NOX ADSORBER DOC (NA-DOC) CATALYST

Abstract

A NOx adsorber diesel oxidation catalyst for the treatment of an exhaust gas, the catalyst comprising: a substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end and a plurality of passages defined by internal walls of the substrate extending therethrough; a first NOx adsorber (NA) coating, said coating comprising palladium supported on a first non-zeolitic oxidic material comprising ceria; a second NOx adsorber (NA) coating, said coating comprising one or more of an alkaline earth metal supported on a support material and a platinum group metal component supported on a second non-zeolitic oxidic material; and a diesel oxidation catalyst (DOC) coating, said coating comprising a platinum group metal component supported on a third non-zeolitic oxidic material.

Claims

1. A NOx adsorber diesel oxidation catalyst (NA-DOC) for the treatment of an exhaust gas, the catalyst comprising: (i) a substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end and a plurality of passages defined by internal walls of the substrate extending therethrough; (ii) a first NOx adsorber (NA) coating, said coating comprising palladium supported on a first non-zeolitic oxidic material comprising ceria; (iii) a second NOx adsorber (NA) coating, said coating comprising one or more of an alkaline earth metal supported on a support material and a platinum group metal component supported on a second non-zeolitic oxidic material; and, (iv) a diesel oxidation catalyst (DOC) coating, said coating comprising a platinum group metal component supported on a third non-zeolitic oxidic material; wherein the first NA coating (ii) is disposed on the surface of the internal walls of the substrate (i) over x % of the substrate axial length from the outlet end toward the inlet end of said substrate, with x being in the range of from 20 to 70; and, wherein the second NA coating (iii) is disposed over y % of the substrate axial length from the inlet end toward the outlet end of said substrate, with y being in the range of from 20 to 70; wherein the DOC coating is disposed on the first NA coating and the second NA coating, or on the first NA coating, the second NA coating and the surface of the internal walls of the substrate, over z % of the substrate axial length, with z being in the range of from 50 to 100.

2. The catalyst of claim 1, wherein from 95 to 100 weight-%, preferably from 98 to 100 weight-%, more preferably from 99 to 100 weight-%, more preferably from 99.5 to 100 weight-%, more preferably from 99.9 to 100 weight-%, of the first non-zeolitic oxidic material comprised in the first NA coating (ii) consist of ceria, calculated as CeO.sub.2.

3. The catalyst of claim 1, wherein the first NA coating (ii) comprises palladium at a loading, calculated as elemental Pd, in the range of from 5 to 150 g/ft.sup.3, preferably in the range of from 10 to 120 g/ft.sup.3, more preferably in the range of from 30 to 100 g/ft.sup.3, more preferably in the range of from 40 to 80 g/ft.sup.3, more preferably in the range of from 45 to 75 g/ft.sup.3.

4. The catalyst of claim 1, wherein the second NA coating (iii) comprises the platinum group metal component, wherein the platinum group metal component is one or more of Pt, Pd, Rh, Ir, Ru and Os, preferably one or more of Pt, Pd and Rh, more preferably one or more of Pt and Pd, more preferably Pt and Pd; wherein the weight ratio of platinum relative to palladium, calculated as Pt:Pd, is preferably in the range of from 5:1 to 15:1, more preferably in the range of from 7:1 to 12:1, more preferably in the range of from 8:1 to 10:1; and, wherein the second NA coating (iii) preferably comprises the platinum group metal component at a loading, calculated as elemental platinum group metal, in the range of from 5 to 150 g/ft.sup.3, more preferably in the range of from 10 to 120 g/ft.sup.3, more preferably in the range of from 30 to 100 g/ft, more preferably in the range of from 40 to 80 g/ft.sup.3, more preferably in the range of from 45 to 75 g/ft.sup.3.

5. The catalyst of claim 1, wherein, in the second NA coating (iii), the second non-zeolitic oxidic material supporting the platinum group metal component is selected from the group consisting of ceria, alumina, zirconia, silica, titania, a mixed oxide comprising one or more of Ce, Al, Zr, Si, and Ti and a mixture of two or more thereof, preferably selected from the group consisting of ceria, alumina and a mixed oxide comprising one or more of Ce and Al, more preferably selected from the group consisting of ceria and a mixed oxide comprising one or more of Ce and Al, more preferably is a mixed oxide comprising Ce and Al, more preferably a mixed oxide of Ce and Al; and, wherein the weight ratio of Ce:AI, calculated as CeO.sub.2:Al.sub.2O.sub.3, more preferably is in the range of from 10:90 to 90:10, more preferably in the range of from 20:80 to 50:50, more preferably in the range of from 25:75 to 50:50.

