SDA-free synthesis of chabazite (CHA) zeolite and uses thereof

Abstract

A method of making a chabazite zeolite is disclosed. The method can include obtaining an aqueous gel comprising silicon dioxide, aluminum oxide, potassium oxide, and a nucleating agent, and hydrothermally treating the aqueous gel to obtain the chabazite zeolite.

Claims

1. A method of making a chabazite zeolite, the method comprising: (a) obtaining an aqueous gel comprising silicon dioxide (SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3), potassium oxide (K.sub.2O), and a nucleating agent; and (b) hydrothermally treating the aqueous gel to obtain the chabazite zeolite; wherein the chabazite zeolite is calcined; wherein the chabazite zeolite is in the form of cuboid particles; and wherein the aqueous gel has a molar composition of: 1SiO.sub.2:0.2Al.sub.2O.sub.3:0.39K.sub.2O:0.3NH.sub.4F:xH.sub.2O, where x is the molar ratio of H.sub.2O/SiO.sub.2 and ranges from 10 to 15.

2. The method of claim 1, wherein the aqueous gel in step (a) is maintained at room temperature for 12 to 24 hours prior to the step (b) hydrothermal treatment.

3. The method of claim 2, wherein the cuboid particles have a particle size of 1.2 to 2 μm.

4. The method of claim 1, wherein x is 15.

5. The method of claim 4, wherein the cuboid particles have a particle size of 1.2 to 2 μm.

6. The method of claim 1, wherein x is 10.

7. The method of claim 1, wherein the gel further comprises Na.sub.2O.

8. The method of claim 1, wherein hydrothermal treatment is performed at a temperature of 130° C.

9. The method of claim 8, wherein the cuboid particles have a particle size of 1.2 to 2 μm.

10. The method of claim 1, further comprising: (c) washing the chabazite zeolite until a pH of about 7 is obtained; and (d) performing an ion-exchange to protonate the chabazite zeolite to produce an H-form of the chabazite zeolite.

11. The method of claim 1, wherein the aqueous gel from step (a) is obtained by: (i) forming an aqueous solution comprising aluminum hydroxide and potassium hydroxide; and (ii) adding ammonium fluoride and colloidal silica to the aqueous solution to form the aqueous gel.

12. The method of claim 1, wherein a templating agent is not used to produce the chabazite zeolite.

13. The method of claim 1, wherein the templating agent is N,N,N-trimethyl-1-adamantammonium iodide.

14. The method of claim 1, wherein the hydrothermal treatment is performed in a PTFE-lined stainless-steel autoclave.

15. The method of claim 1, wherein the cuboid particles have a particle size of 1.2 to 2 μm.

16. The method of claim 15, wherein the cuboid particles are agglomerated to form large interconnected particles ranging in size from 15 to 20 μm.

17. The method of claim 1, wherein the cuboid particles have a particle size of 1.2 μm.

18. A method of making a chabazite zeolite, the method consisting of the steps of: (a) obtaining an aqueous gel comprising silicon dioxide (SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3), potassium oxide (K.sub.2O), and a nucleating agent; and (b) hydrothermally treating the aqueous gel to obtain the chabazite zeolite; wherein the chabazite zeolite is calcined; wherein the aqueous gel has a molar composition of: 1SiO.sub.2:0.2Al.sub.2O.sub.3:0.39K.sub.2O:0.3NH.sub.4F:xH.sub.2O, where x is the molar ratio of H.sub.2O/SiO.sub.2 and ranges from 10 to 15; wherein the cuboid particles are agglomerated to form large interconnected particles ranging in size from 15 to 20 μm, and wherein the cuboid particles have a have a particle size of 1.2 to 2 μm.

19. A method of making a chabazite zeolite, the method consisting of the steps of: (a) obtaining an aqueous gel comprising silicon dioxide (SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3), potassium oxide (K.sub.2O), and a nucleating agent; and (b) hydrothermally treating the aqueous gel to obtain the chabazite zeolite; wherein the chabazite zeolite is calcined; wherein the aqueous gel has a molar composition of: 1SiO.sub.2:0.2Al.sub.2O.sub.3:0.39K.sub.2O:0.3NH.sub.4F:xH.sub.2O, where x is the molar ratio of H.sub.2O/SiO.sub.2 and ranges from 10 to 15; wherein the cuboid particles are agglomerated to form large interconnected particles ranging in size from 15 to 20 μm, wherein the cuboid particles have a have a particle size of 1.2 to 2 μm; and wherein the chabazite zeolite further comprises sodium oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

(2) FIG. 1: a schematic of a system to produce a chemical compound using the supported catalyst of the present invention.

