Patent ID: 12257573

EXAMPLES

Reference Example 1 Determination of Dv10, Dv50 and Dv90 Values

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

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

Reference Example 3 General Coating Method

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)

An incipient wetness impregnation of Pd onto a zirconium based oxidic support (88 weight-% of ZrO2with 10 weight-% La2O3and 2 weight-% HfO2, having a BET specific surface area of 67 m2/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 (FeVO4having 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 V2O5, was present at a loading of 5% of the final loading of the coating in the catalyst after calcination (the loading of FeVO4, calculated as FeVO4, 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-% TiO2doped with 10 weight-% WO3, a BET specific surface area of 90 m2/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+WO3in the catalyst after calcination was of 3.35 g/in3. 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 SiO2loading after calcination was 0.168 g/in3. The final mixture solid content was 43 weight-%.

At this point, the Pd-impregnated ZrO2mixture was mixed into the FeVO4/TiO2mixture 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)2cells 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/in3, 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/in3, including 3.35 g/in3of titania+WO3, 0.47 g/in3of FeVO4(including 0.225 g/in3of vanadium calculated as V2O5), 0.5 g/in3of zirconia+HfO2+La2O3, 0.167 g/in3of silica and a Pd loading of 15 g/ft3.

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

Bottom Coating:

An iron vanadate (FeVO4having 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 V2O5, was present at a loading of 5% of the final loading of the coating in the catalyst after calcination (the loading of FeVO4, calculated as FeVO4, 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-% TiO2doped with 10 weight-% WO3, a BET specific surface area of 90 m2/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+WO3in the catalyst after calcination was of 3.41 g/in3. The pH of the obtained mixture was set to 7. Afterwards, an aqueous colloidal silica binder, such that the final SiO2loading in the catalyst after calcination was 0.171 g/in3, 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)2cells 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/in3, 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/in3, including 3.41 g/in3of titania+WO3, 0.419 g/in3of FeVO4(including 0.2 g/in3of vanadium calculated as V2O5) and 0.171 g/in3of silica.

Top Coating:

An incipient wetness impregnation of Pd onto an alumina based oxidic support (gamma and delta alumina doped with 20% ZrO2and 3% La2O3, a BET specific surface area of 145 m2/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.

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/in3, including 0.44 g/in3of Al-based oxidic support, 0.056 g/in3of zirconia and a Pd loading of 15 g/ft3.

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

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/in3, including 3.41 g/in3of titania+WO3, 0.419 g/in3of FeVO4(including 0.2 g/in3of vanadium calculated as V2O5) and 0.17 g/in3of silica.

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 ZrO2with 10 weight-% La2O3and 2 weight-% HfO2, having a BET specific surface area of 67 m2/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/in3, including 0.435 g/in3of Zr-based oxidic support, 0.056 g/in3of zirconia and a Pd loading of 15 g/ft3.

Example 3 Testing of the Catalysts of Examples 1, 2.1 and 2.2—deNOx and N2O Formation

The NOx conversion of the fresh catalysts of Examples 1, 2.1 and 2.2 was measured, as well as the nitrous oxide (N2O) formation, at different temperatures, namely from 200 to 325° C., (Gas Hourly Space Velocity (GHSV): 40 000 h−1at 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 NH3slip was observed, indicating NH3saturation 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 onFIGS.1and2.

As may be taken fromFIG.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 NH3under these conditions and the catalyst may be used without concern for NH3oxidation up to at least 325° C. Indeed, only Example 2.1 shows any hint of NH3oxidation at 325° C. while Examples 1 and 2.2 still maintain 100% conversion at 325° C.

As may be taken fromFIG.2, all three catalysts do create a low level of N2O; however, Examples 1 and 2.1 produce less N2O across all measured temperatures.

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

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 SiO2: Al2O3of 31, and a BET specific surface area of about 625 m2/g). Further, a soluble zirconium solution (30 weight-% ZrO2) 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/in3, including 2.56 g/in3Cu-CHA, 0.3 g/in3of zirconia+HfO3+La2O3, 0.13 g/in3of zirconia and a Pd loading of 15 g/ft3.

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

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+HfO2, 5 weight-% of La2O3, and 5 weight-% of Pr6O11, having a BET specific surface area of 80 m2/g, a Dv90 of 15 micrometers). The final loading of the coating in the catalyst after calcination was of 3.0 g/in3, including 2.56 g/in3Cu-CHA, 0.3 g/in3of ceria+zirconia+lanthanum+praseodymium, 0.13 g/in3of zirconia and a Pd loading of 15 g/ft3.

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

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).

As may be taken fromFIG.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.

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.

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 1—deNOx and N2O Formation—US-FTP+WHTC

To generate the data presented inFIG.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 10.5″×6″ in size. The NOx conversion and N2O 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 N2O formation is reported as g/kWh based on the generated power over the cycle.

As may be taken fromFIG.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 N2O 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

FIG.1shows 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.

FIG.2shows the N2O formation obtained from the catalysts of Examples 1, 2.1 and 2.2 at inlet temperatures ranging from 200 to 325° C.

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

FIG.4shows the catalytic performances (deNOx and N2O formation) of the catalysts of Examples 1, 2.1, 2.2 and Comparative Example 1.

CITED LITERATURE

US 2015/0375207 A1U.S. Pat. No. 5,371,056WO 2018/224651 A2