Stable CHA Zeolites

Abstract

The present invention provides hydrothermally stable crystalline aluminosilicate zeolites with a CHA framework type, wherein the zeolite has a total proton content of less than 2 mmol per gram. The zeolite may comprise 0.1 to 10 wt.-% of at least one transition metal, calculated as the respective oxide and based on the total weight of the zeolite. It may furthermore comprise at least one alkali or alkaline earth metal in a concentration of 0 to 2 wt.-%, calculated as the respective metal and based on the total weight of the zeolite. The invention furthermore provides a one-pot synthesis method for making the alumino-silicate zeolites with a CHA framework type. An aqueous reaction mixture comprising a tetraethylammonium compound, a silica source, at least one alkali or alkaline earth metal hydroxide, a zeolite of the faujasite framework type and Cu-tetraethylenepentamine are mixed, homogenized and heated, and finally, the product is recovered. The novel hydrothermally stable zeolites comprising a CHA framework type are suitable as catalytically active materials for the selective catalytic reduction of nitrogen oxides by reaction with NH.sub.3 as reductant (NH.sub.3-SCR) wherein said hydrothermally stable zeolites are used.

Claims

1. A crystalline aluminosilicate zeolite comprising a CHA framework type, wherein the zeolite has a total proton content of less than 2 mmol per gram.

2. The crystalline aluminosilicate zeolites zeolite comprising a CHA framework according to claim 1, wherein the SAR is between 2 and 60.

3. The crystalline aluminosilicate zeolite comprising a CHA framework according to claim 1, wherein the zeolite comprises at least one transition metal to a concentration of 0.1 to 10 wt.-%, calculated as the respective oxides and based on the total weight of the zeolite.

4. The crystalline aluminosilicate zeolite comprising a CHA framework type according to claim 3, wherein the at least one transition metal is selected from copper, iron, and mixtures thereof.

5. The crystalline aluminosilicate zeolite according comprising a CHA framework type to claim 1, wherein the zeolite comprises at least one alkali and/or alkaline earth metal to a concentration of 0 to 2 wt.-%, calculated as the respective metals and based on the total weight of the zeolite.

6. The crystalline aluminosilicate zeolite comprising a CHA framework type according to claim 5, wherein the at least one alkali or alkaline earth metal is selected from sodium, potassium and mixtures thereof.

7. The crystalline aluminosilicate zeolite comprising a CHA framework type according to claim 1, wherein the transition metal to aluminium atomic ratio is in the range of between 0.003 and 0.5.

8. The crystalline aluminosilicate zeolite comprising a CHA framework type according to claim 1, wherein the mean crystal size is between 0.3 to 7 μm.

9. A process for the manufacture of the crystalline aluminosilicate zeolite according to claim 1, which comprises the following steps: a) preparing an aqueous reaction mixture comprising a tetraethylammonium compound R1-X, wherein R1 is the tetraethylammonium and X is chosen from hydroxide, chloride, bromide, and mixtures thereof, a silica source, at least one compound M(OH).sub.n, wherein M is chosen from lithium, sodium, potassium, rubidium, cesium, ammonium, magnesium, calcium, strontium, and barium, and wherein n is 1 or 2, a zeolite of the faujasite framework type, Cu-tetraethylenepentamien (Cu-TEPA), wherein the aqueous reaction mixture has the following molar composition
SiO.sub.2:a Al.sub.2O.sub.3:b Cu-TEPA:c R1-X:d Me(OH).sub.n:e H.sub.2O, wherein a ranges between 0.01 and 0.08, preferably between 0.04 and 0.045, b ranges between 0.02 and 0.1, preferably between 0.03 and 0.08, c ranges between 0.5 and 1.0, preferably between 0.7 and 0.8, Me(OH).sub.n is an alkali or alkaline earth metal hydroxide, wherein Me is selected from Li, Na, K, Rb, Cs, Ca, Mg, Sr, Ba, and mixtures thereof, n=1 for an alkali metal selected from Li, Na, K, Rb, Cs, n=2 for an alkaline earth metal selected from Ca, Mg, Sr, Ba, and d ranges between 0.1 and 1.4 for n=1, and d ranges between 0.05 and 0.7 for n=2, and the product d*n ranges between 0.1 and 1.2, e ranges between 30 and 70, preferably between 60 and 65, b) homogenizing the aqueous reaction mixture obtained after step a), c) heating the reaction mixture under dynamic conditions, d) recovering the reaction product.

