Catalytic system for the treatment of an exhaust gas of a combustion engine

Abstract

The present invention relates a system for the treatment of an exhaust gas of a diesel combustion engine, said system comprising a specific NOx adsorber component, a diesel oxidation catalyst (DOC) component, a selective catalytic reduction (SCR) component, a gas heating component, and a reductant injector, wherein in said system, the specific NOx adsorber component is arranged upstream of the gas heating component, the reductant injector is arranged up-stream of the SCR component, the gas heating component is arranged upstream of the reductant injector, the DOC component is arranged upstream of the reductant injector, and the DOC component and the gas heating component are directly consecutive components. Further, the present invention relates a process for preparing such a system and use thereof.

Claims

1. A system for the treatment of an exhaust gas of a diesel combustion engine, said system comprising an NOx adsorber component, a diesel oxidation catalyst (DOC) component, a selective catalytic reduction (SCR) component, a gas heating component, and a reductant injector, wherein in said system, the NOx adsorber component is arranged upstream of the gas heating component, the reductant injector is arranged upstream of the SCR component, the gas heating component is arranged upstream of the reductant injector, the DOC component is arranged upstream of the reductant injector, and the DOC component and the gas heating component are directly consecutive components, wherein the NOx adsorber component is comprised in (i) a catalyst which comprises (i.1) a first substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the first substrate, and a plurality of passages defined by internal walls of the first substrate extending therethrough; (i.2) an NOx adsorber coating being said NOx adsorber component, said coating being disposed on the surface of the internal walls of the first substrate over at least 50% of the substrate axial length of the first substrate, the NOx adsorber coating comprising a platinum group metal component and a 10-membered ring pore zeolitic material having a framework type selected from the group consisting of FER, TON, MTT, SZR, MWW, AEL, HEU, AFO, a mixture of two or more thereof and a mixed type of two or more thereof.

2. The system of claim 1, wherein the platinum group metal component of the NOx adsorber coating according to (i.2) is comprised in the 10-membered ring pore zeolitic material of the NOx adsorber coating according to (i.2).

3. The system of claim 1, wherein the DOC component is arranged upstream of the gas heating component.

4. The system of claim 1, wherein the catalyst according to (i) further comprises (i.3) a diesel oxidation catalyst (DOC) coating being said DOC component, said DOC coating being at least partially disposed on the NOx adsorber coating over at least 70% of the substrate axial length of the first substrate, the DOC coating comprising a platinum group metal component and a non-zeolitic oxidic material comprising one or more of alumina, silica, zirconia and titania.

5. The system of claim 1, wherein (ii) the gas heating component comprises (ii.1) a second substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the second substrate, and a plurality of passages defined by internal walls of the second substrate extending therethrough; wherein the inlet end of the second substrate according to (ii.1) and the outlet end of the first substrate according to (i.1) are coupled to allow exhaust gas exiting from the passages of the first substrate to enter the passages of the second substrate; wherein the internal walls of the second substrate are thermally conductive to allow heating thereof for heating of exhaust gas flowing through the passages of the second substrate.

6. The system of claim 5, wherein the gas heating component according to (ii) further comprises (ii.2) optionally an NOx adsorber coating disposed on the surface of the internal walls of the second substrate over at least 50% of the substrate axial length of the second substrate, the NOx adsorber coating comprising a platinum group metal component and a 10-membered ring pore zeolitic material having a framework type selected from the group consisting of FER, TON, MTT, SZR, MWW, AEL, HEU, AFO, a mixture of two or more thereof and a mixed type of two or more thereof; (ii.3) a diesel oxidation catalyst (DOC) coating at least partially disposed on the surface of the internal walls of the second substrate and/or at least partially disposed on the optional NOx adsorber coating according to (ii.2) and extending over at least 70% of the substrate axial length of the second substrate, the DOC coating comprising a platinum group metal component and a non-zeolitic oxidic material comprising one or more of alumina, silica, zirconia and titania.

7. The system of claim 1, wherein the DOC component is arranged downstream of the gas heating component.

8. The system of claim 7, wherein the DOC component is comprised in (iii) a catalyst comprising (iii.1) a third substrate which comprises an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the third substrate, and a plurality of passages defined by internal walls of the third substrate extending therethrough; (iii.2) a first DOC coating disposed on the surface of the internal walls of the third substrate over at least 70% of the substrate axial length of the third substrate, the first DOC coating comprising a platinum group metal component and a non-zeolitic oxidic material comprising one or more of alumina, silica, zirconia and titania; and (iii.3) optionally a second DOC coating at least partially disposed on the first DOC coating and extending over at least 20% of the substrate axial length of the third substrate, the second DOC coating comprising a platinum group metal component and a non-zeolitic oxidic material comprising one or more of alumina, silica, zirconia and titania.

9. The system of claim 7, wherein (ii) the gas heating component comprises (ii.1) a second substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the second substrate, and a plurality of passages defined by internal walls of the second substrate extending therethrough; wherein the inlet end of the second substrate according to (ii.1) and the outlet end of the first substrate according to (i.1) are coupled to allow gas exiting from the passages of the first substrate according to (i.1) to enter the passages of the second substrate according to (ii.1); wherein the inlet end of the third substrate according to (iii.1) and the outlet end of the second substrate according to (ii.1) are coupled to allow gas exiting from the passages of the second substrate to enter the passages of the third substrate according to (iii.1); wherein the internal walls of the second substrate according to (ii.1) are thermally conductive to allow heating thereof for heating of exhaust gas flowing through the passages of the second substrate.

