Platinum/palladium zeolite catalyst

Abstract

The invention relates to a method for producing a bimetallic catalyst containing palladium and platinum on a zeolitic carrier material, to a bimetallic catalyst that can be obtained by means of the method, and to the use of the catalyst in oxidation catalysis.

Claims

1. A method for producing a bimetallic catalyst comprising the steps of: a) impregnating a zeolitic support material with sulfur-free Pt and Pd precursor compounds, wherein the Pt and Pd precursor compounds are solutions of nitrates, b) drying the impregnated zeolitic support material in air, and c) calcinating the impregnated and dried zeolitic support material under protective gas, wherein the zeolitic support material has a structure type of BEA and wherein the structure type corresponds to the IUPAC Commission of Zeolite Nomenclature.

2. The method as claimed in claim 1 , wherein the calcinating step takes place at temperatures from 350 to 650 C.

3. The method as claimed in claim 1, wherein the drying of the impregnated zeolitic support material takes place below the decomposition point of the Pt and Pd precursor compounds.

4. The method as claimed in claim 1, comprising the further steps: d) producing a washcoat from the impregnated and calcined zeolitic support material, e) coating a support body with the washcoat, and f) drying and calcinating the coated support body in air.

5. The method as claimed in claim 4, wherein the calcinating step takes place at temperatures from 300 to 600 C.

6. A catalyst comprising a bimetallic catalytically active composition comprising Pt and Pd on a zeolitic support material made by a method comprising the steps of: a)impregnating a zeolitic support material with sulfur-free Pt and Pd precursor compounds, wherein the Pt and Pd precursor compounds are solutions of nitrates, b) drying the impregnated zeolitic support material in air, and c) calcinating the impregnated and dried zeolitic support material under protective gas, wherein the zeolitic support material has a structure type of BEA and wherein the structure type corresponds to the IUPAC Commission of Zeolite Nomenclature.

7. The catalyst as claimed in claim 6, wherein the bimetallic catalytically active composition has a BET surface area of more than 400 m.sup.2/g.

8. The catalyst as claimed in claim 6, wherein the bimetallic catalytically active composition has a Pt content of 0.2 to 1.5% by weight, based on the catalytically active composition.

9. The catalyst as claimed in claim 6, wherein the bimetallic catalytically active composition has a Pd content of 0.8 to 4.0% by weight, based on the catalytically active composition.

10. The catalyst as claimed in claim 6, wherein the catalytically active composition is applied as a washcoat coating to a support body.

11. The catalyst as claimed in claim 10, wherein the catalyst has 0.5 to 3% by weight of Pt based on the coated washcoat.

12. The catalyst as claimed in claim 10 where the catalyst has 1 to 5% by weight of Pd based on the coated washcoat.

13. The catalyst as claimed in claim 10 wherein the bimetallic catalytically active composition or the washcoat coating has a Pd/Pt weight ratio of 6:1 to 1:1.

14. The catalyst as claimed in claim 6, wherein the Pt and Pd is located essentially in the pores of the zeolitic support material.

15. The catalyst as claimed in claim 6, wherein the Pt and Pd is present in aggregates of <5 nm.

16. An oxidation catalyst comprising a catalyst as claimed in claim 6.

17. A method for producing a bimetallic catalyst comprising the steps of: a)impregnating a zeolitic support material with sulfur-free Pt and Pd precursor compounds, wherein the Pt and Pd precursor compounds are solutions of nitrates, b) drying the impregnated zeolitic support material in air, c) calcinating the impregnated and dried zeolitic support material under protective gas, d) producing a washcoat from the impregnated and calcined zeolitic support material, e) coating a support body with the washcoat, and f) drying and calcinating the coated support body in air, wherein the calcinating step takes place at temperatures from 300 to 600 C. and wherein the zeolitic support material has a structure type of BEA and wherein the structure type corresponds to the IUPAC Commission of Zeolite Nomenclature.

18. A method for producing a bimetallic catalyst comprising the steps of a) impregnating a zeolitic support material with sulfur-free Pt and Pd precursor compounds, wherein the Pt and Pd precursor compounds are solutions of nitrates, b) drying the impregnated zeolitic support materia in air, c) calcinating the impregnated and dried zeolitic support material under protective gas, d) producing a washcoat from the impregnated and calcined zeolitic support material and a silicatic binder, e) coating a support body with the washcoat, and f) drying and calcinating the coated support body in air, wherein the calcinating step takes place at temperatures from 300 to 600 C. and wherein the zeolitic support material has a structure type selected from the group consisting of BEA and MFI, and wherein the structure type corresponds to the IUPAC Commission of Zeolite Nomenclature.