(3) FIG. 2: XRD patterns of the as-synthesized CHA (Run #5) prepared by direct crystallization from amorphous silicoaluminate gel in the absence of SDA as compared to the reference CHA zeolite.

(4) FIG. 3: XRD patterns of samples prepared from Gel #1 at different H.sub.2O/SiO.sub.2 ratios; (A) H.sub.2O/SiO.sub.2=35, (B) H.sub.2O/SiO.sub.2=28, (C)H.sub.2O/SiO.sub.2=25, (D) H.sub.2O/SiO.sub.2=20, (E) H.sub.2O/SiO.sub.2=15, (F) H.sub.2O/SiO.sub.2=10. Peaks with * symbol represents the MER phase.

(5) FIG. 4: The .sup.27A1 MAS NMR spectra of the synthesized CHA before and after ion-exchange and calcination.

(6) FIG. 5: XRD patterns of samples prepared from Gel #1 with H.sub.2O/SiO.sub.2 of 15 at 6 h of aging time for different crystallization times.

(7) FIG. 6: Formation of CHA zeolite at different aging and crystallization times.

(8) FIG. 7: FE-SEM images at different magnifications of CHA zeolites prepared at different aging times: 6 h (a, b and c), 24 h (d, e and f), and 48 h (g, h and i) at a minimum time of crystallization.

(9) FIG. 8: XRD patterns of samples prepared at different bulk Si/Al ratios.

(10) FIG. 9: N.sub.2 adsorption/desorption isotherms of the as-synthesized CHA (K-CHA), and after ion-exchanged with ammonium nitrate (H-CHA).

(11) FIG. 10: Micropores of synthesized and modified CHA zeolite samples using Horvath-Kawazoe model.

(12) FIG. 11: NH.sub.3-TPD profiles of the as-prepared CHA zeolite in K-Form (K-CHA) and after ion-exchanged with 2 M of ammonium nitrate and calcination (H-CHA).

(13) FIG. 12: Conversion of methanol over Al-rich CHA as a function of time on stream (TOS).

(14) FIG. 13: Selectivity to olefins as a function of time on stream (TOS) over H-CHA zeolite at different temperatures.

(15) FIG. 14: Comparison of olefins selectivity of Al-rich CHA with the commercial ZSM-5.

(16) While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

(17) The present invention provides a solution to at least some of the cost inefficiencies and complexities surrounding the production of commercially viable chabazite (CHA) zeolites. In particular, the present invention provides for a direct and reproducible CHA zeolite synthesis method from basic chemicals without the need for templating agents or FAU zeolites as starting materials. This results in a time and cost-efficient production process that can be scalable for commercial use by the chemical industry. As illustrated in a non-limiting manner in the below examples, CHA zeolites of the present invention have good catalytic activity for the methanol to olefin reaction. It is also expected that the CHA zeolites of the present invention can be used to catalyze the ammonia selective catalytic reduction (NH.sub.3-SCR) reaction.

(18) These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to the figures.

(19) A. Methods of Making the CHA Zeolite

(20) The general process for making the CHA zeolite of the present invention can include obtaining an aqueous gel comprising silicon dioxide (SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3), potassium oxide (K.sub.2O), and a nucleating agent. The aqueous gel can be prepared by (i) forming an aqueous solution comprising an aluminum ion source, preferably aluminum hydroxide, and a potassium ion source, preferably potassium hydroxide. This step can be performed under heat (e.g., 50° C. to 100° C.) for a sufficient time to ensure a homogenous solution is obtained (e.g., 15 minutes, 30 minutes, 1 2, 3, or 4 or more hours). The solution can be cooled to room temperature followed by adding a fluoride source, preferably ammonium fluoride, and a silica source, preferably colloidal silica, to the aqueous solution to form the aqueous gel. The aqueous solution can be stirred/mixed for varying periods of time to age the gel (e.g., 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 30, 36, 42, or 48 hours, or more).

