PGM catalyst coupled with a non-PGM catalyst with HC oxidation capability

Abstract

The present invention relates to a diesel oxidation catalyst comprising a substrate and a wash-coat comprising a first layer and a second layer, wherein the substrate has a substrate length, a front end and a rear end, the washcoat comprising the first layer comprising a first metal oxide and comprising a platinum group metal supported on a metal oxide support material; the second layer comprising a second metal oxide and comprising one or more of an oxidic compound of vanadium, an oxidic compound of tungsten and a zeolitic material comprising one or more of Fe and Cu; wherein the first layer is at least partially disposed directly on the substrate, or is at least partially disposed directly on an intermediate layer which is disposed directly on the substrate over the entire length of the substrate, on x % of the length of the substrate from the front end of the substrate, and wherein the second layer is at least partially disposed directly on the substrate, or is at least partially disposed directly on the intermediate layer which is disposed directly on the substrate over the entire length of the substrate, on y % of the length of the substrate from the rear end of the substrate, wherein x is in the range of from 25 to 75 and y is in the range of from 25 to 75 and wherein x+y is in the range of from 95 to 105, wherein the intermediate layer comprises alumina.

Claims

1. A diesel oxidation catalyst comprising a substrate and a washcoat comprising a first layer and a second layer, wherein the substrate has a substrate length, a front end and a rear end, the first layer comprising a first metal oxide and a platinum group metal supported on titania, wherein the platinum group metal is not supported on the first metal oxide; the second layer comprising a second metal oxide, and an oxidic compound of vanadium; wherein the first layer is at least partially disposed directly on the substrate or is at least partially disposed directly on an intermediate layer which is disposed directly on the substrate over the entire length of the substrate, wherein the first layer is disposed, directly or indirectly, on x % of the length of the substrate from the front end of the substrate, wherein the second layer is at least partially disposed directly on the substrate or is at least partially disposed directly on the intermediate layer which is disposed directly on the substrate over the entire length of the substrate, wherein the second layer is disposed, directly or indirectly, on y % of the length of the substrate from the rear end of the substrate, wherein x is in the range of from 25 to 75 and y is in the range of from 25 to 75 and wherein x+y is in the range of from 95 to 105, and wherein the intermediate layer comprises alumina.

2. The diesel oxidation catalyst of claim 1, wherein x ranges from 30 to 70.

3. The diesel oxidation catalyst of claim 1, wherein y ranges from 30 to 70.

4. The diesel oxidation catalyst of claim 1, wherein x+y ranges from 96 to 104.

5. The diesel oxidation catalyst of claim 1, wherein the substrate has a plurality of longitudinally extending passages formed by longitudinally extending walls bounding and defining the passages and a longitudinal total length extending between the front end and the rear end of the substrate.

6. The diesel oxidation catalyst of claim 1, wherein the first metal oxide is one or more of gamma-alumina, zirconia-alumina, silica-alumina, silica, lanthana, lanthana-alumina, alumina-zirconia-lanthana, titania, zirconia-titania, ceria, ceria-zirconia, or ceria-alumina.

7. The diesel oxidation catalyst of claim 1 wherein the platinum group metal is one or more of Pt, Pd, or Rh.

8. The diesel oxidation catalyst of claim 1, wherein the second metal oxide is one or more of gamma-alumina, zirconia-alumina, silica-alumina, silica, lanthana, lanthana-alumina, alumina-zirconia-lanthana, titania, titania-silica, zirconia-titania, ceria, ceria-zirconia, ceria-alumina, or ferrous oxide.

9. The diesel oxidation catalyst of claim 1, wherein the oxidic compound of vanadium is one or more of an ammonium vanadate, a sodium vanadate, an iron vanadate, vanadium pentoxide, or vanadium pentoxide stabilized with ferric oxide.

10. A process for selective catalytic reduction of NO.sub.x, and/or oxidation of one or more of carbon monoxide, nitrogen monoxide, or a hydrocarbon, the process comprising contacting one or more of NO.sub.x, carbon monoxide, nitrogen monoxide, or a hydrocarbon with the diesel oxidation catalyst of claim 1.