6. The catalyst of claim 1, wherein the second NA coating (iii) further comprises an oxidic component selected from the group consisting of ceria, zirconia, alumina, silica, titania, a mixed oxide comprising one or more of Ce, Zr, Al, Si, and Ti and a mixture of two or more thereof, more preferably selected from the group consisting of ceria, zirconia, alumina and titania, more preferably selected from the group consisting of ceria, zirconia, and alumina, more preferably is ceria.

7. The catalyst of claim 1, wherein at most 0.01 weight-%, preferably at most 0.001 weight-%, more preferably at most 0.0001 weight-% of the second NA coating consist of barium, calculated as BaO.

8. The catalyst of claim 1, wherein the second NA coating (iii) comprises the alkaline earth metal supported on a support material and the platinum group metal component supported on a second non-zeolitic oxidic material; wherein, in the second NA coating (iii), the weight ratio of the second non-zeolitic oxidic material relative to the support material is in the range of from 0.05:1 to 0.9:1, more preferably in the range of from 0.1:1 to 0.7:1, more preferably in the range of from 0.15:1 to 0.5:1, more preferably in the range of from 0.17:1 to 0.25:1; wherein said alkaline earth metal is preferably selected from the group consisting of barium, strontium, calcium and magnesium, more preferably selected from the group consisting of barium, strontium and magnesium, more preferably is barium; and, wherein preferably the support material supporting the alkaline earth metal in the second NA coating (iii), more preferably barium, is selected from the group consisting of ceria, zirconia, alumina, silica, titania, a mixed oxide comprising one or more of Ce, Zr, Al, Si, and Ti and a mixture of two or more thereof, more preferably selected from the group consisting of ceria, zirconia, alumina and titania, more preferably selected from the group consisting of ceria, zirconia, and alumina, more preferably is ceria.

9. The catalyst of claim 1, wherein the platinum group metal component comprised in the DOC coating (iv) is one or more of Pt, Pd, Rh, Ir, Ru and Os, preferably one or more of Pt, Pd and Rh, more preferably one or more of Pt and Pd, more preferably Pt and Pd; and, wherein the weight ratio of platinum relative to palladium, calculated as Pt:Pd, is preferably in the range of from 2:1 to 20:1, more preferably in the range of from 5:1 to 15:1, more preferably in the range of from 7:1 to 12:1, more preferably in the range of from 8:1 to 10:1.

10. The catalyst of claim 1, wherein the third non-zeolitic oxidic material comprised in the DOC coating (iv) is selected from the group consisting of alumina, zirconia, silica, titania, a mixed oxide comprising one or more of Al, Zr, Si, and Ti and a mixture of two or more thereof, preferably selected from the group consisting of silica, alumina and a mixed oxide comprising one or more of Si and Al, more preferably selected from the group consisting of alumina and a mixed oxide comprising one or more of Si and Al, more preferably is a mixed oxide comprising Si and Al, more preferably a mixed oxide of Si and Al; and, wherein preferably from 90 to 99 weight-%, more preferably from 92 to 98 weight-%, more preferably from 93 to 97 weight-%, of the second non-zeolitic material comprised in the DOC coating (iv) consist of alumina, and wherein preferably from 1 to 10 weight-%, more preferably from 2 to 8 weight-%, more preferably from 3 to 7 weight-%, of the DOC coating (iv) consist of silica.

11. The catalyst of claim 1, wherein the DOC coating (iv) further comprises a zeolitic material comprising one or more of iron and copper, preferably a zeolitic material comprising iron; wherein the DOC coating (iii) comprises iron in an amount, calculated as Fe.sub.2Os, in the range of from 0.25 to 4 weight-%, more preferably in the range of from 0.5 to 3 weight-%, more preferably in the range of from 0.75 to 2.5 weight-%, based on the weight of the zeolitic material comprising iron comprised in the DOC coating (iv); or, wherein the DOC coating (iv) further comprises a zeolitic material it is H- and/or NH.sub.4-form; and, wherein the zeolitic material comprised in the DOC coating (iv) preferably is a 12-membered ring pore zeolitic material, wherein said zeolitic material more preferably has a framework type selected from the group consisting of BEA, MOR, FAU, GME, OFF a mixture of two or more thereof and a mixed type of two or more thereof, more preferably selected from the group consisting of BEA, MOR, FAU, a mixture of two or more thereof and a mixed type of two or more thereof, more preferably selected from the group consisting of BEA and FAU, wherein more preferably the 12-membered ring pore zeolitic material comprised in the DOC coating (iv) has a framework type BEA.

