Copper-promoted GMElinite and use thereof in the selective catalytic reduction of NOX

Abstract

A catalyst for the selective catalytic reduction of NOx comprises a zeolitic material which comprises (A) one or more zeolites having a GME framework structure containing YO.sub.2 and X.sub.2O.sub.3, and optionally further comprises one or more zeolites having a CHA framework structure containing YO.sub.2 and X.sub.2O.sub.3, and/or comprises, (B) one or more zeolite intergrowth phases of one or more zeolites having a GME framework structure containing YO.sub.2 and X.sub.2O.sub.3 and one or more zeolites having a CHA framework structure containing YO.sub.2 and X.sub.2O.sub.3, wherein Y is a tetravalent element, and X is a trivalent element, and the zeolitic material contains Cu and/or Fe as non-framework elements in an amount ranging from 0.1 to 15 wt. % calculated as the element and based on 100 wt. % of YO contained in the zeolitic material. Also provided are a process for its preparation, and a use in a method for the selective catalytic reduction of NOx.

Claims

1. A process for producing a catalyst comprising a zeolitic material, the process comprising: crystallizing a mixture comprising a source of SiO.sub.2, a source of Al.sub.2O.sub.3, and optionally comprising a seed crystal, to obtain a first zeolitic material comprising a GME framework zeolite and a CHA framework zeolite, and/or to obtain a second zeolitic material comprising a zeolite intergrowth phase comprising a GME framework zeolite and a CHA framework zeolite; optionally isolating the first and/or second zeolitic material; optionally washing the first and/or second zeolitic material; and optionally drying the first and/or second zeolitic material; ion-exchanging the first and/or second zeolitic material with Cu and/or Fe; and obtaining the catalyst which is suitable for selective catalytic reduction of NOx, wherein the zeolitic material of the catalyst comprises: Cu and/or Fe; and (A) a GME framework zeolite comprising SiO.sub.2 and Al.sub.2O.sub.3, and a CHA framework zeolite comprising SiO.sub.2 and Al.sub.2O.sub.3: and/or (B) a zeolite intergrowth phase comprising a GME framework zeolite comprising SiO.sub.2 and Al.sub.2O.sub.3 and a CHA framework zeolite comprising SiO.sub.2 and Al.sub.2O.sub.3, and wherein a relative amount of the CHA framework zeolite in the zeolitic material, calculated from an X-ray powder diffraction pattern of the zeolitic material using a Relative Intensity Ratio method, and based on 100% of phases in the zeolitic material comprising the GME and CHA framework zeolite, is in a range of from 10 to 60%.

2. The process of claim 1, wherein the mixture in the crystallizing further comprises a solvent system comprising a solvent.

3. The process of claim 1, wherein the mixture in the crystallizing comprises substantially no phosphorous and/or phosphorous containing compounds.

4. A catalyst, produced by the process comprising: crystallizing a mixture comprising a source of SiO.sub.2, a source of Al.sub.2O.sub.3, and optionally comprising a seed crystal, to obtain a first zeolitic material comprising a GME framework zeolite and a CHA framework zeolite, and/or to obtain a second zeolitic material comprising a zeolite intergrowth phase comprising a GME framework zeolite and a CHA framework zeolite; ion-exchanging the first and/or second zeolitic material with Cu and/or Fe; and obtaining the catalyst which is suitable for selective catalytic reduction of NOx, wherein the first and/or second zeolitic material of the catalyst comprises: Cu and/or Fe: and (A) a GME framework zeolite comprising SiO.sub.2 and Al.sub.2O.sub.3 and a CHA framework zeolite comprising SiO.sub.2 and Al.sub.2O.sub.3: and/or (B) a zeolite intergrowth phase comprising a GME framework zeolite comprising SiO.sub.2 and Al.sub.2O.sub.3 and a CHA framework zeolite comprising SiO.sub.2 and Al.sub.2O.sub.3, and wherein a relative amount of the CHA framework zeolite in the zeolitic material, calculated from an X-ray powder diffraction pattern of the zeolitic material using a Relative Intensity Ratio method, and based on 100% of phases in the zeolitic material comprising the GME and CHA framework zeolite, is in a range of from 10% to 60%; and wherein the zeolite material has a degree of crystallinity greater than 50%.