10. The system of claim 9, wherein the gas heating component according to (ii) further comprises (ii.2) a first DOC coating disposed on the surface of the internal walls of the second substrate according to (ii.1) over at least 50% of the substrate axial length of the second substrate according to (ii.1), the first DOC coating comprising a platinum group metal component and a non-zeolitic oxidic material comprising one or more of alumina, silica, zirconia and titania; (ii.3) optionally a second DOC coating at least partially disposed on the first DOC coating according to (ii.2) and extending over at least 50% of the substrate axial length of the second substrate according to (ii.1), the second DOC coating comprising a platinum group metal component and a non-zeolitic oxidic material comprising one or more of alumina, silica, zirconia and titania.

11. The system of claim 8, wherein the SCR component is comprised in (iv) a selective catalytic reduction (SCR) catalyst comprising (iv.1) a fourth substrate comprising an inlet end, an outlet end, and a substrate axial length extending from the inlet end to the outlet end of the fourth substrate; (iv.2) a selective catalytic reduction (SCR) coating disposed on the fourth substrate according to (iv.1); wherein the inlet end of the fourth substrate according to (iv.1) and either: a) the outlet end of the second substrate, where the second substrate comprises an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the second substrate, and a plurality of passages defined by internal walls of the second substrate extending therethrough; wherein the inlet end of the second substrate and the outlet end of the first substrate are coupled to allow exhaust gas exiting from the passages of the first substrate to enter the passages of the second substrate; wherein the internal walls of the second substrate are thermally conductive to allow heating thereof for heating of exhaust gas flowing through the passages of the second substrate, or b) the outlet end of the third substrate; are coupled to allow exhaust gas exiting from the passages of the second substrate or exiting from the passages of the third substrate to enter the fourth substrate.

12. A process for preparing a system for the treatment of an exhaust gas of a diesel combustion engine, comprising (1) providing an NOx adsorber component, a diesel oxidation catalyst (DOC) component, a selective catalytic reduction (SCR) component, a gas heating component, and a reductant injector, wherein the NOx adsorber component is comprised in (i) a catalyst which comprises (i.1) a first substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the first substrate, and a plurality of passages defined by internal walls of the first substrate extending therethrough; (i.2) an NOx adsorber coating being said NOx adsorber component, said coating being disposed on the surface of the internal walls of the first substrate over at least 50% of the substrate axial length of the first substrate, the NOx adsorber coating comprising a platinum group metal component and a 10-membered ring pore zeolitic material having a framework type selected from the group consisting of FER, TON, MTT, SZR, MWW, AEL, HEU, AFO, a mixture of two or more thereof and a mixed type of two or more thereof; (2) arranging the NOx adsorber component upstream of the gas heating component; (3) arranging the reductant injector upstream of the SCR component; (4) arranging the gas heating component upstream of the reductant injector; (5) arranging the DOC component upstream of the reductant injector; (6) arranging the DOC component and the gas heating component in directly consecutive order.

13. A system for the treatment of an exhaust gas of a diesel combustion engine obtainable or obtained by a process according to claim 12.

14. A method for the treatment of an exhaust gas of a diesel combustion engine, comprising providing an exhaust gas from a diesel combustion engine and passing said exhaust gas through a system according to claim 1.

Description

EXAMPLES

Reference Example 1

1.1 Determination of the Volume-Based Particle Size Distribution, in Particular of Dv10, Dv50, Dv90 Values

(1) The volume-based particle size distributions were determined by a static light scattering method using a state of the art equipment, wherein the optical concentration of the sample was in the range of from 5 to 10 weight-%.

1.2 Measurement of the BET Specific Surface Area

(2) The BET specific surface area was determined according to DIN 66131 or DIN ISO 9277 using liquid nitrogen.

1.3 Determination of the Crystallinity

(3) 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.

Reference Example 2: Preparation of a NOx Adsorber with a DOC Function Catalyst (Layered CatalystFER)

(4) Bottom Coating:

(5) An ammonium ferrierite (having framework structure type FER, a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 21 and a crystallinity vs. standard (XRD)>80%) zeolitic material was wet impregnated with an aqueous palladium nitrate solution, to attain a Pd loading of 2.31 weight-% based on the weight of the final material (zeolitic material+palladium) dispersed in water. An uncoated flow-through metallic substrate (total volume 1.81 L, 400 cpsi and 40 micrometers wall thickness, cylindrical shape, diameter: 5.2 incheslength: 5.3 inches), was immersed in the obtained slurry over 100% of the substrate axial length, forming a bottom coating. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a bottom coating. The loading of palladium in the bottom coating was 120 g/ft.sup.3 and the total bottom coating loading was 3 g/in.sup.3.

