MULTI-FUNCATIONAL CATALYSTS FOR THE OXIDATION OF NO, THE OXIDATION OF NH3 AND THE SELECTIVE CATALYTIC REDUCTION OF NOX

Abstract

The present invention relates to a catalyst for the oxidation of NO, for the oxidation of ammonia and for the selective catalytic reduction of NOx, the catalyst comprising a flow-through substrate, a first coating comprising one or more of a vanadium oxide and a zeolitic material comprising one or more of copper and iron, a second coating comprising a platinum group metal component supported on a non-zeolitic oxidic material and further comprising one or more of a vanadium oxide and a zeolitic material comprising one or more of copper and iron and a third coating comprising a platinum group metal component supported on an oxidic material. The present invention further relates to an exhaust gas treatment system comprising said catalyst.

Claims

1-15. (canceled)

16. A catalyst for the oxidation of NO, for the oxidation of ammonia, and for the selective catalytic reduction of NOx, comprising: (i) a flow-through 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 flow-through substrate extending therethrough, wherein the interface between the passages and the internal walls is defined by the surface of the internal walls; (ii) a first coating comprising one or more of a vanadium oxide and a zeolitic material comprising one or more of copper and iron; (iii) a second coating comprising a platinum group metal component supported on a non-zeolitic oxidic material and further comprising one or more of a vanadium oxide and a zeolitic material comprising one or more of copper and iron; and (iv) a third coating comprising a platinum group metal component supported on an oxidic material; wherein the third coating is disposed on the surface of the internal walls over z % of the axial length of the substrate from the outlet end to the inlet end, wherein z ranges from 20 to 80; wherein the second coating extends over y % of the axial length of the substrate from the inlet end to the outlet end and is disposed on the surface of the internal walls, wherein y ranges from 20 to 80; wherein the first coating extends over x % of the axial length of the substrate from the inlet end to the outlet end and is disposed on the second coating and on the third coating, wherein x ranges from 95 to 100.

17. The catalyst of claim 16, wherein y ranges from 20 to (100−z).

18. The catalyst of claim 16, wherein the first coating comprises a zeolitic material comprising one or more of copper and iron; wherein the zeolitic material comprised in the first coating has a framework type chosen from AEI, GME, CHA, MFI, BEA, FAU, MOR, a mixture of two or more thereof, and a mixed type of two or more thereof.

19. The catalyst of claim 16, wherein the first coating comprises a vanadium oxide.

20. The catalyst of claim 16, wherein the first coating has from 0 weight-% to 0.001 weight-% palladium.

21. The catalyst of claim 16, wherein the platinum group metal component of the second coating is one or more of platinum, palladium, and rhodium.

22. The catalyst of claim 16, wherein the second coating comprises the platinum group metal component at a loading, calculated as elemental platinum group metal, ranging from 0.3 g/ft.sup.3 to 10 g/ft.sup.3; wherein the second coating comprises the platinum group metal component at an amount ranging from 0.1 weight-% to 2 weight, based on the weight of the non-zeolitic oxidic material of the second coating.

23. The catalyst of claim 16, wherein the non-zeolitic oxidic material onto which the platinum group metal component of the second coating is supported comprises one or more of alumina, zirconia, titania, silica, ceria, and a mixed oxide comprising two or more of Al, Zr, Ti, Si, and Ce; and wherein the second coating comprises the non-zeolitic oxidic material at a loading ranging from 0.1 g/in.sup.3 to 3 g/in.sup.3.

24. The catalyst of claim 16, wherein the second coating comprises a zeolitic material comprising one or more of copper and iron; wherein the zeolitic material of the second coating has a framework type chosen from AEI, GME, CHA, MFI, BEA, FAU, MOR, a mixture of two or more thereof, and a mixed type of two or more thereof.

25. The catalyst of claim 16, wherein the second coating and the third coating together have a platinum group metal component loading in the catalyst, calculated as elemental platinum group metal, ranging from 1 g/ft.sup.3 to 40 g/ft.sup.3.

26. The catalyst of claim 16, wherein the platinum group metal component of the third coating is one or more of platinum, palladium, and rhodium.

