CATALYTICALLY ACTIVE COMPOSITION CONTAINING RUTHENIUM FOR CATALYSTS FOR THE EXHAUST-GAS AFTERTREATMENT

Abstract

The present invention relates to a ruthenium-containing catalytically active composition for exhaust-gas aftertreatment catalysts, which composition contains a doped refractory oxide which is provided at least with ruthenium and is selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof, and composite oxides of two or more thereof and a cerium-zirconium oxide which comprises at least one element other than cerium from the group of rare earths. The invention also relates to a preparation containing the catalytically active composition, to methods for preparing same, to a catalyst having the catalytically active composition, and to a method in which the composition is used.

Claims

1. A catalytically active composition, comprising a) a doped refractory oxide which is provided at least with ruthenium and is selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof and composite oxides of two or more thereof, and b) a cerium-zirconium oxide which comprises at least one element other than cerium from the group of rare earths.

2. The catalytically active composition according to claim 1, wherein the doped refractory oxide is an aluminum oxide or a mixed oxide or composite oxide of aluminum oxide.

3. The catalytically active composition according to claim 1, wherein the doped refractory oxide is a lanthanum oxide-doped aluminum oxide, a lanthanum oxide-doped mixed oxide of aluminum oxide or a lanthanum oxide-doped composite oxide of aluminum oxide.

4. The catalytically active composition according to claim 1, wherein the proportion of doped refractory oxide is in the range of 10 to 95 wt. %.

5. The catalytically active composition according to claim 1, wherein the doped refractory oxide is provided with 0.1 wt. % to 25 wt. % ruthenium, based on the total amount of doped refractory oxide and ruthenium.

6. The catalytically active composition according to claim 1, wherein the catalytically active composition comprises ruthenium in an amount of 0.05 to 20 wt. %, based on the total amount of doped refractory oxide, ruthenium and cerium-zirconium oxide.

7. The catalytically active composition according to claim 1, wherein the doped refractory oxide is provided with at least one other noble metal selected from the group consisting of platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh) and combinations thereof.

8. The catalytically active composition according to claim 7, wherein the doped refractory oxide is provided with a combination of ruthenium and iridium; ruthenium and platinum; ruthenium and palladium; ruthenium, platinum and iridium; ruthenium, palladium and iridium or ruthenium, palladium and platinum.

9. The catalytically active composition according to claim 7, wherein the doped refractory oxide is provided with ruthenium and the at least one other noble metal in an amount of 0.2 to 30 wt. %, based on the total amount of doped refractory oxide, ruthenium and the at least one other noble metal.

10. The catalytically active composition according to claim 1, wherein the cerium-zirconium oxide is provided with at least one noble metal.

11. The catalytically active composition according to claim 1, wherein the noble metal provisions for the doped refractory oxide and the cerium-zirconium oxide are different.

12. A method for preparing a catalytically active composition according to claim 1, comprising the steps of: i) providing the doped refractory oxide which is provided at least with ruthenium and is selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, molybdenum oxide, tungsten oxide, titanium oxide, mixtures thereof and composite oxides of two or more thereof, ii) providing the cerium-zirconium oxide which comprises at least one element other than cerium from the group of rare earths, iii) mixing the doped refractory oxide provided at least with ruthenium, and the cerium-zirconium oxide.

13. A preparation, containing a) a catalytically active composition according to claim 1, and b) a liquid.

14. A catalyst comprising the catalytically active composition according to claim 1 and a heat-resistant carrier.

15. A method for exhaust-gas aftertreatment, wherein an exhaust gas stream is brought into contact with a catalytically active composition according to claim 1.

Description

[0180] FIG. 1 shows the temperature-dependent conversion of NO.sub.x and HC of the freshly prepared catalyst.

IE1 (Ru/Al.SUB.2.O.SUB.3.)

[0181] 80 g Al.sub.2O.sub.3 were impregnated with an RuNN solution containing 90% of the Ru to be applied and then dried, and 20 g of CeZr oxide were also treated with an RuNN solution containing 10% of the Ru to be applied. For calcination, the dried material was treated in an oven at 500 C. for 4 h. The Al.sub.2O.sub.3 provided with Ru was slurried in water, then the CeZr oxide provided with Ru was added and the entire suspension was ground. The ground suspension was applied to a ceramic honeycomb substrate. The coated honeycomb was calcined at 550 C. for 4 h. The resulting washcoat loading was 100 g/L, which corresponded to a ruthenium content of 10.6 g/L.

[0182] Using the NO.sub.x and HC conversion, FIG. 2 illustrates the catalyst performance of the catalyst prepared according to the invention.

IE2 (Ru/Al.SUB.2.O.SUB.3.)