10. The process according to claim 9, wherein the aqueous reaction mixture according to step a) additionally comprises a hexamethonium compound R2-Y, wherein R2 stands for the N,N,N,N′,N′,N′-hexamethylhexane ammonium cation, and Y is chosen from hydroxide, chloride, bromide, and mixtures thereof.

11. The process according to claim 9, wherein the aqueous reaction mixture according to step a) additionally comprises at least one salt AB and/or AB2, wherein the cation A is chosen from lithium, sodium, potassium, rubidium, cesium, ammonium, magnesium, calcium, strontium, and barium, and the anion B is chosen from chloride, bromide, and iodide.

12. The process according to claim 9, wherein the reaction mixture obtained after step b) of the process is aged for 0 to 24 hours at a temperature of 20° C. to 30° C.

13. The process according to claim 9, wherein the zeolite obtained after step d) is subsequently calcined at a temperature of between 400° C. and 850° C. for 4 to 10 hours.

14. A process for the removal of NOx from automotive combustion exhaust gases wherein a zeolite according to claim 1 is used as the SCR catalytically active material for the conversion of NOx.

15. A catalysed substrate monolith comprising an SCR catalytically active material for the conversion of NOx for use in treating automotive combustion exhaust gases, wherein said SCR catalytically active material for the conversion of NOx is a zeolite according to claim 1.

16. The catalysed substrate monolith according to claim 15, wherein the zeolite is present in the form of a washcoat on a carrier substrate.

17. The catalysed substrate monolith according to claim 16, wherein the carrier substrate is a flow-through substrate or a wall-flow filter.

18. The catalysed substrate monolith according to claim 15, wherein the catalysed substrate monolith is an extruded catalysed substrate monolith.

19. An exhaust gas purification system comprising a particulate filter coated with an SCR catalyst, wherein the SCR catalytically active material is a crystalline aluminosilicate zeolite according to claim 1.

20. An exhaust gas purification system comprising a PNA catalyst, wherein the PNA catalytically active material comprises a crystalline aluminosilicate zeolite according to claim 1 and at least one platinum group metal selected from ruthenium, rhodium, palladium, osmium, iridium, platinum,. and mixtures thereof.

21. The exhaust gas purification system according to claim 20, wherein the platinum group metal is palladium, and the palladium is present in a concentration of 0.5 to 5 wt.-%, calculated as Pd and based on the total weight of the zeolite.

22. An exhaust gas purification system comprising an ASC catalyst, wherein the ASC catalytically active material comprises a crystalline aluminosilicate zeolite according to claim 1 and at least one platinum group metal selected from ruthenium, rhodium, palladium, osmium, iridium, platinum and mixtures thereof.

23. The exhaust gas purification system according to claim 22, wherein the platinum group metal is platinum, and the platinum is added in the form of a precursor salt to a washcoat slurry and applied to the carrier monolith, and the platinum is present in a concentration of 0.1 to 1 wt.-%, calculated as Pt and based on the total weight of the washcoat loading.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0203] The FIGS. 1 to 7 show SEM images of the embodiments. The following abbreviations are used:

[0204] HV=high vacuum

[0205] CBS=concentric backscatter detector

[0206] WD=working distance

[0207] mag=magnification

[0208] HFW=horizontal field width

[0209] In all embodiments, a CBS was used as the detector.