27. The catalyst of claim 16, wherein the oxidic material supporting the platinum group metal component of the third coating comprises one or more of alumina, zirconia, titania, silica, ceria, and a mixed oxide comprising two or more of Al, Zr, Ti, Si, and Ce; wherein from 90 weight-% to 100 weight-% of the oxidic material of the third coating is titania.

28. A method for preparing a catalyst for the oxidation of NO, for the oxidation of ammonia, and for the selective catalytic reduction of NOx comprising: (a) providing an uncoated flow-through substrate, the 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, wherein the interface between the passages and the internal walls is defined by the surface of the internal walls; (b) providing a slurry comprising a platinum group metal component, an oxidic material, and a solvent, disposing the slurry on the surface of the internal walls of the substrate, over z % of the substrate axial length from the outlet end to the inlet end, wherein z ranges from 20 to 80, calcining the slurry disposed on the substrate, obtaining a third coating disposed on the substrate; (c) providing a slurry comprising a platinum group metal component, a non-zeolitic oxidic material and one or more of a vanadium oxide and a zeolitic material comprising one or more of copper and iron, and a solvent, disposing the slurry on the surface of the internal walls over y % of the substrate axial length from the inlet end to the outlet end, wherein y ranges from 20 to 80, calcining the slurry disposed on the substrate, obtaining a second coating disposed on the substrate; and (d) providing a slurry comprising one or more of a vanadium oxide and a zeolitic material comprising one or more of copper and iron, and a solvent, disposing the slurry over x % of the substrate axial length on the second coating from the inlet end to the outlet end, wherein x ranges from 95 to 100, calcining the slurry disposed on the substrate, obtaining the catalyst for the oxidation of NO, for the oxidation of ammonia and for the selective catalytic reduction of NOx.

29. A catalyst for the oxidation of NO, for the oxidation of ammonia and for the selective catalytic reduction of NOx, prepared by the process according to claim 28.

30. An exhaust gas treatment system for treating an exhaust gas stream exiting an internal combustion engine, the exhaust gas treatment system having an upstream end for introducing the exhaust gas stream into the exhaust gas treatment system, wherein the exhaust gas treatment system comprises the catalyst according to claim 16 and one or more of a selective catalytic reduction catalyst, an ammonia oxidation catalyst, and a diesel particulate filter.

Description

EXAMPLES

Reference Example 1: Determination of the Dv20, Dv50 and Dv90 Values

[0267] The particle size distributions were determined by a static light scattering method using Sympatec HELOS equipment, wherein the optical concentration of the sample was in the range of from 5 to 10%.

Reference Example 2: Measurement of the BET Specific Surface Area

[0268] The BET specific surface area was determined according to DIN 66131 or DIN ISO 9277 using liquid nitrogen.

Reference Example 3: General Coating Method

[0269] In order to coat the flow-through substrate with one or more coatings, the flow-through substrate was suitably immersed vertically in a portion of a given slurry for a specific length of the substrate which was equal to the targeted length of the coating to be applied. In this manner, the slurry contacted the walls of the substrate.

Comparative Example 1: Preparation of a Catalyst not According to the Present Invention (with a Single Coating)

[0270] To a Zr-doped alumina powder (20 weight-% ZrO.sub.2, a BET specific surface area of 200 m.sup.2/g, Dv90 of 125 microns and a total pore volume of 0.425 ml/g) was added a platinum ammine solution. After calcination at 590° C. the final Pt/Zr-alumina had a Pt content of 1.85 weight-% based on the weight of Zr-alumina. This material was added to water and the slurry was milled until the resulting Dv90 was 10 microns, as described in Reference Example 1. To an aqueous slurry of Cu-CHA zeolitic material (with about 3.75 weight-% of CuO and a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of about 25) was added a zirconyl-acetate solution to achieve 5 weight-% of ZrO.sub.2 after calcination based on the weight of the zeolitic material. The milled Pt/Zr-alumina slurry was added to the Zr/Cu-CHA slurry and mixed. The final slurry was then disposed over the full length of an uncoated honeycomb flow-through cordierite monolith substrate (diameter: 26.67 cm (10.5 inches)×length: 7.62 cm (3 inches) cylindrically shaped substrate with 400/(2.54).sup.2 cells per square centimeter and 0.1 mm (4 mil) wall thickness). Afterwards, the substrate was dried and calcined. The loading of the coating in the catalyst after calcination was about 3.0 g/in.sup.3 with a Cu-CHA loading of 2.6 g/in.sup.3, a ZrO.sub.2 loading of 0.13 g/in.sup.3, a Zr-alumina of 0.25 g/in.sup.3 a Pt loading of 8 g/ft.sup.3.