[0183] The preparation procedure was carried out analogously to the method given in IE1, but only the Al.sub.2O.sub.3 was treated with an RuNN solution containing 100% of the Ru to be applied. The resulting washcoat loading was 100 g/L, corresponding to a ruthenium content of 3.5 g/L.

[0184] FIG. 3 shows the catalyst performance of this catalyst according to the invention. In addition to the catalyst performance of the freshly prepared catalyst (pre-T), the performance after artificial aging (post-T) is compared. The almost identical curves illustrate the particular stability of the catalyst.

IE3 (Ru/Al.SUB.2.O.SUB.3.)

[0185] The preparation procedure was carried out analogously to the method given in IE2, but less RuNN was used in the solution. The resulting washcoat loading was 100 g/L, which corresponded to a ruthenium content of 1.8 g/L.

[0186] FIG. 4 shows the catalyst performance of this catalyst according to the invention.

IE4 (RuIr/Al.SUB.2.O.SUB.3.)

[0187] The preparation procedure was carried out analogously to the method given in IE2. For impregnation of the Al.sub.2O.sub.3, a solution of RuNN and iridium as iridium chloride in water was used. The resulting washcoat loading was 100 g/L, which corresponded to a ruthenium content of 1.8 g/L.

[0188] FIG. 5 shows the catalyst performance of this catalyst according to the invention.

IE5 (RuPt/Al.SUB.2.O.SUB.3.)

[0189] The preparation procedure was carried out analogously to the method given in IE2. For impregnation of the Al.sub.2O.sub.3, a solution of RuNN and platinum as platinum nitrate in water was used. The resulting washcoat loading was 100 g/L, which corresponded to a ruthenium content of 1.8 g/L.

[0190] FIG. 6 shows the catalyst performance of this catalyst according to the invention.

IE6 (RuIr/Al.SUB.2.O.SUB.3.+RuPt/CeZr oxide)

[0191] Al.sub.2O.sub.3 was slurried in water and mixed with an RuNN solution and iridium chloride in water. The suspension was heated, then an NaOH solution was added and the solid phase was separated from the liquid phase by filtration.

[0192] CeZr oxide was slurried in water and mixed with an RuNN solution and platinum nitrate in water. The suspension was heated, an NaOH solution was then added and the solid phase was separated from the liquid phase by filtration.

[0193] The two oxides provided with the precipitated noble metals were mixed, dried and treated for calcination purposes in an oven at 400 C. for 2 h. The calcined material was slurried in water and ground.

[0194] The coating of a ceramic honeycomb body was carried out in a similar way to that described in IE2. The resulting loading was 100 g/L, which corresponded to a ruthenium content of 1.8 g/L.

[0195] FIG. 7 shows the catalyst performance of this catalyst according to the invention.

TABLE-US-00001 TABLE 1 summarizes the features of the tested catalysts and the corresponding total noble metal loading. Precious metal loading [g/L] CE Ru/Al.sub.2O.sub.3 3.5 Ru/CeZr oxide IE1 Ru/Al.sub.2O.sub.3 10.6 CeZr oxide IE2 Ru/Al.sub.2O.sub.3 3.5 CeZr oxide IE3 Ru/Al.sub.2O.sub.3 1.8 CeZr oxide IE4 Rulr/Al.sub.2O.sub.3 2.7 CeZr oxide IE5 RuPt/Al.sub.2O.sub.3 3.5 CeZr oxide IE6 RuPtIr/Al.sub.2O.sub.3 4.4 Rulr/CeZr oxide

[0196] The results of IE1 to IE6 demonstrate that the various embodiments of the catalysts according to the invention are active in the removal of nitrogen oxides. Even a relatively low noble metal loading, as in IE3, is sufficiently effective. In particular, the combination of ruthenium with another noble metal also showed a beneficial reduction in T50.

[0197] FIG. 8 compares the catalytic activity for the NOx conversion of the catalysts according to CE, IE1 and IE2 containing only ruthenium before (pre-T) and after (post-T) temperature treatment. Before temperature treatment, the catalyst performances were similar. However, the catalytic activity, in particular the light-off temperature, of the catalysts according to the invention showed only a slight change after this artificial aging, whereas the catalyst of the comparative example (CE) clearly lost catalytic activity. In particular, the comparison between the catalysts of CE and IE2, which have the same ruthenium loading, illustrates the increased stability of the catalysts according to the invention. The carrying of the ruthenium on the Al.sub.2O.sub.3 presumably increases its stability and thus the catalytic effectiveness under operating conditions, making it possible to minimize the noble metal provision in the catalysts.

[0198] FIG. 9 compares the determined T50 values for the NOx conversion of the tested catalysts in the fresh and aged state. The T50 value could no longer be determined for the catalyst of the comparative example. In addition to lowering the light-off temperature, the combination of ruthenium with another noble metal, in particular iridium, proved to be beneficial for the stability of the catalysts.