METHOD FOR PRODUCING MOTOR VEHICLE EXHAUST GAS CATALYSTS

Abstract

The present invention is directed to a method and a device for coating substrates of motor vehicle exhaust gas catalysts. In this respect, the substrates can be flow-though substrates or filter systems (“wall flow”). The invention particularly describes an improvement in such coating processes in which a suspension (washcoat) containing the catalytically active material is applied to or delivered onto such a vertically oriented substrate (monolithic substrate) from above (“metered charge” process).

Claims

1. Method for producing catalytically coated monolithic substrates for exhaust gas aftertreatment, wherein the monolithic substrates have two end faces A and B and an outer surface that extends over a length L from end face A to end face B, and wherein the monolithic substrates are traversed by parallel channels which extend from end face A to end face B, characterized in that a) the monolithic substrate is oriented vertically so that one end face A points upward and the other end face B points downward, b) a defined distribution of one or more materials inducing the catalytic activity is metered over end face A by using a device which is movable horizontally and optionally vertically relative to the monolithic substrate in the x/y direction, wherein the metering device used has one or more outlet openings, with which a defined amount of material inducing the catalytic activity can be deposited at each point above the end face, c) the metered material is transported into the monolithic substrate by applying a pressure difference over the monolithic substrate, d) the catalytically coated monolithic substrate is finally dried and calcined, if applicable.

2. Method according to claim 1, characterized in that the material is present as a suspension, a liquid, an emulsion or a foam.

3. Method according to claim 1, characterized in that the material as suspensions, emulsions or foam has a flow limit and a contact angle between material and substrate of >45°.

4. Method according to claim 1, characterized in that a device permeable to the material is located on the end face so that the material inducing the catalytic activity remains first at or on said permeable device and penetrates into the monolithic substrate only after application of the pressure difference in step c).

5. (canceled)

6. Method according to claim 1, characterized in that identical or different materials are metered over the end face.

7. Method according to claim 6, characterized in that the different materials are transported into the substrate simultaneously by applying a pressure difference.

8. Method according to claim 1, characterized in that in the metering device having a plurality of outlet openings, the outlet openings open or close at different times when metering the material.

9. Method according to claim 1, characterized in that the metering device having a plurality of outlet openings meters different materials simultaneously.

10. Method according to claim 1, characterized in that the transporting of the material into the monolithic substrate is controlled by a diffuser mounted below end face B.

11. Apparatus for carrying out a method according to claim 1, characterized in that the following are present: a) a device for vertically orienting the monolithic substrates, b) at least one device movable in the x/y direction horizontally relative to the monolithic substrate for metering a material inducing the catalytic activity from above onto the monolithic substrate, and c) a device for applying a pressure difference over the monolithic substrate to transport the material into the monolithic substrate.

Description

[0053] The invention is explained below in more detail by means of the exemplary figures and examples.

[0054] FIG. 1: Schematic diagram of a monolithic substrate to be coated with a side view and top view; it shows, in particular, the collar (2) around the upper end face of the substrate, which prevents any washcoat from running down the outer wall of the substrate (1).

[0055] FIG. 2: Monolithic substrate (1) with collar (2) and provided coating suspension (3)

[0056] FIG. 2a: Theoretical, uniform profile without taking into account the flow conditions.

[0057] FIG. 2b: Coating profile in the substrate (1) that ensues after suction.

[0058] FIG. 3a: Coating profile using a leveling of coating compound (3) on the upper end face of the monolithic substrate (1)

[0059] FIGS. 3b1-3: Results of a real coating test in comparison with (no. 2) and without (nos. 1/3) leveling of the coating compound on the upper end face.

[0060] FIG. 4: Annularly provided coating suspension according to the invention for producing a coating (3) in outer regions of the substrate (1)

[0061] FIG. 5: Centrally provided coating suspension according to the invention for producing a coating (3) in inner regions of the substrate (1)

[0062] FIG. 6: Template according to the invention of the coating suspension (3a, 3b) with different amounts in the central region and the edge regions

[0063] FIG. 8: Template according to the invention of the coating suspension (3a, 3b) with different amounts in the central region and the edge regions

[0064] FIG. 9: Template according to the invention of the coating suspension (3a, 3b, 3c) with different amounts in three different regions

[0065] FIG. 10: Template according to the invention of the coating suspension (3a, 3b, 3c) with different amounts in three different regions

[0066] FIG. 11a-d: Possible embodiments of multi-nozzle layouts

[0067] FIG. 12: Schematic description of contact angles from 0° to 95° between a porous substrate structure and the coating material

[0068] FIG. 13: Real image of contact angles between coating material and substrate <0° to >90 and its consequences

EXAMPLES

[0069] A ceramic substrate (flow-through substrate) made of cordierite having the following features

Diameter: 118 mm

Length: 114 mm

[0070] Cell density: 93/cm2
Wall thickness: 100 μm
is coated with a washcoat (WC) having a three-way catalyst function. The washcoat has a solid content of 38% (solid dry residue at 350° C.). A simple and rapid measuring method with the Bostwick consistometer ZXCON was used to determine the flow properties of the washcoat (https://www.warensortiment.de/technische-daten/bostwick-consistometer-zxcon.htm). The flow path of a propagating liquid or of a pasty material in a certain time is determined with the Bostwick consistometer. The consistometer consists of a metal channel set up horizontally, which is separated into two differently sized chambers by a vertically movable slider. The washcoat to be measured is filled into the smaller chamber up to a defined height. The larger chamber has a distance scale of 1 cm to 24 cm at the bottom of the channel, on which distance scale the length of the washcoat which has flowed out can be read thirty seconds after the slider has been opened. The flow length is a measure of the flowability of the washcoat (or in other words, the contour stability of the applied washcoat) and physically depends on its viscosity and the flow limit. The washcoat used in this example had a flow length of 3.5 cm and thus a pronounced contour stability.

[0071] The washcoat is applied directly to the upper end face of the flow-through substrate in a circular movement using a movable spray nozzle which has a round opening of Ø 7.0 mm. During metering of the washcoat, different, defined WC profiles are generated on the end face

(FIG. 3b1) more WC in the center of the substrate than on the outside
(FIG. 3b2) uniform WC distribution
(FIG. 3b3) more WC on the outside than in the center of the substrate,
so that a defined WC profile is produced in the substrate. In the second step, the washcoat is then sucked into the substrate with a short pulse (250 mbar, 1 sec.), The different WC distributions of the washcoats on the end face also produce different WC distributions in the substrate after coating.