Comparative Example 2: Preparation of a Catalyst not According to the Present Invention (with Three Coatings)

[0271] Third Coating (Outlet Bottom Coating):

[0272] To a Si-doped titanic powder (10 weight % SiO.sub.2, a BET specific surface area of 200 m.sup.2/g and a Dv90 of 20 micrometers) was added a platinum ammine solution, such that the Si-titania had after calcination a Pt content of 1.1 weight-% based on the weight of Si-titania. This material was added to water and the resulting slurry was milled until the resulting Dv90 was 10 microns, as described in Reference Example 1. The resulting slurry was then disposed from the outlet side of an uncoated honeycomb flow-through cordierite monolith substrate toward the inlet side over half of the length of the substrate using the coating method described in Reference Example 3 (diameter: 26.67 cm (10.5 inches)×length: 7.62 cm (3 inches) cylindrically shaped substrate with 400/(2.54).sup.2 cells per square centimeter and 0.1 millimeter (4 mil) wall thickness) to form the third coating. Afterwards, the coated substrate was dried and calcined. The loading of the third coating after calcination was about 0.51 g/in.sup.3, including a final platinum loading in the third coating of 10 g/ft.sup.3.

[0273] Second Coating (Full-Length Middle Coating):

[0274] To a Si-doped titania powder (10 weight-% SiO.sub.2, a BET specific surface area of 200 m.sup.2/g and a

[0275] Dv90 of 20 micrometers) was added a platinum ammine solution, such that the Si-titania had after calcination a Pt content of 0.35 weight-% based on the weight of Si-titania. This material was added to water and the resulting slurry was milled until the resulting Dv90 was 10 microns, as described in Reference Example 1. To an aqueous slurry of Cu-CHA zeolitic material (5.1 weight-% CuO and a SiO.sub.2: Al.sub.2O.sub.3 molar ratio of 18) is added a zirconyl-acetate solution to achieve 5 weight % ZrO.sub.2 after calcination based on the weight of the zeolitic material. To this Cu-CHA slurry, the Pt-containing slurry was added and stirred, creating the final slurry. The final slurry was then disposed over the full length of the honeycomb cordierite monolith substrate, already coated with the third coating, from the inlet side of the substrate towards the outlet side and covering the third coating using the coating method described in Reference Example 3. Afterwards, the coated substrate was dried and calcined. The loading of the second coating after calcination was 2.5 g/in.sup.3, including 1.9 g/in.sup.3 of Cu-CHA, 0.1 g/in.sup.3 of ZrO.sub.2, 0.5 g/in.sup.3 of Si—TiO.sub.2 and a final platinum loading of 3 g/ft.sup.3.

[0276] First Coating (Full-Length Top Coating):

[0277] To an aqueous slurry of Cu-CHA zeolitic material (5.1 weight-% CuO and a SiO.sub.2: Al.sub.2O.sub.3 molar ratio of 18) was added a zirconyl-acetate solution to achieve 5 weight % ZrO.sub.2 after calcination based on the weight of the zeolitic material. The final slurry was then disposed over the full length of the honeycomb flow-through cordierite monolith substrate, coated with the third and second coatings, from the inlet side of the substrate towards the outlet side and covering the second and third coatings using the coating method described in Reference Example 3. Afterwards, the coated substrate was dried and calcined. The loading of the first coating after calcination was 1.0 g/in.sup.3. The final catalytic loading (1.sup.st, 2.sup.nd and 3.sup.rd coatings) in the catalyst after calcination was 3.75 g/in.sup.3.

