DOUBLE-LAYER THREE-WAY CATALYST WITH FURTHER IMPROVED AGEING STABILITY

Abstract

The present invention relates to a catalyst comprising two layers on an inert catalyst carrier, a layer A containing at least palladium as a platinum group metal, in addition to a cerium/zirconium/lanthanum/yttrium mixed oxide, and a layer B, which is applied to layer A, containing at least rhodium as the platinum group metal, in addition to a cerium/zirconium/lanthanum/yttrium mixed oxide.

Claims

1. Catalyst comprising two layers arranged on top of each other on an inert catalyst support, wherein a layer A contains at least palladium as a platinum group metal as well as a cerium/zirconium/lanthanum/yttrium mixed oxide, and a layer B applied to layer A contains at least rhodium as a platinum group metal, as well as a cerium/zirconium/lanthanum/yttrium mixed oxide, characterized in that, in both layers A and B, the lanthanum oxide content is between 1% by weight and 5% by weight, based on the cerium/zirconium/lanthanum/yttrium mixed oxide, and the yttrium oxide content is between 8% by weight and 20% by weight, based on the cerium/zirconium/lanthanum/yttrium mixed oxide.

2. Catalyst according to claim 1, characterized in that layer A and/or layer B, independently of one another, additionally contain platinum as a further platinum group metal.

3. Catalyst according to claim 1, characterized in that layer A contains only palladium and layer B only rhodium or layer B only palladium and rhodium as platinum group metal.

4. Catalyst according to claim 1, characterized in that layer A and layer B contain active aluminum oxide.

5. Catalyst according to claim 4, characterized in that the platinum group metal in layer A and/or in layer B is supported wholly or in part on active aluminum oxide.

6. Catalyst according to claim 1, characterized in that the weight ratio of cerium oxide to zirconium oxide in the cerium/zirconium/RE metal mixed oxide in layer A and layer B is 0.1 to 1.0.

7. Catalyst according to claim 1, characterized in that layer A lies directly on the inert catalyst support.

Description

EXAMPLES

[0034] In the following example 1 and in comparative example 1, double-layer catalysts were produced by twice coating flow-through honeycomb bodies made from ceramic with 93 cells per cm.sup.2 and with a wall thickness of 0.11 mm, as well as dimensions of 10.6 cm in diameter and 11.4 cm in length. To this end, two different suspensions were produced, respectively for layer A and B. The support was first coated with the suspension for layer A and then calcined in air for 4 hours at 550° C. Subsequently, the support coated with layer A was coated with the suspension for layer B and then calcined under the same conditions as for layer A.

Example 1

[0035] A double-layer catalyst was produced by first producing two suspensions. The composition of the first suspension for layer A (based on the volume of the catalyst support) was 66 g/L with 4% by weight of La.sub.2O.sub.3 stabilized activated aluminum oxide, 66 g/L of cerium/zirconium/lanthanum/yttrium mixed oxide with 24% by weight of CeO.sub.2, 60% by weight of ZrO.sub.2, 3.5% by weight of La.sub.2O.sub.3 and 12.5% by weight of Y.sub.2O.sub.3, 16 g/L BaSO.sub.4, 1.413 g/L Pd.

[0036] The composition of the second suspension for layer B (based on the volume of the catalyst support) was 60 g/L with 4% by weight of La.sub.2O.sub.3 stabilized activated aluminum oxide, 47 g/L of cerium/zirconium/lanthanum/yttrium mixed oxide with 24% by weight of CeO.sub.2, 60% by weight of ZrO.sub.2, 3.5% by weight of La.sub.2O.sub.3 and 12.5% by weight of Y.sub.2O.sub.3, 0.177 g/L Rh.

Comparative Example 1

According to EP3045226A1

[0037] A double-layer catalyst was produced analogously to example 1. The composition of the first suspension for layer A was 66 g/L with 4% by weight of La.sub.2O.sub.3 stabilized activated aluminum oxide, 66 g/L of cerium/zirconium/lanthanum/yttrium mixed oxide with 25% by weight of CeO.sub.2, 67.5% by weight of ZrO.sub.2, 3.5% by weight of La.sub.2O.sub.3 and 4% by weight of Y.sub.2O.sub.3, 16 g/L BaSO.sub.4, 1.143 g/L Pd.

[0038] The composition of the second suspension for layer B was 60 g/L with 4% by weight of La.sub.2O.sub.3 stabilized activated aluminum oxide, 47 g/L of cerium/zirconium/lanthanum/yttrium mixed oxide with 24% by weight of CeO.sub.2, 60% by weight of ZrO.sub.2, 3.5% by weight of La.sub.2O.sub.3 and 12.5% by weight of Y.sub.2O.sub.3, 0.177 g/L Rh.

[0039] Example 1 and comparative example 1 were aged in an engine test bench aging process. In each case, two similar catalysts were exposed to the hot exhaust gas one after the other. The aging process consisted of an overrun cut-off aging process with an exhaust gas temperature of 950° C. before the catalyst input. This resulted in a maximum bed temperature of 1100° C. in the first catalyst (CC1) and a maximum bed temperature of 1040° C. in the second catalyst (CC2). The aging time was 100 hours.

[0040] Subsequently, an engine test bench was used to test the start-up performance at a constant average air ratio λ, and the dynamic conversion with a change in λ.

[0041] Table 1 contains the temperatures T.sub.50 at which in each case 50% of the component in question are converted. Here, the start-up performance with a stoichiometric exhaust gas composition (λ=0.999 with ±3.4% amplitude) was determined.

TABLE-US-00001 T.sub.50 HC T.sub.50 CO T.sub.50 NOx stoichiometric stoichiometric stoichiometric Comparative 476  >500° C.  >500° C. example 1 CC1 Example 1 CC1 428 464 452 Comparative 404 410 412 example 1 CC2 Example 1 CC2 364 362 363

[0042] The dynamic conversion performance was determined in a range for λ of 0.99 to 1.01 at a constant temperature of 510° C. The amplitude of λ in this case was ±3.4%. Table 2 contains the conversion at the point of intersection of the CO and NOx conversion curves, as well as the associated HC conversion.

TABLE-US-00002 HC conversion CO/NOx at λ of the conversion at CO/NOx the point of point of intersection intersection Comparative   46% 81% example 1 CC1 Example 1 CC1   60% 86% Comparative 74.5% 91   example 1 CC2 Example 1 CC2   93% 94.5 

[0043] Example 1 according to the invention shows a significant improvement in the start-up performance and in the dynamic CO/NOx conversion after aging.