[0210] FIG. 1:

[0211] SEM image of embodiment 1: CHA zeolite (GV251)

[0212] HV: 2.00 kV

[0213] WD: 4.6 mm

[0214] Mag: 40 000×

[0215] FIG. 2:

[0216] SEM image of embodiment 2: CHA zeolite (GV280)

[0217] HV: 2.00 kV

[0218] WD: 4.0 mm

[0219] Mag: 30 000×

[0220] HFW: 9.95 μm

[0221] FIG. 3:

[0222] SEM image of embodiment 3: CHA zeolite (GV289)

[0223] HV: 2.00 kV

[0224] WD: 4.8 mm

[0225] Mag: 40 000×

[0226] HFW: 7.46 μm

[0227] FIG. 4:

[0228] SEM image of embodiment 4: CHA zeolite (GV252)

[0229] HV: 2.00 kV

[0230] WD: 4.5 mm

[0231] Mag: 24 000×

[0232] FIG. 5:

[0233] SEM image of embodiment 5: CHA zeolite (GV287)

[0234] HV: 2.00 kV

[0235] WD: 4.7 mm

[0236] Mag: 50 000×

[0237] HFW: 5.97 μm

[0238] FIG. 6:

[0239] SEM image of embodiment 6: CHA zeolite (GV291)

[0240] HV: 2.00 kV

[0241] WD: 4.7 mm

[0242] Mag: 40 000×

[0243] HFW: 7.46 μm

[0244] FIG. 7:

[0245] SEM image of embodiment 7: CHA zeolite (GV292)

[0246] HV: 2.00 kV

[0247] WD: 4.1 mm

[0248] Mag: 50 000×

[0249] HFW: 5.97 μm

EMBODIMENTS

[0250] Synthesis of Cu-Tetraethylenpentamine (Cu-TEPA)

[0251] The Cu-tetraethylenepentamine complex (Cu-TEPA) was synthesized by adding 37.9 g tetraethylenepentamine (0.2 mole, Sigma-Aldrich) to a solution consisting of 50 g CuSO4*5H.sub.2O (0.2 mole, Sigma-Aldrich) in 200 g of H.sub.2O (1 M solution) upon stirring. This solution continued stirring for 2 h at room temperature. The synthesis of Cu-TEPA has also been disclosed in WO 2017/080722 A1.

Embodiment 1

[0252] Synthesis of CHA Zeolite

[0253] 22.73 g tetraethylammonium hydroxide (TEAOH, 35 wt. %, Sigma-Aldrich) was added to a glass beaker. To this solution, 8.51 g Ludox AS-40 (Sigma-Aldrich) was added drop wise upon stirring. Afterwards 3.02 g hexamethonium bromide (R2-Br, Acros), 29.4 g of a 0.21 M potassium chloride solution (LabChem), 30 g of a 1.13 M sodium hydroxide solution (Fisher Scientific), 1.78 g CBV-500 (Zeolyst) and 2.74 g of a 1 M Cu-TEPA solution was added slowly upon stirring. The final gel has the following molar ratios: SiO.sub.2/0.043 Al.sub.2O.sub.3/0.46 NaOH/0.08 KCl/0.037 Cu-TEPA/0.73 TEAOH/0.11 R2-Br/62 H.sub.2O where R is the hexamethonium organic template. The resulting mixture was homogenized by vigorous stirring for 10 minutes and afterwards transferred to a stainless steel autoclave. This mixture was heated for 168 h at 160° C. under dynamic conditions. The solid product was recovered by filtration and washing, and was dried at 60° C. for 16 h.

[0254] The zeolite produced has a CHA framework type with a SAR of 17.2 and contains 3.89 wt.-% CuO based on the total weight of the zeolite. The amount Na and K is 0.87 wt.-% and 0.38 wt.-%, respectively, calculated as pure metals and based on the total weight of the zeolite.

Embodiments 2 to 7

[0255] Various zeolites were synthesized in the same manner as described above for embodiment 1. The syntheses were performed in identical manner with varying compositions of the molar ratios of the final gels.

[0256] The compositions of the final gels and the products obtained are listed in Table 2. SEM images of the embodiments 1 to 7 are shown in FIGS. 1 to 7.