(21) Once the gel is obtained, it can be hydrothermally treated to obtain the CHA zeolite. Hydrothermal treatment can be performed under autogenous pressure. It can be performed in a PTFE-lined stainless-steel autoclave. After hydrothermal treatment, the CHA zeolite can be washed/rinsed, preferably with deionized water followed by drying (e.g., air drying or with heat). In some aspects, the dried CHA zeolite can then be subjected to an ion-exchange step so as to protonate the CHA zeolite and produce the protonated (H-form) of the CHA zeolite. The ion-exchange step can be performed with a proton source (e.g., NH.sub.4NO.sub.3) by subjecting the CHA zeolite to a solution having the proton source and treating under reflux (e.g., 50° C. to 100° C., preferably 80° C.) for a sufficient period of time (1 hour to 5 hours, preferably 3 hours). This step can be repeated as needed. Subsequently, the CHA zeolite can be calcined at 400° C. to 600° C., preferably 500° C. for a sufficient period of time (e.g., 2 hours to 12 hours, preferably about 5 hours) using a muffle furnace. The heating rate can be 2 to 15° C./min., or about 10° C./min.

(22) B. System for Production of Chemical Compounds

(23) CHA zeolites of the present invention can be used for a variety of chemical reactions. In preferred instances, the CHA zeolites can be used for the methanol to olefin reaction (MTO reaction) or the ammonia selective catalytic reduction (NH.sub.3-SCR) reaction.

(24) FIG. 1 depicts a schematic for a system to produce a chemical compound. The system 100 can include an inlet 102 for a first reactant feed, an inlet 104 for a second reactant feed, a reaction zone 106 (e.g., a continuous flow reactor selected from a fixed-bed reactor, a fluidized reactor, or a moving bed reactor) that is configured to be in fluid communication with the inlets 102 and 104, and an outlet 108 configured to be in fluid communication with the reaction zone 106 and configured to remove a product stream from the reaction zone. In some instances, a second reactant feed may not be needed and second inlet 104 may also not be needed. The reactant zone 106 can include a CHA zeolite of the present invention. The first reactant feed can enter the reaction zone 106 via the inlet 102. After a sufficient amount of the first reactant and catalyst have been placed in the reaction zone 106, and if desired, a second reactant feed can enter the reaction zone through the feed inlet 104. In some embodiments, the first or second reactant feeds can be used to maintain a pressure in the reaction zone 306. In some embodiments, the reactant feed streams include inert gas (e.g., nitrogen or argon). In some embodiments, the reactant feeds are provided at the same timer or in reverse order. In some embodiments, only one reactant feed is used. In other embodiments, three or more reactant feeds are used. After a sufficient amount of time, the product stream can be removed from the reaction zone 106 via product outlet 108. The product stream can be sent to other processing units, stored, and/or transported.

(25) System 100 can include one or more heating and/or cooling devices (e.g., insulation, electrical heaters, jacketed heat exchangers in the wall) or controllers (e.g., computers, flow valves, automated values, etc.) that are necessary to control the reaction temperature and pressure of the reaction mixture. While only one reactor is shown, it should be understood that multiple reactors can be housed in one unit or a plurality of reactors housed in one heat transfer unit.

EXAMPLES

(26) The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

(27) Materials: Colloidal silica TM-40 colloidal silica, 40 wt. %, suspended in water (Aldrich), De-ionized water (produced in CENT labs.), ammonium fluoride, aluminum hydroxide PRS (Panreac), ammonium nitrate >=98% (Sigma-Aldrich), and potassium hydroxide 85% pellets (Panreac) were used in the following examples.

(28) Characterization Techniques: The structure analysis was investigated using .sup.27Al, and .sup.29Si Nuclear Magnetic Resonance (NMR) spectroscopy and X-ray diffraction (XRD). The XRD patterns were recorded using Rigaku Miniflex diffractometer equipped with Cu Kα radiation (λ=0.15406 nm) at 2θ ranging from 5 to 50° with a scan speed of 3° per min and step size of 0.02.

(29) Ammonia temperature programmed desorption (NH.sub.3-TPD) was conducted to investigate the acidity of the zeolites. The NH.sub.3-TPD analysis was performed on Chemisorb 2750 Micrometrics chemisorption analyzer over 100 mg of the prepared zeolites. The sample was preheated at 600° C. (heating rate 30° C.min.sup.1) under the flow of He (25 ml. min.sup.−1) for 30 min After allowing the sample to cool to 100° C., NH.sub.3 was allowed to flow over the ample with a flow rate of 25 mL. min.sup.−1 for 30 min. Subsequently, He flow was reconnected for 1 h to remove the weakly adsorb of NH.sub.3. Finally, the temperature was ramped to 800 at ramping rate of 10 and the amount desorbed of ammonia was recorded using the TCD detector on a 0.5 s basis.