5. A catalyst, comprising a zeolitic material comprising: (A) a zeolite having a GME framework structure comprising SiO.sub.2 and Al.sub.2O.sub.3 and a zeolite having a CHA framework structure comprising SiO.sub.2 and Al.sub.2O.sub.3, and/or (B) a zeolite intergrowth phase of one or more zeolites having a GME framework structure comprising SiO.sub.2 and Al.sub.2O.sub.3 and one or more zeolites having a CHA framework structure comprising SiO.sub.2 and Al.sub.2O.sub.3, wherein the zeolitic material comprises Cu and/or Fe as a non-framework element in a range of from 0.1 wt.-% to 15 wt.-% calculated as an element and based on 100 wt.-% of SiO.sub.2 contained in the zeolitic material, and wherein the catalyst is suitable for selective catalytic reduction of NOx, and wherein a relative amount of the CHA framework structure in the zeolitic material, calculated from an X-ray powder diffraction pattern of the zeolitic material using a Relative Intensity Ratio method, and based on 100% of phases in the zeolitic material comprising the GME and CHA framework structure, is in a range of from 10% to 60%; and wherein the zeolite material has a degree of crystallinity greater than 50%.

6. The catalyst of claim 5, wherein a framework of the zeolitic material comprises substantially no phosphorous.

7. A method for selective catalytic reduction of NOx, the method comprising contacting a gas stream comprising NOx with the catalyst of claim 4.

8. A method, comprising: contacting a gas stream comprising NOx with the catalyst according to claim 4.

9. The catalyst of claim 5, wherein the zeolitic material comprises (A) the zeolite having a GME framework structure comprising SiO.sub.2 and Al.sub.2O.sub.3 and the zeolite having a CHA framework structure comprising SiO.sub.2 and Al.sub.2O.sub.3.

10. The catalyst of claim 5, wherein the zeolitic material comprises (B) the zeolite intergrowth phase of one or more zeolites having a GME framework structure comprising SiO.sub.2 and Al.sub.2O.sub.3 and the one or more zeolites having a CHA framework structure comprising SiO.sub.2 and Al.sub.2O.sub.3.

11. The catalyst of claim 5, wherein the non-framework element comprises Cu.

12. The catalyst of claim 5, wherein the non-framework element comprises Fe.

13. The catalyst of claim 5, wherein the non-framework element comprises Cu and Fe.

14. The catalyst of claim 5, wherein Cu and/or Fe are present in a range of from 0.5 wt.-% to 10 wt.-%.

15. The catalyst of claim 5, wherein Cu and/or Fe are present in a range of from 2 wt.-% to 5 wt.-%.

16. The catalyst of claim 5, wherein the relative amount is in a range of from 15 to 50%.

17. The catalyst of claim 5, wherein the relative amount is in a range of from 20 to 45%.

18. The catalyst of claim 5, wherein the zeolitic material comprises the SiO.sub.2 and the Al.sub.2O.sub.3 in an SiO.sub.2:Al.sub.2O.sub.3 molar ratio in a range of from 2 to 50.

19. The catalyst of claim 5, wherein the zeolitic material comprises the SiO.sub.2 and the Al.sub.2O.sub.3 in an SiO.sub.2:Al.sub.2O.sub.3 molar ratio in a range of from 5 to 12.

Description

DESCRIPTION OF THE FIGURES

(1) The X-ray diffraction (XRD) patterns shown in the Figures were respectively measured using Cu K alpha-1 radiation. In the respective diffractograms, the diffraction angle 2 theta in ° is shown along the abscissa and the intensities are plotted along the ordinate.