TABLE-US-00003 TABLE 2 Final gel compositions and products obtained in Embodiments 2 to 7. The number refer to the molar ratios of the components. Embodiment SiO.sub.2 Al.sub.2O.sub.3 NaOH NH.sub.4OH KCl Cu-TEPA TEAOH R2-Br H.sub.2O 2 (GV280) 1 0.043 0.46 0 0.08 0.055 0.73 0.11 62 3 (GV289) 1 0.043 0.46 0 0.08 0.074 0.73 0.11 62 4 (GV252) 1 0.043 0.46 0 0 0.037 0.73 0.11 62 5 (GV287) 1 0.043 0.46 0.86 0.08 0.037 0.73 0.11 62 6 (GV291) 1 0.043 0.46 0 0.08 0.037 0.73 0.06 62 7 (GV292) 1 0.043 0.46 0 0.08 0.037 0.73 0 62

Embodiment 8: Post-Synthesis Treatment of CHA Zeolite

[0257] A solution of 500 mL deionized 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 as made material obtained in Embodiment 1 is added to this solution. The suspension is then heated under reflux conditions for 4 hours upon stirring, followed by centrifugation This procedure is performed twice. Afterwards, the zeolite is recovered by centrifugation, washed with deionized water and dried at 60° C. for 24 hours.

[0258] The zeolite was calcined for 5h at 400° C. under a N.sub.2 flow, followed by 16 h at 550° C. under an O.sub.2 flow. Heating was performed with a temperature ramp of 5° C./min.

[0259] A solution of 400 mL deionized H.sub.2O and 10.7 g NH.sub.4Cl (MP Biomedicals LLC) was prepared in a 1000 mL round bottom flask (0.5 M NH.sub.4Cl solution). 4 grams of the calcined material is added to this solution. The suspension is then heated under reflux conditions for 4 hours upon stirring, followed by centrifugation. This procedure is performed three times. Afterwards, the zeolite in its ammonium form is recovered by centrifugation, washed with deionized water and dried at 60° C. for 24 hours.

[0260] A solution of 300 mL distilled water and 0.28 g copper acetate (Sigma-Aldrich) was prepared in a PP bottle. 3 grams of the material in its ammonium form 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 performed two times. The final material is then washed with distilled water by centrifugation and dried at 60° C. for 48 hours.

[0261] The zeolite produced has a SAR of 17.2 and contains 2.77 wt.-% CuO based on the total weight of the zeolite. The amount Na and K is 0.09 wt.-% and 0.004 wt.-%, respectively, calculated as pure metals and based on the total weight of the zeolite.

Embodiment 9: NH.SUB.3.-SCR Performance

[0262] The hydrothermal stability was determined by heating zeolite catalyst pellets to 900° C. in a quartz tube under air flow (2 mL/min) with an absolute humidity of 12 vol. % for 3 h with a heating rate of 5° C./min. Cooling was performed under a 40 mL/min dry nitrogen flow. Prior to this experiment, the powder was pelletized to a particle size between 125 and 250 μm to avoid pressure build-up in the quartz tube.

[0263] Catalyst pellets (125-250 μm) consisting of compressed zeolite powder obtained in Embodiment 8 are loaded in a quartz fixed bed tubular continuous flow reactor with online reaction product analysis. The catalyst first undergoes a pretreatment under simulated air flow conditions, i.e. 5% O.sub.2 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-1, obtained with 0.5 cm3 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.

[0264] The results of the NH.sub.3-SCR performance testing are shown in Tab. 3 and FIG. 1.

TABLE-US-00004 TABLE 3 NH.sub.3-SCR performance testing of the chabazite according to Embodiment 8 Fresh Hydrothermally aged 900° C. Temperature (° C.) NO.sub.x conversion (%) 150 84.0 81.1 175 96.6 95.1 200 96.9 92.2 250 90.0 88.4 300 89.7 88.1 350 89.2 86.7 400 88.0 85.0 450 87.6 82.6 150 84.6 80.7

Embodiment 10: Determination of Proton Content

[0265] The as made zeolite was calcined in air at 550° C. for 8 hours with a heating rate of 1° C./min. Afterwards the calcined zeolite was suspended in a 0.5 M NH.sub.4Cl solution (100 ml per g of sample) and kept under reflux conditions for 4 hours. This procedure is repeated twice and followed by a drying step at 60° C. in air for 16 h. Subsequently, the zeolite is calcined in air at 650° C. for 8 hours with a heating rate of 1° C./min. Finally, the samples were packed in a 4 mm zirconia solid state NMR rotor and dried under vacuum (1 mbar) at 90° C. for 30 min and at 200° C. for 16 h. After flushing with N.sub.2 gas, the rotor was sealed.

