Hydrocarbon trap catalyst

Abstract

The present invention relates to a catalyst comprising a carrier substrate of the length L extending between substrate ends a and b and two washcoat zones A and B, wherein washcoat zone A comprises a redox active base metal and palladium supported on a zeolite and/or refractory oxide support and extends starting from substrate end a over a part of the length L, and washcoat zone B comprises the same components as washcoat A and an additional amount of palladium and extends from substrate end b over a part of the length L, wherein L=L.sub.A+L.sub.B, wherein L.sub.A is the length of washcoat zone A and L.sub.B is the length of substrate length B.

Claims

1. Catalyst comprising a carrier substrate of the length L extending between substrate ends a and b and two washcoat zones A and B, wherein washcoat zone A comprises a compound of a redox active base metal, selected from the group consisting of Cu, Ni, Co, Mn, Fe, Cr, Ce, Pr, Tb, Sn and In, and palladium, with one or both of the compound and palladium being supported on a zeolite and/or a support oxide, and wherein washcoat zone A extends, starting from substrate end a, over a part of the length L, and washcoat zone B comprises the same components as washcoat zone A and an additional amount of palladium and extends from substrate end b over a part of the length L, wherein L=L.sub.A+L.sub.B, wherein L.sub.A is the length of washcoat zone A and L.sub.B is the length of washcoat zone B.

2. Catalyst according to claim 1, wherein washcoat zone A comprises two layers A1 and A2, which both extend over the length L.sub.A, wherein layer A1 comprises zeolite, the compound of a redox active base metal selected from the group consisting of Cu, Ni, Co, Mn, Fe, Cr, Ce, Pr, Tb, Sn and In, and palladium, with the compound being supported on the zeolite, and layer A2 comprises rhodium, and washcoat zone B comprises two layers B1 and B2, which both extend over the length L.sub.B, wherein layer B1 comprises the same components as layer A1 and layer B2 comprises the same components as layer A2 and wherein layers B1 and B2 comprise an additional amount of palladium compared to layers A1 and A2.

3. Catalyst according to claim 1, wherein the redox active base metal is copper, manganese or iron.

4. Catalyst according to claim 1, wherein the redox active base metal is iron.

5. Catalyst according to claim 4, wherein the iron compound is in washcoat zones A and B in an amount of 1.0 to 30 g/l, based on the volume of the carrier substrate zone and calculated as Fe.sub.2O.sub.3.

6. Catalyst according to claim 4, wherein the zeolite is present and the iron compound and palladium in washcoat zone A are both supported on the zeolite.

7. Catalyst according to claim 6, wherein the iron compound and palladium are present in cationic form within the zeolite structure or in oxidic and metallic form, respectively, within and/or on the surface of the zeolite.

8. Catalyst according to claim 1, wherein the redox active base metal is present in cationic or in oxidic form.

9. Catalyst according to claim 1, wherein the zeolite is present and the zeolite belongs to the structure type code BEA, FAU, FER, MFI or MOR.

10. Catalyst according to claim 1, wherein the zeolite is present and the zeolite is beta zeolite.

11. Catalyst according to claim 1, wherein the zeolite is present in washcoat zones A and B in an amount of 120 to 340 g/l based on the volume of the carrier substrate.

12. Catalyst according to claim 1, wherein the support oxide is present and the support oxide is alumina, silica, magnesia, titania, ceria, zirconia or mixtures or mixed oxides comprising at least two of these materials.

13. Catalyst according to claim 1, wherein palladium is present in cationic, metallic or oxidic form.

14. Catalyst according to claim 1, wherein it comprises palladium is present in washcoat zone A in an amount of 0.04 to 4.0 g/l, based on the volume of the carrier substrate and calculated as palladium metal.

15. Catalyst according to claim 14, wherein palladium is present in washcoat zone B in an amount of 2 to 20 g/l, based on the volume of the carrier substrate and calculated as palladium metal.

16. Catalyst according to claim 15, wherein the compound is an iron compound that is in washcoat zones A and B in an amount of 1.0 to 30 g/l, based on the volume of the carrier substrate zone and calculated as Fe.sub.2O.sub.3, and wherein both the zeolite and the support oxide are present with each providing support to one or both of the iron compound and the palladium.

17. Catalyst according to claim 1, wherein palladium is present in washcoat zone B in an amount of 2 to 20 g/l, based on the volume of the carrier substrate and calculated as palladium metal.

18. Catalyst according to claim 1, wherein washcoat zone A extends over 70 to 95% of the length L of the carrier substrate and washcoat zone B extends over 5 to 30% of the length L of the carrier substrate.