(6) Top Coating:

(7) A high porous gamma-alumina support material comprising 5% by weight MnO.sub.2 (Al.sub.2O.sub.3 95 weight-% with Mn 5 weight-%, calculated as MnO.sub.2) was impregnated with a solution of stabilized platinum complexes via a wet impregnation process to attain a Pt loading of 3.2 weight-% based on the weight of the final material (Mn-alumina+platinum). Ammonium Beta zeolitic material (BEA, a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 23 and a crystallinity vs. standard (XRD)>90%) was added to the Pt-alumina mixture. The weight ratio of the alumina doped with Mn to the Beta zeolitic material was of 3.14:1. The substrate coated with the bottom coating was coated with the obtained slurry over 100% of the substrate axial length. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a top coating. The loading of platinum in the top coating was 60 g/ft.sup.3 and the total top coating loading was 1.45 g/in.sup.3. The catalyst of Reference Example 1 was represented in FIG. 3 (with an optional SCRoF (2)).

Reference Example 3: Gas Heating Component

(8) As electrical heating substrate and, thus as gas heating component, an uncoated flow-through metallic substrate having a total volume of 0.164 L, diameter: 5.66 incheslength 0.4 inch, 130 cpsi and 50 micrometers wall thickness was used. The substrate was electrically heatable, whereby a voltage of 48 V was used for Example 1 and Comparative Example 1 and a voltage of 12 V for Examples 4 and 5 and Comparative Examples 2 and 3.

Comparative Example 1: Preparation of a NOx Adsorber (NA) with a DOC Function Catalyst (Layered Catalyst on a Substrate Including an Upstream Heating SubstrateFER)

(9) The catalyst of Comparative Example 1 not according to the present invention was prepared by applying a Pd-FER slurry, as the one prepared in Reference Example 2 for the bottom coating, onto a substrate which was made of, in its upstream portion, an uncoated electrical heating substrate (total volume 0.164 L, 48 Volts, diameter: 5.7 incheslength 0.4 inch, 130 cpsi and 50 micrometers wall thickness) electrically connected to an uncoated flow-through metallic substrate (total volume 1.85 L, 400 cpsi and 40 micrometers wall thickness, diameter: 5.7 incheslength: 4.45 inches) in its downstream portion. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a bottom coating. The bottom coating covered 100% of the substrate axial length. Further, a Pt/Mn-alumina/BEA slurry, as the one prepared in Reference Example 2 for the top coating, was applied on the substrate coated with the bottom coating over 100% of the substrate axial length. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a top coating. The catalyst of Comparative Example 1 is shown in FIG. 3 (there with an optional SCRoF 2).

Example 1: Preparation of a NOx Adsorber (NA) with a DOC Function Catalyst (Layered Catalyst on a Substrate Including a Downstream Heating SubstrateFER)

(10) The catalyst of Example 1 according to the present invention was prepared by applying a Pd-FER slurry, as the one prepared in Reference Example 2 for the bottom coating, onto a substrate which was made of, in its upstream portion, an uncoated flow-through metallic substrate (total volume 1.81 L, 400 cpsi and 40 micrometers wall thickness, diameter: 5.7 incheslength: 4.45 inches) connected to an uncoated electrical heating flow-through metallic substrate (total volume 0.164 L, 48 Volts, diameter: 5.7 incheslength 0.4 inch, 130 cpsi and 50 micrometers wall thickness) in its downstream portion. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a bottom coating. The bottom coating covered 100% of the substrate axial length. Further, a Pt/Mn-alumina/BEA slurry, as the one prepared in Reference Example 2 for the top coating, was applied on the substrate coated with the bottom coating over 100% of the substrate axial length. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a top coating. The catalyst of Example 1 is shown in FIG. 3 (with an optional SCRoF 2).

Example 2: Testing of the NA-DOC Catalyst of Reference Example 2Simulated Low Temperature City Driving Cycle, NOx Adsorption Evaluation

(11) The catalyst of Reference Example 2 was tested in a simulated low temperature city driving mode on a 2 L diesel engine after aging for 16 hours at 800 C. in 10% steam/air. The driving cycle was compiled from city driving mode of the New European Driving Cycle (NEDC). The average temperature of the cycle was about 170 C. The cycle was driven twice for 1880 s. The test was conducted with an SCR catalyst article downstream from the NOx adsorber-DOC sample from Reference Example 2 noted above. The SCR catalyst article comprises Cu-CHA coated on a filter substrate. Between the NOx adsorber-DOC article and the SCR catalyst article an injector for urea dosing was applied to deliver the reductant for the SCR reaction. The tested system was represented in FIG. 3. Prior to the first test the temperature of the NOx adsorber-DOC sample was increased to 650 C. for 10 min.

(12) FIG. 1 provides the test results of the first test run. All formulations adsorb NO.sub.x in the exhaust leaving the engine up to about 500 s. FIG. 2 provides the test results of the second test run. In the 2.sup.nd test run, it is shown that the emissions of the tested system are caused by an insufficient NOx handshake with the downstream SCR of NA-DOC of Reference Example 2 meaning that the desorbed NOx from the NA-DOC is not fully converted by the downstream SCR.