12. Process for preparing a NOx adsorber diesel oxidation catalyst (NA-DOC) according to claim 1, comprising (a) preparing a first mixture comprising water, a source of palladium and a first non-zeolitic oxidic material comprising ceria; (b) disposing the first mixture obtained according to (a) on the surface of the internal walls of a substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end and a plurality of passages defined by internal walls of the substrate extending therethrough, over x % of the substrate axial length from the outlet end toward the inlet end of said substrate, with x being in the range of from 20 to 70; calcining, obtaining a substrate having a first NOx adsorber (NA) coating thereon; (c) preparing a second mixture comprising water and one or more of an alkaline earth metal with a support material for the alkaline earth metal and a source of a platinum group metal component with a second non-zeolitic oxidic material for supporting the platinum group metal component; (d) disposing the second mixture obtained according to (c) on the substrate, having the first NA coating thereon, over y % of the substrate axial length from the inlet end toward the outlet end of said substrate, with y being in the range of from 20 to 70; calcining, obtaining a substrate having a first NA coating and a second NA coating thereon; (e) preparing a third mixture comprising water, a source of a platinum group metal component and a third non-zeolitic oxidic material; (f) disposing the third mixture obtained according to (e) on the substrate, having the first NA coating and the second NA coating thereon, over z % of the substrate axial length, with z being in the range of from 50 to 100; and, (g) calcining the substrate obtained according to (f), obtaining a substrate having a first NA coating, a second NA coating and a DOC coating thereon.

13. A NOx adsorber diesel oxidation catalyst (NA-DOC) obtained or obtainable by a process according to claim 12.

14. Use of a NOx adsorber diesel oxidation catalyst (NA-DOC) according to claim 1 for the NOx adsorption/desorption and the conversion of HC and CO.

15. An exhaust treatment system for the treatment of an exhaust gas, the system comprising a NOx adsorber diesel oxidation (NA-DOC) catalyst according to claim 1; the system preferably further comprises one or more of a selective catalytic reduction (SCR) catalyst, a selective catalytic reduction catalyst on a filter (SCRoF) and an ammonia oxidation (AMOX) catalyst.

Description

EXAMPLES

Reference Example 1

1.1 Measurement of the BET Specific Surface Area

[0252] The BET specific surface area was determined according to DIN 66131 or DIN ISO 9277 using liquid nitrogen.

1.2 Determination of the Crystallinity

[0253] The determination of the relative crystallinity of a zeolite was performed via x-ray diffraction using a test method under the jurisdiction of ASTM Committee D32 on catalysts, in particular of Subcommittee D32.05 on zeolites. The current edition was approved on Mar. 10, 2001 and published in May 2001, which was originally published as D 5758-95.

1.3 Determination of the Total Pore Volume

[0254] The total pore volume was determined according to ISO 15901-2:2006.

Catalyst Preparation

[0255] A total of 4 catalysts were prepared as listed in Table 1. Example 2.2 describes the preparation of a NOx-adsorber DOC catalyst according to the present invention. The performance benefits of the inventive Example was demonstrated over Comparative Example 2.1. To demonstrate the impact of the additional feature 2 weight-% barium on ceria of Comparative Example 2.1, two additional Comparative Examples 1.1 and 1.2 were prepared.

TABLE-US-00001 TABLE 1 List of the prepared catalysts Barium in Exam- Length of the Length of the bottom Pd on ples bottom coating top coating coating ceria 1.1 70% 100% (50% inlet coating + 50% outlet coating) 1.2 70% 100% 2 weight-% (50% inlet coating + on ceria 50% outlet coating) 2.1 100% 100% 2 weight-% (50% inlet coating + on ceria 50% outlet coating) 2.2 100% 100% yes (inven- (50% inlet coating + tive) 50% outlet coating)

Comparative Example 1.1: Preparation of a NOx Adsorber DOC (NA-DOC)

Bottom Coating:

[0256] A support material (a mixed oxide of Ce and Al with a ceria to alumina weight ratio of 50:50, having a BET specific surface area of 140 m.sup.2/g and a pore volume of 0.7 ml/g), was impregnated with platinum (using an aqueous solution containing an amine stabilized hydroxo Pt(IV) complex, said solution having a Pt content between 15 weight-%) and palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 15 to 23 weight-%) in a weight ratio of 9:1, calculated as elements, respectively, via a wet impregnation process.

