In a process for producing an SCR catalyst for the selective reduction of NOx in NOx-containing exhaust gases of internal combustion engines, a support layer is applied to a substrate body. An iron salt dissolved in a liquid is applied to the support layer in such an amount that no excess of iron salt is present.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows, very schematically, an embodiment of the structure of the catalyst of the invention; and
FIG. 2 schematically shows an apparatus according to the invention for the selective reduction of NOx.
Claims
1. A process for producing an SCR catalyst for the selective reduction of NOx in NOx-containing exhaust gases of internal combustion engines, said process comprising the steps of: applying a support layer to a substrate body, and applying to said support layer an iron salt dissolved in a liquid in such an amount that no excess of iron salt is present.
2. A process as claimed in claim 1, wherein said liquid is water.
3. A process as claimed in claim 1, wherein said support layer comprises a zeolite.
4. A process as claimed in claim 1, wherein said support layer comprises a nanosize oxidic material.
5. A process as claimed in claim 1, wherein application of said iron salt to said support layer forms an iron oxide such that the proportion of iron within such support layer is 0.1-5 per cent by mass.
6. A process as claimed in claim 1, wherein at least one promoter is applied to said support layer in addition to said iron oxide.
7. A process as claimed in claim 1, wherein said substrate body comprises a ceramic material serving as particle filter.
8. A process as claimed in claim 1, wherein said substrate body comprises a metal.
9. A catalyst for use in a selective reduction of NOx in NOx-containing exhaust gases of internal combustion engines with introduction of a reducing agent into the exhaust gases, said catalyst comprising: a substrate body, a support layer applied to the substrate body, an active component applied to said support layer and at least one promoter applied to said support layer, said active component comprising iron oxide and said at least one promoter being selected from the group consisting of tungsten, zirconium and molybdenum.
10. A catalyst as claimed in claim 9, wherein said support layer has a surface area of at least 50 m2/g, in particular at least 100 m2/g.
11. A catalyst as claimed in claim 9, wherein the substrate body comprises a honeycomb body which is composed of a ceramic material and serves as a particle filter.
12. A catalyst as claimed in claim 9, wherein said substrate body comprises a metal substrate.
13. An apparatus for the selective reduction of NOx in NOx-containing exhaust gases of internal combustion engines, said apparatus, comprising: a catalyst, a reducing agent feed facility for introducing a reducing agent into an exhaust gas line in which said catalyst is located, said reducing agent being selected from the group consisting of ammonia and an NH3 precursor.
14. An apparatus as claimed in claim 13, wherein said reducing agent feed facility comprises a feed opening which communicates with said exhaust gas line and further comprises a closure whose openness can be altered by means of a control device.
15. An apparatus as claimed in claim 14, wherein said control device is connected to at least one of: (i) an NOx sensor and, (ii) a temperature sensor.
16. A process for the selective reduction of NOx in NOx-containing exhaust gases of an internal combustion engine, said process comprising the steps of:
(a) providing a catalyst, said catalyst comprising a substrate body, a support layer on said substrate body, an active component on said support layer and at least one promoter on said support layer, and(b) introducing into an exhaust gas line through which said exhaust gases flow, a substance which comprises at least one of (i) a reducing agent, and (ii) a precursor of a reducing agent.
17. A process as claimed in claim 16, wherein said substance comprises NH3.
18. A process as claimed in claim 16 wherein said substance comprises urea.
19. A process as claimed in claim 16 wherein said promoter is selected from the group consisting of tungsten, zirconium and molybdenum.
20. A process as claimed in claim 16 wherein said substance is introduced into said exhaust line by way of a valve coupled to a control device.
21. A process as claimed in claim 20 wherein said control device is coupled to at least one of: (i) a NOx sensor and (ii) a temperature sensor.
22. A process as claimed in claim 20 wherein said support layer is impregnated with iron by means of a process which comprises the step of applying to said support layer an iron salt solution.
23. A process as claimed in claim 22 said solution contains an amount of iron salt selected such that the presence of excess iron salt on the support layer is avoided.
Patent Application
20070173404