[0266] .sup.1H MAS NMR experiments were performed at 295 K on a Bruker Ultrashield Plus 500 MHz spectrometer (static magnetic field of 11.7 T) equipped with a 4 mm H/X/Y magic angle spinning (MAS) solid-state probe. Samples were spun at 10 kHz. .sup.1H spectra were recorded using a π/2 flip angle with a pulse length of 2.95 μs and a repetition delay of 5 s. Adamantane was used as an external secondary reference for the chemical shift referencing to TMS. The .sup.1H spectra were integrated between 20 and −8 ppm (between 2 and −8 ppm) using Bruker Topspin 3.5 software. Absolute quantification of the integrated areas was performed as described in M Houlleberghs, A Hoffmann, D Dom, C E A Kirschhock, F Taulelle, J A Martens and E Breynaert: “Absolute Quantification of Water in Microporous Solids with .sup.1H Magic Angel Spinning NMR and Standard Addition”, Anal Chem 2017, 89, 6940-6943”.

Embodiment 11: Determination of Hydrothermal Stability

[0267] The as made zeolite was calcined in air at 550° C. for 8 hours with a heating rate of 1° C./min. A 0.5 M NH.sub.4Cl solution is made by dissolving 13.4 g NH.sub.4Cl (MP Biomedicals LLC) in 500 mL deionized H.sub.2O. The calcined zeolite is suspended in the 0.5 M NH.sub.4Cl solution (1 g zeolite in 100 mL) and heated under reflux conditions for 4 hours upon stirring, followed by centrifugation. The combination of ion-exchange and centrifugation was performed three times. The solid product was recovered by centrifugation after washing with deionized water and was dried at 60° C. for 24 hours. A solution of 300 mL deionized water and 0.28 g copper acetate (Sigma-Aldrich) was prepared in a PP bottle. 3 grams of the zeolite 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 deionized water by centrifugation and dried at 60° C. for 48 hours. The hydrothermal stability was determined by heating Cu loaded zeolite catalyst pellets to 900° C. in a quartz tube under air flow (2 mL/min) with an absolute humidity of 12 vol. % for 3 h with a heating rate of 5° C./min. Cooling was per-formed under a 40 mL/min dry nitrogen flow. Prior to this experiment, the powder was pelletized to a particle size between 125 and 250 μm to avoid pressure build-up in the quartz tube.

Embodiment 11: Proton Content—Decomposition

[0268] When decomposing the spectrum, the baseline is corrected through a cubic spline interpolation method incorporated in the Topspin 3.5 software. The decomposition is performed using the DmFit Software (Version ‘dmfit/release #20180327’) using Lorentzian curves. The signals fitted between 1 and 2 ppm are defined as silanol species, the signals between 2 and 3.5 ppm are defined as aluminol species or other defect-related sites and the signals between 3.5 and 5 ppm are defined as Brønsted acid sites.

[0269] Absolute quantification of the Si—OH region was ensured with the combination of .sup.1H MAS NMR detection with standard addition of water. The dried spectrum was used to derive the total spectrum surface area and the Si—OH region surface area. The dried sample within the rotor was then hydrated with known amounts of water by adding a known mass of water to the packed rotor and afterwards equilibrating the capped rotor overnight at 333 K to ensure homogeneous distribution of water throughout the sample. A sample-dependent linear correlation function (y=Ax+B) was obtained showing the integrated .sup.1H NMR signals of the (de)hydrated zeolite samples (y) plotted against water addition (x). The absolute Si—OH content can be derived using the slope A and the Si—OH surface area, corrected for sample weight and number of scans. Probe tuning and matching was carried out using a vectorial Network Analyzer to ensure comparable Q factors between the (de)hydrated states as to maximize accuracy and reproducibility when acquiring the linear correlation function for each sample (M Houlleberghs, A Hoffmann, D Dom, C E A Kirschhock, F Taulelle, J A Martens and E Breynaert: “Absolute Quantification of Water in Microporous Solids with .sup.1H Magic Angel Spinning NMR and Standard Addition”, Anal Chem 2017, 89, 6940-6943”).

