A MULTIFUNCTIONAL CATALYST FOR HYDROCARBON OXIDATION AND SELECTIVE CATALYTIC REDUCTION OF NOX

Abstract

The present invention relates to a catalyst for the oxidation of hydrocarbon and the selective catalytic reduction of nitrogen oxides, 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; and a coating disposed on the surface of the internal walls of the substrate, wherein the surface de-fines the interface between the passages and the internal walls, wherein the coating comprises a platinum group metal component supported on a first oxidic material and further comprises a mixed oxide of vanadium and one or more of iron, erbium, bismuth, cerium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, praseodymium, promethium, samarium, scandium, terbium, thulium, ytterbium, yttrium, molybdenum, tungsten, manganese, cobalt, nickel, copper, aluminum and antimony, wherein the mixed oxide is supported on a second oxidic material.

Claims

1-15. (canceled)

16. A catalyst for the oxidation of hydrocarbon and the selective catalytic reduction of nitrogen oxides, 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; and (ii) a coating disposed on the surface of the internal walls of the substrate, wherein the surface defines the interface between the passages and the internal walls, wherein the coating comprises a platinum group metal component supported on a first oxidic material and further comprises a mixed oxide of vanadium and one or more of iron, erbium, bismuth, cerium, europium, gadolinium, holmium, lanthanum, lutetium, neo-dymium, praseodymium, promethium, samarium, scandium, terbium, thulium, ytterbium, yttrium, molybdenum, tungsten, manganese, cobalt, nickel, copper, aluminum, and antimony, and wherein the mixed oxide is supported on a second oxidic material.

17. The catalyst of claim 16, wherein the first oxidic material comprises one or more oxides.

18. The catalyst of claim 16, wherein from 75 weight-% to 100 weight-%, of the first oxidic material consist of zirconia, wherein the first oxidic material further comprises one or more of a hafnium oxide and a lanthanum oxide; or wherein from 70 weight-% to 100 weight-%, of the first oxidic material consist of alumina, wherein the first oxidic material further comprises one or more of a lanthanum oxide and a zirconium oxide.

19. The catalyst of claim 16, wherein the coating comprises the first oxidic material at a loading ranging from 0.25 to 1 g/in.sup.3.

20. The catalyst of claim 16, wherein the mixed oxide is a mixed oxide of vanadium and one or more of iron, erbium, bismuth, aluminum, and antimony.

21. The catalyst of claim 16, wherein the second oxidic material supporting the mixed oxide comprises one or more oxides; wherein from 75 to 100 weight of the second oxidic material consist of titania.

22. The catalyst of claim 16, wherein the coating further comprises an oxidic binder, wherein the oxidic binder comprises one or more of zirconia, alumina, titania, silica and a mixed oxide comprising two or more of Zr, Al, Ti and Si.

23. The catalyst of claim 16, wherein the catalyst comprises the coating at a loading ranging from 2.5 to 10 g/in.sup.3.

24. The catalyst of claim 16, wherein the coating according to (ii) consists of: (ii.1) a bottom coat comprising the mixed oxide supported on the second oxidic material; (ii.2) a top coat comprising the platinum group metal component supported on the first oxidic material; wherein the bottom coat is disposed on the surface of the internal walls of the substrate over x % of the substrate axial length, wherein x ranges from 90 to 100; and wherein the top coat is disposed on the bottom coat over y % of the substrate axial length, wherein y ranges from 90 to 100.

25. The catalyst of claim 24, wherein from 0 to 0.001 weight-%, of the bottom coat according to (ii.1) consist of palladium.

26. The catalyst of claim 16, wherein the coating according to (ii) consists of one coat, wherein the coat is disposed on the surface of the internal walls of the substrate over z % of the substrate axial length, wherein z ranges from 90 to 100.