Example 1: Preparation of a Catalyst According to the Present Invention (with Three Coatings)

[0278] Third Coating (Outlet Bottom Coating):

[0279] To a Si-doped titania powder (10 weight-% of SiO.sub.2, a BET specific surface area of 200 m.sup.2/g and a Dv90 of 20 micrometers) was added a platinum ammine solution, such that the Si-titania had after calcination a Pt content of 0.81 weight-% based on the weight of Si-titania. This material was added to water and the slurry was milled until the resulting Dv90 was 5.2 microns, as described in Reference Example 1. Finally, a colloidal silica binder was mixed into the slurry at a level calculated to be 2.5 weight-% SiO.sub.2 (from the binder) after calcination based on the weight of Si-titania. The resulting mixture was then disposed from the outlet side of an uncoated honeycomb flow-through cordierite monolith substrate toward the inlet side over half of the length of the substrate using the coating method described in Reference Example 3 (diameter: 26.67 cm (10.5 inches)×length: 7.62 cm (3 inches) cylindrically shaped substrate with 400/(2.54).sup.2 cells per square centimeter and 0.1 millimeter (4 mil) wall thickness) to form the third coating. Afterwards, the coated substrate was dried and calcined. The loading of the third coating after calcination was about 1 g/in.sup.3, including a platinum loading in the third coating of 14 g/ft.sup.3.

[0280] Second Coating (Inlet Bottom Coating):

[0281] To a Si-doped titania powder (10 wt % SiO.sub.2, BET specific surface area of 200 m.sup.2/g, a Dv90 of 20 microns) was added a platinum ammine solution. After calcination at 590° C. the final Pt/Si-titania had a Pt content of 0.46 weight-% based on the weight of Si-titania. This material was added to water and the slurry was milled until the resulting Dv90 was 10 microns, as described in Reference Example 1. To an aqueous slurry of Cu-CHA zeolitic material (5.1 weight-% CuO and a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 18) was added a zirconyl-acetate solution to achieve 5 weight-% ZrO.sub.2 after calcination based on the weight of the zeolitic material. To this Cu-CHA slurry, the Pt-containing slurry was added and stirred, creating the final slurry. The final slurry was then disposed over half the length of the honeycomb cordierite monolith substrate, coated with the third coating, from the inlet side of the substrate towards the outlet side, ensuring that the second coating does not overlap the third coating and using the coating method described in Reference Example 3. Afterwards, the coated substrate was dried and calcined. The loading of the second coating, after calcination was about 2 g/in.sup.3 with a Cu-CHA loading of 1.67 g/in.sup.3, a ZrO.sub.2 loading of 0.08 g/in.sup.3, a Si-titania loading of 0.25 g/in.sup.3 and a PGM loading of 2 g/ft.sup.3.

[0282] First Coating (Full-Length Top Coating):

[0283] To an aqueous slurry of Cu-CHA zeolitic material (5.1 weight-% CuO and a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 18) was added a zirconyl-acetate solution to achieve 5 weight-% ZrO.sub.2 after calcination based on the weight of the zeolitic material. The slurry was then disposed over the full length of the honeycomb cordierite monolith substrate, coated with the third and second coatings, from the inlet side of the substrate towards the outlet side and covering the second and third coatings using the coating method described in Reference Example 3. Afterwards, the coated substrate was dried and calcined. The loading of this first coating after calcination was 1.0 g/in.sup.3. The final catalytic loading (1.sup.st, 2.sup.nd and 3.sup.rd coatings) in the catalyst after calcination was about 2.5 g/in.sup.3.

Example 2: Preparation of a Catalyst According to the Present Invention (with Three Coatings)

[0284] Third Coating (Outlet Bottom Coating):

