Catalytic Devices for the Abatement of NH3 and Nox Emissions From Internal Combustion Engines

Abstract

Disclosed is a catalytic device for the removal of nitrogen oxides and ammonia from the exhaust gas of lean-burn combustion engines, comprising an upstream SCR catalyst comprising a carrier substrate, and a first washcoat comprising a first SCR catalytically active composition SCRfirst and optionally at least one first binder, wherein the first washcoat is applied to the carrier substrate; and a downstream ASC catalyst comprising a carrier substrate, and a bottom layer comprising a third washcoat comprising an oxidation catalyst and optionally at least one third binder, said bottom layer being applied directly onto the carrier substrate, and a top layer comprising a second washcoat comprising a second SCR catalytically active composition SCRsecond and optionally at least one second binder and, said top layer being applied onto the bottom layer; wherein the upstream SCR catalyst and the downstream ASC catalyst are present on a single carrier substrate or on two different carrier substrates, and the first and the second SCR catalytically active compositions are the same or different from one another, and the optionally comprised at least one first, second and third binders are the same or different from one another, the ratio (AA) of the loadings of the first and the second SCR catalytically active compositions, given in g/L, in the first and the second washcoat is 1.2:1 to 2:1. The first and second SCR catalytically active compositions preferably comprise a molecular sieve, and the oxidation catalyst preferably comprises a platinum group metal. The catalytic device can be used for the removal of nitrogen oxides and ammonia from the exhaust gas of lean-burn combustion engines.

Claims

1-21. (canceled)

22. A catalytic device for the removal of nitrogen oxides and ammonia from the exhaust gas of lean-burn combustion engines, comprising: a) an upstream SCR catalyst comprising i) a carrier substrate, and ii) a first washcoat comprising a first SCR catalytically active composition SCR.sub.first and optionally at least one first binder, wherein the first washcoat is applied to the carrier substrate, b) a downstream ASC catalyst comprising i) a carrier substrate, and ii) a bottom layer comprising a third washcoat comprising an oxidation catalyst and optionally at least one third binder, said bottom layer being applied directly onto the carrier substrate, and iii) a top layer comprising a second washcoat comprising a second SCR catalytically active composition SCR.sub.second and optionally at least one second binder and, said top layer being applied onto the bottom layer, wherein the upstream SCR catalyst and the downstream ASC catalyst are present on a single carrier substrate or on two different carrier substrates, the first and the second SCR catalytically active compositions are the same or different from one another, the optionally comprised at least one first, second and third binders are the same or different from one another, and the ratio $\frac{{\mathrm{SCR}}_{\mathrm{first}}}{{\mathrm{SCR}}_{\mathrm{second}}}$ of the loadings of the first and the second SCR catalytically active compositions, given in g/L, in the first and the second washcoat is 1.2:1 to 2:1.

23. The catalytic device according to claim 22, wherein the first and the second SCR catalytically active composition are, independently from one another, selected from molecular sieves.

24. The catalytic device according to claim 23, wherein the molecular sieves are crystalline aluminosilicate zeolites selected from ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, BEA, BIK, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, ESV, ETL, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON and mixtures and intergrowths that contain at least one of these framework types.

25. The catalytic device according to claim 24, wherein the crystalline aluminosilicate zeolites have a SAR value of 5 to 100.

26. The catalytic device according to claim 24, wherein the crystalline aluminosilicate zeolites are promoted with copper, and wherein the copper to aluminum atomic ratio is in the range of between 0.005 to 0.555.

27. The catalytic device according to claim 24, wherein the aluminosilicate zeolites are promoted with iron, and wherein the iron to aluminum atomic ratio is in the range of between 0.005 to 0.555.

28. The catalytic device according to claim 24, wherein the aluminosilicate zeolites are promoted with both copper and iron, and wherein the (Cu+Fe):Al atomic ratio is in the range of between 0.005 to 0.555.