27. A process for preparing a catalyst for the oxidation of hydrocarbon and the selective catalytic reduction of nitrogen oxides comprising: (a) providing 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; (b) providing one or more mixtures comprising a source of a platinum group metal component, particles of a first oxidic material, water, particles of a mixed oxide of vanadium and one or more of iron, erbium, bismuth, cerium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, praseodymium, promethium, samarium, scandium, terbium, thulium, ytterbium, yttrium, molybdenum, tungsten, manganese, cobalt, nickel, copper, aluminum and antimony, a second oxidic material and preferably an oxidic binder, disposing the one or more mixtures over z % of the substrate axial length, wherein z ranges from 90 to 100, and calcining the one or more mixtures disposed on the substrate.

28. An aqueous suspension comprising a source of a platinum group metal component, particles of a first oxidic material, water, particles of a mixed oxide of vanadium and one or more of iron, erbium, bismuth, cerium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, praseodymium, promethium, samarium, scandium, terbium, thulium, ytterbium, yttrium, molybdenum, tungsten, manganese, cobalt, nickel, copper, aluminum and antimony, and a second oxidic material.

29. A catalyst for the oxidation of hydrocarbon and the selective catalytic reduction of nitrogen oxides obtainable or obtained by a process according to claim 27.

30. An exhaust gas treatment system for treating exhaust gas from an internal combustion engine, preferably from a diesel engine, the system comprising a catalyst according to claim 16, and one or more of an ammonia oxidation catalyst, a diesel oxidation catalyst, a selective catalytic reduction catalyst and a catalyzed particulate filter.

Description

EXAMPLES

Reference Example 1 Determination of Dv10, Dv50 and Dv90 Values

[0263] 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

[0264] The BET specific surface area was determined according to DIN 66131 or DIN ISO 9277 using liquid nitrogen.

Reference Example 3 General Coating Method

[0265] In order to coat a flow-through substrate with one or more coats, the flow-through substrate was immersed vertically in a given mixture for a specific length of the substrate (usually about 1 inch), to fill the substrate with a charge of the mixture. In this manner, the mixture contacted the walls of the substrate. The substrate was left in the mixture for a specific period of time, usually for 1-10 seconds. Vacuum was applied to draw the mixture into the substrate. The substrate was then removed from the mixture. The substrate was rotated about its axis such that the immersed side now points up and a high pressure of air forces the charged mixture through the substrate.

Example 1 Preparation of a Multifunctional Mixed Catalyst (with a Pd/Zirconia Component and a V-Containing Mixed Oxide)

[0266] An incipient wetness impregnation of Pd onto a zirconium based oxidic support (88 weight-% of ZrO.sub.2 with 10 weight-% La.sub.2O.sub.3 and 2 weight-% HfO.sub.2, having a BET specific surface area of 67 m.sup.2/g, a Dv50 of 3 micrometers and a Dv90 of 16 micrometers). Firstly, the available pore volume of the oxidic support was determined and, based on this value, a diluted palladium salt solution with a volume equal to the available pore volume was made. The diluted solution was then added dropwise to the Zr-based oxidic support over 30 minutes under constant stirring resulting in a moist material. The resulting material was then calcined in an oven at 590 C. and allowed to cool. After calcination, the resulting powder was mixed with distilled water to form an aqueous mixture with 40% solids and the pH was adjusted to 3.75 using an organic acid. At this point, the slurry was milled until the particles of the mixture had a Dv90 of 10 micrometers. Separately, a vanadium mixture was made by mixing iron vanadate (FeVO.sub.4 having a molar ratio of Fe:V of 1:1, a Dv50 of about 2 micrometers and a Dv90 of about 11 micrometers) powder with distilled water. The solid content of the obtained mixture was 10 weight-% based on the weight of the obtained mixture. The amount of iron vanadate used was calculated such that the vanadium (from the iron vanadate), calculated as V.sub.2O.sub.5, was present at a loading of 5% of the final loading of the coating in the catalyst after calcination (the loading of FeVO.sub.4, calculated as FeVO.sub.4, was 10.48% of the final loading of the coating in the catalyst after calcination). To this mixture an acrylic based dispersant (5 weight-% based on the final coating loading) was added and afterwards a tungsten-doped titania oxide (about 90 weight-% TiO.sub.2 doped with 10 weight-% WO.sub.3, a BET specific surface area of 90 m.sup.2/g, a Dv10 of 0.5 micrometer, a Dv50 of 1.2 micrometer and a Dv90 of 3.7 micrometers), such that the final loading of titania+WO.sub.3 in the catalyst after calcination was of 3.35 g/in.sup.3. The pH of the said mixture was then set to 7 with the addition of a base. Afterwards, an aqueous colloidal silica binder was added, such that the final SiO.sub.2 loading after calcination was 0.168 g/in.sup.3The final mixture solid content was 43 weight-%.