[0257] A slurry containing the resulting impregnated support material, ceria, a zeolitic material having a framework type BEA in its H-form (having a silica-to-alumina molar ratio, SiO.sub.2:Al.sub.2O.sub.3, of 12.5:1 and a crystallinity determined by XRD>80%), zirconium acetate, such that the amount of zirconia in the bottom coating, calculated as ZrO.sub.2, was 0.05 g/in.sup.3, and magnesium acetate, such that the amount of magnesium oxide in the bottom coating, calculated as MgO, was 0.05 g/in.sup.3, was prepared. An uncoated round flow-through honeycomb substrate, cordierite (total volume 1.9 L, 400 cpsi and 4 mil wall thickness, diameter: 143.8 mmlength: 114.3 mm), and was coated with the obtained slurry from the inlet end of the substrate toward the outlet end over 70% of the axial length of said substrate. Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The first coating (bottom coating) contained 76.9 g/ft.sup.3 of platinum and 8.8 g/ft.sup.3 of palladium, 0.8 g/in.sup.3 of Ce/Al mixed oxide, 3.9 g/in.sup.3 of ceria, 0.35 g/in.sup.3 of H-BEA, 0.05 g/in.sup.3 of ZrO.sub.2 and 0.05 g/in.sup.3 of MgO. The loading of the first coating was 5.20 g/in.sup.3.

Inlet Top Coating:

[0258] A support material (alumina doped with 5 weight-% SiO.sub.2 having a BET specific surface area of 170 m.sup.2/g and a pore volume of 0.7 ml/g), was impregnated with platinum (using an aqueous solution of stabilized Platinum complexes) and palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 19 weight-%) at a weight ratio of 1:1, calculated as elements, respectively, via a wet impregnation process subsequent chemically fixation using barium hydroxide. Then, a slurry containing the resulting impregnated support material and a zeolitic material having a framework type BEA in its H-form (having a silica-to-alumina molar ratio, SiO.sub.2:Al.sub.2O.sub.3, of 12.5:1 and a crystallinity determined by XRD>80%) was prepared.

[0259] The substrate coated with the bottom coating was then coated with the obtained slurry from the inlet end toward the outlet end of the substrate over 50% of the axial length of said substrate, forming the inlet top coat. Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The inlet top coat comprises 14.0 g/ft.sup.3 of platinum, 14.0 g/ft.sup.3 of palladium, 0.7 g/in.sup.3 of Si-Alumina, 0.25 g/in.sup.3 of H-BEA and 0.02 g/in.sup.3 of BaO. The loading of the inlet coat was 0.97 g/in.sup.3

Outlet Top Coating:

[0260] A support material (alumina doped with 5 weight-% MnO.sub.2 having a BET specific surface area of 120 m.sup.2/g and a pore volume of 0.7 ml/g), was impregnated with platinum (using an aqueous solution of stabilized Platinum complexes) and palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 19 weight-%) in a weight ratio of 9:1, calculated as elements, respectively, via a wet impregnation process subsequent chemically fixation using barium hydroxide.

[0261] The substrate with the bottom coating and the inlet coat thereon was further coated with a slurry containing the resulting impregnated support material from the outlet end toward the inlet end of the substrate over 50% of the axial length of said substrate. Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The outlet top coat contained 82.8 g/ft.sup.3 of platinum and 9.2 g/ft.sup.3 of palladium. The loading of the outlet top coat was 1.36 g/in.sup.3. The loading of the second coating (inlet coat+outlet coat) was about 1.16 g/in.sup.3.

