Integrated SCR and AMOx catalyst systems

• US 8,524,185 B2
• Filed: 11/03/2008
• Issued: 09/03/2013
• Est. Priority Date: 11/03/2008
• Status: Active Grant

• Current Assignee: BASF Corporation (BASF SE)
• Original Assignee: BASF Corporation (BASF SE)
• Inventors: Caudle, Matthew Tyler, Dieterle, Martin, Buzby, Scott E.
• Primary Examiner(s): Mayes, Melvin Curtis
• Assistant Examiner(s): DAVIS, SHENG HAN
• Application Number:
  US12/263,871
• Publication Number:
  US 20100111796A1
• Time in Patent Office: 1,765 Days
• Field of Search: None
• US Class Current: 423/237
• CPC Class Codes: B01D 2251/2062 Ammonia
• CPC Class Codes: B01D 2255/102 Platinum group metals
• CPC Class Codes: B01D 2255/104 Silver
• CPC Class Codes: B01D 2255/106 Gold
• CPC Class Codes: B01D 2255/20738 Iron
• CPC Class Codes: B01D 2255/20761 Copper
• CPC Class Codes: B01D 2255/50 Zeolites
• CPC Class Codes: B01D 2258/012 Diesel engines and lean burn gasoline engines
• CPC Class Codes: B01D 53/9418 for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• CPC Class Codes: B01D 53/9436 Ammonia
• CPC Class Codes: B01D 53/9468 in different layers
• CPC Class Codes: B01J 23/42 Platinum
• CPC Class Codes: B01J 29/72 containing iron group metals, noble metals or copper
• CPC Class Codes: B01J 29/7615 Zeolite Beta
• CPC Class Codes: B01J 35/19 Catalysts containing parts with different compositions
• CPC Class Codes: B01J 35/56 Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
• CPC Class Codes: B01J 37/0225 of metal substrates
• CPC Class Codes: B01J 37/0244 Coatings comprising several layers
• CPC Class Codes: B01J 37/0246 Coatings comprising a zeolite
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02C 20/10 : of nitrous oxide (N2O)
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies
• CPC Class Codes: Y10T 428/24149 : Honeycomb-like

Abstract

Catalysts, methods of preparing catalyst, and methods for treating exhaust gas streams are described. In one or more embodiments, a catalyst system includes an upstream zone effective to catalyze the conversion of a mixture of NO_x and NH₃ to N₂, and a downstream zone effective for the conversion of ammonia to N₂ in the presence or absence of NO_x. In an embodiment, a method for preparing a catalyst system includes: first coating one end of a substrate along at least 5% of its length with an undercoat washcoat layer containing a material composition effective to catalyze the removal of ammonia; second coating with an overcoat layer containing a material composition effective to catalyze the conversion of a mixture of NO_x and NH₃ to N₂. A method for treating the exhaust gas stream is provided, which includes injecting ammonia or an ammonia precursor into an exhaust gas stream of a vehicle, passing the engine exhaust gas stream containing NO_x and NH₃ through the upstream zone of a catalyst system to remove NO_x and then passing the exhaust gas stream through the downstream zone of the catalyst system to remove NH₃, as well as other oxidizable species such as hydrocarbons and CO.

Claims

1. A catalyst system for treating an exhaust gas stream containing NOx, the system comprising:

at least one monolithic catalyst substrate having an inlet end and an outlet end;

an undercoat washcoat layer coated on one the outlet end of the monolithic substrate and which covers less than 100% of the total length of the monolithic substrate, and containing a material composition A effective for catalyzing NH3 oxidation;

an overcoat washcoat layer coated over a total length of the monolithic substrate from the inlet end to the outlet end sufficient to overlay the undercoat washcoat layer, and containing a material composition B effective to catalyze selective catalytic reduction (SCR) of NOx; and

wherein material composition A and material composition B are maintained as physically separate catalytic compositions.

2. The catalyst system of claim 1, wherein the monolithic substrate is a flow-through honeycomb substrate comprising a plurality of fine, substantially parallel gas flow passages extending along the longitudinal axis of the substrate.

3. The catalyst system of claim 2, wherein the undercoat washcoat layer covers in the range of about 10% and 40% of the total substrate length, and the overcoat washcoat layer covers in the range of about 5% and 100% of the total substrate length.

4. The catalyst system of claim 2, wherein the substrate is a single monolithic substrate.

5. The catalyst system of claim 2, wherein the undercoat washcoat layer also contains a material composition further effective to catalyze SCR of NO_x.

6. The catalyst system of claim 2, wherein the material composition B contains a zeolitic or non-zeolitic molecular sieve.

7. The catalyst system of claim 6, wherein the material composition B contains an aluminosilicate molecular sieve having the one of the crystal framework types FAU, MFI, MOR, and BEA.

8. The catalyst system of claim 6, wherein the material composition B contains an aluminosilicate molecular sieve having a CHA crystal framework type.

9. The catalyst system of claim 6, wherein the material composition B contains a silicoaluminophosphate molecular sieve having the CHA crystal framework type.

10. The catalyst system of claim 6, wherein the molecular sieve contains a metal from one of the groups VB, VIIB, VIIB, VIIIB, IB, or IIB of the periodic table distributed on or within the molecular sieve, the metal being present in an amount between 0.1% and 10% by wt. of the molecular sieve.

11. The catalyst system of claim 10, wherein the metal is selected from Cu, Fe, and mixtures or combinations thereof.

12. The catalyst system of claim 10, wherein the metal is Fe.

13. The catalyst system of claim 10, wherein the metal is Cu.

14. The catalyst system of claim 2, wherein the material composition A comprises a precious metal component dispersed on support particles.

15. The catalyst system of claim 14, wherein the support particles comprise a refractory metal oxide containing alumina, silica, zirconia, titania, ceria, and physical mixtures or chemical combinations thereof, including atomically doped combinations.

16. The catalyst system of claim 14, wherein the precious metal component comprises ruthenium, rhodium, iridium, palladium, platinum, silver, or gold and physical mixtures or chemical combinations thereof, including atomically doped combinations.

17. A catalyst system for treating an exhaust gas stream containing NO_x, the system comprising:

at least one flow-through honeycomb substrate comprising a plurality of fine, substantially parallel gas flow passages extending along the longitudinal axis of the substrate;

an undercoat washcoat layer coated on the outlet end of the honeycomb substrate, and containing a material composition A comprising a precious metal effective for catalyzing NH₃ oxidation;

an overcoat washcoat layer coated over a total length of the honeycomb substrate from the inlet end to the outlet end of the substrate sufficient to overlay the undercoat washcoat layer, and containing a material composition B free from precious metal effective for catalyzing selective catalytic reduction (SCR) of NO_x;

wherein the undercoat washcoat layer covers in the range of about 10% to about 40% of the total honeycomb substrate length, and wherein material composition A and material composition B are maintained as physically separate catalytic compositions.