[0285] To a Si-doped titania powder (10 weight-% of SiO.sub.2, a BET specific surface area of 200 m.sup.2/g and a Dv90 of 20 microns) was added a platinum ammine solution. After calcination at 590° C. the final Pt/Si-titania had a Pt content of 0.81 weight-% based on the weight of Si-titania. This material was added to water and the slurry was milled until the resulting Dv90 was 5.2 microns, as described in Reference Example 1. Finally, a colloidal silica binder was mixed into the slurry at a level calculated to be 2.5 weight-% after calcination based on the weight of Si-titania. The resulting slurry was then disposed from the outlet end of an uncoated honeycomb flow-through cordierite monolith substrate toward the inlet side over half of the length of the substrate using the coating method described in Reference Example 5 (diameter: 26.67 cm (10.5 inches)×length: 7.62 cm (3 inches) cylindrically shaped substrate with 400/(2.54).sup.2 cells per square centimeter and 0.1 millimeter (4 mil) wall thickness) to form the third coating. Afterwards, the coated substrate was dried and calcined. The loading of the third coating in the catalyst after calcination was about 1 g/in.sup.3, including a platinum loading of 14 g/ft.sup.3.

[0286] Second Coating (Inlet Bottom Coating):

[0287] To a Si-doped titanic powder (10 weight-% of SiO.sub.2, a BET specific surface area of 200 m.sup.2/g and a Dv90 of 20 microns) was added a platinum ammine solution. After calcination at 590° C. the final Pt/Si-titania had a Pt content of 0.46 weight-% based on the weight of Si-titania. This material was added to water and the slurry was milled until the resulting Dv90 was 10 microns, as described in Reference Example 1. To an aqueous slurry of Cu-CHA zeolitic material (5.1 weight-% CuO and a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 18) was added a zirconyl-acetate solution to achieve 5 weight-% ZrO.sub.2 after calcination based on the weight of the zeolitic material. To this Cu-CHA slurry, the Pt-containing slurry was added and stirred, creating a final mixture. The final mixture was then disposed over half the length of the honeycomb cordierite monolith substrate, coated with the third coating, from the inlet side of the substrate towards the outlet side, ensuring that the second coating does not overlap the third coating and using the coating method described in Reference Example 3. Afterwards, the coated substrate was dried and calcined. The loading of the second coating after calcination was 1 g/in.sup.3 with 0.71 g/in.sup.3 of Cu-CHA, 0.25 g/in.sup.3 of Si-titania and a PGM loading of 2 g/ft.sup.3.

[0288] First Coating (Full-Length Top Coating):

[0289] To an aqueous slurry of Cu-CHA zeolitic material (5.1 weight-% CuO and a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 18) was added a zirconyl-acetate solution to achieve 5 weight-% ZrO.sub.2 after calcination based on the weight of the zeolitic material. The slurry was then disposed over the full length of the honeycomb cordierite monolith substrate, coated with the third and second coatings, from the inlet side of the substrate towards the outlet side and covering the second and third coatings using the coating method described in Reference Example 3. Afterwards, the coated substrate was dried and calcined. The loading of this first coat was 2.0 g/in.sup.3. The final catalytic loading (1.sup.st, 2.sup.nd and 3.sup.rd coatings) in the catalyst after calcination was about 3 g/in.sup.3.

Example 3: Testing of the Catalysts of Comparative Examples 1 and 2 and of Examples 1 and 2-DeNOx Performance and N.SUB.2.O Formation

[0290] The catalysts were evaluated on a motor test cell. The motor in this case was 6.7 L off-road calibrated engine. In all cases, each catalyst was tested alone, without any upstream oxidation or downstream SCR catalysts. The resulting space velocity was 80 k/h for the SCR test (160 k/h for the highest temperature point). The SCR test was an ammonia to NOx ratio (ANR) sweep test with different stoichiometric ratios between NH.sub.3 and NOx evaluated. For the data presented in FIGS. 2 and 3, the NOx conversion is always provided at ANR=1.1 and the N.sub.2O formation at ANR=1.0 (ANR, which is the stoichiometric ammonia to NOx ratio, allows one to determine the correct amount of urea to inject based on the given exhaust mass flow and NOx concentration). Five SCR inlet temperatures were chosen, and the engine conditions set appropriately to reach the targeted space velocities. The catalyst activity was allowed to attain a steady-state equilibrium at each engine load (temperature) and ANR step before moving on to the next step. Both the NOx conversion presented in FIG. 2 and the N.sub.2O formation presented in FIG. 3 were measured on the same test.