Comparative Example 1.2: Preparation of a Ba/Ce-Containing NOx Adsorber DOC (NA-DOC)

Bottom Coating:

[0262] A support material (a mixed oxide of Ce and Al with a ceria to alumina weight ratio of 50:50, having a BET specific surface area of 140 m.sup.2/g and a pore volume of 0.7 ml/g), was impregnated with platinum (using an aqueous solution containing an amine stabilized hydroxo Pt(IV) complex, said solution having a Pt content between 15 weight-%) and palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 15 to 23 weight-%) in a weight ratio of 9:1, calculated as elements, respectively, via a wet impregnation process. Then, an oxidic material, being ceria (having a BET specific surface area of 120 m.sup.2/g), was impregnated with barium acetate, such that the amount of barium, calculated as BaO, was 2 weight-% based on the weight of the oxidic material (ceria), via a wet impregnation process and subsequently calcined at 590 C. for 2 h. A slurry was formed with the obtained Pt/Pd impregnated support material, the Ba impregnated oxidic material and a zeolitic material having a framework type BEA (having a silica-to-alumina molar ratio, SiO.sub.2:Al.sub.2O.sub.3, of 12.5:1 and a crystallinity determined by XRD>80%), zirconium acetate, such that the amount of zirconia in the bottom coating, calculated as ZrO.sub.2, was 0.05 g/in.sup.3, and magnesium acetate, such that the amount of magnesium oxide in the bottom coating, calculated as MgO, was 0.05 g/in.sup.3, was prepared. An uncoated round flow-through honeycomb substrate, cordierite (total volume 1.9 L, 400 cpsi and 4 mil wall thickness, diameter: 143.8 mmlength: 114.3 mm), and was coated with the obtained slurry from the inlet end of the substrate toward the outlet end over 70% of the axial length of said substrate. Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The first coating (bottom coating) contained 76.9 g/ft.sup.3 platinum and 8.8 g/ft.sup.3 palladium, 0.8 g/in.sup.3 of Ce/Al mixed oxide, 3.9 g/in.sup.3 of Ba/ceria, 0.35 of H-BEA, 0.05 g/in.sup.3 of ZrO.sub.2 and 0.05 g/in.sup.3 of MgO. The loading of the first coating was 5.20 g/in.sup.3.

Top Coatings:

[0263] The inlet top coating and the outlet top coating of said example were prepared as the inlet coating and the outlet coating of Comparative Example 1.1 and disposed in the same manner on the substrate coated with the bottom coating.

Comparative Example 2.1: Preparation of a Ba/Ce-Containing NOx Adsorber DOC (NA-DOC)

Bottom Coating:

[0264] A support material (a mixed oxide of Ce and Al with a ceria to alumina weight ratio of 50:50, having a BET specific surface area of 140 m.sup.2/g and a pore volume of 0.7 ml/g), was impregnated with platinum (using an aqueous solution containing an amine stabilized hydroxo Pt(IV) complex, said solution having a Pt content between 15 weight-%) and palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 15 to 23 weight-%) in a weight ratio of 9:1, calculated as elements, respectively, via a wet impregnation process.

[0265] Then, an oxidic material, being ceria (having a BET specific surface area of higher than 120 m.sup.2/g), was impregnated with barium acetate, such that the amount of barium, calculated as BaO, was 2 weight-% based on the weight of the oxidic material (ceria), via a wet impregnation process and subsequently calcined at 590 C. for 2 h. A slurry was formed with the obtained Pt/Pd impregnated support material, the Ba impregnated oxidic material and a zeolitic material having a framework type BEA in its H-form (having a silica-to-alumina molar ratio, SiO.sub.2:Al.sub.2O.sub.3, of 12.5:1 and a crystallinity determined by XRD>80%), zirconium acetate, such that the amount of zirconia in the bottom coating, calculated as ZrO.sub.2, was 0.05 g/in.sup.3, and magnesium acetate, such that the amount of magnesium oxide in the bottom coating, calculated as MgO, was 0.05 g/in.sup.3, was prepared. An uncoated round flow-through honeycomb substrate, cordierite (total volume 1.9 L, 400 cpsi and 4 mil wall thickness, diameter: 143.8 mmlength: 114.3 mm), and was coated with the obtained slurry from the inlet end of the substrate toward the outlet end over 100% of the axial length of said substrate. Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The first coating (bottom coating) contained 53.8 g/ft.sup.3 of platinum, 6.2 g/ft.sup.3 of palladium, 0.8 g/in.sup.3 of Ce/Al mixed oxide, 3.9 g/in.sup.3 of Ba/ceria, 0.5 of H-BEA, 0.05 g/in.sup.3 of ZrO.sub.2 and 0.05 g/in.sup.3 of MgO. The loading of the first coating was 5.35 g/in.sup.3.