[0267] At this point, the Pd-impregnated ZrO.sub.2 mixture was mixed into the FeVO.sub.4/TiO.sub.2 mixture and the pH was again adjusted to 7. The final mixture was ready for disposal on a honeycomb flow-through monolith cordierite substrate (diameter: 26.67 cm (10.5 inches)length: 15.24 cm (6 inches) cylindrically shaped substrate with 400/(2.54).sup.2 cells per square centimeter and 0.10 millimeter (4 mil) wall thickness). The substrate was coated with the final mixture according to the coating method defined in Reference Example 3 herein. To achieve the targeted washcoat loading of 4.5 g/in.sup.3, the substrate was coated twice along its entire length, once from the inlet end of the substrate and once from the outlet end of the substrate, with a drying and calcination steps after each coating step. To dry a coated substrate, the substrate was placed in an oven at 90 C. for about 30 minutes. After drying, the coated substrate was calcined for 30 minutes at 590 C. The final loading of the coating in the catalyst after calcination was of 4.5 g/in.sup.3, including 3.35 g/in.sup.3 of titania+WO.sub.3, 0.47 g/in.sup.3 of FeVO.sub.4 (including 0.225 g/in.sup.3 of vanadium calculated as V.sub.2O.sub.5), 0.5 g/in.sup.3 of zirconia+HfO.sub.2+La.sub.2O.sub.3, 0.167 g/in.sup.3 of silica and a Pd loading of 15 g/ft.sup.3.

Example 2.1 Preparation of a Multifunctional Layered Catalyst (with a Pd/Alumina and a V Mixed Oxide)

Bottom Coating:

[0268] An iron vanadate (FeVO.sub.4 having a molar ratio of Fe:V of 1:1) powder was mixed with distilled water. The solid content of the obtained mixture was 10 weight-% based on the weight of the obtained mixture. The amount of iron vanadate used was calculated such that the vanadium (from the iron vanadate), calculated as V.sub.2O.sub.5, was present at a loading of 5% of the final loading of the coating in the catalyst after calcination (the loading of FeVO.sub.4, calculated as FeVO.sub.4, was 10.48% of the final loading of the coating in the catalyst after calcination). To this mixture an acrylic based dispersant was added and afterwards a tungsten-doped titania oxide (about 90 weight-% TiO.sub.2 doped with 10 weight-% WO.sub.3, a BET specific surface area of 90 m.sup.2/g, a Dv10 of 0.5 micrometer, a Dv50 of 1.2 micrometers and a Dv90 of 3.7 micrometers), such that the final loading of titania+WO.sub.3 in the catalyst after calcination was of 3.41 g/in.sup.3. The pH of the obtained mixture was set to 7. Afterwards, an aqueous colloidal silica binder, such that the final SiO.sub.2 loading in the catalyst after calcination was 0.171 g/in.sup.3, along with additional distilled water to obtain a final mixture solid content of 43 weight-% based on the weight of said mixture. A honeycomb flow-through monolith cordierite substrate (diameter: 26.67 cm (10.5 inches)length: 15.24 cm (6 inches) cylindrically shaped substrate with 400/(2.54).sup.2 cells per square centimeter and 0.10 millimeter (4 mil) wall thickness) was coated with the final mixture according to the coating method defined in Reference Example 3 herein. To achieve the targeted washcoat loading of 4 g/in.sup.3, the substrate was coated twice along its entire length, once from the inlet end of the substrate and once from the outlet end of the substrate, with a drying and calcination steps after each coating step. The coating, drying, and calcination procedures are identical to those of Example 1. The final loading of the bottom coating in the catalyst after calcination was 4 g/in.sup.3, including 3.41 g/in.sup.3 of titania+WO.sub.3, 0.419 g/in.sup.3 of FeVO.sub.4 (including 0.2 g/in.sup.3 of vanadium calculated as V.sub.2O.sub.5) and 0.171 g/in.sup.3 of silica.