29. The catalytic device according to claim 22, wherein the oxidation catalyst comprises a platinum group metal, a platinum group metal oxide, a mixture of two or more platinum group metals, a mixture of two or more platinum group metal oxides, or a mixture of at least one platinum group metal and at least one platinum group metal oxide, wherein the platinum group metal is selected from ruthenium, rhodium, palladium, iridium and platinum.

30. The catalytic device according to claim 22, wherein the first, second and third binder are, independently from one another, selected from alumina, silica, non-zeolitic silica-alumina, naturally occurring clay, TiO.sub.2, ZrO.sub.2, CeO.sub.2, SnO.sub.2 and mixtures and combinations thereof.

31. The catalytic device according to claim 22, wherein the washcoat loading of the first SCR catalytically active composition is between 100 and 230 g/L, and the washcoat loading of the second SCR catalytically active composition is between 70 and 170 g/L, under the proviso that the ratio $\frac{{\mathrm{SCR}}_{\mathrm{first}}}{{\mathrm{SCR}}_{\mathrm{second}}}$ of the loadings of the first and the second SCR catalytically active compositions, given in g/L, in the first and the second washcoat is between 1.2:1 to 2:1.

32. The catalytic device according to claim 22, wherein the washcoat loading of the third washcoat is between 10 and 100 g/L, and the platinum group metal concentration within the third washcoat is between 0.5 and 25 g/ft.sup.3.

33. The catalytic device according to claim 22, wherein the upstream SCR catalyst and the downstream ASC catalyst are present as two adjacent zones on one single carrier substrate, the upstream SCR catalyst extends on an axial length of the carrier substrate from the upstream end to 40 to 80% of the entire length of the carrier substrate, the downstream ASC catalyst extends on an axial length of the carrier substrate from the downstream end to 40 to 80% of the entire length of the carrier substrate, and there is substantially no overlap nor a gap between the SCR catalyst zone and the ASC catalyst zone, and the lengths of both zones account for 100% of the total axial length of the carrier.

34. The catalytic device according to claim 33, wherein the carrier substrate is selected from ceramic, metallic and corrugated carrier substrates.

35. The catalytic device according to claim 34, wherein the carrier substrate is a ceramic carrier substrate selected from flow-through carrier substrates and wall-flow filters.

36. The catalytic device according to claim 22, wherein the upstream SCR catalyst and the downstream ASC catalyst are present on two different carrier substrates which are immediately adjacent to one another.

37. The catalytic device according to claim 36, wherein the carrier substrates are, independently from one another, selected from ceramic, metallic and corrugated carrier substrates.

38. The catalytic device according to claim 37, wherein the carrier substrates are ceramic carrier substrate which are selected, independently from one another, from flowthrough carrier substrates and wall-flow filters.

39. A system for the removal of nitrogen oxides and ammonia from the exhaust gas of lean-burn combustion engines, comprising: a) means for injecting ammonia or an ammonia precursor solution into the exhaust stream, b) a catalytic device according to claim 22 arranged immediately downstream of the means for injecting ammonia or an ammonia precursor solution according to a).

40. The system for the removal of nitrogen oxides and ammonia from the exhaust gas of lean-burn combustion engines according to claim 39, further comprising an oxidation catalyst for the oxidation of volatile organic compounds, carbon monoxide and hydrocarbons, said catalyst being located directly upstream of the means for injecting ammonia or an ammonia precursor solution into the exhaust system.

41. The system for the removal of nitrogen oxides and ammonia from the exhaust gas of lean-burn combustion engines according to claim 39, further comprising a filter for the removal of particulate matter, said filter being located immediately downstream of the oxidation catalyst and immediately upstream of the means for injecting ammonia or an ammonia precursor solution into the exhaust stream.

