High-filtration efficiency wall-flow filter

Abstract

The invention relates to a method for producing a wall-flow filter for removing fine particulate solids from gases, and to the use thereof for cleaning exhaust gases of an internal combustion engine. The invention also relates to a correspondingly produced exhaust-gas filter having a high filtration efficiency.

Claims

1. A method for producing a wall-flow filter for purifying gases from small particulate solids, wherein a dry powder/gas aerosol is applied to the inlet region of the dry filter, characterized in that the powder contains a pyrogenic, high-melting metal compound produced by flame hydrolysis or flame oxidation from a metal precursor in a flame, and the amount of pyrogenic high-melting compound in the filter is less than 5 g/l, and wherein the pyrogenic high-melting compound is subjected to a shear force prior to the application to the filter.

2. Method according to claim 1, characterized in that the pyrogenic high-melting compound is selected from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide, zirconium dioxide, cerium oxide, iron oxide, zinc oxide, mixed oxides of the aforementioned oxides or mixtures thereof.

3. Method according to claim 1, characterized in that the shear force is caused by one or more devices selected from the group consisting of a wear-free atomizer nozzle, a wind sifter, a mill, and a baffle plate.

4. Method according to claim 1, characterized in that the average particle size (d50) of the pyrogenic high-melting compound is between 0.1 μm and 50 μm.

5. Method according to claim 1, characterized in that the pyrogenic high-melting compound has a BET surface area of >50 m.sup.2/g.

6. Method according to claim 1, characterized in that the pyrogenic high-melting compound in the powder/gas aerosol is mixed with further non-pyrogenic high-melting compounds.

7. Method according to claim 1, characterized in that the wall-flow filter has been catalytically coated prior to application of the pyrogenic high-melting compound.

8. Method according to claim 1, characterized in that the pyrogenic and/or non-pyrogenic compounds themselves are catalytically active.

9. Method according to claim 1, wherein the shear force is caused, at least in part, by an atomizer nozzle against which the pyrogenic high-melting compound contacts and is broken up.

10. Method according to claim 1, wherein the shear force is caused, at least in part, by a baffle plate against which the pyrogenic high-melting compound contacts and is broken up.

11. Method according to claim 1, wherein the shear force is caused by contact of the pyrogenic high-melting compound first against an atomizer nozzle and subsequently against a baffle plate.

12. Method according to claim 1, wherein the shear force is caused by at least two devices selected from the group consisting of a wear-free atomizer nozzle, a wind sifter, a mill, and a baffle plate.

13. Method according to claim 1, wherein the pyrogenic high-melting compound in the powder/gas aerosol is a catalytically active pyrogenic high-melting compound and is mixed with a non-pyrogenic high-melting compound which is also catalytically active.

14. Method according to claim 1, wherein the wall-flow filter is catalytically coated with a coating having metal ion exchanged zeolite prior to application of the pyrogenic high-melting compound.

15. Method according to claim 1, wherein the powder contains a pyrogenic, high-melting metal compound produced by flame hydrolysis.

16. Method according to claim 1, wherein the powder contains a pyrogenic, high-melting metal compound produced by flame oxidation.

17. Method according to claim 1, wherein the high-melting metal compound is dispersed within an aerosol gas; and the high-melting metal compound and aerosol gas are then fed into a stream of a diluent transportation gas supply.

18. Method according to claim 17, wherein the diluent transportation gas supply has a lower flow rate than the aerosol gas and high melting compound mixture flow rate that occurs at a time of being subjected to fluid-dynamic stress.

19. A wall-flow filter formed by the method according to claim 1.

20. A method for the purification of automobile gases comprising passing the automobile gases through the wall-flow filter according to claim 19.

Description

EXAMPLE 1

(1) Coating a raw washcoat-free filter having dimensions 4.66″×6.00″ 300/8 with powder.

(2) The pyrogenically produced powder was dispersed with the aid of an atomizer nozzle at 2 bar and sucked into the filter at a rate of 20 m/s.

(3) TABLE-US-00003 Relative* increase Relative* in filtration pressure efficiency increase 0.6 g pyrogenic Al.sub.2O.sub.3/liter filter volume 5.5%   2% 1.2 g pyrogenic Al.sub.2O.sub.3/liter filter volume 9% 3% 0.3 g pyrogenic Al.sub.2O.sub.3 + 1.2 g Al.sub.2O.sub.3 6% 1% with a d50 of 3 μm/liter filter volume *Relative to an uncoated raw filter substrate without additional powder coating

Example 2

(4) In a 1st step, the filter was coated with 50 g/l washcoat in the porous filter wall, dried and calcined. It was then coated with 2 g/l pyrogenically produced powder. The powder was dispersed at 2 bar with the aid of a wear-free atomizer nozzle and sucked into the filter at a rate of 20 m/s. The filtration efficiency increase and the increase in pressure loss were determined at 600 m.sup.3/h relative to the powder-free filter.

(5) TABLE-US-00004 Relative* increase Relative* in filtration pressure efficiency increase 2 g pyrogenic Al.sub.2O.sub.3/liter filter volume 47% 10% *Relative to the substrate coated only with washcoat