Top Coating:

[0269] An incipient wetness impregnation of Pd onto an alumina based oxidic support (gamma and delta alumina doped with 20% ZrO.sub.2 and 3% La.sub.2O.sub.3, a BET specific surface area of 145 m.sup.2/g, a Dv50 of 32 micrometers and a Dv90 of 62.5 micrometers). Firstly, the available pore volume of the given oxidic support was determined and, based on this value, a diluted palladium salt solution with a volume equal to the available pore volume was made. The diluted solution was then added dropwise to the Al-based oxidic support over 30 minutes under constant stirring resulting in a moist material. The resulting material was then calcined in an oven at 590 C. and allowed to cool. After calcination, the resulting powder was mixed with distilled water to form a mixture, and the pH of the aqueous phase of the mixture was set to 3.75 using an organic acid. At this point, the slurry was milled until the particles of the mixture had a Dv90 of 10 micrometers.

[0270] After milling, a soluble zirconium binder was added to the mixture, calculated such that it represented 11% of the Al-based oxidic support. The obtained final mixture had a solid content de-creased to 38 weight-% based on the weight of said final mixture. At this point, the mixture was ready for disposal over the substrate already coated with the bottom coating. The substrate coated with the bottom coating was coated once with said final mixture over the entire length of the substrate, according to the coating method as defined in Reference Example 3 herein. Drying conditions remained the same as for Example 1. However, after drying, the coated substrate was calcined for 30 minutes at 450 C. The final loading of the top coating in the catalyst after calcination was 0.5 g/in.sup.3, including 0.44 g/in.sup.3 of Al-based oxidic support, 0.056 g/in.sup.3 of zirconia and a Pd loading of 15 g/ft.sup.3.

Example 2.2 Preparation of a Multifunctional Layered Catalyst (with a Pd/Zirconia and a V Mixed Oxide)

[0271] Bottom coating: The bottom coating of Example 2.2 was prepared as the bottom coating of Example 2.1. Thus, the final loading of the bottom coating in the catalyst after calcination was 4 g/in.sup.3, including 3.41 g/in.sup.3 of titania+WO.sub.3, 0.419 g/in.sup.3 of FeVO.sub.4 (including 0.2 g/in.sup.3 of vanadium calculated as V.sub.2O.sub.5) and 0.17 g/in.sup.3 of silica.

[0272] Top coating: The top coating of Example 2.2 was prepared as the top coating of Example 2.1 except that the alumina based oxidic support was replaced by a zirconium based oxidic support (88 weight-% of ZrO.sub.2 with 10 weight-% La.sub.2O.sub.3 and 2 weight-% HfO.sub.2, having a BET specific surface area of 67 m.sup.2/g, a Dv50 of 3 micrometers and a Dv90 of 16 micrometers). Thus, the final loading of the top coating in the catalyst after calcination was 0.5 g/in.sup.3, including 0.435 g/in.sup.3 of Zr-based oxidic support, 0.056 g/in.sup.3 of zirconia and a Pd loading of 15 g/ft.sup.3.

