LOW TEMPERATURE NITROGEN OXIDE ADSORBER

Abstract

The present invention relates to a composite metal oxide which comprises 80 to 97 wt %, in relation to the weight of the composite metal oxide, of one or more oxides of cerium and 3 to 20 wt %, in relation to the composite metal oxide of a metal oxide comprising tin oxide (SnO.sub.2) and lanthanum oxide (La.sub.2O.sub.3) and/or aluminum oxide (AI.sub.2O.sub.3), a composite material for the storage of nitrogen oxides which comprises such composite metal oxide and palladium, as well as an exhaust gas system containing said composite material.

Claims

1. Composite metal oxide which comprises 80 to 97 wt %, in relation to the weight of the composite metal oxide, of one or more oxides of cerium and 3 to 20 wt %, in relation to the composite metal oxide of a metal oxide comprising tin oxide (SnO.sub.2) and lanthanum oxide (La.sub.2O.sub.3) and/or aluminum oxide (Al.sub.2O.sub.3).

2. Composite metal oxide according to claim 1 which comprises 84 to 96 wt %, in relation to the weight of the composite metal oxide, of one or more oxides of cerium and 4 to 16 wt %, in relation to the composite metal oxide, of a metal oxide comprising tin oxide (SnO.sub.2) and lanthanum oxide (La.sub.2O.sub.3) and/or aluminum oxide (Al.sub.2O.sub.3).

3. Composite metal oxide according to claim 1, wherein the metal oxide consists of tin oxide (SnO.sub.2) and lanthanum oxide (La.sub.2O.sub.3).

4. Composite metal oxide according to claim 3, wherein the weight ratio of tin oxide (SnO.sub.2) and lanthanum oxide (La.sub.2O.sub.3) is 4:1 to 1:1.5.

5. Composite material for the storage of nitrogen oxides comprising a composite metal oxide according to claim 1 and palladium.

6. Composite material according to claim 5, wherein the palladium is present in quantities of 0.01 to 20 wt % in relation to the weight of the composite material and calculated as palladium metal.

7. Composite material according to claim 5, wherein it is present in form of a coating on a carrier substrate of the length L.

8. Composite material according to claim 7, wherein the carrier comprises a further coating which is oxidation-catalytically active.

9. Composite material according to claim 1, wherein the oxidation-catalytically-active coating comprises platinum or palladium, or platinum and palladium on a carrier material.

10. Exhaust gas system comprising a) a composite material according to claim 5 and b) an SCR catalyst.

11. Exhaust gas system according to claim 10, wherein the SCR catalyst is a zeolite which belongs to the framework type, BEA, AEI, AFX, CNA, KFI, ERI, LEV, MER, or DDR, and which is exchanged with cobalt, iron, copper, or mixtures of two or three of these metals.

12. Method for cleaning exhaust gases from motor vehicles that are operated with lean-burn engines, characterized in that the exhaust gas is channeled through an exhaust gas system according to claim 10.

13. Composite metal oxide according to claim 2 which comprises 90 to 96 wt % of one or more oxides of cerium.

14. Composite metal oxide according to claim 13 which comprises 4 to 10 wt % of a metal oxide comprising tin oxide (SnO.sub.2) and lanthanum oxide (La.sub.2O.sub.3) and/or aluminum oxide (Al.sub.2O.sub.3).

15. Composite metal oxide according to claim 2 which comprises 4 to 10 wt % of a metal oxide comprising tin oxide (SnO.sub.2) and lanthanum oxide (La.sub.2O.sub.3) and/or aluminum oxide (Al.sub.2O.sub.3).