Example 3: Testing of the Catalysts of Reference Example 2, of Comparative Example 1 and of Example 1 in a SystemWLTC Evaluation on a Diesel Engine

(13) The catalysts of Reference Example 2, Comparative Example 1 and Example 1 were tested each in a Worldwide Harmonized Light Vehicle Test Cycle (WLTC) on a 3 L diesel engine after aging for 16 h at 800 C. in 10% steam/air. Prior to the first test, the temperature of the NOx adsorber samples was increased to 650 C. for 10 min, to remove pre-adsorbed NOx.

(14) The catalysts of Reference Example 2, Comparative Example 1 and Example 1 were evaluated with a downstream SCR catalyst. The SCR catalyst article comprises Cu-CHA coated on a filter substrate (SCRoF). Between a sample (a component comprising a NOx adsorber function and a DOC function) and the SCR catalyst article an injector for urea dosing was applied to deliver the reductant for the SCR reaction. The tested systems are shown in FIG. 3.

(15) For Comparative Example 1 and Example 1, the electrical heating element was switched on directly after the start of the WLTC for 450 s. After additional 50 s, the heating element was started again for 400 s. The temperature post heating element is increasing to a maximum temperature of 350 C.

(16) FIG. 4 provides the test results. The thicker lines are the emissions from the samples prior to the SCRoF. The thin lines show the NOx emissions after the SCR catalytic article. The catalysts of Reference Example 1 and Example 1 adsorb NO.sub.x in the exhaust leaving the engine up to about 800 s. The catalyst of Comparative Example 1 shows no NOx adsorption caused by too high inlet temperature from the heating element. The catalysts of Reference Example 1 and Example 1 show a high release of NOx after about 800 s. For the inventive Example 1, the downstream SCRoF, which is directly heated by the heating element, fully converts the released NOx.

(17) Table 1 provides the system NOx emissions in mg/km for the total WLTC cycle (23 km) and after 600 s for the city driving part only (3 km). Only Example 1 (inventive) achieves lowest emissions for both the full WLTC and during the urban part of the WLTC. The values were measured at the outlet end of the SCRoF.

(18) TABLE-US-00001 TABLE 1 NOx total NOx after 600 s/3 km of the WLTC/mg/km WLTC mg/km Reference Example 2 44 50 Comparative Example 1 11 60 Example 1 6 19

(19) Table 2 shows the CO and THC emissions in g/km for the full WLTC cycle of the catalyst/systems of Reference Example 1, Comparative Example 1 and Example 1.

(20) TABLE-US-00002 TABLE 2 CO/g/km THC/g/km Reference Example 2 0.23 0.038 Comparative Example 1 0.05 0.012 Example 1 0.15 0.03

(21) As may be taken from these tables and FIG. 4, the system according to Example 1 according to the present invention permits to greatly decrease the NOx emissions as well as CO and THC (total hydrocarbon) compared to a NA-DOC catalyst which is not coupled with a gas heating component (Reference Example 1). Surprisingly, it has been found that the gas heating component should be disposed downstream of the NA-DOC catalyst in order to obtain the best balance for reducing NOx, CO and THC emissions.

Reference Example 4: Preparation of a NOx Adsorber (NA) Catalyst (FER)

(22) An ammonium ferrierite (having framework structure type FER, a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 21 and a crystallinity vs. standard (XRD) greater than 90%) zeolitic material was wet impregnated with an aqueous solution of palladium nitrate to attain a Pd loading of 2.7 weight-% based on the weight of the zeolitic material. An uncoated flow-through honeycomb cordierite substrate (total volume 0.6 L, 400 cpsi and 4 mil wall thickness, diameter: 5.66 incheslength: 1.6 inches), was coated with the obtained slurry over 100% of the substrate axial length. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours. The loading of palladium was 140 g/ft.sup.3 and the total coating loading was 3 g/in.sup.3.

Reference Example 5: Preparation of a DOC Catalyst

(23) Bottom Coating:

(24) A high porous gamma-alumina support material comprising 95 weight-% Al, calculated as Al.sub.2O.sub.3, and 5 weight-% Si, calculated as SiO.sub.2, having a BET specific surface area of greater than 100 m.sup.2/g, and a pore volume of greater than 0.06 cm.sup.3/g, was impregnated with an aqueous solution of stabilized platinum complexes and an aqueous solution of palladium nitrate using incipient wetness technique. The Pd/Pt-alumina powder was slurried in water with the addition of an ammonium-Beta zeolitic material (BEA, a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 23 and a crystallinity vs. standard (XRD) greater than 90%). The weight ratio of the alumina doped with Si to the Beta zeolitic material was of 4.3:1. An uncoated flow-through honeycomb cordierite substrate (total volume 1.24 L, 400 cpsi and 4 mil wall thickness, diameter: 5.66 incheslength: 3 inches), was coated with the obtained slurry over 100% of the substrate axial length. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a bottom coating. The loading of palladium and platinum in the bottom coating was 20 g/ft.sup.3 and 40 g/ft.sup.3, respectively, and the total bottom coating loading was 1.9 g/in.sup.3.