(30) The elemental compositions of the samples were measured using X-ray fluorescence (XRF), while the morphology of the samples were investigated using the field-emission scanning electron microscope (FE-SEM).

(31) The surface area, pore volume and pore size distribution were analyzed using the physisorption of Nitrogen in ASAP 2020 (Micromeritics). Prior to analysis, the samples were heated up to 350° C. and dwelled for 6 hours. The sample temperature during the analysis was maintained at −196° C. The t-plot was used to measure the volume of micropore, surface area, and the external surface area, while the pore size distribution was estimated using Horvath-Kawazoe model method.

(32) Observations About the Following Examples: A cost-effective Al-rich CHA zeolite was successfully synthesized without using an organic structuring agent. The CHA zeolite was formed under the experimental conditions outlined below. The Si/Al ratios of the gel had a role in the formation of pure CHA, with a slight increase in Si/Al ratio (Si/Al=3.3), impurities of other phase (MER) were formed. High H.sub.2O/SiO.sub.2 ratio (from 20 to 35) affected the crystallinity of CHA zeolite, while low H.sub.2O/SiO.sub.2 ratio (H.sub.2O/SiO.sub.2=10) favored the formation of MER phase. The aging time influenced the rate of crystallization and correspondingly affected the morphologies. At longer aging time, smaller CHA particles were obtained with shorter crystallization time. The synthesized CHA zeolite in H-form (H-CHA) showed higher surface area and larger pore volume than the K-form (K-CHA).

(33) The application of H-CHA in MTO showed that a Al-rich CHA zeolite was very selective to olefins. The deactivation rate and initial selectivity to olefins was attributed to the reaction temperature. The selectivity of the Al-rich CHA zeolite in the MTO reaction was high and comparable to the commercial ZSM-5 and SSZ-13 catalysts.

Example 1

Synthesis of CHA Zeolites

(34) 4.21 g of potassium hydroxide was added to 17.23 g of deionized water and placed in an oil-bath at 80° C. To the aqueous solution of potassium hydroxide, 3 g of aluminum hydroxide was added and stirred for 30 min under heating. After cooling to room temperature, 1.07 and 14.44 g of ammonium fluoride and colloidal silica were added, respectively. The final gel (also named as Gel #1) with a molar composition of 1SiO.sub.2: 0.2Al.sub.2O.sub.3: 0.39K.sub.2O: 0.3NH.sub.4F: 15H.sub.2O was aged for x hours at room temperature, x=6, 12, 24, 48. Following this, the final gel was crystallized in a convection oven at 160° C. for y hours, y=48, 60, 72, 96 and 120. Finally, the product was separated and washed with deionized water until neural pH around 7 was obtained. The same procedure was followed in attempting to prepare CHA zeolite from Gel #2, #3, #4 and #5. Table 1 provides the gel molar compositions.

(35) TABLE-US-00001 TABLE 1 (Different gel molar compositions used in the synthesis of CHA zeolite) Gel # Molar composition 1 1SiO.sub.2:0.2Al.sub.2O.sub.3:0.39K.sub.2O:0.3NH.sub.4F:xH.sub.2O 2 1SiO.sub.2:0.2Al.sub.2O.sub.3:0.39K.sub.2O:yNH.sub.4F:15H.sub.2O 3 1SiO.sub.2:zAl.sub.2O.sub.3:0.39K.sub.2O:0.3NH.sub.4F:15H.sub.2O 4 1SiO.sub.2:0.2Al.sub.2O.sub.3:wK.sub.2O:0.3NH.sub.4F:15H.sub.2O 5 1SiO.sub.2:0.2Al.sub.2O.sub.3:wK.sub.2O:0.04Na.sub.2O:0.3NH.sub.4F:15H.sub.2O

(36) The as synthesized samples, which were in potassium form (K-CHA), were ion-exchanged using ammonium nitrate (NH.sub.4NO.sub.3) as a source of proton. For each gram of the sample, 50 mL of 2 M of NH.sub.4NO.sub.3 was used and treated under reflux (80° C.) for 3 h. The ion-exchanged was repeated one more time with fresh solution of ammonium nitrate. To have the samples in the protonated form (H-form), the samples were calcined at 500° C. (heating rate 10° C./min.) for 5 h using a muffle furnace.

