ULTRASOUND-ASSISTED METHOD FOR PRODUCING AN SCR CATALYTIC CONVERTER

Abstract

The present invention relates to a method for producing automobile exhaust gas catalytic converters, to the catalytic converters as such and to the use thereof. In particular, the method comprises a step which results in a smaller particle size of the catalytically active material used.

Claims

1. Method for producing a catalytic converter containing zeolites or zeotypes for the aftertreatment of exhaust gases of a car engine, characterized in that prior to coating onto and/or into a support, the zeolite or zeotype is treated by means of ultrasound in such a way that the particle size thereof is largely reduced to less than 20 m (d50).

2. Method according to claim 1, characterized in that the zeolites or zeotypes are those derived from structure types selected from the group consisting of the CHA, LEV, AEI, AFX, AFI, or KFI framework, or a mixture thereof.

3. Method according to claim 1, characterized in that the zeolite or zeotype is exchanged with iron and/or copper ions.

4. Method according to claim 1, characterized in that the coating comprises a binder selected from the group consisting of aluminum oxide, titanium dioxide, zirconium dioxide, silicon dioxide, or mixtures thereof.

5. Method according to claim 1, characterized in that the support is a wall-flow filter.

6. Method according to claim 1, characterized in that the particle size (d99) is lowered to below 7 m.

7. Method according to claim 1, characterized in that the ultrasound is used with an amplitude of 5 to 100 m.

8. Method according to claim 1, characterized in that the ultrasound has a frequency of 5 to 30 kHz.

9. Method according to claim 1, characterized in that the ultrasound has a power of 500 to 50000 watts.

10. Method according to claim 1, characterized in that the coating suspension is supplied to a pre-drying step after the coating of the support.

11. Catalytic converter for the aftertreatment of exhaust gases of a car engine, produced according to claim 1.

12. Catalytic converter according to claim 11, characterized in that the support is a wall-flow filter.

13. Catalytic converter according to claim 12, characterized in that the support has a loading with the coating of 30 to 200 g/l.

14. A method for the after-treatment of exhaust gases of a car engine comprising placing the exhaust gases in contact with the catalytic converter according to claim 11.

15. Method according to claim 14, characterized in that the exhaust gases are exhaust gases of a lean burning car engine.

16. Method according to claim 14, characterized in that the catalytic converter is a catalytic converter for the selective reduction of nitrogen oxides by means of ammonia.

Description

EXAMPLES

[0066] A ceramic filter consisting of a support body made of silicon carbide (NGK) with a porosity of 63% at an average pore size of 20 m in the dimensions stated in Table 1 was used for the present tests for Examples 1 and 2:

TABLE-US-00001 TABLE 1 Data of the filter support Diameter 165 mm Length 140 mm Cell density 300 cpsi Wall thickness 0.305 mm

[0067] A ceramic flow-through substrate consisting of a support body made of cordierite (NGK) in the dimensions stated in Table 2 was used for the present tests for Examples 3 and 4:

TABLE-US-00002 TABLE 2 Data of the monolithic substrate Diameter 144 mm Length 76 mm Cell density 400 cpsi Wall thickness 0.165 mm

[0068] These are coated in a coating system according to the process described in WO2006021338A1. The following steps are carried out for this purpose:

[0069] a) vertically aligning the flow channels of the support so that one end face is at the bottom and the second end face is at the top;

[0070] b) introducing the coating composition into the support through the flow channels of the support which are open in the lower end face, up to a desired height above the lower end face;

[0071] c) removing excess coating composition toward the bottom.

[0072] During coating, the washcoat is at room temperature, which is usually 20 C. to 40 C., and consists of a suspension of a copper-exchanged zeolite (chabasite) with a solids content of 37%. The suspension is ground in Example 1 and Example 3 by means of a stirred ball mill (for example. Netsch or Hosokawa-Alpine) using zirconium oxide grinding balls having a diameter of 1 mm. After coating, the loading of the support with washcoat is determined by weighing the support. In Examples 2 and 4, the suspension is dispersed to the target particle size by way of an ultrasonic dispersion unit UiP2000 from Hielscher Ultrasonics. In all examples, the d50 value was within the scope of the claims.

EXAMPLES

[0073] 1. Example: Zeolite-containing washcoat milled with a ball mill with d99=6.8 m, dried standing in a convection oven at 120 C. for 30 minutes after coating onto filter substrate, tempered at 350 C. for 30 minutes, subsequently calcined at 550 C. for 2 h (standard process, not according to the invention). [0074] 2. Example: Zeolite-containing washcoat dispersed by means of ultrasound with d99<6.7 m (Hielscher UiP 2000, 2 kW, 3 bar, 100% amplitude) according to the method according to the invention, dried standing in a convection oven at 120 C. for 30 minutes after coating onto filter substrate, tempered at 350 C. for 30 minutes, subsequently calcined at 550 C. for 2 hours. [0075] 3. Example: Zeolite-containing washcoat milled with a ball mill with d99=25.0 m, dried standing in a convection oven at 120 C. for 30 minutes after coating onto flow-through monolith, tempered at 350 C. for 30 minutes, subsequently calcined at 550 C. for 2 h (standard process, not according to the invention). [0076] 4. Example: Zeolite-containing washcoat dispersed by means of ultrasound with d99=25.5 m (Hielscher UiP 2000, 2 kW, 3 bar, 100% amplitude) according to the method according to the invention, dried standing in a convection oven at 120 C. for 30 minutes after coating onto flow-through monolith, tempered at 350 C. for 30 minutes, subsequently calcined at 550 C. for 2 hours.

[0077] In order to determine the catalytic effectiveness of the coated supports, they are aged for 16 hours under hydrothermal conditions (10% water) at 800 C. after calcination and subsequently tested with respect to their activity in the selective catalytic reduction of NOx on a model gas test stand. In the present case, this takes place in a dynamic test based on an ammonia breakthrough criterion under the gas conditions shown in Table 3.

TABLE-US-00003 TABLE 3 Gas composition of the testing of catalytic activity on a model gas test stand at T = 175 C., 225 C., 250 C., and 350 C. Gas Proportion NOx 500 ppm NO2 0 ppm NH3 750 ppm O2 10% by volume CO 350 ppm C3H6 100 ppm H2O 5% by volume N2 Remainder

[0078] Table 4 shows the results of the measurements of the exhaust gas back pressures and NOx conversion rates of the differently manufactured wall-flow filters.

TABLE-US-00004 TABLE 4 Data for characterization of the filters from Examples 1 and 2 Loading Pressure increase at X (NOx) at 250 C. Example (g/L) 600 m.sup.3/h (%) after aging (%) 1 120 49% 68% 2 120 32% 75%

[0079] FIG. 2: NOx conversion of Examples 1 to 2 at T=175 C. to 350 C. on the model gas under the gas composition indicated in Table 3.

[0080] Table 5 shows the results of the measurements of the NOx conversion rates of the differently produced flow-through monoliths.

TABLE-US-00005 TABLE 5 Data for characterization of the flow- through monoliths from Examples 3 and 4 Loading X (NOx) at 250 C. X (NOx) at 650 C. Example (g/L) after aging (%) after aging (%) 3 200 68% 10% 4 200 75% 25%

[0081] FIG. 3: NOx conversion of Examples 3 to 4 at T=175 C. to 350 C. on the model gas under the gas composition indicated in Table 3.