COMPARATIVE EXAMPLE 1

[0270] A synthesis gel with composition 1 SiO.sub.2:0.035 Al.sub.2O.sub.3:0.3 NaOH:0.025 Cu-TEPA:0.4 TEAOH:15 H.sub.2O was prepared by mixing 15g of CBV-720 with 26.62 g water, 2.38 g NaOH pellets, 33.4 g TEAOH solution (35 wt % in water) and 7 g of a Cu-TEPA solution (4.4 wt % Cu). The gel was stirred at room temperature for 30 minutes, and then heated at 150° C. for 3 days. After washing with water, the product was calcined at 550° C. for 8 hours. The resulting product is phase-pure CHA and has a SAR of 13.2, a Cu-content of 0.28 Cu/Al and a proton content of 2.2. No reflections of CHA are present in the XRD pattern of the product after hydrothermal aging for 3 hours at 900° C. Another part of the product was ion-exchanged to remove all Cu and Na ions from the framework, and then ion-exchanged with Cu-acetate. No reflections of CHA are present in the XRD pattern of the product after hydrothermal aging for 3 hours at 900° C. The product had the form of cubes with a sidelength of 0.3 μm.

COMPARATIVE EXAMPLE 2

[0271] A synthesis gel with composition 1 SiO.sub.2:0.035 Al.sub.2O.sub.3:0.15 NaOH:0.028 Cu-TEPA:0.5 TEAOH:15 H.sub.2O was prepared by mixing 800 g of CBV-720 with 1089 g water, 63.55 g NaOH pellets, 2228 TEAOH solution (35 wt % in water) and 426 g of a Cu-TEPA solution (4.4 wt % Cu). The gel was stirred at room temperature for 30 minutes, and then heated at 150° C. for 1.5 days. After washing with water, the product was calcined at 550° C. for 8 hours. The resulting product is phase-pure CHA has a SAR of 19.8, a Cu-content of 0.35 Cu/Al and a proton content of 2.0.

[0272] Part of this product was aged at 900° C.: No reflections of CHA are present in the XRD pattern of the product after hydrothermal aging for 3 hours at 900° C.

[0273] Another part of the product was ion-exchanged to remove all Cu and Na ions from the framework, and then ion-exchanged with Cu-acetate. No reflections of CHA are present in the XRD pattern of the product after hydrothermal aging for 3 hours at 900° C. The product had the form of cubes and a sidelength of 0.4 μm.

COMPARATIVE EXAMPLE 3

[0274] A synthesis gel with composition 31 SiO.sub.2:1 Al.sub.2O.sub.3:3 NaOH:6 TMAdaAOH:850 H.sub.2O was made by mixing of CBV-720, NaOH pellets, trimethyladamantammonium hydroxide (TMAdaOH) solution (20 wt %) and water in appropriate amounts. The resulting gel was stirred at room temperature for 30 minutes, and then heated at 140° C. for 8 days. After washing with water, the product was calcined at 550° C. for 8 hours. The resulting product is phase-pure CHA and has a SAR of 28.2 and a proton content of 2.2. The product was ion-exchanged with NH.sub.4NO.sub.3 at 80° C. The product was then ion-exchanged with Cu-acetate up to a Cu-loading of 0.63 Cu/Al. No reflections of CHA are present in the XRD pattern of the product after hydrothermal aging for 3 hours at 900° C.

