Catalysator element comprised of a mixed metal oxide hydrotalcite-like compound

Abstract

A catalysator element comprising a mixed metal oxide compound for conversion of nitrogen oxides (NO.sub.x). Methods for the preparation of the present mixed metal oxide compound for use in the present catalysator element and to exhaust systems for a combustion engine comprising the present catalysator element for conversion of (NO.sub.x) in exhaust gasses. Specifically, a catalysator element for conversion of nitrogen oxides (NOx) comprises a solid support coated with a calcined mixed metal oxide hydrotalcite-like compound. The calcined mixed metal oxide hydrotalcite-like compound comprises at least one bivalent metal (M.sup.2+) and at least one trivalent metal (M.sup.3+).

Claims

1. A catalysator element, comprising: a solid support coated with a calcined mixed metal oxide hydrotalcite-like compound, wherein said calcined mixed metal oxide hydrotalcite-like compound comprises at least one bivalent metal (M.sup.2+) and at least one trivalent metal (M.sup.3+), and wherein: said at least one bivalent metal (M.sup.2+) is selected from the group consisting of Co.sup.2+, Cu.sup.2+, Fe.sup.2+, Mn.sup.2+, Zn.sup.2+, Ni.sup.2+, Ag.sup.2+, Ca.sup.2+, Pt.sup.2+; Pd.sup.2+; Cd.sup.2+; Mo.sup.2+; W.sup.2+; Ru.sup.2+; Sr.sup.2+; Ba.sup.2+; Nd.sup.2+ and mixtures thereof, and wherein said at least one trivalent metal (M.sup.3+) is selected from the group consisting of Ce.sup.3+, Al.sup.3+, Mn.sup.3+, Fe.sup.3+, Hf.sup.3+, Co.sup.3+, V.sup.3+, Ti.sup.3+, Zr.sup.3+, Y.sup.3+, La.sup.3+ and Pr.sup.3+ and mixtures thereof; or wherein said at least one trivalent metal (M.sup.3+) in combination with Al.sup.3+ is selected from the group consisting of Ce.sup.3+, Mn.sup.3+, Fe.sup.3+, Hf.sup.3+, Co.sup.3+, V.sup.3+, Ti.sup.3+, Zr.sup.3+, Y.sup.3+, La.sup.3+ and Pr.sup.3+ and mixtures thereof; and wherein said catalysator element provides conversion of isocyanic acid to NH.sub.3 via at least one of hydrolysis and conversion of urea to NH.sub.3.

2. The catalysator element according to claim 1, wherein at least one bivalent metal (M.sup.2+) and said at least one trivalent metal (M.sup.3+) are selected from the group of non-stoichiometric combinations consisting of CoAlCe; CoAlMn; CoAlFe; CoAlCo; CoAlV; CoAlTi; CoAlHf; CoAlPr; CoAlLa; CuAlCe; FeAlCe; ZnAlCe; NiAlCe; AgAlCe; CaAlCe; PtAlCe; PdAlCe; CdAlCe; MoAlCe; WAlCe; RuAlCe; SrAlCe; BaAlCe; NdAlCe; CuAlMn; FeAlMn; ZnAlMn; NiAlMn; AgAlMn; CaAlMn; PtAlMn; PdAlMn; CdAlMn; MoAlMn; WAlMn; RuAlMn; SrAlMn; BaAlMn; NdAlMn; CuAlFe; FeAlFe; ZnAlFe; NiAlCe; AgAlCe; CaAlCe; PtAlCe; PdAlCe; CdAlCe; MoAlCe; WAlCe; RuAlCe; SrAlCe; BaAlCe; NdAlCe; CuAlCo; FeAlCo; ZnAlCo; NiAlCo; AgAlCo; CaAlCo; PtAlCo; PdAlCo; CdAlCo; MoAlCo; WAlCo; RuAlCo; SrAlCo; BaAlCo; NdAlCo; CuAlV; FeAlV; ZnAlV; NiAlV; AgAlV; CaAlV; PtAlV; PdAlV; CdAlV; MoAlV; WAlV; RuAlV; SrAlV; BaAlV; NdAlV; CuAlTi; FeAlTi; ZnAlTi; NiAlTi; AgAlTi; CaAlTi; PtAlTi; PdAlTi; CdAlTi; MoAlTi; WAlTi; RuAlTi; SrAlTi; BaAlTi; NdAlTi; CuAlHf; FeAlHf; ZnAlHf; NiAlHf; AgAlHf; CaAlHf; PtAlHf; PdAlHf; CdAlHf; MoAlHf; WAlHf; RuAlHf; SrAlHf; BaAlHf; NdAlHf; CuAlPr; FeAlPr; ZnAlPr; NiAlPr; AgAlPr; CaAlPr; PtAlPr; PdAlPr; CdAlPr; MoAlPr; WAlPr; RuAlPr; SrAlPr; BaAlPr; NdAlPr; CuAlLa; FeAlLa; ZnAlLa; NiAlLa; AgAlLa; CaAlLa; PtAlLa; PdAlLa; CdAlLa; MoAlLa; WAlLa; RuAlLa; SrAlLa; BaAlLa; and NdAlLa.