Description

EXAMPLES 1 TO 4 (NOT ACCORDING TO THE INVENTION)

[0086] Composite metal oxides comprising CeO.sub.2 and SnO.sub.2 were obtained by adding an appropriate amount of CeO.sub.2 to an aqueous solution of an appropriate amount of tin acetate, stirring the mixture 120° C. for 2 hours and maintaining it at 120° C. for further 8 hours. Subsequently the product obtained was milled, evaporated of water and calcined in air at 500° C. for 5 hours. The following products were obtained:

Example 1: 95.8 wt % of CeO.sub.2; 4.2 wt % of SnO.sub.2
Example 2: 88.4 wt % of CeO.sub.2; 11.6 wt % of SnO.sub.2
Example 3: 85.1 wt % of CeO.sub.2; 14.9 wt % of SnO.sub.2
Example 4: 92 wt % of CeO.sub.2; 8 wt % of SnO.sub.2

EXAMPLES 5 TO 11

[0087] Composite metal oxides comprising CeO.sub.2, SnO.sub.2 and La.sub.2O.sub.3 were obtained by adding an appropriate amount of CeO.sub.2 to an aqueous solution comprising appropriate amounts of tin acetate and lanthanum acetate, stirring the mixture 120° C. for 2 hours and maintaining it at 120° C. for further 8 hours. Subsequently the product obtained was milled, separated from the liquid, dried and calcined in air at 500° C. for 5 hours. The following products were obtained:

Example 5: 84.33 wt % of CeO.sub.2; 3.7 wt % of SnO.sub.2; 11.97 of La.sub.2O.sub.3
Example 6: 84.84 wt % of CeO.sub.2; 11.14 wt % of SnO.sub.2; 4.02 of La.sub.2O.sub.3
Example 7: 84.6 wt % of CeO.sub.2; 7.4 wt % of SnO.sub.2; 8 of La.sub.2O.sub.3
Example 8: 95.64 wt % of CeO.sub.2; 2.1 wt % of SnO.sub.2; 2.26 of La.sub.2O.sub.3
Example 9: 91.83 wt % of CeO.sub.2; 6.43 wt % of SnO.sub.2; 1.74 of La.sub.2O.sub.3
Example 10: 91.71 wt % of CeO.sub.2; 4.82 wt % of SnO.sub.2; 3.47 of La.sub.2O.sub.3
Example 11: 91.58 wt % of CeO.sub.2; 3.22 wt % of SnO.sub.2; 5.2 of La.sub.2O.sub.3

EXAMPLES 12 TO 22 (EXAMPLES 12-15 NOT ACCORDING TO THE INVENTION)

[0088] The procedures described above for the manufacture of the composite metal oxides of the Examples 1 to 11 were repeated with the exception that CeO.sub.2 supporting 1.5 wt % of palladium (based on the total weight of CeO.sub.2 and palladium) was used instead of CeO.sub.2 alone. The respective composite materials of Examples 12 to 22 were obtained.

COMPARISON EXAMPLE 1

[0089] Comparison Example 1 is CeO.sub.2 supporting 1.5 wt % of palladium (based on the total weight of CeO.sub.2 and palladium) as commercially available.

COMPARISON TESTS

[0090] a) The products of Comparison Example 1 and Examples 12 to 22 were aged for 16 hours at 800° C. in hydrothermal conditions.
b) The NOx storage capacity of the samples obtained above under a) was determined using the following method:
i) The samples were subjected to an increase of temperature of 10K/min until 550° C. in a lean atmosphere (see Phase 1 in the table below) followed by a cooldown to 100° C.
ii) After that a gas composition comprising NO and NO2 was flown over the samples until full saturation with NOx was observed (see Phase 2 of the table below).

TABLE-US-00001 Phase 1 Pre-treatment Phase 2 RT to 550° C. NOx storage GHSV [1/h] 50000 50000 NO [ppm] 0 50 NO.sub.2 [ppm] 0 50 O.sub.2 [vol %] 8 8 CO.sub.2 [vol %] 10 10 H.sub.2O [vol %] 5 5

[0091] The results obtained are as follows:

TABLE-US-00002 NOx max. NOx 80% conv. NOx 60% conv. Example [mg] [mg] [mg] Example 12 8.01 3.21 5.07 Example 13 7.90 2.99 4.87 Example 14 7.64 2.58 4.61 Example 15 7.85 3.68 5.13 Example 16 7.45 2.19 4.10 Example 17 7.95 3.31 4.95 Example 18 7.91 3.29 4.76 Example 19 8.22 3.11 5.27 Example 20 8.24 3.61 5.33 Example 21 8.39 3.88 5.60 Example 22 8.22 3.49 5.36 Comparison 7.23 2.35 4.32 Example 1