[0291] FIG. 2 shows that the inventive catalysts of Example 1 and Example 2 exhibit improved DeNOx over a wide temperature range, namely from 200 to 500° C., compared to the catalysts of Comparative Examples 1 and 2 not according to the present invention. In particular, at temperature above 250° C., e.g. from 300 to 500° C., the DeNOx activity of the catalysts comprising a top coating with an SCR-only catalyst is largely improved compared to a catalyst prepared with a single coating of mixed catalysts. At 450° C. (inlet temperature), the catalysts according to the present invention exhibit a DeNOx of about 95% while the catalyst of Comparative Example 1 (a single coating) exhibits a DeNOx of about 50%.

[0292] FIG. 3 shows that the catalysts according to the present invention permit to reduce the production of N.sub.2O, in particular the concentration of nitrous oxide formed are lower than 15 ppm while with the catalyst of Comparative Example 1, the concentration of N.sub.2O formed is of more than 20 ppm and up to about 60 ppm at about 350° C. Without wanting to be bound to any theory, it is believed that these results show that the top coating comprising a SCR-only catalyst may be necessary to control the oxidation of ammonia at temperature above 250° C.

Example 4: Testing of the Catalysts of Comparative Examples 1 and 2 and of Examples 1 and 2-NO Oxidation

[0293] The catalysts were evaluated on a motor test cell. The motor in this case was 6.7 L off-road calibrated engine. In all cases, each catalyst was tested alone, without any upstream oxidation or downstream SCR catalysts. The resulting space velocity was 100 k/h for the NOx oxidation test. Prior to this test, the catalysts were degreened in-situ at 450° C. for 2 hours. For the NO oxidation test, the outlet exhaust temperature was increased and decreased step-wise from 200° C. to 500° C. to 200° C. in 25° C. steps while maintaining constant space velocity. Each step was held for 15 minutes to reach equilibrium catalyst conditions. NO oxidation activity is reported as the ratio of NO.sub.2 to total NOx (or NO.sub.2/NOx %).

[0294] FIG. 4 shows that the inventive catalysts of Example 1 and Example 2 exhibit an improved NO oxidation compared to the catalysts of Comparative Examples 1 and 2. This is especially apparent at low temperatures between 200 and 350° C. which is the kinetically controlled region. Furthermore, it is this low temperature region which is most relevant for passive soot oxidation because this condition is most representative of everyday use. At temperatures above 400° C. in the diffusion limited regime, the single coat Comparative Example 1 offers somewhat greater NO oxidation compared with that for Examples 1 and 2, however, the magnitude of the performance difference is not as pronounced as in the kinetically controlled regime.

BRIEF DESCRIPTION OF THE FIGURES

[0295] FIG. 1 shows a schematic depiction of a catalyst according to the present invention. In particular, this figure shows a catalyst 1 of the present invention comprises a substrate 2, such as a flow-through substrate, onto which an inlet coating 3, the second coating of the present invention, is disposed over 50% of the substrate axial length from the inlet end to the outlet end of the substrate and an outlet coating 4, the third coating of the present invention, is disposed over 50 of the substrate axial length from the outlet end to the inlet end. The catalyst 1 further comprises a top coating 5 disposed onto the coating 3 (second coating) and the coating 4 (third coating) over the entire length of the substrate. Generally, a selective catalytic reduction catalyst 14 can be present upstream of the catalyst 1.

[0296] FIG. 2 shows the DeNOx performance of the catalysts of Comparative Examples 1 and 2 and of Examples 1 and 2 at inlet temperatures from about 200 to about 500° C., and at ANR=1.1 and SV of 80 k/h (highest temp point is at 160 k/h).

[0297] FIG. 3 shows the N.sub.2O formation of the catalysts of Comparative Examples 1 and 2 and of Examples 1 and 2 at inlet temperatures from about 200 to about 500° C. and at ANR=1.0 and SV of 80 k/h (highest temp point is at 160 k/h).

[0298] FIG. 4 shows the NO oxidation (NO.sub.2/NOX ratio) of the catalysts of Comparative Examples 1 and 2 and of Examples 1 and 2 at inlet temperatures from about 200 to about 450° C. and SV of 100 k/h.

CITED LITERATURE

[0299] US 2016/0367973 [0300] US 2016/0367974