(25) Top Coating:

(26) A high porous gamma-alumina support material comprising 95 weight-% Al, calculated as Al.sub.2O.sub.3 and 5 weight-% Si calculated as SiO.sub.2, having a BET specific surface area of greater than 100 m.sup.2/g, and a pore volume of greater than 0.06 cm.sup.3/g was impregnated with an aqueous solution of stabilized platinum complexes and an aqueous solution of palladium nitrate using an incipient wetness technique. The Pd/Pt-alumina powder was slurried in water. The substrate coated with the bottom coating was coated with the obtained slurry over 50% of the substrate axial length from the outlet end toward the inlet end of the substrate. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a top coating. The loading of palladium and platinum in the top coating (on 50% of the substrate length) was 17 g/ft.sup.3 and 103 g/ft.sup.3, respectively, and the total top coating loading (onto 50% of the volume of the substrate) was 1.5 g/in.sup.3. The total coating loading (bottom and top coatings) was of 2.65 g/in.sup.3 with a palladium loading of 28.5 g/ft.sup.3 and a platinum loading of 91.5 g/ft.sup.3 (total PGM loading 120 g/ft.sup.3).

Comparative Example 2: Preparation of a System Comprising a DOC, an Electrical Heating Substrate and a DOC

(27) The system of Comparative Example 2 not according to the present invention was prepared by combining two diesel oxidation catalysts according to Reference Example 5 and the electrical heating substrate of Reference Example 3, wherein a first DOC of Reference Example 5 is positioned upstream of the electrical heating substrate of Reference Example 3 and the electrical heating substrate of Reference Example 3 is positioned upstream of a second DOC of Reference Example 5.

Example 4: Preparation of a System Comprising a NOx Adsorber (NA)Catalyst, an Electrical Heating Substrate and a DOC Catalyst

(28) With respect to a test in particular a comparatively lower Pd loading on the zeolitic material having framework structure type FER, Example 4 was prepared which is otherwise very similar to Example 2.

(29) The system of Example 4 according to the present invention was prepared by combining the NOx adsorber catalyst of Reference Example 4, the diesel oxidation catalyst (DOC) of Reference Example 5 and the electrical heating substrate of Reference Example 3, wherein the NOx adsorber catalyst of Reference Example 4 is positioned upstream of the electrical heating substrate of Reference Example 3 and the electrical heating substrate of Reference Example 3 is positioned upstream of the DOC of Reference Example 5.

Reference Example 6: Preparation of a NOx Adsorber (NA) Catalyst (FER)

(30) A ammonium ferrierite (having framework structure type FER, a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 21 and a crystallinity vs. standard (XRD)>90%) zeolitic material was wet impregnated with an aqueous solution of palladium nitrate, dried in air having a temperature of 110 C. for 1 hour and calcined in air at 590 C. for 2 hours to attain a Pd loading of 2.3 weight-% based on the weight of the zeolitic material. This Pd-FER powder was slurried in water. An uncoated flow-through metallic substrate (total volume 0.6 L, 400 cpsi and 40 micrometers wall thickness, diameter: 5.66 incheslength: 1.6 inches), was coated with the obtained slurry over 100% of the substrate axial length. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours. The loading of palladium was 120 g/ft.sup.3 and the total coating loading was 3 g/in.sup.3.

Reference Example 7: Preparation of a DOC Catalyst

(31) Bottom Coating:

(32) A high porous gamma-alumina support material comprising 95 weight-% Al, calculated as Al.sub.2O.sub.3, and 5% weight Si, calculated as SiO.sub.2, having a BET specific surface area of greater than 100 m.sup.2/g, and a pore volume of greater than 0.06 cm.sup.3/g was impregnated with an aqueous solution of stabilized platinum complexes and an aqueous solution of palladium nitrate using an incipient wetness technique The Pd/Pt-alumina powder was slurried in water. An uncoated flow-through honeycomb cordierite substrate (total volume 1.24 L, 400 cpsi and 4 mil wall thickness, diameter: 5.66 incheslength: 3 inches), was coated with the obtained slurry over 100% of the substrate axial length. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a bottom coating. The loading of palladium and platinum in the bottom coating was 32.75 g/ft.sup.3 and 65.5 g/ft.sup.3, respectively, and the total bottom coating loading was 1.5 g/in.sup.3.

(33) Top Coating:

(34) A high porous gamma-alumina support material comprising 95 weight-% Al, calculated as Al.sub.2O.sub.3, and 5% weight Si, calculated as SiO.sub.2, having a BET specific surface area of greater than 100 m.sup.2/g, a pore volume of greater than 0.06 cm.sup.3/g was impregnated with an aqueous solution of palladium nitrate using an incipient wetness technique. The Pd-alumina powder was slurried in water with the addition of an ammonium-Beta zeolitic material (BEA, a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 23 and on the weight of the zeolitic material and a crystallinity vs. standard (XRD) greater than 90%). The substrate coated with the bottom coating was coated with the obtained slurry over 100% of the substrate axial length. The coated substrate was dried in air having a temperature of 110 C. for 1 hour and subsequently calcined in air at 590 C. for 2 hours, forming a top coating. The loading of palladium in the top coating was 32.75 g/ft.sup.3 and the total top coating loading was 1.5 g/in.sup.3.

