Copper containing MOZ zeolite for selective NOx reduction catalysis

Abstract

The present invention relates to crystalline aluminosilicate comprising a MOZ framework type material. The MOZ framework type material comprises between 0.1 and 12.5 wt-% of copper, calculated as CuO, and one or more alkali and alkaline earth metal cations in an amount of 0.3 to 9 wt.-%, calculated as pure metals. The process for making the copper containing MOZ type zeolites comprises a) preparing a first aqueous reaction mixture comprising a silica source and potassium hydroxide, b) preparing a second reaction mixture comprising an alumina source, potassium hydroxide and a structure-directing agent selected from N,N-1,4-dimethyl-1,4-diazabicyclo-[2.2.2]octane difluoride, dichloride, dibromide, diiodide or dihydroxide, c) combining the two aqueous reaction mixtures, d) aging the combined reaction mixtures, e) heating the combined reaction mixtures, e) recovering, washing and drying the zeolite obtained thereof, g) calcining the zeolite, f) introducing copper, and i) washing and drying the copper containing MOZ type zeolite. Furthermore, the present invention discloses a washcoat comprising the copper containing MOZ framework type material, an SCR catalyst comprising said copper containing MOZ framework type material, and an exhaust gas purification system containing said SCR catalyst.

Claims

1. Crystalline aluminosilicate zeolites consisting of a framework in which the tetravalent element is silicon and said framework comprises a MOZ framework type, wherein the MOZ framework type contains 3 to 5 wt.-% copper, calculated as CuO and based on the total weight of the respective zeolite.

2. Crystalline aluminosilicate zeolites according to claim 1, wherein the silica to alumina molar ratio ranges from 5 to 30.

3. Crystalline aluminosilicate zeolites according to claim 1, wherein the copper to aluminium atomic ratio is in the range of between 0.003 to 0.5.

4. Crystalline aluminosilicate zeolites according to claim 1, wherein the zeolites comprise one or more cations selected from the group consisting of ammonium, and cations of at least one alkali or alkaline earth metal selected from lithium, sodium, potassium rubidium, cesium, ammonium, magnesium, calcium, strontium, and barium in an amount of 0.3 to 9 wt.-%, calculated as pure metals and based on the total weight of the zeolites.

5. Crystalline aluminosilicate zeolites according to claim 1, wherein the MOZ framework type is ZSM-10.

6. A process for making the crystalline aluminosilicate zeolites according to claim 1, comprising the following steps: a) preparing a first aqueous reaction mixture comprising a silica source and potassium hydroxide, b) preparing a second aqueous reaction mixture comprising potassium hydroxide, an alumina source, a structure-directing agent selected from N,N′-1,4-dimethyl-1,4-diazoniabicyclo-[2.2.2]octane difluoride, N,N′-1,4-dimethyl-1,4-diazoniabicyclo-[2.2.2]octane dichloride, N,N-′1,4-dimethyl-1,4-diazoniabicyclo-[2.2.2]octane dibromide, N,N′-1,4-dimethyl-1,4-diazoniabicyclo-[2.2.2]octane diiodide, N,N′-1,4-dimethyl-1,4-diazoniabicyclo-[2.2.2]octane dihydroxide and mixtures thereof, c) combining the two aqueous reaction mixtures, d) aging the reaction mixture obtained in step c), e) heating the mixture, f) recovering, washing and drying the zeolite obtained in step e), g) calcining the zeolite, h) introducing of Cu, i) washing and drying the copper containing zeolite obtained in step h).

7. A process for making the crystalline aluminosilicate zeolites according to claim 6, wherein the second aqueous reaction mixture comprises 1.5 to 5 wt.-% of aluminium, calculated as pure aluminium metal per weight of the alkali or alkaline earth metal hydroxide solution.

8. A process for making the crystalline aluminosilicate zeolites according to claim 6, wherein the structure-directing agent is selected from N,N′-1,4-dimethyl-1,4-diazoniabicyclo-[2.2.2]octane diiodide, N,N′-1,4-dimethyl-1,4-diazoniabicyclo-[2.2.2]octane dihydroxide and mixtures thereof.

9. A process for making the crystalline aluminosilicate zeolites according to claim 6, wherein the structure-directing agent is used in a concentration of 0.3 to 0.6 mole per mole of the aluminium source.

10. A process for making the crystalline aluminosilicate zeolites according to claim 6, wherein the calcination in step g) is carried out at temperatures between 500 and 600° C.

11. A process for making the crystalline aluminosilicate zeolites according to claim 6, wherein the introduction of copper in step h) is carried out by performing an NH.sub.4.sup.+liquid ion exchange first, followed by a Cu.sub.2.sup.+liquid ion exchange, incipient wetness impregnation or solid state exchange of Cu.