42. A method of removing nitrogen oxides and ammonia from an exhaust gas of a lean-burn combustion engine, which comprises passing the exhaust gas through the catalytic device according to claim 22.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0111] FIG. 1 shows the temperature, volumetric mass flow, NH.sub.3, NO and NO.sub.2 amount at the inlet of the SCR/ASC catalyst of Example 1 and Comparative Example 1 for the case of an value of 1.4 according to Embodiment 1.

[0112] FIG. 2a shows the NH.sub.3 conversion versus the value of Example 1 and Comparative Example 1 as measured in the World Harmonized Transient Cycle (WHTC) according to Embodiment 1.

[0113] FIG. 2b shows the NO.sub.x conversion versus the value of Example 1 and Comparative Example 1 as measured in the World Harmonized Transient Cycle (WHTC) according to Embodiment 1.

[0114] FIG. 3a shows the NH.sub.3 conversion versus the value of Comparative Example 1 and Comparative Example 2 as measured in the World Harmonized Transient Cycle (WHTC) according to Embodiment 1.

[0115] FIG. 3b shows the NO.sub.x conversion versus the value of Comparative Example 1 and Comparative Example 2 as measured in the World Harmonized Transient Cycle (WHTC) according to Embodiment 1.

[0116] FIG. 4 shows the temperature, volumetric mass flow, NH.sub.3, NO and NO.sub.2 amount at the inlet of the SCR/ASC catalysts according to Example 1 and Comparative Example 1 as measured in the Federal Test Procedure (FTP) cycle according to Embodiment 2.

[0117] FIG. 5a shows the NH.sub.3 conversion versus the value of Example 1 and Comparative Example 1 as measured in the Federal Test Procedure (FTP) cycle according to Embodiment 2.

[0118] FIG. 5b shows the NO.sub.x conversion versus the value of Example 1 and Comparative Example 1 as measured in the Federal Test Procedure (FTP) cycle according to Embodiment 2.

[0119] FIG. 6a shows the NH.sub.3 slip of Example 1 and Comparative Example 1 in the temperature range of from 250 to 500 C. according to Embodiment 3.

[0120] FIG. 6b shows the NO slip of Example 1 and Comparative Example 1 in the temperature range of from 250 to 500 C. according to Embodiment 3.

[0121] FIG. 6c shows the N.sub.2O formation of Example 1 and Comparative Example 1 in the temperature range of from 250 to 500 C. according to Embodiment 3.

[0122] FIG. 7a shows the NH.sub.3 conversion versus the value of Example 2 and Example 3 as measured in the World Harmonized Transient Cycle (WHTC) according to Embodiment 3.

[0123] FIG. 7b shows the NO.sub.x conversion versus the value of Example 2 and Example 2 as measured in the World Harmonized Transient Cycle (WHTC) according to Embodiment 3.

[0124] FIG. 8a shows the NH.sub.3 conversion versus the value of Example 2 and Example 3 as measured in the Federal Test Procedure (FTP) cycle according to Embodiment 4.

[0125] FIG. 8b shows the NO.sub.x conversion versus the value of Example 2 and Example 3 as measured in the Federal Test Procedure (FTP) cycle according to Embodiment 4.

[0126] FIG. 9a shows the NH.sub.3 slip of Example 2 (dashed line) and Example 3 (continuous line) in the FDT test.

[0127] FIG. 9b shows the NO slip of Example 2 (dashed line) and Example 3 (continuous line) in the FDT test.

EMBODIMENTS

Example 1

[0128] A catalytic device according to the present invention is manufactured, wherein the SCR zone is located upstream, and the ASC zone is located downstream on the same carrier substrate. The carrier substrate is a cordierite flow-through carrier having a total length of 8 inches (20.32 cm) and a diameter of 10.5 inches (26.67 cm); 400, cpsi (cells per square inch), 4 mil.