COMPARATIVE EXAMPLE 4

[0275] 1122.2 mg of an aqueous solution of copper sulfate (CuSO.sub.4) was mixed with 266.2 mg of tetraethylenepentamine (TEPA) in order to prepare in-situ the copper organometallic complex, and the resulting mixture was stirred for 2 hours. Afterwards, 9487.3 mg of an aqueous solution of tetraethylammonium hydroxide (TEAOH) (35 wt.-% in water) and 1150.1 mg of an aqueous solution of 20 wt.-% NaOH were added, and the resulting mixture was stirred for 15 minutes. Lastly, 3608.5 mg of a zeolite with a FAU structure (CBV-720, SAR=21) was introduced into the synthesis mixture and stirred for the time required to evaporate the excess water until the desired gel concentration was achieved. The final composition of the gel is SiO.sub.2:0.047 Al.sub.2O.sub.3:0.022 Cu(TEPA).sup.2+:0.4 TEAOH:0.1 NaOH:4 H.sub.2O. The resulting gel was transferred to an autoclave with Teflon liner. The crystallization was carried out at 160° C. for 7 days under static conditions. The solid product was filtered, rinsed with plenty of water, dried at 100° C. and then calcined in air at 550° C. for 4 hours in order to remove the organic residues.

[0276] Proton content: 2.2 mmol/g

[0277] The zeolite obtained was not hydrothermally stable after 900° C. hydrothermal aging.

COMPARATIVE EXAMPLE 5

[0278] 380.2 mg of an aqueous solution of 20 wt.-% of CuSO.sub.4 was mixed with 90.2 mg of tetraethylenepentamine (TEPA) and stirred for 2 hours. Then, 1578.0 mg of an aqueous solution of tetraethylammoniumhydroxide (TEAOH) (35 wt.-%) and 230.1 mg of an aqueous solution of NaOH (20 wt.-% in H.sub.2O) were added, and the resulting mixture was stirred for 15 min. Lastly, 601.3 mg of a zeolite with a FAU structure (CBV-720, SAR=21) was introduced into the synthesis mixture and stirred for the time required to evaporate the excess water until the desired gel concentration was achieved. The final composition of the gel is SiO.sub.2:0.047 Al.sub.2O.sub.3:0.045 Cu(TEPA).sup.2+:0.4 TEAOH:0.1 NaOH:4 H.sub.2O. The resulting gel was transferred to an autoclave with Teflon liner.

[0279] The crystallization was carried out at 160° C. for 7 days under static conditions. The solid product was filtered, rinsed with plenty of water, dried at 100° C. and then calcined in air at 550° C. for 4 hours in order to remove the organic residues.

[0280] Proton content: 2.5 mmol/g

[0281] The zeolite obtained was not hydrothermally stable after 900° C. hydrothermal aging.

COMPARATIVE EXAMPLE 6

[0282] 234.0 mg of an aqueous solution of 20 wt.-% of CuSO.sub.4 was mixed with 53.2 mg of tetraethylenepentamine (TEPA) and stirred for 2 hours. Then, 959.1 mg of an aqueous solution of tetraethylammoniumhydroxide (TEAOH) (35 wt.-%) and 225.1 mg of an aqueous solution of NaOH (20 wt.-% in H.sub.2O) were added, and the resulting mixture was stirred for 15 min. Lastly, 365.3 mg of a zeolite with a FAU structure (CBV-720, SAR=21) was introduced into the synthesis mixture and stirred for the time required to evaporate the excess water until the desired gel concentration was achieved. The final composition of the gel is SiO.sub.2:0.047 Al.sub.2O.sub.3:0.045 Cu(TEPA).sup.2+:0.4 TEAOH:0.2 NaOH:13 H.sub.2O. The resulting gel was transferred to an autoclave with Teflon liner.

[0283] The crystallization was carried out at 160° C. for 7 days under static conditions. The solid product was filtered, rinsed with plenty of water, dried at 100° C. and then calcined in air at 550° C. for 4 hours in order to remove the organic residues.

[0284] Proton content: 2.2 mmol/g

[0285] The zeolite obtained was not hydrothermally stable after 900° C. hydrothermal aging.

COMPARATIVE EXAMPLE 7

[0286] a) Synthesis of Cu-Tetraethylenepentamine complex (Cu-TEPA): 37.9 g tetraethylenepentamine (0.2 mole) was added under stirring to a solution consisting of 50 g CuSO.sub.4.5H.sub.2O (0.2 mole) in 200 g of H.sub.2O (1 M solution) and left to stir for 2 h at room temperature.