Example 3 Testing of the Catalysts of Examples 1, 2.1 and 2.2deNOx and N.SUB.2.O Formation

[0273] The NOx conversion of the fresh catalysts of Examples 1, 2.1 and 2.2 was measured, as well as the nitrous oxide (N.sub.2O) formation, at different temperatures, namely from 200 to 325 C., (Gas Hourly Space Velocity (GHSV): 40 000 h.sup.1 at 200, 240, 275, 300 and 325 C.). The catalysts were allowed to stabilize at each load point and afterwards urea was injected at ANR (Ammonia to NOx Ratio) of either 1.5 (200 and 240 C.), 1.2 (275 C.) or 1.0 (300 and 325 C.) until NH.sub.3 slip was observed, indicating NH.sub.3 saturation of the catalyst. At each temperature, if ANR pre-conditioning was greater than 1.0, ANR was reduced to 1.0 and the system was allowed to reach equilibrium, whereupon the exhaust emissions were monitored. The results were dis-played on FIGS. 1 and 2.

[0274] As may be taken from FIG. 1, all three Pd containing V-SCR catalysts offer a high level of NOx conversion. This indicates that the PGM does not oxidize a significant fraction of NH.sub.3 under these conditions and the catalyst may be used without concern for NH.sub.3 oxidation up to at least 325 C. Indeed, only Example 2.1 shows any hint of NH.sub.3 oxidation at 325 C. while Examples 1 and 2.2 still maintain 100% conversion at 325 C.

[0275] As may be taken from FIG. 2, all three catalysts do create a low level of N.sub.2O; however, Examples 1 and 2.1 produce less N.sub.2O across all measured temperatures.

Comparative Example 1 Preparation of a Mixed Catalyst (with a Pd/Zirconia and Cu-Zeolite)

[0276] The catalyst of Comparative Example 1 was prepared as the catalyst of Example 1 except that iron vanadate on the titania support was replaced by a Cu-CHA zeolitic material (Cu: 3.25 weight-%, calculated as CuO, based on the weight of the Cu-CHA, CHA having a Dv90 of 25 micrometers, a SiO.sub.2: Al.sub.2O.sub.3 of 31, and a BET specific surface area of about 625 m.sup.2/g). Further, a soluble zirconium solution (30 weight-% ZrO.sub.2) was added as a binder to the mixture comprising water and Cu-CHA but no colloidal silica binder was added. The final loading of the coating in the catalyst after calcination was of 3.0 g/in.sup.3, including 2.56 g/in.sup.3 Cu-CHA, 0.3 g/in.sup.3 of zirconia+HfO.sub.3+La.sub.2O.sub.3, 0.13 g/in.sup.3 of zirconia and a Pd loading of 15 g/ft.sup.3.

Comparative Example 2 Preparation of a Mixed Catalyst (with a Pd/Ceria-Zirconia and Cu-Zeolite)

[0277] The catalyst of Comparative Example 2 was prepared as the catalyst of Comparative Example 1 except that the zirconium based oxidic support was replaced by a Ce/Zr oxidic support (40 weight-% of ceria, 50 weight-% of zirconia+HfO.sub.2, 5 weight-% of La.sub.2O.sub.3, and 5 weight-% of Pr.sub.6O.sub.11, having a BET specific surface area of 80 m.sup.2/g, a Dv90 of 15 micrometers). The final loading of the coating in the catalyst after calcination was of 3.0 g/in.sup.3, including 2.56 g/in.sup.3 Cu-CHA, 0.3 g/in.sup.3 of ceria+zirconia+lanthanum+praseodymium, 0.13 g/in.sup.3 of zirconia and a Pd loading of 15 g/ft.sup.3.

Example 4 Testing of the Catalysts of Examples 1, 2.1 and 2.2 and Comparative Examples 1 to 3HC Light-Off Performance

[0278] Hydrocarbon was injected upstream of the catalysts of Examples 1, 2.1 and 2.2 and Comparative Examples 1 to 2 at different inlet temperatures (275 C., 290 C., 305 C. and 320 C.) in order to determine if it was possible to obtain a targeted temperature of 450 C. at the outlet end of each catalysts (Space velocity: 60 k/h).