19. A catalyst comprising a bimetallic catalytically active composition comprising Pt and Pd on a zeolitic support material made by a method comprising the steps of: a)impregnating a zeolitic support material with sulfur-free Pt and Pd precursor compounds, wherein the Pt and Pd precursor compounds are solutions of nitrates, b) drying the impregnated zeolitic support material in air, c) calcinating the impregnated and dried zeolitic support material under protective gas, d) producing, a washcoat from the impregnated and calcined zeolitic support material and a silicatic binder, e)coating a support body with the washcoat, and f) drying and calcinating the coated support body in air, wherein the calcinating step takes place at temperatures from 300 to 600 C. and wherein the zeolitic support material has a structure type selected from the group consisting of BEA and MFI, and wherein the structure type corresponds to the IUPAC Commission of Zeolite Nomenclature.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1: shows the XRD spectrum of a PtPd-BEA150 zeolite produced according to the invention (bottom) and also of comparative example 1 (top);

(2) FIGS. 2 and 3: show IR spectra of the PtPd-BEA150 zeolite according to the invention, and also of comparative example 1 following CO chemisorption with and without metered addition of adamantanecarbonitrile;

(3) FIGS. 4a, 4b: show performance data in the oxidation of alkanes (methane, ethane) of the PtPd-BEA150 zeolite according to the invention, and also of comparative examples 1 and 2, in each case with different precious metal chargings in the fresh state;

(4) FIGS. 5a, 5b: show performance data in the oxidation of alkanes (methane, ethane) of the PtPd-BEA150 zeolite according to the invention, and also of comparative example 2 with different precious metal chargings in the fresh state, following thermal aging and after poisoning with SO.sub.2;

(5) FIGS. 6a, 6b: show performance data in the oxidation of ethylene and ethyl acetate of the PtPd-BEA150 zeolite according to the invention, and also of comparative example 2, in each case fresh, following thermal aging and after poisoning with SO.sub.2;

EXAMPLE 1

(6) The catalysts according to the invention were produced in a 2-step process. In a first step, a BEA150 zeolite was supplied with a solution of platinum nitrate and palladium nitrate by means of incipient wetness technology. The supplied zeolite was then dried for 16 h under air at 90 C. and then calcined under argon for 5 h at 550 C.

COMPARATIVE EXAMPLE 1

(7) As comparative example 1, a BEA150 zeolite was supplied in an analogous manner with platinum nitrate and palladium nitrate by means of incipient wetness technology, dried at 90 C. and then calcined under air for 5 h at 550 C.

(8) Table 1 summarizes the properties of the zeolite samples (formulation according to the invention and comparative example 1) produced in the course of the investigation.

EXAMPLE 2

Production of a Washcoat

(9) In a second step, the calcined PtPd zeolite according to the invention and also that of comparative example 1 were processed with Bindzil (binder material) and water to give a washcoat and this washcoat was then coated onto corderite honeycombs. The coated corderite honeycombs were blown out with compressed air, then dried overnight at 150 C. under air and finally calcined for 3 h at 550 C.

(10) TABLE-US-00001 TABLE 1 PtPd-BEA150 zeolites (step 1) Formulation according Comparative to the invention, formulation 1, Batch PtPd-BEA150 calcination under argon calcination under air Pt [% by weight] 0.69 0.78 Pd [% by weight] 2.1 2.3 BET surface area [m.sup.2/g] 601 585

(11) FIG. 1 shows the XRD spectrum of a PtPD-BEA150 zeolite according to the invention produced according to the above procedure, as well as that of the comparison formulation. In both samples, no reflections for metallic Pt and Pd are present. The signals for precious metal oxides are also barely detectable. All large reflections contain virtually exclusively signal fractions of the BEA150 zeolite. It can be concluded from this that both Pt and also Pd are present in highly disperse form favorable for the performance. The absence of precious metal agglomerates >5 nm is thus clearly demonstrated.

(12) FIGS. 2 and 3 show the IR spectra of the PtPd-BEA150 zeolite according to the invention, as well as of comparative example 1 following CO chemisorption with and without the metered addition of adamantanecarbonitrile. Measuring IR spectra after CO chemisorption is a widespread technique for investigating the nature and dispersion of precious metal species in precious-metal-containing catalysts. CO can here achieve precious metal species both on the inside and outside of the pores and interact with them and, in so doing, generate signals that can be evaluated by means of IR spectroscopy.

(13) Nitriles such as adamantanecarbonitrile enter into a greater interaction with precious metal species and are therefore preferentially adsorbed by these. It is therefore possible to mask precious metal species for the CO chemisorption with the help of nitriles. Nitrile molecules with diameters greater than or equal to the pores of the zeolites are unable to penetrate into zeolite pores and therefore selectively mask precious metal species on the outside of the pores. Adamantanecarbonitrile has a molecular diameter >0.6 nm. This is comparable to the diameters of the pore openings of the BEA zeolite (0.56-0.7 nm), and consequently adamantanecarbonitrile can be used in order to mask precious metal species on the outside of the zeolite pores in a selective manner for the CO chemisorption. The IR absorption bands of adamantanecarbonitrile itself do not interfere here with the IR absorption bands of the CO chemisorption on precious metal species.