(2) FIGS. 1-5 respectively show the X-ray diffraction pattern of the zeolitic material obtained from Reference Examples 1-5. As a reference, the diffractograms further include a line patterns which are typical for the respective GME- and CHA-type framework structures.

(3) FIG. 6 displays the X-ray diffraction pattern of the calcined product obtained according to Reference Example 7. For comparative purposes, the line pattern of the CHA type framework structure is indicated in the diffractogram.

EXAMPLES

(4) In the following examples, the relative amounts of the GME- and CHA-type framework structures in the respective samples were determined by X-ray diffraction quantification using the Relative Intensity Ratio (RIR) method as described in described in Chung, F. H. in Journal of Applied Crystallography, Volume 7, Issue 6, pages 519-525, December 1974, which is a standardless method without the need for calibration. To this effect, the Diffraction data for the analysis was collected on a D8 Advance Series II diffractometer (Bruker AXS GmbH, Karlsruhe). It was setup in Bragg-Brentano geometry using a LYNXEYE detector (window set to 3° opening). The data was collected using a fixed divergent slit set to 0.3° and an angular range from 5°(2q) to 70°(2q). The step width was set to 0.02°(2q) and the scan time chosen to achieve at least 50.000 counts peak intensity. The relative amounts of the respective GME and CHA framework phases in the samples were then determined by analysis of the X-ray diffraction data with the software package DIFFRAC.EVA V2 (Bruker AXS GmbH, Karlsruhe, see DIFFRAC.SUITE User Manual, DIFFRAC.EVA, 2011, pp. 111). The PDF Databases as described in Acta Cryst. (2002), B58, 333-337 were used to identify the crystalline phases within the samples. I/I.sub.cor values from respective entries in the databases were employed, these values describing the relative intensity of the strongest diffraction peak of the respective compound to the main reflection of corundum in a 50% mixture.

Reference Example 1: Preparation of a Zeolitic Material Having the GME and CHA Framework Structures

(5) In a teflon beaker, 8.26 g NaAlO.sub.2 were dissolved in 92.52 g H.sub.2O (DI). Under stirring, 0.89 g Chabazite seed crystals (3 wt.-% based on SiO.sub.2) are then dispersed followed by the slow addition of 69.69 g waterglass (26 wt-% SiO.sub.2, 8 wt-% Na.sub.2O, 66 wt-% H.sub.2O). Finally, 28.97 g LUDOX AS 40 (40 wt-% SiO.sub.2 in H.sub.2O) is given in the stirred reaction mixture. The resulting reaction gel accordingly displays an SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O molar ratio of 40.3:3.5:12.0:750. The reaction mixture is then transferred into a static autoclave and is heated for 120 h to 120° C. Afterwards the dispersion is cooled down and the solid is separated from the supernatant by filtration and subsequent washing with H.sub.2O (DI) until a conductivity of 200 μS is reached. In order to fully remove the residual H.sub.2O, the sample was dried for 16 h at 120° C. in a static oven under air. 56 g of a white powder was obtained.

(6) As may be taken from the X-ray diffraction of the obtained product displayed in FIG. 1, the product reveals a zeolitic material having both the GME and CHA framework structures wherein the relative amounts of the GME and CHA framework structures in the zeolitic material as determined using the Relative Intensity Ratio (RIR) method are respectively 50%. The crystallinity of the product as determined from the diffractogram was 57%.

Reference Example 2: Preparation of a Zeolitic Material Having the GME Framework Structure

(7) In a teflon beaker, 15.84 g NaAlO.sub.2 were homogenized under stirring in 218.86 g waterglass (26 wt-% SiO.sub.2, 8 wt-% Na.sub.2O, 66 wt-% H.sub.2O). This results in a milky, white gel in which 5.84 g Chabazite seeds (10 wt.-% based on SiO.sub.2) are added. The resulting reaction gel accordingly displays an SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O molar ratio of 40.3:3.5:16.8:341. The reaction mixture is transferred into a static autoclave and is heated for 120 h to 120° C. Afterwards the dispersion is cooled down and the solid is separated from the supernatant by filtration and subsequent washing with H.sub.2O (DI) until a conductivity of 200 μS is reached. In order to fully remove the residual H.sub.2O, the sample was dried for 16 h at 120° C. in a static oven under air. 30 g of a white powder was obtained.