[0129] SCR catalyst composition in the SCR part: 194 g/L of catalytically active material (Cu-CHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. Length of the SCR zone: 6 inches (15.24 cm)

[0130] ASC Part: [0131] Oxidation catalyst: Pt particles supported on TiO.sub.2, loading 25 g/L, 2 g/ft.sup.3 (0.0707 g/L) precious metal loading. [0132] SCR catalyst: 135 g/L of catalytically active material (Cu-CHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. [0133] Length of the ASC zone: 2 inches (5.08 cm). [0134] The ratio SCR.sub.first/SCR.sub.second is 1.4. [0135] The binder used for the SCR catalysts in both the SCR and the ASC zone is alumina.

Comparative Example 1

[0136] A catalytic device is manufactured, wherein the SCR zone is located upstream, and the ASC zone is located downstream on the same carrier substrate. The carrier substrate is a cordierite flow-through carrier having a total length of 8 inches (20.32 cm) and a diameter of 10.5 inches (26.67 cm); 400, cpsi (cells per square inch), 4 mil. The loading of the SCR catalytically active substance in both the SCR and the ASC zone is identical.

[0137] SCR catalyst composition in the SCR part: 180 g/L of catalytically active material (Cu-CHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. Length of the SCR zone: 6 inches (15.24 cm)

[0138] ASC Part: [0139] Oxidation catalyst: Pt particles supported on TiO.sub.2, loading 25 g/L, 2 g/ft.sup.3 (0.0707 g/L) precious metal loading. [0140] SCR catalyst: 180 g/L of catalytically active material (Cu-CHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. [0141] The ratio SCR.sub.first/SCR.sub.second is 1.0. [0142] The binder used for the SCR catalysts in both the SCR and the ASC zone is alumina.

Comparative Example 2

[0143] A catalytic device is manufactured, wherein the SCR zone is located upstream, and the ASC zone is located downstream on the same carrier substrate. The carrier substrate is a cordierite flow-through carrier having a total length of 8 inches (20.32 cm) and a diameter of 10.5 inches (26.67 cm); 400, cpsi (cells per square inch), 4 mil. The loading of the SCR catalytically active substance in SCR zone is lower than that in the ASC zone.

[0144] SCR catalyst composition in the SCR part: 171 g/L of catalytically active material (Cu-CHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. Length of the SCR zone: 6 inches (15.24 cm)

[0145] ASC Part: [0146] Oxidation catalyst: Pt particles supported on TiO.sub.2, loading 25 g/L, 2 g/ft.sup.3 (0.0707 g/L) precious metal loading. [0147] SCR catalyst: 207 g/L of catalytically active material (Cu-CHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. [0148] The ratio SCR.sub.first/SCR.sub.second is 0.83. [0149] The binder used for the SCR catalysts in both the SCR and the ASC zone is alumina.

Embodiment 1

[0150] In this embodiment, the performance of Example 1, Comparative Example 1 and Comparative Example 2 are evaluated in a World Harmonized Transient Cycle (WHTC). Upstream the SCR/ASC catalysts a Diesel Oxidation Catalyst (DOC) and coated Diesel Particulate Filter (cDPF) are used.

[0151] Three consecutive WHTC cycles are carried out and the results of the third test are presented. The amount of NH.sub.3 entering the SCR catalyst is adjusted based on the amount of NOx entering the SCR catalyst, such that the value is changed from a value of 0.9-1.5, where the value is the NH.sub.3 concentration divided by the NO.sub.x concentration:

[00009]$=\frac{\left[{\mathrm{NH}}_3\right]}{\left[{\mathrm{NO}}_x\right]}$

[0152] The temperature, volumetric mass flow, NH.sub.3, NO and NO.sub.2 amount at the inlet of the SCR/ASC catalyst are shown in FIG. 1 for the case of an value of 1.4.

[0153] The NH.sub.3 and NO.sub.x conversions of Example 1 and Comparative Example 1 for this embodiment are shown in Table 1 and FIGS. 2a and 2b.