12. A coating suspension comprising a crystalline aluminosilicate zeolite according to claim 1.

13. A method of selective catalytic reduction of nitrogen oxides, which comprises contacting the nitrogen oxides with a reductant in the presence of a crystalline aluminosilicate zeolite according to claim 1.

14. An SCR catalyst comprising a crystalline aluminosilicate zeolite according to claim 1.

15. An SCR catalyst comprising the coating suspension according to claim 12.

16. An exhaust gas purification system containing an SCR catalyst according to claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the graphical representation of the NO.sub.x conversion test performed in Embodiment 6.

(2) FIG. 2 shows the graphical representation of the NO.sub.x conversion test performed in Embodiment 7.

(3) FIG. 3a shows the SEM image of embodiment 3 at a HFW of 1.87 μm and a magnification of 159,930×.

(4) FIG. 3 b shows the SEM image of embodiment 3 at a HFW of 59.7 μm and a magnification of 5,000×.

EMBODIMENTS

Synthesis of N,N′-1,4-Dimethyl-1,4-diazoniabicyclo-[2.2.2]octane diiode

(5) 9.3 mL (0.15 mol) of iodomethane (Sigma-Aldrich) was added dropwise under reflux conditions to a solution containing 8.415 g (0.075 mol) 1,4-Diazabicyclo[2.2.2]octane (DABCO, Sigma-Aldrich), 300 mL of ethanol and 37.5 mL of H.sub.2O. The mixture was left to react under reflux conditions for 2 hours, and then allowed to cool for slow crystallization. This process was improved by further cooling the mixture at lower temperatures (4° C.). The crystals were recovered by filtration and washed with 30 mL of ethanol. The N,N′-1,4-dimethyl-1,4-diazoniabicyclo-[2.2.2]octane diiode thus obtained is hereinafter referred to as diquat diiodide.

Ion exchange of N,N′-1,4-Dimethyl-1,4-diazoniabicyclo-[2.2.2]octane diiode

(6) The 1,4-Dimethyl-1,4-diazoniabicyclo-[2.2.2]octane diiode obtained above was ion-exchanged in batch to the hydroxide form with Amberlite IRA 402 resin (Alfa Aesar). The 1,4-Dimethyl-1,4-diazoniabicyclo-[2.2.2]octane dihydroxide is hereinafter referred to as diquat dihydroxide.

Embodiment 1

(7) A first solution was prepared by dissolving 7 g KOH solution (50 wt % KOH) in 47 g of H.sub.2O. 9.2 g SiO.sub.2 (Hi-sil 233, PPG) was added to the solution, that was stirred until it was clear.

(8) A second solution was prepared by dissolving 3.3 g of diquat diiodide in 25.6 g H.sub.2O. To this solution, 7.2 g of a solution (97 g/L Al, 284 g/L K) of boehmite (PLURAL SB-1 UHPA) in KOH was added.

(9) Solution 2 was slowly added to solution 1, and stirred for 30 minutes. The gel composition was: 14.7 SiO.sub.2: 1 Al.sub.2O.sub.3: 10.3 KOH: 0.85 diquat diiodide: 450 H.sub.2O.

(10) The gel was aged for 3 days at room temperature. Next the gel was transferred into a Teflon liner and autoclave and heated to 150° C. in 48 hours with end-over-end rotation, and kept at 150° C. for 5 days.

(11) The obtained zeolite was recovered and washed by centrifugation and dried at 65° C. overnight.

(12) The as prepared zeolite had a molar composition of SiO.sub.2:Al.sub.2O.sub.3:K.sub.2O:Na.sub.2O of 7.20:1:0.8:0.02.

Embodiment 2

(13) A first solution is prepared by mixing 4.93 g of KOH and 48.4 mL of H.sub.2O. To this solution, 8.8 g of Cab-O-Sil M5 is added slowly and the mixture was stirred for 3.5 hours in a closed bottle.

(14) A second solution is made by mixing 1.98 g KOH and 15.4 mL of H.sub.2O. To this solution, 0.54 g of aluminium powder is added slowly and the mixture was stirred for 3.5 hours. Afterwards 3.35 g diquat diiodide was dissolved in 17 g H.sub.2O, and then added to the aluminium suspension. This mixture was stirred for 30 minutes.

(15) The aluminium/diquat diiodide suspension is added slowly to the first solution and stirred for 30 minutes until a homogeneous mixture is obtained. This mixture is then aged for 3 days at room temperature. The final molar oxide ratio from the synthesis gel is 14.7 SiO.sub.2:Al.sub.2O.sub.3:0.85 diquat diiodide:12.3 KOH:448 H.sub.2O. Afterwards the mixture is transferred to a stainless steel autoclave and heated at 110° C. for 13 days with a temperature ramp of 1° C./min under static conditions. The obtained zeolite was recovered and washed by centrifugation and dried at 65° C. overnight. The as prepared zeolite was calcined at 550° C. for 8 hours with a temperature ramp of 1° C./min.