11. An exhaust gas treatment system, comprising the diesel oxidation catalyst of claim 1.

12. A process for preparing the diesel oxidation catalyst of claim 1, wherein the diesel oxidation catalyst comprises one substrate, the process comprising (a) optionally disposing an intermediate slurry directly on the substrate wherein the intermediate slurry comprises alumina, thereby obtaining an intermediate slurry-treated substrate; (b1) disposing a second slurry on the substrate, or on the intermediate slurry-treated substrate, thereby obtaining a second slurry-treated substrate, wherein the second slurry comprises the second metal oxide and; (c1) drying the second slurry-treated substrate; (d1) calcining the dried second slurry-treated substrate, thereby obtaining a substrate having the second layer disposed thereon; (e1) disposing a first slurry on the substrate having the second layer disposed thereon, thereby obtaining a first slurry-treated substrate having the second layer disposed thereon, wherein the first slurry comprises the first metal oxide and the platinum group metal supported on titania, wherein the platinum group metal is not supported on the first metal oxide; (f1) drying the first slurry-treated substrate having the second layer disposed thereon; and (g1) calcining the dried first slurry-treated substrate having the second layer disposed thereon, thereby obtaining a substrate having the first and the second layer disposed thereon; wherein the first layer is disposed, directly or indirectly, on x % of the length of the substrate from the front end of the substrate, wherein the second layer is at least partially disposed directly on the substrate or is at least partially disposed directly on the intermediate layer which is disposed directly on the substrate over the entire length of the substrate, and wherein the second layer is disposed, directly or indirectly, on y % of the length of the substrate from the rear end of the substrate, wherein x is in the range of from 25 to 75 and y is in the range of from 25 to 75 and wherein x+y is in the range of from 95 to 105; or (a) optionally disposing an intermediate slurry directly on the substrate wherein the intermediate slurry comprises alumina, thereby obtaining an intermediate slurry-treated substrate; (b2) disposing a first slurry on the substrate, or on the intermediate slurry-treated substrate, thereby obtaining a first slurry-treated substrate, wherein the first slurry comprises the first metal oxide and the platinum group metal supported on titania, wherein the platinum group metal is not supported on the first metal oxide; (c2) drying the first slurry-treated substrate; (d2) calcining the dried first slurry-treated substrate, thereby obtaining a substrate having the first layer disposed thereon; (e2) disposing a second slurry on the substrate having the first layer disposed thereon, thereby obtaining a second slurry-treated substrate having the first layer disposed thereon, wherein the second slurry comprises the second metal oxide and an oxidic compound of vanadium; (f2) drying the second slurry-treated substrate having the first layer disposed thereon; and (g2) calcining the dried second slurry-treated substrate having the first layer disposed thereon, thereby obtaining a substrate having the first and the second layer disposed thereon; wherein the first layer is disposed, directly or indirectly, on x % of the length of the substrate from the front end of the substrate, wherein the second layer is at least partially disposed directly on the substrate or is at least partially disposed directly on the intermediate layer which is disposed directly on the substrate over the entire length of the substrate, and wherein the second layer is disposed, directly or indirectly, on y % of the length of the substrate from the rear end of the substrate, wherein x is in the range of from 25 to 75 and y is in the range of from 25 to 75 and wherein x+y is in the range of from 95 to 105.

13. A diesel oxidation catalyst obtained by the process of claim 12.

Description

EXAMPLES

Reference Example 1: Determination of the D90 Values

(1) The D90 particle size as referred to in the context of the present invention was measured with a Sympatec Particle Size instrument using laser diffraction (Sympatec's HELOS system allowing the determination of the particle size distribution in the range of from 0.1 to 8,750 micrometer). According to this method, the particle size distribution was evaluated with a parameter-free and model-independent mathematical algorithm, accomplished by the introduction of the Phillips-Twomey algorithm for the inversion process.

Example 1: Diesel Oxidation Catalyst Having Two Layers

(2) For the second layer, a second slurry was prepared by slowly adding 32,000 g TiO.sub.2 (DT-52 TiO.sub.2 containing about 10 weight-% WO.sub.3, Cristal Chemical Company) to a solution of 850 g vanadium oxalate in distilled water resulting in dispersion 1. After stirring for 5 minutes, ammonium hydroxide was added to dispersion 1 as an aqueous solution containing 1.67 weight-% of the total weight of dispersion 1 to adjust the pH in the range of from 4.5 to 5.5. The resulting dispersion was stirred for another 5 minutes. Then, 1,600 g of a silica dispersion (Ludox® AS-40 colloidal silica) was added thereto while stirring for 10 minutes resulting in the second slurry. The second slurry was then disposed onto 50% of the length of the substrate (NGK high porous cordierite, 10.5″×6″ cylindrically shaped substrate with 360 cells per square inch and 8 mil wall thickness) from the rear end of the substrate at a total loading of 5.5 g/in.sup.3. The resulting substrate was dried at 120° C. and then calcined at 450° C. resulting in a substrate having the second layer disposed thereon. In the second layer, the loading of vanadium calculated as vanadium pentoxide was 0.13 g/m.sup.3 and the loading of the titania was 5.09 g/in.sup.3.