(8) As may be taken from the X-ray diffraction of the obtained product displayed in FIG. 2, the product reveals a zeolitic material having a GME framework structure, practically no CHA phase being apparent in the diffractogram.

Reference Example 3: Preparation of a Zeolitic Material Having the GME and CHA Framework Structures

(9) In a teflon beaker, 9.60 g NaAlO.sub.2 were homogenized under stirring in 185.81 g waterglass (26 wt-% SiO.sub.2, 8 wt-% Na.sub.2O, 66 wt-% H.sub.2O). This results in a milky, white gel in which 4.95 g Chabazite seeds (10 wt.-% based on SiO.sub.2) are added. The resulting reaction gel accordingly displays an SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O molar ratio of 40.3:2.5:15.3:341. The reaction mixture is transferred into a static autoclave and is heated for 120 h to 120° C. Afterwards the dispersion is cooled down, and the solid is separated from the supernatant by filtration and subsequent washing with H.sub.2O (DI) until a conductivity of 200 μS is reached. In order to fully remove the residual H.sub.2O, the sample was dried for 16 h at 120° C. in a static oven under air. 30 g of a white powder was obtained.

(10) As may be taken from the X-ray diffraction of the obtained product displayed in FIG. 3, the product reveals a zeolitic material having mainly a GME framework structure, only minor amounts of phases having a CHA framework structure being apparent in the diffractogram.

Reference Example 4: Preparation of a Zeolitic Material Having the GME and CHA Framework Structures

(11) In a teflon beaker, 24.33 g NaAlO.sub.2 were homogenized under stirring in 219.03 g waterglass (26 wt-% SiO.sub.2, 8 wt-% Na.sub.2O, 66 wt-% H.sub.2O). This results in a milky, white gel in which 5.69 g Chabazite seeds (10 wt.-% based on SiO.sub.2) are added. The resulting reaction gel accordingly displays an SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O molar ratio of 40.3:3.5:16.9:341. The reaction mixture is transferred into a static autoclave and is heated for 120 h to 120° C. Afterwards the dispersion is cooled down, and the solid is separated from the supernatant by filtration and subsequent washing with H.sub.2O (DI) until a conductivity of 200 μS is reached. In order to fully remove the residual H.sub.2O, the sample was dried for 16 h at 120° C. in a static oven under air. 60 g of a white powder was obtained.

(12) As may be taken from the X-ray diffraction of the obtained product displayed in FIG. 4, the product reveals a zeolitic material having both the GME and CHA framework structures wherein the relative amounts of the GME and CHA framework structures in the zeolitic material as determined using the Relative Intensity Ratio (RIR) method are respectively 73% GME and 15% CHA, a further phase being assigned to analcime as a side product. Accordingly, the relative amounts of GME and CHA based on the total (100%) of the GME and CHA phases in the sample as determined using the Relative Intensity Ratio (RIR) method are respectively 83% GME and 17% CHA. The crystallinity of the product as determined from the diffractogram was 71%.

Reference Example 5: Preparation of a Zeolitic Material Having the GME and CHA Framework Structures Without Employing Seed Crystals

(13) In a teflon beaker, 74.38 g NaAlO.sub.2 were homogenized under stirring in 832.64 g waterglass (26 wt-% SiO.sub.2, 8 wt-% Na.sub.2O, 66 wt-% H.sub.2O). This results in a milky, white gel. The resulting reaction gel accordingly displays an SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O molar ratio of 40.3:3.5:12.0:705. No Chabazite seed crystals were added. The reaction mixture is transferred into a stirred autoclave and is heated for 60 h to 120° C. Afterwards the dispersion is cooled down, and the solid is separated from the supernatant by filtration and subsequent washing with H.sub.2O (DI) until a conductivity of 200 μS is reached. In order to fully remove the residual H.sub.2O, the sample was dried for 16 h at 120° C. in a static oven under air. 247 g of a white powder was obtained.