(14) For the IR investigations described below, samples of the PtPd-BEA150 zeolite according to the invention and of comparative sample 1 were firstly degassed at 10.sup.6 mbar for 3 hours at 400 C. and then reduced with nitrogen for 30 min the IR measuring cell. The samples were then supplied with 20 mbar of CO and a first IR spectrum was recorded. The CO was then further removed by gassing at 400 C. under vacuum for 30-60 min. After cooling, adamantanecarbonitrile vapor was dosed onto the samples in order to mask the precious metal species on the outside of the zeolite pores, followed by a further supplying with 20 mbar of CO. The second IR spectrum was then recorded. The difference between the two IR spectra shows the precious metal species which are located on the outside of the zeolite pores and can therefore be masked by adamantanecarbonitrile vapor. All the spectra themselves were recorded using a thermo 4700 FTIR spectrometer with a resolution of 4 cm.sup.1.

(15) FIG. 2 shows the IR spectra of the CO chemisorption of the Pt-Pd-BEA150 zeolite according to the invention, FIG. 3 shows that of comparative example 1, in each case before and after selective masking of the precious metal species on the outside of the zeolite pores with adamantanecarbonitrile. Firstly to be noted are for both samples the two main bands around 2000 cm.sup.1 (assignable to Pd) and 2100 cm.sup.1 (assignable to Pt). Both bands are attenuated by the adamantanecarbonitrile addition, the attenuation in the case of the Pt-Pd-BEA150 zeolite according to the invention being less marked than in the case of comparative example 1. This means there are more precious metal species in the zeolite pores in the Pt-Pd-BEA150 zeolite according to the invention than in comparative example 1. Furthermore, in the case of comparative example 1, at 1900 cm.sup.1 there is an absorption band that can be masked virtually completely by adamantanecarbonitrile addition and which is not present in the Pt-Pd-BEA150 zeolite according to the invention.

(16) Also in the case of more highly charged (supercharged) PtPd-BEA150/Ar zeolites, the 1900 cm.sup.1 band can arise, for example at 1.13% Pt and 3.4% Pd, but not at 0.92% Pt/2.8% Pd. However, the former material exhibits a considerably lower performance in the alkane oxidation.

(17) Table 2 shows the catalyst sample produced therefrom (including comparison sample). FIGS. 4a-c and 5a, 5b summarize the performance data obtained, measured in the simultaneous oxidation of 800 ppmv CO, 1000 ppmv methane, 360 ppmv ethane, 200 ppmv ethylene and 180 ppmv propane in a carrier gas consisting of 10% oxygen and 3% water in nitrogen. The measurements were carried out at a GHSV of 40 000 h.sup.1. The catalyst samples were then tested again in the oxidation of 200 ppmv ethyl acetate in air at a GHSV of 40 000 h.sup.1. The aging was carried out with the samples of the fresh test, these were treated for 24 h at 650 C. in a muffle furnace and then tested again. For the thionation, fresh samples were exposed to a mixture of 100 ppm SO.sub.2, 250 ppm C.sub.3H.sub.8 and 5% H.sub.2O in air for 125 h at 500 C. The activity loss of EnviCat 50300 in the alkane oxidation is typically about 60-75% under these conditions.

(18) TABLE-US-00002 TABLE 2 Produced PtPd-BEA150 zeolite catalyst samples (step 2) and comparison samples Honeycomb Pt Pd number [% by weight] [% by weight] PtPd-BEA150 - 1 0.13 0.39 formulation according to 2 0.37 1.11 the invention and catalyst PtPd-BEA150 - 1 0.17 0.49 comparative example 1 2 0.70 2.1 Comparative example 2 1 0.35 1.05 (EnviCat 50300) 2 0.62 1.85

(19) The data shown in FIGS. 4a, 4b and 5a, 5b show that the catalyst honeycombs based on the formulation according to the invention have a performance in the alkane oxidation that is considerably increased compared to comparative example 2 (Envicat 50300), with a comparable conversion level being achieved in the case of the formulation according to the invention with only half of the precious metal content compared to Envicat 50300. This is true for fresh, aged and sulfur-poisoned catalyst samples. Comparative example 1, by contrast, exhibits barely any significant activity. As can be seen in FIGS. 6a and 6b, the advantages of the catalysts according to the invention are also given in the oxidation of ethyl acetate. In the case of the oxidation of ethylene, catalysts according to the invention and comparison catalysts exhibit an approximately identical performance.