[0287] b) 3 g of zeolite Y with SAR=30 (Si/Al=15) (CBV720 supplied by Zeolyst International) was suspended in 27 mL of a 1.2 M solution of sodium hydroxide. To this solution 1.5 mL of a 1 M Cu-TEPA solution was added. The final gel had the following molar ratios: 1 SiO.sub.2/0.033 Al.sub.2O.sub.3/0.033 Cu-TEPA/0.70 NaOH/34 H.sub.2O. The suspension was stirred for 10 minutes at room temperature, before being transferred to an oven at 95° C. and left statically for 7 days. After cooling to room temperature, the powder was separated from the mother liquor by filtration, washed with demineralized water and dried at 60° C. for 12 h. The zeolite produced was determined to have the CHA framework type code according to X-ray diffraction (see FIG. 1) with a Si/Al ratio of 4.3 and a CuO content of 7.5 wt. %, calculated as CuO.

[0288] Proton content: 4.02 mmol/g

[0289] The zeolite obtained was not hydrothermally stable after 900° C. hydrothermal aging.

TABLE-US-00005 TABLE 4 Proton content and hydrothermal stability of the Embodiments and the Comparative Examples Proton content Maximum hydrothermal (mmol/g) stability (° C.) Embodiment 1 1.8 900 Embodiment 2 1.7 Embodiment 3 1.6 900 Embodiment 4 1.2 Embodiment 5 1.6 900 Embodiment 6 1.6 Embodiment 7 1.2 900 Comparative example 1 2.2 <900 Comparative example 2 2.0 <900 Comparative example 3 2.2 <900 Comparative example 4 2.2 <900 Comparative example 5 2.5 <900 Comparative example 6 2.2 <900 Comparative example 7 4.0 <900

TABLE-US-00006 TABLE 5 Composition of the synthesis gels of the Embodiments and Comparative Examples Embodi- Heating Heating Hydrothermal ment Cu- time temp. Gel Proton Stability No. SiO.sub.2 Al.sub.2O.sub.3 TEPA.sup.2+ TEAOH NaOH H.sub.2O NH.sub.4OH KCl RBr gel gelg ageing Content Cu (° C.) 1 1 0.043 0.037 0.73 0.46 62 0.08 0.11 7 d 160 dyn 1.8 3.0 900 2 1 0.043 0.055 0.73 0.46 62 0.08 0.11 7 d 160 dyn 1.7 3 1 0.043 0.074 0.73 0.46 62 0.08 0.11 7 d 160 dyn 1.6 900 4 1 0.043 0.037 0.73 0.46 62 0.11 7 d 160 dyn 5 1 0.043 0.037 0.73 0.46 62 0.86 0.08 0.11 7 d 160 dyn 1.6 900 6 1 0.043 0.037 0.73 0.46 62 0.08 0.06 7 d 160 dyn 1.6 900 7 1 0.043 0.037 0.73 0.46 62 0.08 7 d 160 dyn 1.2 CE 1 1 0.035 0.025 0.4 0.3 15 3 d 150 Dyn 2.2 <900 CE 2 1 0.035 0.028 0.5 0.15 15 1.5 d   150 Dyn 2.0 <900 CE 3 1 0.032 0.194* 0.097 27.5 dyn 2.2 <900 CE 4 1 0.047 0.022 0.4 0.1 4 7 d 160 st 2.2 <900 CE 5 1 0.047 0.045 0.4 0.1 4 7 d 160 St 2.5 <900 CE 6 1 0.47 0.045 0.4 0.2 13 7 d 160 St 2.2 <900 CE 7 1 0.033 0.7 34 7 d 95 st 4.02 7.5 <900 Heating time gel: days [d] Heating temp. gel: heating temperature of the gel in ° C. Gel ageing: dynamic (dyn) or static (st) Proton content: mmol Protons/g Zeolite Cu: Cu content in wt.-%, calculated as CuO Examples: Numbers 1-7: Embodiments 1 to 7 (according to the invention) CE 1 to CE 7: Comparative Examples 1 to 7 CE 3: SDA was TMAdaOH instead of Cu-TEPA CE4-CE7: decomposition far below 900° C. Still to be added: Tables + diagrams from the Excel file “Stability vs. Proton content”