(16) Afterwards, the calcined zeolite was subjected to an ammonium and copper exchange as described above. The final zeolite had a molar composition of SiO.sub.2:Al.sub.2O.sub.3:K.sub.2O:CuO of 7.28:1:0.26:0.28.

Embodiment 3

(17) A first solution is prepared by mixing 2 g of KOH and 24 mL of H.sub.2O. To this solution, 4.6 g of Cab-O-Sil M5 is added slowly and the mixture was stirred for 3.5 hours in a closed bottle.

(18) A second solution is made by mixing 1 g KOH and 8 mL of H.sub.2O. To this solution, 0.27 g of aluminium powder is added slowly and the mixture was stirred for 3.5 hours. Afterwards, 8.7 mL diquat dihydroxide (1.2 N) was added to the aluminium suspension. This mixture was stirred for 30 minutes.

(19) The aluminium/diquat dihydroxide suspension is added slowly to the first solution and stirred for 30 minutes until a homogeneous mixture is obtained. This mixture is then aged for 3 days at room temperature. The final molar oxide ratio from the synthesis gel is 15.3 SiO.sub.2:Al.sub.2O.sub.3: 1.03 diquat dihydroxide:10.7 KOH:450 H.sub.2O. Afterwards the mixture is transferred to a stainless steel autoclave and heated at 88° C. for 94 days under dynamic conditions. The obtained zeolite was recovered and washed by centrifugation and dried at 65° C. overnight. The as prepared zeolite was calcined at 550° C. for 8 hours with a temperature ramp of 1° C./min.

(20) Afterwards, the calcined zeolite was subjected to an ammonium and copper exchange as described above. The final zeolite had a molar composition of SiO.sub.2:Al.sub.2O.sub.3:K.sub.2O:CuO of 7.69:1:0.26:0.30.

(21) Scanning Electron Microscopy (SEM) images were recorded on a Nova NanoSEM450 (FEI). Samples were prepared by dispersing the zeolite powders on carbon sticker and measured without conductive coating. Samples were imaged at low landing voltage of 1.00 kV using a circular backscattered detector.

(22) Two SEM images were recorded. The first one was recorded at an HFM (horizontal field width) of 1.87 μm and a magnification of 159,930×. The second one was recorded at an HFM of 59.7 μm and a magnification of 5,000×. The first SEM image is shown in FIG. 3a and the second one in FIG. 3b.

(23) SEM revealed the material to be micrometer sized aggregates composed of nanocrystallites of ca. 30-70 nm.

Embodiment 4

(24) A solution of 500 mL distilled H.sub.2O and 13.4 g NH.sub.4Cl (MP Biomedicals LLC) was prepared in a 1000 mL round bottom flask (0.5 M NH.sub.4Cl solution). 5 grams of the material obtained in embodiment 2 is added to this solution. The suspension is then heated under reflux conditions for 4 hours upon stirring. Afterwards, the zeolite in its ammonium form is recovered by centrifugation, washed with distilled water and dried at 60° C. for 24 hours.

Embodiment 5

(25) A solution of 500 mL distilled water and 0.47 g copper acetate (Sigma-Aldrich) was prepared in a PP bottle. 5 grams of the material obtained in embodiment 4 is added to this solution. The suspension is stirred at room temperature in a closed PP bottle for 20 hours. Afterwards, the zeolite in its copper exchanged form is recovered by centrifugation. This procedure is repeated twice. The final material is then washed with distilled water by centrifugation and dried at 60° C. for 48 hours. The Cu-containing MOZ-type zeolite has a copper oxide content of 3.24 wt.-%, and is based on the total weight of the zeolite.

(26) The final zeolite had a molar composition of SiO.sub.2:Al.sub.2O.sub.3:K.sub.2O:CuO of 7.28:1:0.26:0.28.

Embodiment 6

(27) Catalyst pellets consisting of compressed zeolite powder obtained in Embodiment 5 are loaded in a quartz fixed bed tubular continuous flow reactor with on-line reaction product analysis. The catalyst first undergoes a pretreatment under simulated air flow conditions, i.e. 5% 02 and 95% N.sub.2, at 450° C., the highest temperature of the catalytic testing. After pretreatment, the catalyst temperature is decreased to 150° C. A typical gas composition for NH.sub.3—SCR performance evaluation consists of 500 ppm NO, 450 ppm NH.sub.3, 5% O.sub.2, 2% CO.sub.2, 2.2% H.sub.2O. The gas hourly space velocity (GHSV) will be fixed at 30 000 h.sup.−1, obtained with 0.5 cm.sup.3 catalyst bed and a gas flow of 250 mL/min. The temperature will be stepwise increased from 150 to 450° C. with fixed temperature ramps, and 50° C. intervals. Isothermal periods of 60 to 120 minutes are foreseen before reaction product sampling at each temperature plateau. A return point to 150° C. enables detection of degradation of catalytic performance during the testing.

