus ammonia in the exhaust gas.

15. The selective catalytic reduction type catalyst according to claim 2, characterized in that content of the component (ii) in the lower-layer catalyst layer (A) per unit volume of the monolithic type carrier (C) is 5 to 80 g/L.

16. The selective catalytic reduction type catalyst according to claim 2, characterized in that the component (iii) in the lower-layer catalyst layer (A) or the upper-layer catalyst layer (B) comprises β

-type zeolite and/or MFI-type zeolite.

17. The selective catalytic reduction type catalyst according to claim 2, characterized in that the component (iii) in the lower-layer catalyst layer (A) or the upper-layer catalyst layer (B) comprises at least one kind of iron component or cerium component.

18. The selective catalytic reduction type catalyst according to claim 2, characterized in that content of the component (iii) in the lower-layer catalyst layer (A) per unit volume of the monolithic type carrier (C) is 5 to 80 g/L.

19. The selective catalytic reduction type catalyst according to claim 2, characterized in that the lower-layer catalyst layer (A) or the upper-layer catalyst layer (B) further comprises the following component (iv) as a catalytic promoter component:

(iv) one or more kinds of oxides selected from rare earth oxides, transition metal oxides, tin oxide, or composite oxides thereof.

20. The selective catalytic reduction type catalyst according to claim 2, characterized in that thicknesses of the lower-layer catalyst layer (A) and the upper-layer catalyst layer (B) are each substantially in a range from 5 to 200 μ

m.