3. The catalysator element according to claim 2, wherein at least one bivalent metal (M.sup.2+) and said at least one trivalent metal (M.sup.3+) are selected from the group of combinations consisting of CoAlCe; CoAlMn; CoAlFe; CoAlCo; CoAlV; CoAlTi; CoAlPr; CoAlLa; CuAlCe; FeAlCe; ZnAlCe; NiAlCe; AgAlCe; CaAlCe; PtAlCe; PdAlCe; CdAlCe; MoAlCe; RuAlCe; SrAlCe; BaAlCe; NdAlCe; PdAlMn; RuAlMn; CdAlCe; MoAlCe; WAlCe; RuAlCe; CuAlCo; FeAlCo; ZnAlCo; NiAlCo; CdAlCo; MoAlCo; WAlCo; RuAlCo; NdAlCo; CuAlPr; FeAlPr; NiAlPr; AgAlPr; CaAlPr; CdAlPr; CuAlLa; FeAlLa; NiAlLa; AgAlLa; CaAlLa; CdAlLa; MoAlLa; WAlLa; SrAlLa; BaAlLa; and NdAlLa.

4. The catalysator element according to claim 1, wherein said calcined mixed metal oxide hydrotalcite-like compound is obtained by calcining a mixed metal oxide hydrotalcite-like compound comprising at least one bivalent metal (M.sup.2+) and at least one trivalent metal (M.sup.3+) at a temperature of between 200° C. to 600° C., for at least 1 hour.

5. The catalysator element according to claim 1 wherein said solid support is a metallic support or a ceramic support either zone coated or fully coated.

6. The catalysator element according to claim 1, wherein said catalysator element is comprised in an exhaust system of a combustion engine or said catalysator element is comprised in a system that guides exhaust gases of a combustion engine.

7. The catalysator element according to claim 1, wherein said calcined mixed metal oxide hydrotalcite-like compound has a catalytic surface area of at least 80 m.sup.2/g.

8. The catalysator element according to claim 1, wherein said calcined mixed metal oxide hydrotalcite-like compound has an average pore diameter of at least 4 nm.

9. The catalysator element according to claim 1, wherein said at least one bivalent metal (M.sup.2+) has an atomic radius ranging from 0.3 {acute over (Å)} to 1.05 {acute over (Å)}, and wherein said at least one trivalent metal (M.sup.3+) has an atomic radius ranging from 0.5 {acute over (Å)} to 1.1 {acute over (Å)}.

10. The catalysator element according to claim 1, wherein said calcined mixed metal oxide hydrotalcite-like compound has an urea to NH.sub.3 conversion rate of at least 50% at a temperature below 125° C.

11. The catalysator element according to claim 1, wherein said calcined mixed metal oxide hydrotalcite-like compound has a total metal wt % ratio of M.sup.2+ to M.sup.3+ of between 0.05 and 0.8.

12. The catalysator element according to claim 1, wherein said calcined mixed metal oxide hydrotalcite-like compound is comprised of a total metal wt % between 50 to 90 wt % of Co.sup.2+, between 4 to 30 wt % of Ce.sup.3+ and between 2 to 30 wt % of Al.sup.3+.

13. The catalysator element according to claim 1, wherein said calcined mixed metal oxide hydrotalcite-like compound is Co.sub.6Ce.sub.0.8Al.sub.1.2O.sub.9.

14. The catalysator element according to claim 1 wherein said solid support is selected from the list consisting of metal wiremesh, corrugated metal plates forming a metal substrate, ceramic mixers or other ceramic components guiding or influencing the flow, ceramic substrates, and substrates for SCR, SCRF or DPNR.

15. A method for the preparation of a calcined mixed metal oxide hydrotalcite-like compound according to claim 1, wherein the method comprises; a) mixing of at least one bivalent metal nitrite (M.sup.2+(NO.sub.3).sub.x) with at least one trivalent metal nitrite (M.sup.3+(NO.sub.3).sub.x) in an ammonium carbonate solution (NH.sub.4CO.sub.3), b) precipitating a mixed metal oxide hydrotalcite-like compound from the mixture, c) recovering the mixed metal oxide hydrotalcite-like compound by drying, and calcining the dried mixed metal oxide hydrotalcite-like compound at between 200° C. to 600° C., for at least 1 hour.

16. The method according to claim 15, wherein the calcined mixed metal oxide hydrotalcite-like compound is Co.sub.6Ce.sub.0.8Al.sub.1.2O.sub.9.

17. A calcined mixed metal oxide hydrotalcite-like compound obtainable by a method according to claim 15.

18. An exhaust system for a combustion engine or a system that guides exhaust gases of a combustion engine comprising a catalysator element according to claim 1.