19. Catalyst according to claim 1, wherein the carrier substrate of the length L is a flow-through or filter substrate.

20. Method of treating exhaust gases of a combustion engine, wherein the exhaust gas is passed over the catalyst of claim 1, and wherein the exhaust gas enters the catalyst at substrate end a and exits at substrate end b.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 illustrates catalysts according to the present invention.

(2) FIG. 2 shows the total HC out emissions for both CC2 and C2.

DETAILED DESCRIPTION

(3) FIG. 1 illustrates catalysts according to the present invention.

(4) The upper part shows a detail of an inventive catalyst (1) which comprises a carrier substrate (3) which extends between substrate ends a and b and which carries washcoat zone A (4) and washcoat zone B (5).

(5) The lower part shows a detail of another embodiment of the invention. Catalyst (2) comprises a carrier substrate (3) which extends between substrate ends a and b. Washcoat zone A comprises layer A1 (6) and A2 (7) whereas washcoat zone B comprises layer B1 (9) and layer B2 (8). Layers A1 (6) and B1 (9) differ only in that B1 (9) comprises a higher amount of palladium compared to A1 (6). Likewise, layers A2 (7) and B2 (8) differ only in that B2 (8) comprises a higher amount of palladium compared to A2 (7).

Comparison Example 1

(6) a) Slurry preparation begins with addition of an alumina stabilized silica sol (Aeroperl 3375/20 purchased from Evonik) to water and mixing. This material represents 4.5 wt % of the final calcined washcoat loading. This step is followed by the addition of a boehmite (SASOL SCF-55 purchased from Sasol) and iron nitrate at contents of 1.0 and 4.5 wt % respectively of the final calcined washcoat. Finally, beta zeolite in the ammonium form and having a SAR value of 25 was added and the slurry was then aged for two days.
b) This slurry was then coated onto a ceramic substrate having 400 cpsi/4.3 mill cell structure and 4.66 round by 4.5 long giving a total volume of 1.26 Liters and a WC load of 3.636 g/in.sup.3 or 222 g/l. Calcination of the coated trap was done at 540 C. in air.
c) After the application of the trap layer in step b), a thin coating of a three-way catalyst (TWC) layer was applied. The washcoat loading of the TWC layer was 1.5 g/in.sup.3 and the platinum group metal loading was 10 g/ft.sup.3 with a Pt:Pd:Rh=0:1:1.

(7) The catalyst obtained is called CC1.

Example 1

(8) An inventive catalyst was prepared as described in Example 1 but in this case a Pd solution band was applied by dipping one end of the catalyst in a Pd nitrate solution containing citric acid and 2 wt % ethanol. The substrate used was a 400 cpsi/4.3 mill cell structure, 4.66 round by 4.5 long giving a total volume of 1.26 Liters. The concentration of the dipped solution was adjusted such that with a solution band length of 3 cm (1.2) long the Pd concentration was 250 g/ft.sup.3 in the dipped zone. The PGM loading averaged over the full part was 60 g/ft.sup.3 @ 0:11:1 (includes the Pd in the band and in the TWC layer).

(9) The catalyst obtained is called C1

(10) Comparison of Comparison Example 1 and Example 1

(11) a) CC1 and C1 both have the same three-way catalyst washcoat and the same platinum group metal loading of 10 g/ft.sup.3 with Pt:Pd:Rh=0:1:1, the only difference being the presence of the Pd band at the outlet for C1.

(12) b) Before testing catalysts CC1 and C1 were conditioned for 2 hours in a 4-Mode 60 second cycle as follows:

(13) Operate engine at speed load to produce exhaust mass flow of 502.5 g/s per converter. Catalyst Inlet Temperature (Inlet) 156010 F. during steady state (mode 1) O.sub.2 is set at 4.50.1% for mode 3. Since flow balancing is only done before the aging begins, O.sub.2 concentration may not be exactly the same for all four legs. Further, only one leg was used to measure the 4.50.1% oxygen level in mode 3. CO is set at 4.00.1% for mode 2, and 2.50.1% for mode 3 4-Mode 60 second cycle: Mode 1: 40 s @ =1.000, no secondary air injection Mode 2: 6 s @ 4% CO (rich), no secondary air Injection Mode 3: 10 s @ 2.5% CO (rich), secondary air injection on Mode 4: 4 s @ =1.000, secondary air injection on
c) After conditioning catalysts CC1 and C1 were aged for 23 Hrs. as follows: Operate engine at speed load to produce exhaust mass flow of 472.5 g/s per converter. Catalyst Front Bed Temperature (FBed) 158010 F. during steady state (mode 1) Catalyst Front Bed Temperature (FBed) 174010 F. during spike (mode 3) O.sub.2 is set at 4.50.1% for mode 3. Since flow balancing is only done before the aging begins, O.sub.2 concentration may not be exactly the same for all four legs. Further, only one leg was used to measure the 4.50.1% oxygen level in mode 3. CO is set at 4.00.1% for mode 2, and 2.50.1% for mode 3 If spikes do not reach 174010 F., first lower O.sub.2 down to a minimum of 3.20.1% If spikes still have not reached 174010 F., raise mode 3 CO up to a max of 3.00.1%
4-Mode 60 second cycle: Mode 1: 40 s @ =1.000, no secondary air injection Mode 2: 6 s @ 4% CO (rich), no secondary air injection Mode 3: 10 s @ 2.5% CO (rich), secondary air injection on Mode 4: 4 s @ =1.000, secondary air injection on
d) The light-off temperatures (T.sub.50-value) of the conditioned and aged catalysts CC1 and C1 were determined as follows: A Ford 4.6 L MPFI engine operating at 1700 RPM was used for the test. The GHSV was set to 35K and a temperature ramp from 125.fwdarw.500 C. was carried out at 51 C./minute. During the temperature ramp the lambda was set to 1.000.045 @ 1 Hz. The fuel used was Indolene clear and contained 20 ppm Sulfur

(14) The following results were obtained:

(15) TABLE-US-00001 T.sub.50 [ C.] Catalyst HC CO NOx CC1 324 333 310 C1 252 254 211
e) The integral % Conversion of HC in the Lambda traverse test at 450, 500 and 600 C. of the conditioned and aged catalysts CC1 and C1 were determined as follows. For the 450 C. traverse test a Ford 4.6 L MPFI engine was used operating at 1700 RPM. The GHSV was set to 70K and a continuous Lambda sweep from 1.044/Lean.fwdarw.0.948/Rich over 458 seconds was carried out. The lambda at stoich=1.000.045 @ 1 Hz. The fuel used was Indolene clear with 20 ppm Sulfur. An Integral Performance Number for each component was calculated based on conversion between Lambda 1.01 and 0.99. The 500 C. test differed from the 450 C. sweep in that it was done over a time period of 680 seconds and the lambda at stoichiometry was 1.000.055 @ 1 Hz. The 600 C. sweep was done under the same conditions as the 500 C. one except for the higher temperature.

(16) The following results were obtained:

(17) TABLE-US-00002 Integral % Conversion of HC Catalyst 450 C. 500 C. 600 C. CC1 89.4 88.7 89.8 C1 93.4 91.7 96.0

Comparison Example 2

(18) Comparison Example 1 was repeated with the only difference that the PGM content of the TWC layer was higher and consisted of Pd+Rh=50 g/ft.sup.3 @0:10:1. The catalyst obtained is called CC2

Example 2

(19) An inventive catalyst was prepared as described in Comparison Example 2 above except that in this case part of the Pd=25 g/ft.sup.3 was added to the trap layer to give a homogeneous distribution through the full length of the part. All the Rh was added to the TWC layer at 5 g/ft.sup.3. The remainder of the Pd was then applied as a short band by dipping one end of the catalyst in a Pd nitrate solution containing citric acid and 2 wt % ethanol. The targeted band length was 0.5 Inches. The concentration of the dipped solution was adjusted such that with a solution band length of 1.25 cm (0.5) long the total Pd concentration was 250 g/ft.sup.3 in the dipped zone. The PGM loading averaged over the full part was 55 g/ft.sup.3 @ 0:10:1 (includes the Pd in the band and in the trap layer). The catalyst obtained is called C2.

(20) Comparison of Comparison Example 2 and Example 2

(21) The catalysts were aged as described above using the 2 Hr 4-mode pre-conditioning step followed by a 23 hour 4-mode aging step with P present in the fuel. Testing was carried out using the procedure as described in Nunan et. al. SAE 2013-01-1297. The results are summarized in FIG. 2 where the total HC out emissions for both CC2 and C2 are compared. It is evident that the catalyst of the present invention with the Pd band at the rear has lower Trap out emissions, both for the initial adsorption step in the temperature range of 30-55 C. and the high T release of the strongly bound HCs in the temperature range of 230-330 C. Thus, the presence of the Pd band at the rear has improved both HC adsorption but also conversion at higher temperatures resulting reduced HC emissions.