TWO-LAYER, THREE-WAY CATALYST WITH SIGNIFICANTLY IMPROVED CO CONVERSION

Abstract

The present invention relates to a catalyst comprising two layers on an inert catalyst carrier. Layer A contains at least palladium as a platinum group metal, alumina, and a first cerium/zirconium/lanthanum/yttrium mixed oxide. A layer B applied to layer A contains at least rhodium as a platinum group metal, alumina, and a second cerium/zirconium/lanthanum/yttrium mixed oxide.

Claims

1. A catalyst comprising two layers arranged one above the other on an inert catalyst carrier, wherein a layer A contains at least palladium as a platinum group metal, alumina, and a first cerium/zirconium/lanthanum/yttrium mixed oxide, and a layer B applied to layer A contains at least rhodium as a platinum group metal, alumina, and a second cerium/zirconium/lanthanum/yttrium mixed oxide, characterized in that in layer A, the cerium oxide content is between 40 wt. % and 50 wt. % relative to the first cerium/zirconium/lanthanum/yttrium mixed oxide, the lanthanum oxide content is between 2 wt. % and 10 wt. % relative to the first cerium/zirconium/lanthanum/yttrium mixed oxide, and the yttrium oxide content is between 2 wt. % and 8 wt. % relative to the first cerium/zirconium/lanthanum/yttrium mixed oxide, and the mass ratio of the first cerium/zirconium/lanthanum/yttrium mixed oxide to alumina is at least 1.5:1 and at most 1.75:1, and in layer B, the cerium oxide content is between 20 wt. % and 30 wt. % relative to the second cerium/zirconium/lanthanum/yttrium mixed oxide, the lanthanum oxide content is between 1 wt. % and 5 wt. % relative to the second cerium/zirconium/lanthanum/yttrium mixed oxide, and the yttrium oxide content is between 8 wt. % and 20 wt. % relative to the second cerium/zirconium/lanthanum/yttrium mixed oxide.

2. The 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. The catalyst according to claim 1, characterized in that, as a platinum group metal, layer A contains only palladium and layer B contains only rhodium, or layer B contains only palladium and rhodium.

4. The catalyst according to claim 1, characterized in that layer A and layer B contain active alumina.

5. The catalyst according to claim 4, characterized in that the platinum group metal is carried in layer A and/or in layer B entirely or partially on active alumina.

6. The catalyst according to claim 1, characterized in that, in layer B, the mass ratio of the second cerium/zirconium/lanthanum/yttrium mixed oxide to alumina is at least 1:1 and at most 1.5:1.

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

8. An exhaust system for reducing the harmful components in the exhaust of an internal combustion engine, which is operated in particular primarily stoichiometrically, the exhaust system comprising a catalyst according to claim 1.

9. The exhaust system according to claim 8, characterized in that it further comprises a particulate filter.

10. A use of a catalyst according to claim 1 to reduce the harmful components in the exhaust of an internal combustion engine, which is operated in particular primarily stoichiometrically.

11. The use according to claim 10, characterized in that it relates to an internal combustion engine that it spends more than 90% of its operating time in a state of not combusting any rich exhaust mixture.

Description

EXAMPLES

[0039] In the following Example 1 and Comparative Examples 1-3, two-layer catalysts were produced by twice coating honeycomb carriers made of ceramic with 93 cells per cm.sup.2 and wall thickness 0.11 mm, with dimensions of 11.8 cm in diameter and 11.4 cm in length. For this purpose, two different suspensions for layer A and B were produced. The carrier was first coated with the suspension for layer A and subsequently calcined in air for 4 hours at 550 C. Thereafter, the carrier coated with layer A was coated with the suspension for layer B and subsequently calcined under the same conditions as layer A.

[0040] Example 1 according to the present invention contains a higher proportion of mixed oxide in layer A than Comparative Examples 1-3. The mass ratio of mixed oxide to alumina in Example 1 is 1.66:1, while the Comparative Examples each have a ratio of mixed oxide to alumina of 1:1.

Example 1 (According to the Invention)

[0041] A two-layer catalyst was prepared by first producing two suspensions. The composition of the first suspension for Layer A (relative to the volume of the catalyst carrier) was 49.4 g/L with 4 wt % La.sub.2O.sub.3 stabilized activated alumina, 82.3 g/L cerium/zirconium/lanthanum/yttrium mixed oxide with 44.5 wt % CeO.sub.2, 44.5 wt % ZrO.sub.2, 6 wt % La.sub.2O.sub.3, and 5 wt % Y.sub.2O.sub.3, 16 g/L BaSO.sub.4, 0.954 g/L Pd.