(28) The results are shown in FIG. 1.

(29) Table 1 shows the NO.sub.x conversion for each temperature measured.

(30) TABLE-US-00001 TABLE 1 NO.sub.x conversion of the zeolite powder obtained in Embodiment 5. The gas composition consisted of 500 ppm NO, 450 ppm NH.sub.3, 5% O.sub.2, 2% CO.sub.2, 2.2% H.sub.2O, and the gas hourly space velocity (GHSV) was fixed at 30 000 h.sup.−1, obtained with 0.5 cm.sup.3 catalyst bed and a gas flow of 250 mL/min. The bottom row of the table shows the NO.sub.x conversion at the return point of 150° C. The bottom row demonstrates that there was no degradation of catalytic performance during the testing as the NO.sub.x conversion did not decrease in comparison to the start. The start was also at 150° C., see top row, and the NO.sub.x conversion rates at the start and at the end (top and bottom row) were almost identical. Temperature (° C.) NO.sub.x conversion (%) 150 66.6 175 93.3 200 100.0 250 100.0 300 96.6 350 85.8 400 85.6 450 86.0 150 67.9

Embodiment 7

(31) A solution of 500 mL distilled H.sub.2O and 13.4 g NH.sub.4Cl (MP Biomedicals LLC) was prepared in a 1000 mL round bottom flask (0.5 M NH.sub.4Cl solution). 5 grams of the material obtained in embodiment 1 is added to this solution. The suspension is stirred and heated under reflux conditions for 4 hours. The zeolite is recovered and this procedure is repeated twice. Afterwards, the zeolite in its ammonium form is recovered by centrifugation, washed with distilled water and dried at 60° C. for 24 hours.

(32) The ammonium exchanged material is loaded with different amounts of copper via liquid ion exchange using different concentrations of aqueous copper acetate solutions. The ammonium exchanged material was divided into four aliquots of 1 gram and suspended in solutions of 0.031, 0.094, 0.188 and 0.283 g copper acetate (Sigma-Aldrich) dissolved in 100 mL of distilled water. The suspensions are stirred at room temperature in a closed PP bottle for 20 hours. Afterwards, the zeolite in its copper exchanged form is recovered by centrifugation. This copper exchange procedure is repeated for the materials exchanged with the three highest copper acetate concentrations. The final materials are recovered and washed with distilled water by centrifugation and dried at 60° C. for 48 hours. The four Cu-exchanged zeolites have a copper oxide content, based on the total weight of the zeolite, of 1.3 wt.-%, 3.3 wt.-%, 4.0 wt-%, 4.4 wt.-%, increasing accordingly with concentration of copper acetate in the exchange solutions.

(33) Zeolites were converted into catalyst pellets and tested for NH.sub.3-SCR according to the procedure in Embodiment 6. Table 2 shows NO.sub.x conversion for the respective zeolites in function of temperature.

(34) The results are shown in FIG. 2.

(35) TABLE-US-00002 TABLE 2 NO.sub.x conversion of the zeolite powders obtained in Embodiment 7. The gas composition consisted of 500 ppm NO, 450 ppm NH.sub.3, 5% O.sub.2, 2% CO.sub.2, 2.2% H.sub.2O, and the gas hourly space velocity (GHSV) was fixed at 30 000 h.sup.−1, obtained with 0.5 cm.sup.3 catalyst bed and a gas flow of 250 mL/min. The bottom row of the table shows the NO.sub.x conversion at the return point of 150° C. The bottom row demonstrates that there was no degradation of catalytic performance during the testing as the NO.sub.x conversion did not decrease in comparison to the start. The start was also at 150° C., see top row in FIG. 2, and the NO.sub.x conversion rates at the start and at the end (top and bottom row in FIG. 2) were almost identical. NO.sub.x conversion (%) Temperature 1.3 wt.-% 3.3 wt.-% 4.0 wt.-% 4.4 wt.-% (° C.) CuO CuO CuO CuO 150 29.4 60.5 64.0 68.2 175 57.2 91.7 94.6 95.5 200 81.4 94.7 95.4 94.0 250 94.8 96.6 94.1 84.9 300 89.1 81.1 82.2 81.7 350 70.6 79.1 80.3 82.0 400 72.7 80.3 80.5 79.7 450 72.2 78.5 79.4 78.4 150 30.2 58.6 60.0 65.8