19. A method for conversion of nitrogen oxides (NOx) in exhaust gasses comprising contacting said exhaust gasses with a catalysator element according to claim 1 during a sufficient time for allowing catalytic conversion of nitrogen oxides (NOx) comprising contacting urea with the catalysator element to generate NH.sub.3, followed by reduction of NOx with NH.sub.3 over a SCR catalysator element.

20. A method for prevention of the formation of deposits including cyanuric acid downstream of an SCR catalyst or an SCRF catalyst including in the EGR system comprising contacting isocyanic acid with a catalysator element according to claim 1 thereby preventing the formation of cyanuric acid.

21. Method for conversion of urea (NH.sub.2).sub.2CO) into ammonia (NH.sub.3) comprising contacting said urea with a catalysator element according to claim 1 during a sufficient time for allowing catalytic conversion of urea into ammonia.

22. Method of decomposing urea deposits in an exhaust system by contacting the deposits with a catalysator element according to claim 1 and by increasing the temperature over 140° C.

Description

(1) The present invention will be further detailed in the following examples and figures wherein:

(2) FIG. 1: shows that the impact of exposure to high temperatures is beneficial;

(3) FIG. 2: shows urea conversion experiments of materials produced via incipient wetness impregnation;

(4) FIG. 3: shows urea conversion experiments of materials produced via hydrotalcite method;

(5) FIG. 4: shows decomposition of cyanuric acid with a series of catalysts;

(6) FIG. 5: shows a comparison between ureum conversion following adblue injection at temperatures between 140° and 340° C. over a cordierite core (light green line) and lotus (Co.sub.6Ce.sub.0.8Al.sub.1.2O.sub.9) coated cordierite core (black line).

EXAMPLES

Example 1: Preparation of Co.SUB.6.Ce.SUB.0.8.Al.SUB.1.2.O.SUB.9 .Using the Hydrotalcite Method

(7) Hydrotalcites were prepared by a co-precipitation method by mixing specific amounts of the metal nitrates (i.e. cobalt nitrate, ceria nitrate, alumina nitrate) with a NH.sub.4CO.sub.3 solution at a pH of 10.5. Metal nitrates were mixed at 60° C. The precipitate was recovered and dried at 110° C. for 24 hours. The resulting material is a cobalt ceria alumina hydrotalcites like compound (laminar hydroxides). The catalytic surface area of the produced cobalt ceria alumina hydrotalcites like compound was 80 m.sup.2/g.

(8) After drying, the cobalt ceria aluminium hydrotalcites are placed in a furnace at 400 to 500° C. (calcined) for 5 hours to decompose the lamellar, hydrotalcite structure and allow the departure of the CO.sub.3.sup.2− and NO.sup.3− anions creating a stable metal oxide compound, Co.sub.6Ce.sub.0.8Al.sub.1.2O.sub.9. This compound had a particle size of 8.6 {acute over (Å)} as measured by X Ray Diffraction (using Scherrer equation) and Transmission Electron Microscopy and an average pore diameter of 5.59 nm as measured with N.sub.2 BET. Furthermore, the catalytic surface area was increased to approximately 120 m.sup.2/g, due to escaping gases which create porosity in the compound structure.

(9) Surprisingly, results furthermore show that additional calcining the materials at 900° C. for 12 hours only had a minor impact on catalytic surface area decreasing it about 84 m.sup.2/g in dry atmosphere and 75 m.sup.2/g in presence of water from 123 m.sup.2/g recorded on materials calcined at 500° C.

(10) This is an indication that the materials should be able to survive high temperature exposure observed even during DPF uncontrolled regeneration.

(11) TABLE-US-00001 TABLE 1 Physical characteristics of powders exposed to high temperatures in presence and absence of water versus samples calcined at 500° C. Pore S.sub.BET Volume Average pore Sample name (m.sup.2/g) (cm.sup.3/g) diameter (nm) CoAlCeHT calcined at 500° C. 123 0.62 5.6 CoAlCeHT calcined at 900° C. 84 0.56 27.2 CoAlCeHTcalcined at 900° C. 78 0.48 33.3 with H.sub.2O

Example 2

(12) Referring to FIG. 4, uncatalysed decomposition occurs over 270° C., a temperature much higher than the one that can be generated in LP EGR conditions. Equipment: in situ DRIFTS+MS, Test condition: 50 mg catalyst, 10 mg cyanuric acid impregnated at RT, Temperature ramped from 50-400° C. with 2 degr/min in a flow of 20 mL/min of 10% O2/Ar, According the T.sub.50: Co6Al1.2Ce0.8Ox>20 wt % CoOx 6 wt % CeOx/Al2O3>ZrO2>TiO2

Example 3

(13) Referring to FIG. 5, experimental conditions: 158 kg/h exhaust flow, adblue injection 820 g/h, dosing frequency: 4 Hz, Duty cycle 25%, dosing time: 300 s. The experiment starts with adblue injection=0 g/h for 300 s followed by adblue injection for 300 s. Temperature was generated using a Leister electric furnace 32 Kw, adblue injection was generated using a DeNOxtronic 3.0 (Bosch).