Inlet Top Coating:

[0266] A support material (alumina doped with 5 weight-% SiO.sub.2 having a BET specific surface area of higher than 170 m.sup.2/g and a pore volume of higher than 0.7 ml/g), was impregnated with platinum (using an aqueous solution of stabilized platinum complexes) and palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 15 to 23 weight-%) at a weight ratio of 1:1, calculated as elements, respectively, via a wet impregnation process subsequent chemically fixation using barium hydroxide. Then, a slurry containing the resulting impregnated support material was prepared. The substrate coated with the bottom coating was then coated with the obtained slurry from the inlet end toward the outlet end of the substrate over 50% of the axial length of said substrate, forming the inlet top coat. Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The inlet top coat comprises 30.0 g/ft.sup.3 of platinum, 30.0 g/ft.sup.3 of palladium, 0.7 g/in.sup.3 of Si-Alumina and 0.02 g/in.sup.3 of BaO. The loading of the inlet coat was 0.73 g/in.sup.3

Outlet Top Coating:

[0267] A support material (alumina doped with 5 weight-% SiO.sub.2 having a BET specific surface area of higher than 170 m.sup.2/g and a pore volume of higher than 0.7 ml/g), was impregnated with platinum (using an aqueous solution of stabilized Platinum complexes) and palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 19 weight-%) in a weight ratio of 9:1, calculated as elements, respectively, via a wet impregnation process subsequent chemically fixation using barium hydroxide. The substrate with the bottom coating and the inlet coat thereon was further coated with a slurry containing the resulting impregnated support material from the outlet end toward the inlet end of the substrate over 50% of the axial length of said substrate. Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The outlet top coat contained 54.0 g/ft.sup.3 of platinum, 6.0 g/ft.sup.3 of palladium, 1.3 g/in.sup.3 of Si/Alumina and 0.01 g/in.sup.3 of BaO. The loading of the outlet top coating was 1.36 g/in.sup.3.

Example 2.2: Preparation of a Pd/Ce-Containing NOx Adsorber DOC (NA-DOC)

NA Coating (Inlet Bottom Coating):

[0268] A support material (a Ce/Al mixed oxide with a ceria to alumina weight ratio of 30:70, having a BET specific surface area of 170 m.sup.2/g and a pore volume of 0.8 ml/g), was impregnated with platinum (using an aqueous solution containing an ammine stabilized hydroxo Pt(IV) complex, said solution having a Pt content between 15 weight-%) and palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 15 to 23 weight-%) in a weight ratio of 9:1, calculated as elements, respectively, via a wet impregnation process.

[0269] Then, an oxidic material, being ceria (having a BET specific surface area of 120 m.sup.2/g), was impregnated with barium acetate, such that the amount of barium, calculated as BaO, was 2 weight-% based on the weight of the oxidic material (ceria), via a wet impregnation process and subsequently calcined at 590 C. for 2 h. A slurry was formed with the obtained Pt/Pd impregnated support material, an oxidic material, being ceria (having a BET specific surface area of 120 m.sup.2/g), zirconium acetate, such that the amount of zirconia in the bottom coating, calculated as ZrO.sub.2, was 0.05 g/in.sup.3, and magnesium acetate, such that the amount of magnesium oxide in the bottom coating, calculated as MgO, was 0.05 g/in.sup.3.

[0270] An uncoated round flow-through honeycomb substrate, cordierite (total volume 1.9 L, 400 cpsi and 4 mil wall thickness, diameter: 143.8 mmlength: 114.3 mm), and was coated with the obtained slurry from the inlet end of the substrate toward the outlet end over 50% of the axial length of said substrate, to form the inlet bottom coating. Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The inlet bottom coating contained 53.8 g/ft.sup.3 of platinum, 6.2 g/ft.sup.3 of palladium, 0.8 g/in.sup.3 of Ce/Al mixed oxide, 3.9 g/in.sup.3 of ceria, 0.05 g/in.sup.3 of ZrO.sub.2 and 0.05 g/in.sup.3 of MgO. The loading of the inlet bottom coating was 4.85 g/in.sup.3.