[0279] As may be taken from FIG. 3, with the catalyst of Example 2.1 (layered catalyst-2 coats) it was possible after HC injection at an inlet temperature of 275 C. to attain the targeted outlet temperature of 450 C. while with the catalysts of Comparative Examples 1 and 2 (mixed catalysts), after HC injection at inlet temperatures of 275 C., 290 C., 305 C. and 320 C. it was only possible to attain an outlet temperature between 275 and 320 C., respectively. With these comparative examples, the inlet and outlet temperatures were the same. Therefore, this illustrates that little to no HC oxidation is occurring over these catalysts and that the HC oxidation reaction is quickly quenched. The catalyst from Example 2.1 achieves the targeted outlet temperature of 450 C. for all four inlet temperature steps while the catalyst from Example 2.2 achieves the targeted outlet temperature of 450 C., at inlet temperatures of 290 C. and above. This clearly demonstrates activity towards HC oxidation from the catalysts of Examples 2.1 and 2.2, despite having identical amounts of Pd as Comparative Examples 2 and 3.

[0280] Further, with the catalyst of Example 1 (mixed catalyst), it was possible after HC injection at an inlet temperature of 305 C. to obtain an increased outlet temperature of 350 C. and at an inlet temperature of 320 C. to obtain an increased outlet temperature of about 410 C.

[0281] In contrast thereto, with the catalysts of Comparative Examples 1 and 2 (mixed catalyst with Cu-CHA and not a V mixed oxide), after HC injection it was only possible to obtain an exotherm but that outlet temperature always equaled to the inlet temperature. Therefore, this example demonstrates that the presence of a mixed oxide of V permits to increase the HC light-off performance in a multifunctional catalyst.

Example 6 Testing of the Catalysts of Examples 1, 2.1, 2.2 and Comparative Example 1deNOx and N.SUB.2.O FormationUS-FTP+WHTC

[0282] To generate the data presented in FIG. 4, each catalyst was mounted separately in a motor test cell, downstream from a 6.7 L diesel engine and a urea injector. Each catalyst was 10.56 in size. The NOx conversion and N.sub.2O make were assessed via the US-FTP and WHTC transient cycles, over which the test cell engine produced approximately 6.8 and 6.0 g/kWh, respectively. To assure equilibrium was achieved, the given transient cycle was run 13 times: 2 at ANR=0.1, 5 at ANR=0.8, 3 at ANR=1.0, and 3 at ANR=1.2. The data reported here was taken from the last cycle with ANR=1.2. The deNOx was reported as the mass-averaged NOx conversion and N.sub.2O formation is reported as g/kWh based on the generated power over the cycle.

[0283] As may be taken from FIG. 4, the deNOx activity of Examples 1 and 2.1 were only slightly behind that of Comparative Example 2 over the US-FTP cycle. Over the somewhat warmer WHTC cycle, Examples 1, 2.1 and 2.2 all possess comparable conversion. Significantly, Examples 1, 2.1 and 2.2 also create far less N.sub.2O over the US-FTP cycle than Comparative Example 1, which is an important feature to meet current and future legislation.

BRIEF DESCRIPTION OF THE FIGURES

[0284] FIG. 1 shows the NOx conversion at steady-state conditions of the catalysts of Examples 1, 2.1 and 2.2 at inlet temperatures ranging from 200 to 325 C.

[0285] FIG. 2 shows the N.sub.2O formation obtained from the catalysts of Examples 1, 2.1 and 2.2 at inlet temperatures ranging from 200 to 325 C.

[0286] FIG. 3 shows the HC light-off performance of the catalysts of Examples 1, 2.1 and 2.2 and Comparative Examples 1 to 3.

[0287] FIG. 4 shows the catalytic performances (deNOx and N.sub.2O formation) of the catalysts of Examples 1, 2.1, 2.2 and Comparative Example 1.

CITED LITERATURE

[0288] US 2015/0375207 A1 [0289] U.S. Pat. No. 5,371,056 [0290] WO 2018/224651 A2