(3) For the first layer, a first slurry was prepared by mixing 9,000 g of silica-alumina (Siralox 1,5/100, Sasol) with a diluted aqueous HNO.sub.3 solution resulting in a silica-alumina containing slurry. Separately, a mixture of acetic acid, water and 3600 g of Zr(OH).sub.4 (MEL Chemicals) was prepared. Said mixture was then added to the silica-alumina containing slurry. Further, 900 g of a zirconium acetate solution (30 weight-% in distilled water) was added thereto. The resulting slurry was then milled until the D90 particle size determined as described in Reference Example 1 herein was between 9 micrometer and 11 micrometer in diameter. Thus, a Zr/silica-alumina containing slurry is obtained. Separately, 18,000 g of TiO.sub.2 (titanium dioxide type II, Sachtleben) was wet impregnated with platinum using a platinum precursor with platinum as an ammine stabilized hydroxo Pt(IV) complex (Pt content between 10 and 20 weight-%) resulting in a Pt/TiO.sub.2 containing mixture. To this Pt/TiO.sub.2 containing mixture, acetic acid and water were added to give the final Pt/TiO.sub.2 containing slurry.

(4) Finally, the Zr/silica-alumina containing slurry, octanol and the final Pt/TiO.sub.2 containing slurry were mixed to obtain the first slurry. The first slurry was then coated from the front end of the substrate at a total loading of 1.013 g/in.sup.3 onto 50% of the length of the substrate having the second layer disposed thereon. The obtained substrate was dried at around 120° C. and then calcined at 450° C. In the first layer, the platinum loading was 15 g/ft.sup.3, the sum of the loading of silica-alumina and of zirconia was 0.341 g/in.sup.3, and the loading of titania was 0.663 g/in.sup.3.

(5) Accordingly, the loading of platinum on the substrate was about 2.25 g.

Example 2: Diesel Oxidation Catalyst Having Two Layers

(6) Example 2 was prepared as Example 1 whereby the geometrical order of the layer was inversed.

(7) Thus, the first slurry and the second slurry were prepared as in Example 1. The first slurry was disposed onto 50% of the length of the substrate (NGK high porous cordierite, 10.5″×6″ cylindrically shaped substrate with 360 cells per square inch and 8 mil wall thickness) from the rear end of the substrate at a loading of 1.013 g/in.sup.3. The resulting substrate was dried at 120° C. and then calcined at 450° C. resulting in a substrate having the first layer disposed thereon. In the first layer, the loading of the platinum was 15 g/ft.sup.3, the sum of the loading of silica-alumina and of the loading of zirconia was 0.341 g/in.sup.3 and the loading of titania was 0.663 g/in.sup.3. Then, the second slurry was coated from the front end of the substrate at a loading of 5.5 g/in.sup.3 onto 50% of the length of the substrate having a first layer disposed thereon. The obtained substrate was dried at around 120° C. and then calcined at 450° C. In the second layer, the loading of vanadium calculated as vanadium pentoxide was 0.13 g/in.sup.3 and the loading of the titania was 5.09 g/in.sup.3. Accordingly, the loading of platinum on the substrate was about 2.25 g.

Example 3: Diesel Oxidation Catalyst Having One Layer

(8) A slurry was prepared as the first slurry in Example 1. The slurry was then coated onto 100% of the length of the substrate (NGK cordierite, 12″×6″ cylindrically shaped substrate with 400 cells per square inch and 4 mil wall thickness) at a total loading of 1.013 g/in.sup.3. The obtained substrate was dried at around 120° C. and then calcined at 450° C. In the layer, the platinum loading was 10 g/ft.sup.3, the sum of the loading of silica-alumina and of the loading of zirconia was 0.341 g/in.sup.3 and the loading of titania was 0.663 g/in.sup.3. Accordingly, the loading of platinum on the substrate was about 3.93 g.

Example 4: Use of the DOCs According to Examples 1, 2 and 3—Exotherm, NO.SUB.2 .Make, DOC.SUB.out .HC Slip

(9) The diesel oxidation according to Examples 1, 2 and 3 were tested on an EU V 13 L engine. Upstream of the DOC to be tested a hydrocarbon injector was set (PWM controlled). Gas composition measurements were carried out using a FTIR spectrometer (Horiba MEXA-6000-FT), NO.sub.x-Sensors (CSM NO.sub.x CANg for the gas stream before entering the DOC, Continental/BMW AG 5WK96610L 11787587-05 for gas stream exiting the DOC), a chemoluminescence detector (Horiba MEXA-1170NX) and a hydrocarbon detector (Horiba MEXA-1170HFID), whereas temperature measurements were carried out using thermocouples (Hettstett GmbH, Typ K).