NA Coating (Outlet Bottom Coating):

[0271] An oxidic material, being ceria having a BET specific surface area of 120 m.sup.2/g, was impregnated with palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 15 to 23 weight-%). A slurry containing the resulting impregnated oxidic material was prepared and the substrate coated with the inlet bottom coat was then coated from the outlet end toward the inlet end of the substrate over 50% of the axial length of said substrate. Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The outlet bottom coating contained 3.90 g/in.sup.3 of Pd/ceria including 60.0 g/ft.sup.3 of palladium. The loading of the outlet coating was 3.93 g/in.sup.3.

DOC Coating (Top Coating):

[0272] A support material (alumina doped with 5 weight-% SiO.sub.2 having a BET specific surface area of higher than 170 m.sup.2/g and a pore volume of higher than 0.7 ml/g), was impregnated with platinum (using an aqueous solution of stabilized platinum complexes) and palladium (using an aqueous solution containing Pd nitrate and having a concentration in the range of 15 to 23 weight-%) at a weight ratio of 9:1, calculated as elements, respectively, via a wet impregnation process subsequent chemically fixation using barium hydroxide.

[0273] A slurry containing the resulting impregnated support material and a zeolitic material having a framework type BEA (having a silica-to-alumina molar ratio, SiO.sub.2:Al.sub.2O.sub.3, of 26:1 and a crystallinity determined by XRD>90% and containing 1.4 weight-% Fe, determined by XRD and calculated as Fe.sub.2O.sub.3) was prepared and coated on the cordierite flow-through substrate, with the inlet and outlet bottom coats, from the inlet end toward the outlet end over 100% of the axial length of said substrate Then, the coated substrate was dried in air at 110 C. for 1 h and calcined in air at 590 C. for 2 h. The second coating (top coating) contained 54.0 g/ft.sup.3 of platinum, 6.0 g/ft.sup.3 of palladium, 1.2 g/in.sup.3 of Si/alumina, 0.35 g/in.sup.3 of Fe-BEA and 0.1 g/in.sup.3 of BaO. The loading of the second coating was about 1.70 g/in.sup.3.

Example 3: WLTC Evaluation of NA-DOC of Comparative Examples 1.1, 1.2 and 2.1 and Example 2.2 on a Diesel Engine

[0274] The catalysts of Comparative Examples 1.1, 1.2 and 2.1 and Example 2.2 were tested in a Worldwide Harmonized Light Vehicle Test Cycle (WLTC) on a 2 L diesel engine after hydrothermal aging at 800 C. for 16 hours in 10% steam (water)/air and subsequent sulfation and lean desulfation procedure (50 cycles). The preconditioning to the test reported was a temperature treatment of 650 C. for 10 min to purge any pre-adsorbed NOx and a shortened WLTC with a maximum temperature of 280 C. for controlled prefilling of NOx.

[0275] FIG. 1 provides the cumulated NOx storage on the NOx adsorber DOC in the cold start region of the WLTC. All formulations adsorb NOx from the exhaust leaving the engine. A net desorption of NOx adsorbed during preconditioning was not observed for any of the samples. The comparison of Comparative Examples 1.1 and 1.2 shows the benefit in NOx storage efficiency of adding barium to the formulation. Despite the fact, that in contrast to Comparative Example 2.1, the catalyst of Example 2.2 does not contain barium on ceria as NOx storage material, a significant increase in NOx storage efficiency is observed. Without wanting to be bound by any theory, it is believed that his can be attributed to the Pd/Ce feature in the outlet bottom coat of Example 2.2. Also, the stability against sulfation and lean desulfation was demonstrated with this procedure.

Example 4 Preparation of a Pd/Ce-Containing NOx Adsorber DOC (NA-DOC)

[0276] Inlet bottom coating: the inlet bottom coating of Example 4 was prepared as the inlet bottom coating of Example 2.2 except that the platinum group metal loading was increased and that barium hydroxide was used to impregnate the 3.9 g/in.sup.3 of ceria. Thus, the loading of the inlet bottom coating was it contained 63 g/ft.sup.3 of platinum, 7 g/ft.sup.3 of palladium, 0.8 g/in.sup.3 of Ce/Al mixed oxide, 0.08 g/in.sup.3 of BaO, 3.0 g/in.sup.3 of ceria, 0.05 g/in.sup.3 of MgO and 0.05 g/in.sup.3 of ZrO.sub.2. 4.92 g/in.sup.3.