(14) As may be taken from the X-ray diffraction of the obtained product displayed in FIG. 4, the product reveals a zeolitic material having both the GME and CHA framework structures wherein the relative amounts of the GME and CHA framework structures in the zeolitic material as determined using the Relative Intensity Ratio (RIR) method are respectively 47% GME and 45% CHA, in addition to minor impurities. Accordingly, the relative amounts of GME and CHA based on the total (100%) of the GME and CHA phases in the sample as determined using the Relative Intensity Ratio (RIR) method are respectively 51% GME and 49% CHA. The crystallinity of the product as determined from the diffractogram was 68%.

Reference Example 6: Preparation of a Zeolitic Material Having the GME and CHA Framework Structures

(15) In a teflon beaker 74.38 g NaAlO.sub.2 were homogenized under stirring in 832.64 g waterglass (26 wt-% SiO.sub.2, 8 wt-% Na.sub.2O, 66 wt-% H.sub.2O). This results in a milky, white gel in which 8.02 g Chabazite seeds (3.7 wt.-% based on SiO2) are added. The resulting reaction gel accordingly displays an SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O molar ratio of 40.3:3.5:12.0:705. The reaction mixture is transferred into a stirred autoclave and is heated for 60 h to 120° C. Afterwards the dispersion is cooled down, and the solid is separated from the supernatant by filtration and subsequent washing with H.sub.2O (DI) until a conductivity of 200 μS is reached. In order to fully remove the residual H.sub.2O, the sample was dried for 16 h at 120° C. in a static oven under air. 121 g of a white powder was obtained.

(16) As determined by X-ray diffraction, the product reveals a zeolitic material having mainly the CHA framework structure in addition to a phase having the GME framework structure. The relative amounts of the GME and CHA framework structures in the zeolitic material as determined using the Relative Intensity Ratio (RIR) method are 93% CHA and 7% GME. The crystallinity of the product as determined from the diffractogram was 71%.

Reference Example 7: Preparation of a Zeolitic Material Having the CHA Framework Structure

(17) 276.8 kg N,N,N-trimethylcyclohexylammoniumhydroxide (20 wt-% solution in H.sub.2O) were mixed with 34.80 kg of aluminiumtriisopropylate and 77.99 kg tetramethylammoniumhydroxide (25 wt-% solution in H.sub.2O). Afterwards, 358.32 kg LUDOX AS 40 (40 wt-% colloidal solution in H.sub.2O) and 5.73 kg CHA seeds were added to the stirred mixture. The resulting gel was placed in a stirred autoclave with a total volume of 1600 L. The autoclave was heated within 7 h to 170° C. The temperature was kept constant for 18 h. Afterwards the autoclave was cooled down to room temperature. Then, the solids were separated by filtration and intensive washing until the washwater had a pH of 7. Finally the solid was dried for 10 hours at 120° C. The material was calcined at 550° C. for 5 hours.

(18) The characterization of the calcined material via XRD is displayed in FIG. 6 and displays the CHA-type framework structure. No phase having a GME framework structure is apparent in the diffractogram. The crystallinity of the product as determined from the diffractogram was 92%.

Example 1: Copper Ion Exchange of Reference Example 1

(19) 50 g of the zeolite powder obtained from Reference Example 1 were dispersed in a solution of 50 g NH.sub.4NO.sub.3 in 500 g H.sub.2O (DI). Under stirring, the mixture was heated for 2 hours to 80° C. Then, the solid was separated from the aqueous phase by filtration and subsequent washing with H.sub.2O until no nitrate can be detected in the washing water. The obtained white solid powder was dried at 120° C. for 16 h under air.