[0042] The composition of the second suspension for layer B (relative to the volume of the catalyst carrier) was 47 g/L with 4 wt % La.sub.2O.sub.3 stabilized activated alumina, 60 g/L cerium/zirconium/lanthanum/yttrium mixed oxide with 24 wt % CeO.sub.2, 60 wt % ZrO.sub.2, 3.5 wt % La.sub.2O.sub.3, and 12.5 wt % Y.sub.2O.sub.3, 0.106 g/L Rh.

Comparative Example 1 (According to EP3045226A1)

[0043] A two-layer catalyst was prepared analogously to Example 1. The composition of the first suspension for Layer A was 66 g/L with 4 wt % La.sub.2O.sub.3 stabilized activated alumina, 66 g/L cerium/zirconium/lanthanum/yttrium mixed oxide with 25 wt % CeO.sub.2, 67.5 wt % ZrO.sub.2, 3.5 wt % La.sub.2O.sub.3, and 4 wt % Y.sub.2O.sub.3, 16 g/L BaSO.sub.4, 0.954 g/L Pd.

[0044] The composition of the second suspension for layer B was the same as in Example 1.

Comparative Example 2 (According to EP4096811A1)

[0045] A two-layer catalyst was prepared analogously to Example 1. The composition of the first suspension for Layer A (relative to the volume of the catalyst carrier) was 66 g/L with 4 wt % La.sub.2O.sub.3 stabilized activated alumina, 66 g/L cerium/zirconium/lanthanum/yttrium mixed oxide with 24 wt % CeO.sub.2, 60 wt % ZrO.sub.2, 3.5 wt % La.sub.2O.sub.3 and 12.5 wt % Y.sub.2O.sub.3, 16 g/L BaSO.sub.4, 0.954 g/L Pd.

[0046] The composition of the second suspension for layer B was the same as in Example 1.

Comparative Example 3 (According to EP1974809B1)

[0047] A two-layer catalyst was prepared analogously to Example 1. The composition of the first suspension for layer A (relative to the volume of the catalyst carrier) was 66 g/L with 4 wt % La.sub.2O.sub.3 stabilized activated alumina, 66 g/L cerium/zirconium/lanthanum/yttrium mixed oxide with 44.5 wt % CeO.sub.2, 44.5 wt % ZrO.sub.2, 6 wt % La.sub.2O.sub.3, and 5 wt % Y.sub.2O.sub.3, 16 g/L BaSO.sub.4, 0.954 g/L Pd.

[0048] The composition of the second suspension for layer B was the same as in Example 1.

[0049] Example 1 and Comparative Examples 1-3 were aged in an engine test bench aging process. The aging consisted of an overrun fuel cut-off aging with a 950 C. exhaust temperature in front of the catalyst inlet. This resulted in a maximum bed temperature of 1020 C. in the catalyst. The aging time was 38 hours.

[0050] Subsequently, the dynamic conversion was determined on an engine test bench in a range for I from 0.99 to 1.01 at a constant temperature of 510 C. The amplitude of I was 6.8%, and the exhaust mass flow was 190 kg/h. Table 2 shows the conversion at the intersection of the CO and NOx conversion curves, as well as the associated HC conversion.

[0051] Table 1 shows the conversion at the intersection of the CO and NOx conversion curves, as well as the associated HC conversion.

TABLE-US-00001 TABLE 1 Dynamic conversion CO/NOx conversion HC conversion at the cross-over at I the CO/NOx point cross-over point Example 1 87% 91% Comparative Example 1 83.5% 91% Comparative Example 2 85.5% 91 Comparative Example 3 84% 90.5

[0052] Example 1 according to the invention shows a clear improvement in dynamic CO/NOx conversion after aging, compared to all Comparative Examples.

[0053] Furthermore, emissions were determined on a highly dynamic engine test bench with a 1.2 L gasoline direct-injection engine and exhaust turbocharger in a very dynamic travel cycle (RTS 95 or RTS Aggressive RTS 95 Cycle (dieselnet.com)). Table 2 shows the measured emissions.

TABLE-US-00002 TABLE 2 Emissions in RTS 95 Cycle CO Emission NOx Emission HC Emission (mg/km) (mg/km) (mg/km) Example 1 732 72 61 Comparative 878 68 56 Example 1 Comparative 875 69 57 Example 2 Comparative 833 74 60 Example 3

[0054] Example 1 according to the invention shows a very clear improvement over Comparative Example 1 of almost 17% in CO emissions and only slight disadvantages in NOx (<6%) and HC emissions (<9%).