[0154] Tab. 1 shows the NH.sub.3 conversion and the NO.sub.x conversion versus alpha for Example 1 and Comparative Example 1 in Embodiment 1.

TABLE-US-00001 3rd Hot WHTC Comparative Example 1 Example 1 NH.sub.3 Conv. NO.sub.x Conv. NH.sub.3 Conv. NO.sub.x Conv. Alpha (%) (%) (%) (%) 0.9 100.0 89.5 100.0 89.4 1.0 99.8 94.9 99.9 95.3 1.1 99.5 97.7 99.7 97.8 1.2 98.8 98.4 99.3 98.3 1.3 98.1 98.7 98.8 98.5 1.4 97.5 98.8 98.4 98.6 1.5 96.9 98.9 97.9 98.6

[0155] FIG. 2a shows the NH.sub.3 conversion versus the value. The washcoat loading of 150 g/L of the second washcoat of Example 1, compared to 200 g/L in the SCR layer of the ASC in Comparative Example 1, allows for a higher NH.sub.3 conversion.

[0156] FIG. 2b shows the NO.sub.x conversion versus the value. Due to the fact that more NH.sub.3 is oxidized in the WHTC, the NO.sub.x conversion of Example 1 is slightly lower than that of Comparative Example 1.

[0157] Tab. 2 shows the NH.sub.3 conversion and the NO.sub.x conversion versus alpha for Comparative Example 1 and Comparative Example 2 in Embodiment 1.

TABLE-US-00002 3rd Hot WHTC Comparative Example 1 Comparative Example 2 NH.sub.3 Conv. NO.sub.x Conv. NH.sub.3 Conv. NO.sub.x Conv. Alpha (%) (%) (%) (%) 0.9 100.0 89.5 100.0 89.5 1.0 99.8 94.9 99.8 94.8 1.1 99.5 97.7 99.3 97.7 1.2 98.8 98.4 98.4 98.4 1.3 98.1 98.7 97.6 98.7 1.4 97.5 98.8 96.9 98.8 1.5 96.9 98.9 96.3 98.9

[0158] FIG. 3a shows the NH.sub.3 conversion versus the value. The washcoat loading of 230 g/L of the second washcoat of Comparative Example 2, compared to 200 g/L in the SCR layer of the ASC in Comparative Example 1, result in lower NH.sub.3 conversion.

[0159] FIG. 3b shows the NO.sub.x conversion versus the value. No differences are observed for between Comparative Example 1 and Comparative Example 2.

Embodiment 2

[0160] In this embodiment, both catalyst configurations shown in Example 1 and Comparative Example 1 are evaluated during a Federal Test Procedure (FTP) cycle. Upstream the SCR/ASC catalysts a Diesel Oxidation Catalyst (DOC) and coated Diesel Particulate Filter (cDPF) are used.

[0161] Three consecutive FTP cycles are carried out and the results of the third test are presented. The amount of NH.sub.3 entering the SCR catalyst is adjusted based on the amount of NO.sub.x entering the SCR catalyst, such that the value is changed from a value of 0.9-1.5, where the value is defined as in Embodiment 1. The temperature, volumetric mass flow, NH.sub.3, NO and NO.sub.2 amount at the inlet of the SCR/ASC catalyst are shown in FIG. 4 for the case of an value of 1.2.

[0162] The NH.sub.3 and NO.sub.x conversions of Example 1 and Comparative Example 1 for this embodiment are shown in Table 3 and FIG. 5.

[0163] Tab. 3 shows the NH.sub.3 conversion and the NO.sub.x conversion versus alpha for Example 1 and Comparative Example 1 in Embodiment 2.