(20) The ion-exchange was repeated one more time in order to remove the remaining Na.sub.2O from the synthesis quantitatively. Finally, the zeolite was transferred into the H-Form by means of calcination at 500° C. for 6 hours in a static oven under air.

(21) The H-form of the sample as obtained after calcination was then subject to ion exchange with Cu.sup.2+. To this effect, 49 g of the calcined zeolite powder was dispersed under stirring in 318 g H.sub.2O (DI). The dispersion was heated up to 60° C. After 30 min, 5.6 g Cu.sup.2+-acetate-monohydrate were added together with 0.54 g acetic acid (70 wt-% solution in H.sub.2O) in the aqueous phase. After 1 h reaction time, 238 g cold H.sub.2O were added rapidly into the mixture to stop the ion-exchange. The solid was filtered and washed with H.sub.2O (DI) until a conductivity of 200 μS was reached. The light blue powder was dried at 120° C. for 16 h for obtaining the copper ion exchanged product.

(22) Elemental analysis of the copper ion-exchanged sample obtained afforded the following values: SiO.sub.2=75.6 wt-%, Al.sub.2O.sub.3=20.9 wt-%, Na.sub.2O=0.05 wt-%, and CuO=3.4 wt-%. The X-ray diffraction pattern of the copper-exchanged sample revealed relative amounts of the GME and CHA framework structures as determined using the Relative Intensity Ratio (RIR) method of 63% GME and 37% CHA. The crystallinity of the product as determined from the diffractogram was 55%.

Comparative Example 1: Copper Ion Exchange of Reference Example 7

(23) The procedure of Example 1 was repeated with Reference Example 7 for affording a copper ion-exchanged comparative example having the CHA-type framework structure.

Example 2: SCR Testing

(24) The copper-exchanged samples obtained in Example 1 and Comparative Example 1 were subsequently tested under selective catalytic reduction conditions relative to their NOx conversion capacity. To this effect the samples were contacted at various temperatures (200° C., 300° C., 450° C., and 600° C.) with a gas stream containing 500 ppm nitrogen oxide, 500 ppm ammonia, 5 volume percent water, 10 volume percent oxygen (as air) and balance nitrogen at a weight hourly space velocity (WHSV) of 80,000 h.sup.−1. The samples were then aged at 650° C. for 50 hours in an atmosphere containing 10 volume percent of water, and then tested anew. The results of said testing are displayed in table 1 below.

(25) TABLE-US-00001 TABLE 1 Results from selective catalytic reduction testing conducted on the powder samples. NO.sub.x conversion fresh catalyst after aging at 650° C. at: Example 1 Comp. Ex. 1 Example 1 Comp. Ex. 1 200° C. 94% 93% 85% 89% 300° C. 99% 98% 93% 88% 450° C. 96% 93% 95% 86% 600° C. 87% 67% 87% 73%

(26) Thus, as may be taken from the results from selective catalytic reduction testing, it has surprisingly been found that the results obtained with the inventive sample clearly outperform those obtained with the comparative example, wherein the advantage is particularly pronounced at high temperatures. Furthermore, it has quite unexpectedly been found that the same applies after aging of the catalyst, such that the inventive catalyst effectively displays a superior performance during the entire lifetime of the catalyst for selective catalytic reduction. Thus, although after aging the activity of the inventive catalyst lies slightly below that of the comparative example at the lowest temperature of 200° C., the inventive catalyst clearly outperforms the comparative catalyst sample at all of the higher temperatures and in particular in the range of temperatures between 300 and 450° C. at which the highest conversion rates are observed for both the fresh and aged samples. Consequently, it has surprisingly been found that a copper loaded catalyst for selective catalytic reduction comprising a zeolite having the GME framework structure displays a clearly better performance in the abatement of NO.sub.x via selective catalytic reduction for comparable metal loading levels, in particular in the temperature range for which optimal conversion levels may be achieved.