(10) The test protocol was as follows:

(11) 1. HC was injected for 570 seconds to provide stable measurements

(12) 2. HC slip measurement was carried out for 30 seconds

(13) 3. HC injection was turned off (time spent: 300 seconds)

(14) 4. Cool off for 600 seconds

(15) 5. Conditioning was performed before NO oxidation measurement for 1800 seconds

(16) 6. NO oxidation measurement 30 seconds

(17) Measurement of Exotherm

(18) For measurements of an exotherm, the temperature of the gas was determined in the DOC after 3 inches from the front end of the substrate of an example and after the DOC. Each of the two resulting curves represents an exotherm. Accordingly, the exotherm for Example 1 is shown in FIG. 1 and the exotherm for Example 2 is shown in FIG. 2. Thus, it has been found that the exotherm for Example 2 shows a temperature peak between 25000 and 30000 seconds. In contrast, the exotherm for Example 1 does not show such a peak. However, such a temperature peak may lead to an irreversible damage of the washcoat of a catalyst resulting in diminished catalyst performance. Accordingly, the catalyst according to Example 1 shows a better performance in view of the generation of a favorable temperature especially for regeneration of a downstream CSF.

(19) Measurement of NO.sub.2/NO.sub.x Ratio

(20) The tests for measuring the NO.sub.2 make were carried out under NO.sub.x only conditions, this means that no ammonia was added. The space velocity for each test run was set at 300 to 350 kg/h. Thus, the NO.sub.2/NO.sub.x ratio was determined relative to the temperature of the gas at five different temperatures in the range of from 200 to 400° C. The amount of NO.sub.x equals the sum of the amounts of NO and NO.sub.2. The resulting curve represents the light-off curve. The light-off curve was measured for diesel oxidation catalysts of Examples 1, 2 and 3. The results for the light-off are shown in FIG. 3. As can be taken from FIG. 3, it has been found that the diesel oxidation catalyst of Example 3 shows the highest NO.sub.2/NO.sub.x ratio in the temperature range of from 200 to 400° C. However, it has to be taken into account that Example 3 contains a much higher loading of platinum group metal being 3.93 g of Pt whereas Examples 1 and 2 each contain only 2.25 g of Pt. The diesel oxidation catalyst of Example 1 shows a higher NO.sub.2/NO.sub.x ratio than the DOC of Example 2 at a temperature of about 330° C. Overall, the NO.sub.2/NO.sub.x ratio for the DOCs of Examples 1 and 2 are very similar.

(21) Measurement of DOC(Out) HC Slip

(22) In order to determine the hydrocarbon slip exiting a DOC (DOC.sub.out HC slip), hydrocarbon measurements were conducted at steady state points. Eleven steady state points (designated as load points) have been chosen to balance test expediency. Thus, the three diesel oxidation catalysts according to Examples 1 to 3 have been tested in view of their DOC.sub.out HC slip. The characteristics of the eleven steady state points (LP1 to LP12) are shown in Table 1 below. Thus, the DOC.sub.out HC slip was determined relative to each steady state point. The results are shown in FIG. 4.

(23) TABLE-US-00001 TABLE 1 Characteristics of the eleven steady state points measurements DOC.sub.in Temp Exhaust Massflow NO.sub.x Load Point [° C.] [kg/h] [ppm] LP1 365 928 777 LP2 370 659 1095 LP3 394 295 2424 LP4 316 959 622 LP5 325 704 622 LP6 335 317 1552 LP7 292 1050 458 LP8 296 722 587 LP9 305 341 941 LP10 277 728 493 LP11 286 362 794

(24) As can be taken from FIG. 4, the diesel oxidation catalyst of Example 3 is outperformed by the other two catalysts especially when the DOC.sub.in temperature is comparatively low and the exhaust mass flow comparatively high, in particular at LP4, LP5, LP7 and LP8. Overall, the catalysts of Example 1 and 2 perform comparatively well.

BRIEF DESCRIPTION OF FIGURES

(25) FIG. 1: shows the exotherm according to Example 4 of the inventive diesel oxidation catalyst according to Example 1. In the figure, the time is shown on the abscissa and the temperature is shown on the ordinate.

(26) FIG. 2: shows the exotherm according to Example 4 of the diesel oxidation catalyst according to Example 2. In the figure, the time is shown on the abscissa and the temperature is shown on the ordinate.

(27) FIG. 3: shows the light-off curve of the diesel oxidation catalyst of Examples 1, 2 and 3. In the figure, the temperature is shown on the abscissa and the NO.sub.2/NO.sub.x ratio is shown on the ordinate.

(28) FIG. 4: shows the DOC.sub.out hydrocarbon slip of the diesel oxidation catalyst of Examples 1, 2 and 3 for each of the eleven steady state points. In the figure, the DOC.sub.nut HC slip is shown on the left ordinate and the DOC.sub.out temperature is shown on the right ordinate relative to each of the eleven steady state points on the abscissa.

CITED LITERATURE

(29) WO 2015/189680 A1