TABLE-US-00003 Comparative Example 1 Example 1 NH3 Conv. NOx Conv. NH3 Conv. NOx Conv. Alpha (%) (%) (%) (%) 0.9 99.4 85.1 99.6 85.1 1.0 99.0 90.4 99.3 90.4 1.1 98.2 93.9 98.8 93.6 1.2 97.2 96.0 98.1 95.6 1.3 95.9 97.3 97.2 96.7

[0164] FIG. 5a shows the NH.sub.3 conversion versus the value. The washcoat loading of 150 g/L of the second washcoat of Example 1, compared to 200 g/L in the SCR layer of the ASC in Comparative Example 1, allows for a higher NH.sub.3 conversion.

[0165] FIG. 5b shows the NO.sub.x conversion versus the value. Due to the fact that more NH.sub.3 is oxidized in the FTP, the NO.sub.x conversion of Example 1 is slightly lower than that of Comparative Example 1.

Embodiment 3

[0166] In this embodiment a feed of 750 ppm NH.sub.3, 500 ppm NO, 5% O.sub.2, 5% H.sub.2O, and N.sub.2 as the balance gas are passed across Example 1 and Comparative Example 1 until steady state was reached. The temperature during this time is held constant at 200 C. and the space velocity is 60000 h.sup.1. Once steady state is reached (i.e. no variation in the concentration of the measured gas species and temperature), the following feed modifications takes place simultaneously: NH.sub.3 is removed from the feed, the space velocity is suddenly increased to 100000 h.sup.1, and the temperature is ramped to 500 C. at a rate of 250 K/min. This sudden change in feed conditions is done to mimic a change in load during real driving conditions, which stresses the SCR and ASC catalyst with NH.sub.3 slip. This test is hereinafter referred to as the Fast Desorption Test (FDT).

[0167] The NH.sub.3 slip, NO slip, and N.sub.2O formation across Example 1 (dotted line) and Comparative Example 1 (continuous line) during the temperature increase phase are shown in FIGS. 6a, 6b and 6c respectively. Here the benefit of Example 1 in decreasing NH.sub.3 and NO slip compared to Comparative Example 1 can be seen.

Example 2

[0168] A catalytic device according to the present invention is manufactured, wherein the SCR zone is located upstream, and the ASC zone is located downstream on the same carrier substrate. The carrier substrate is a cordierite flow-through carrier having a total length of 8 inches (20.32 cm) and a diameter of 10.5 inches (26.67 cm); 400, cpsi (cells per square inch), 4 mil.

[0169] SCR catalyst composition in the SCR part: 200 g/L of catalytically active material (CuCHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. Length of the SCR zone: 6 inches (15.24 cm)

[0170] ASC Part: [0171] Oxidation catalyst: Pt particles supported on TiO.sub.2, loading 25 g/L, 2 g/ft.sup.3 (0.0707 g/L) precious metal loading. [0172] SCR catalyst: 125 g/L of catalytically active material (Cu-CHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. [0173] Length of the ASC zone: 2 inches (5.08 cm). [0174] The ratio SCR.sub.first/SCR.sub.second is 1.6. [0175] The binder used for the SCR catalysts in both the SCR and the ASC zone is alumina.

Example 3

[0176] A catalytic device according to the present invention is manufactured, wherein the SCR zone is located upstream, and the ASC zone is located downstream on the same carrier substrate. The carrier substrate is a cordierite flow-through carrier having a total length of 8 inches (20.32 cm) and a diameter of 10.5 inches (26.67 cm); 400, cpsi (cells per square inch), 4 mil.

[0177] SCR catalyst composition in the SCR part: 200 g/L of catalytically active material (CuCHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. Length of the SCR zone: 5 inches (12.7 cm)

[0178] ASC Part: [0179] Oxidation catalyst: Pt particles supported on TiO.sub.2, loading 25 g/L, 2 g/ft.sup.3 (0.0707 g/L) precious metal loading. [0180] SCR catalyst: 150 g/L of catalytically active material (Cu-CHA), SAR=13; 5.5 wt.-% of Cu, calculated as CuO and based on the total weight of the zeolite. [0181] Length of the ASC zone: 3 inches (7.62 cm). [0182] The ratio SCR.sub.first/SCR.sub.second is 1.3. [0183] The binder used for the SCR catalysts in both the SCR and the ASC zone is alumina.