Comparative Example 3: Preparation of a System Comprising a DOC, an Electrical Heating Substrate and a DOC

(35) The system of Comparative Example 3, not according to the present invention, was prepared by combining the diesel oxidation catalyst of Reference Example 7, the diesel oxidation catalyst of Reference Example 5 and the electrical heating substrate of Reference Example 3, wherein the DOC of Reference Example 7 is positioned upstream of the electrical heating substrate of Reference Example 3 and the electrical heating substrate of Reference Example 3 is positioned upstream of the DOC of Reference Example 5.

Example 5: Preparation of a System Comprising a NOx Adsorber (NA)Catalyst, an Electrical Heating Substrate and a DOC Catalyst

(36) The system of Example 5 according to the present invention was prepared by combining the NOx adsorber catalyst of Reference Example 6, the diesel oxidation catalyst (DOC) of Reference Example 5 and the gas heating component of Reference Example 3, wherein the NOx adsorber catalyst of Reference Example 6 is positioned upstream of the gas heating component of Reference Example 3 and the electrical heating substrate of Reference Example 3 is positioned upstream of the DOC of Reference Example 5.

Example 6: Testing of the System of Comparative Examples 2 and 3 and of Examples 4 and 5WLTC Evaluation on a Diesel EngineNOx Emissions

(37) The systems of Comparative Examples 2 and 3 and of Examples 4 and 5 were tested in a Worldwide Harmonized Light Vehicle Test Cycle (WLTC) on a 2 L diesel engine after aging for 16 h at 800 C. in 10% steam/air. Prior to the first test the temperature of the NOx adsorber samples (in Examples 4 and 5) was increased to 650 C. for 10 min, to remove pre-adsorbed NOx.

(38) The systems of Comparative Examples 2 and 3 and of Examples 4 and 5 were evaluated with a downstream SCRoF. The SCR catalyst article comprises Cu-CHA coated on a filter substrate (SCRoF). Between the NOx adsorber and DOC article and the SCR catalyst article an injector for urea dosing was applied to deliver the reductant for the SCR reaction. The tested systems of Comparative Example 2 and Example 4 are shown in FIG. 3.

(39) The electrical heating element for all systems was switched on directly after the start of the WLTC. The temperature in front of the SCR article was adjusted between 200 and 250 C. The temperature directly behind the heating element was increasing to a maximum temperature of 380 C.

(40) Table 3 provides the system NOx emissions in mg/km for the total WLTC cycle (23 km) and after 600 s for the city driving part only (3 km). The system of Example 4 achieves lowest emissions for both the full WLTC and during the urban part of WLTC. The system of Example 5 achieves lower emissions for both the full WLTC compared to the systems of Comparative Examples 2 and 3.

(41) TABLE-US-00003 TABLE 3 NOx total WLTC NOx after 600 s of [mg/km] the WLTC [mg/km] Example 4 5 20 Comparative Example 2 8 45 Example 5 8 32 Comparative Example 3 10 53

(42) Table 4 shows the CO and THC emissions in g/km for the full WLTC cycle of systems of Comparative Example 2 and Example 4. Both examples show very low CO and THC emissions from the high temperatures in the DOC behind the heating element. The CO and THC emissions are also lowered compare to the emissions obtained with the system of Comparative Example 1. The system of Example 5 shows similar results for CO emissions.

(43) TABLE-US-00004 TABLE 4 CO/g/km THC/g/km Example 4 0.04 0.010 Comparative Example 2 0.04 0.010 Comparative Example 1 0.05 0.012 Example 5 0.04 0.011 Comparative Example 3 0.05 0.010

(44) As may be taken from these tables, the system of Example 4 provides the lowest emissions for all three components, CO, THC and NOx. Therefore, it has been surprisingly found that a further treatment system which uses an electrical heating element between a NA catalyst and a DOC (inventive system) permits to obtain the lowest NOx, CO and THC emissions.

(45) Further, it has been surprisingly found that both types of substrate, namely cordierite and metallic, for supporting a NA catalyst permits to obtain great reduction in NOx, CO and THC emissions compared to the emissions obtained with the comparative examples.

Example 7: Testing of the Systems of Comparative Example 2 and Example 4WLTC Evaluation on a Diesel EngineN.SUB.2.O Formation

(46) The systems of Comparative Example 2 and Example 4 were tested in a Worldwide Harmonized Light Vehicle Test Cycle (WLTC) on a 2 L diesel engine after aging for 16 h at 800 C. in 10% steam/air. Between the DOC component and the SCR catalyst of a system an reductant injector for urea dosing was arranged to deliver the reductant for the SCR reaction.

(47) FIG. 5 displays the NOx emissions divided by the distance of the WLTC vs. the distance of the WLTC. From this data plot, the system of Example 4 achieves after 2 km driving NOx emissions below 30 mg/km. For the system of Comparative Example 2 NOx emissions below 30 mg/km are reached after 4 longer driving, i.e., 8 km. FIG. 6 provides the emissions of the greenhouse gas, N.sub.2O, over the WLTC. The system of Comparative Example 2 is showing higher N.sub.2O emissions compared to the system of Example 4.