[0277] Outlet bottom coating: the outlet bottom coating of Example was prepared as the outlet bottom coating of Example 2.2 except that the outlet bottom coat contained 3.90 g/in.sup.3 of Pd/ceria and 50.0 g/ft.sup.3 of palladium. The loading of the outlet bottom coating was 3.93 g/in.sup.3.

Top Coating:

[0278] The top coating of Example 4 was prepared as the top coating of Example 2.2 except that it contained 54.0 g/ft.sup.3 of platinum, 6.0 g/ft.sup.3 of palladium, 1.2 g/in.sup.3 of Si/alumina, 0.5 g/in.sup.3 of Fe-BEA and 0.1 g/in.sup.3 of BaO. The loading of the top coating was about 1.85 g/in.sup.3.

Example 5 Testing of the Catalysts of Example 1.1 and Example 4HC and CO Light-Off Temperatures

[0279] The HC and CO light-off temperatures of the catalysts of Comparative Example 1.1 and Example 4 were measured on a 3 L diesel engine after hydrothermal aging at 800 C. for 16 hours in 10% steam (water)/air. Light-off temperatures were determined in the state of highest deactivation (10 min lean filter regeneration mode at 650 C.). Space velocity was around 30K h.sup.1, concentrations: 830-1270 ppm of CO, 160-220 ppm of THC, and 40-80 ppm of NOx. The results are shown in FIGS. 2 and 3.

[0280] As may be taken from FIGS. 2 and 3, the catalyst of Example 4 presents a lower temperature at which 50% of CO is converted, namely a CO T.sub.50 of 167 C. (deactivated), compared to the temperature measured for the comparative Example, namely CO T.sub.50 of 187 C. (deactivated). This is also true for the HC conversion, namely the catalyst of the present invention presents a lower HC T.sub.70 of 177 C. (temperature at which 70% of HC is converted) than the comparative catalyst (187 C.). Thus, it has been demonstrated that the inventive catalyst presents improved CO and HC oxidation performance.

Example 6: WLTC Evaluation of NA-DOC of Comparative Example 1.1 and Example 4 on a Diesel Engine

[0281] The catalysts of Comparative Examples 1.1 and Example 4 were tested in a Worldwide Harmonized Light Vehicle Test Cycle (WLTC) on a 3 L diesel engine after hydrothermal aging at 800 C. for 16 hours in 10% steam (water)/air. The preconditioning to the test reported was a temperature treatment of 650 C. for 10 min to purge any pre-adsorbed NOx and a full WLTC with a maximum temperature of 350 (FIG. 4) and shortened WLTC with a maximum temperature of 320 C. (FIG. 5) for controlled prefilling of NOx

[0282] FIGS. 4 and 5 provide the cumulated NOx storage on the NOx adsorber DOC in the cold start region of the WLTC. All formulations adsorb NOx from the exhaust leaving the engine. A net desorption of NOx adsorbed during preconditioning was not observed for any of the samples. The comparison of Comparative Examples 1.1 Example 4 shows the benefit in NOx storage efficiency of adding barium and the Pd/Ce feature to the formulation. From the comparison of Comparative Examples 1.1, 1.2 and 2.1 and Example 2.2, the main benefit in NOx adsorption can be attributed to the Pd/Ce feature. The different conditions in NOx prefilling demonstrate the capability of the catalyst to provide NOx storage efficiency under all cold start conditions.

BRIEF DESCRIPTION OF THE FIGURES

[0283] FIG. 1 shows the cumulated NOx storage of the catalysts of Comparative Examples 1.1, 1.2 and 2.1 and Example 2.2 in a WLTC after steam aging at 800 C. for 16 h and subsequent sulfation and lean desulfation (50 cycles).

[0284] FIG. 2 shows the CO light-off temperature (CO T.sub.50) of the catalysts of Comparative Example 1.1 and Example 4 after ageing (deactivated).

[0285] FIG. 3 shows the HC light-off temperature (HC T.sub.70) of the catalysts of Comparative Example 1.1 and Example 4 after ageing (deactivated).

[0286] FIG. 4 shows the cumulated NOx storage of the catalysts of Comparative Example 1.1 and Example 4 in a WLTC after steam aging at 800 C. for 16 h.

[0287] FIG. 5 shows the cumulated NOx storage of the catalysts of Comparative Example 1.1 and Example 4 in a WLTC after steam aging at 800 C. for 16 h.

CITED LITERATURE

[0288] WO 2016/141142 A1 [0289] WO 2020/236879 A1