Embodiment 4

[0184] The performances of Examples 2 and 3 are evaluated in the WHTC cycle in the same manner as described in Embodiment 1.

[0185] Tab. 4 shows the NH.sub.3 conversion and the NO.sub.x conversion versus alpha for Example 2 and Example 3 in Embodiment 4.

TABLE-US-00004 3rd Hot WHTC Example 2 Example 3 NH.sub.3 Conv. NO.sub.x Conv. NH.sub.3 Conv. NO.sub.x Conv. Alpha (%) (%) (%) (%) 0.9 100.0 89.5 100.0 89.4 1.0 99.9 94.6 100.0 93.9 1.1 99.8 97.2 99.9 96.6 1.2 99.4 97.8 99.8 97.5 1.3 99.0 98.0 99.6 97.8 1.4 98.6 98.1 99.5 97.9 1.5 98.3 98.2 99.4 98.0

[0186] FIG. 7a shows the NH.sub.3 conversion versus the value. The washcoat loading of 150 g/L of the second washcoat of Example 2, compared to 125 g/L in the SCR layer of the ASC in Example 3, allows for a higher NH.sub.3 conversion.

[0187] FIG. 7b shows the NO.sub.x conversion versus the value. Due to the fact that more NH.sub.3 is oxidized in the WHTC, the NO.sub.x conversion of Example 3 is slightly lower than that of Example 2.

[0188] The NH.sub.3 and NO.sub.x conversions of Example 2 and Example 3 are shown in Table 4 and FIGS. 7a and 7b.

Embodiment 5

[0189] The performances of Examples 2 and 3 are evaluated in the FTP cycle in the same manner as described in Embodiment 2.

[0190] The NH.sub.3 and NO.sub.x conversions of Example 2 and Example 3 are shown in Table 5 and FIGS. 8a and 8b.

[0191] Tab. 5 shows the NH.sub.3 conversion and the NO.sub.x conversion versus alpha for Example 1 and Example 2 in Embodiment 4.

TABLE-US-00005 Example 2 Example 3 NH3 Conv. NOx Conv. NH3 Conv. NOx Conv. Alpha (%) (%) (%) (%) 0.9 99.7 84.7 99.8 84.2 1.0 99.4 89.8 99.6 89.2 1.1 98.9 93.0 99.3 92.4 1.2 98.3 94.9 98.9 94.5 1.3 97.4 96.0 98.3 95.7 1.4 96.4 96.6 97.8 96.4 1.5 95.5 96.9 97.4 96.9

[0192] FIG. 8a shows the NH.sub.3 conversion versus the value. The washcoat loading of 150 g/L of the second washcoat of Example 3, compared to 125 g/L in the SCR layer of the ASC in Example 2, allows for a higher NH.sub.3 conversion.

[0193] FIG. 8b shows the NO.sub.x conversion versus the value. Due to the fact that more NH.sub.3 is oxidized in the FTP, the NO.sub.x conversion of Example 3 is slightly lower than that of Example 2.

Embodiment 6

[0194] An FDT test is performed with Examples 2 and 3 in the same manner as described in Embodiment 3.

[0195] FIG. 9a shows the NH.sub.3 slip of Example 2 (dashed line) and Example 3 (continuous line). The washcoat loading of 150 g/L of the second washcoat of Example 3, compared to 125 g/L in the SCR layer of the ASC in Example 2, allows for a lower ammonia slip.

[0196] FIG. 9b shows the NO slip of Example 2 (dashed line) and Example 3 (continuous line). The washcoat loading of 150 g/L of the second washcoat of Example 3, compared to 125 g/L in the SCR layer of the ASC in Example 2, allows for a lower NO slip.