Reference Example 8: Preparation of a NOx Adsorber (NA) with a DOC Function Catalyst (Layered Catalyst on a Substrate Including a Downstream Heating SubstrateFER)

(48) Bottom Coating (NOx Adsorber Coating):

(49) An ammonium ferrierite zeolitic material (a zeolitic material having framework structure type FER, a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 21:1 and a crystallinity vs. standard (XRD)>80%) was wet impregnated with an aqueous palladium nitrate solution to attain a Pd loading of 1.48 weight-% based on the weight of the final material (zeolitic material+palladium). To the resulting slurry a zirconium acetate mixture was added. The amount of zirconium acetate was calculated such that the amount of zirconia in the bottom coating, calculated as ZrO.sub.2, was 5 weight-% based on the weight of the zeolitic material.

(50) A porous uncoated round flow-through honeycomb cordierite substrate (having a total volume of 1.85 L, 400 cpsi and 4 mil wall thickness, a diameter of 5.66 inches and a length of 4.5 inches), was coated with the obtained slurry over 100% of the substrate axial length. The coated substrate was dried in air at 110 C. for 1 h and subsequently calcined in air at 590 C. for 2 h, forming a bottom coating. The loading of palladium in the bottom coating was 70 g/ft.sup.3, the loading of the FER in the bottom coating was 2.7 g/in.sup.3 and the loading of ZrO.sub.2 was 0.135 g/in.sup.3. The loading of the bottom coating was 2.9 g/in.sup.3.

(51) Top Coating (DOC Coating):

(52) For the outlet top coating, an Al.sub.2O.sub.3 support material comprising 5 weight-% MnO.sub.2 (Al.sub.2O.sub.395 weight-% with Mn 5 weight-%, calculated as MnO.sub.2, having a BET specific surface area of greater than 100 m.sup.2/g, and a pore volume of greater than 0.06 cm.sup.3/g) was impregnated with platinum via a wet impregnation process. A slurry containing the resulting material was coated over 50% of the substrate axial length from the outlet end towards the inlet end of the cordierite substrate carrying the Pd-FER bottom coating. The outlet top coating contained 80 g/ft.sup.3 platinum and the loading of the outlet coating was 1.3 g/in.sup.3.

(53) For the inlet top coating, an alumina support material comprising 5 weight-% SiO.sub.2 was impregnated with platinum and palladium in a weight ratio of 2:1 via a wet impregnation process. A Fe-Beta zeolitic material (a zeolitic material having framework structure type BEA, a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 23:1 and a crystallinity vs. standard (XRD)>90% and an Fe content, calculated as Fe.sub.2O.sub.3 of 4.3 weight-% based on the weight of the zeolitic material) was added to the Pt/Pd-alumina slurry. The weight ratio of the alumina doped with Si to the Beta zeolitic material was 1:1. The resulting slurry was coated over 50% of the substrate axial length from the inlet end towards the outlet end of the cordierite substrate coated with the Pd-FER bottom layer and the outlet top coating. The inlet top coating contained 13.3 g/ft.sup.3 platinum and 6.7 g/ft.sup.3 Pd. The loading of the inlet top coating was 1.41 g/in.sup.3.

(54) The total loading of the top coating (outlet top coating+inlet top coating) was 1.355 g/in.sup.3.

Reference Example 9: Preparation of a NOx Adsorber Catalyst (NA)

(55) A H-chabazite zeolitic material (having framework structure type CNA, a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 14 and a crystallinity vs. standard (XRD)>90%) was wet impregnated with an aqueous palladium nitrate solution and calcined in air at 590 C. for 2 hours. The resulting Pd-impregnated chabazite had a Pd loading of 1.22 weight-% based on the weight of the final material (zeolitic material+palladium). Said Pd-impregnated chabazite was dispersed in water to obtain a slurry.

(56) A porous uncoated flow-through cordierite honeycomb substrate (having a total volume of 1.85 L, 400 cpsi and 4 mil wall thickness, a diameter of 5.66 inches and a length of 4.5 inches) was coated with said slurry over 100% of the substrate axial length. The coated substrate was dried in air having a temperature of 110 C. for 1 h and subsequently calcined in air at 590 C. for 2 h. The loading of palladium on the coated substrate was 60 g/ft.sup.3 and the total washcoat loading was 2.85 g/in.sup.3.

Example 8: Preparation of a System Comprising a Catalyst with NOx Adsorber (Pd-FER) Component and a DOC Component and an Electrical Heating Substrate

(57) The system of Example 8 according to the present invention was prepared by combining the catalyst of Reference Example 8 which comprises a NOx adsorber component and a diesel oxidation catalyst (DOC) component and the gas heating component of Reference Example 3, wherein the catalyst of Reference Example 8 was positioned upstream of the gas heating component of Reference Example 3.

Comparative Example 4: Preparation of a System Comprising a NOx Adsorber (Pd-CHA) Catalyst, and an Electrical Heating Substrate

(58) The system of Comparative Example 4 according to the present invention was prepared by combining the catalyst of Reference Example 9 which comprises a NOx adsorber component and the gas heating component of Reference Example 3, wherein the catalyst of Reference Example 9 was positioned upstream of the gas heating component of Reference Example 3.

Example 9: Testing of Inventive and Comparative ExamplesSimulated Low Temperature City Driving Cycle, NOx Adsorption Evaluation

(59) The system according to Example 8 and the system according to Comparative Example 4 were each tested using a simulated low temperature city driving mode on a 2 L diesel engine after hydrothermal aging at 800 C. for 16 hours in 10% steam (water)/air. The systems according to Example 8 and Comparative Example 4 were tested independently from one another with a selective catalytic reduction (SCR) catalyst positioned downstream thereto. The SCR catalyst comprised a Cu-CHA zeolite coated on a 3 L filter substrate. Between the system and the SCR catalyst an injector for urea dosing was applied suitable for delivering a reductant for the SCR reaction.

(60) The driving cycle was compiled from city driving mode of the New European Driving Cycle (NEDC). The average temperature of the cycle was about 170 C. The cycle was driven twice for 1880 s. Prior to the first test run the temperature of the NOx adsorber catalyst was increased to 650 C. for 10 min, to purge pre-adsorbed NOx.

(61) The test results of the first test run are shown in FIG. 7. Both systems adsorb some NOx from the exhaust leaving the engine up to about 500 s. The NOx catalyst comprising a Pd-CHA zeolite comprised in the system according to Comparative Example 4 shows a lower NOx adsorption during the first 500 s and also a lower NOx release at the end of the first test run compared to the NOx adsorber catalyst comprised in the system according to Example 8.

(62) Prior to the second test run, the systems were cooled to room temperature and no high temperature preconditioning was conducted. The test results of the second test run are shown in FIG. 8. In the second test run, the system according to Comparative Example 4, thus comprising a NOx adsorber catalyst with a Pd-CHA zeolite, did not show a NOx adsorption but a strong NOx release instead since the NOx was not released during the first cold city cycle. Therefore, the system according to Comparative Example 4 would require an undesirable thermal treatment to release the stored NOx, if it is run on such a cold city cycle. The system according to Example 8, thus comprising a NOx adsorber catalyst with a Pd-FER zeolite, shows still a good NOx adsorption in the second cold city cycle.

BRIEF DESCRIPTION OF THE FIGURES

(63) FIG. 1 shows the simulated low temperature city driving cycle and NOx adsorption evaluation of Reference Example 2 (1.sup.st test run).

(64) FIG. 2 shows the simulated low temperature city driving cycle and NOx adsorption evaluation of Reference Example 2 (2.sup.nd test run).

(65) FIG. 3 shows a schematic depiction of systems for treating NOx, CO and THC emissions. In particular, this figure first shows a first system not according to the present invention comprising the NA-DOC catalyst 1 comprising a substrate coated with a NA (NOx adsorber) coating and a DOC (diesel oxidation catalyst) coating on the NA coating of Reference Example 2 and a selective catalytic reduction catalyst on a filter substrate (SCRoF) 2 downstream of said NA-DOC catalyst 1 (the coatings are not shown in the figure). Further, a urea injector positioned between the NA-DOC 1 and the SCRoF 2 can be added. Further, this figure shows a second system not according to the present invention comprising a NA-DOC catalyst according to Comparative Example 1 comprising a NA coating and a DOC coating disposed on the NA coating (coatings not shown in the figure), wherein the NA coating is disposed on a single substrate comprising a gas heating component 3 positioned upstream of a flow-through substrate 4 (the coating is not shown in the figure) and a selective catalytic reduction catalyst on a filter substrate (SCRoF) 2 downstream of the NA-DOC catalyst (3+4+coatings). Further, a urea injector positioned between the NA-DOC catalyst and the SCRoF 2 can be added. Furthermore, this figure shows a system according to the present invention comprising a NA-DOC catalyst according to Example 1 comprising a NA coating and a DOC coating disposed on the NA coating (the coatings are not shown in the figure), wherein the NA coating is disposed on a single substrate comprising a flow-through substrate 4 positioned upstream of a gas heating component 3 (the coatings are not shown in the figure) and an optional selective catalytic reduction catalyst on a filter substrate (SCRoF) 2 downstream of said NA-DOC catalyst (4+3+coatings). Further, a urea injector positioned between the NA-DOC catalyst and the optional SCRoF 2 can be added.

(66) FIG. 4 shows the WLTC Evaluation of NOx adsorber DOC of Reference Example 2, Example 1 and Comparative Example 1 with electrical heating on a diesel engine (NOx emissions).

(67) FIG. 5 shows the WLTC Evaluation of the systems of Comparative 2 and Example 4 with electrical heating on a diesel engine (NOx emissions).

(68) FIG. 6 shows the WLTC Evaluation of the systems of Comparative 2 and Example 4 with electrical heating on a diesel engine (N.sub.2O emission).

(69) FIG. 7 shows the simulated low temperature city driving cycle and NOx adsorption evaluation of the system according to Example 8 and the system according to Comparative Example 4 (1.sup.st test run).

(70) FIG. 8 shows the simulated low temperature city driving cycle and NOx adsorption evaluation of the system according to Example 8 and the system according to Comparative Example 4 (2.sup.nd test run).

CITED LITERATURE

(71) DE 10 2018 101929 US 2017/0284250A1 U.S. Pat. No. 10,480,369 B1