Example 2

Effect of H.SUB.2.O/SiO.SUB.2 .Ratio on CHA Formation

(37) Above Table 1 shows different formula of the silicoaluminate gel used in this study. Firstly, gel #1 was used with x=35 (H.sub.2O/SiO.sub.2=35), which had the same gel composition as reported in the literature (B. Liu, Y. Zheng, N. Hu, T. Gui, Y. Li, F. Zhang, R. Zhou, X. Chen, H. Kita, Synthesis of low-silica CHA zeolite chabazite in fluoride media without organic structural directing agents and zeolites, Microporous and Mesoporous Materials, 196 (2014) 270-276.) However, the published procedure was not reproducible, and the inventors were unable to synthesize pure CHA from this batch even at a prolonged crystallization time of up to 5 days. Nevertheless, by altering the water content of the first batch and fixing the crystallization time to 5 days as shown in Table 2 (Run #5) pure CHA zeolite was successfully formed with H.sub.2O/SiO.sub.2 molar ratio of 15. FIG. 2 shows the XRD patterns of the CHA zeolite prepared at x=15 and the reference CHA. It is clear that the XRD patterns of the prepared CHA at x=15 are in well agreement with the reference; all characteristic peaks and even small peaks are matching with the reference one. A further decrease in H.sub.2O/SiO.sub.2 ratio down to 10 resulted in CHA phase but with Merlinoite (MER) phase as an impurity. The XRD patterns of the CHA zeolite synthesized at different water contents are shown in FIG. 3. From the XRD patterns, the increase in H.sub.2O/SiO.sub.2 ratio from 15 up to 35, did not favor the formation of CHA zeolite and amorphous phases were dominating.

(38) TABLE-US-00002 TABLE 2 (Water content and crystallization time under which CHA zeolite was formed using Gel # 1; crystallization temperature 160° C., gel Si/Al ratio 2.5, aging time 6 h) Crystallization # x time(h) Phase 1 35 120 Am. 2 28.5 120 Am. 3 25 120 Am. 4 20 120 Am. (Oth.) 5 15 120 CHA 6 10 120 CHA* 7 15 108 CHA 8 15 96 CHA (am.) 9 15 72 Am. (CHA) 10 15 48 Am.

(39) FIG. 4 shows the solid-state .sup.27A1 magic-angle spinning (MAS) NMR spectra of the CHA zeolites before (K-CHA) and after ion-exchanged and calcination (H-CHA). The typical spectrum reveals a peak around 58 ppm attributed to tetrahedral coordination of Al species. A small peak corresponding to the octahedral coordination of Al was observed at around 0 ppm after the ion-exchange and calcination. This additional structure of Al species (the octahedral) might be because of the ion-exchange (H. Imai, N. Hayashida, T. Yokoi, T. Tatsumi, Direct crystallization of CHA-type zeolite from amorphous aluminosilicate gel by seed-assisted method in the absence of organic-structure-directing agents, Microporous and Mesoporous Materials, 196 (2014) 341-348.) or by the calcination as dealumination takes place (B. A. Aufdembrink, D. P. Dee, P. L. McDaniel, T. Mebrahtu, T. L. Slager, Spectroscopic Characterization of Acidity in Chabazite, The Journal of Physical Chemistry B, 107 (2003) 10025-10031).

Example 3

Effect of Aging Time On Crystallization

(40) The effect of aging time has been investigated using Gel#1 with x=15. The effect of aging time was studied at 4 different periods as presented in Table 3. The aging time had a significant influence on the crystallization time. Samples aged for longer time, required less crystallization time. For example, the minimum crystallization time for the samples aged for 6 h was between 96 and 108 h, while for those aged for 48 h required only 60 h to get pure and highly crystalline CHA zeolite. The XRD patterns of samples aged for 6 h at different crystallized times are shown in FIG. 5. A picture for understanding the formation of CHA zeolite under different aging and crystallization time is depicted in FIG. 6. The higher the aging time was, the lower the crystallization time required. All points on the dotted line and above it (referred to as the crystalline region) represent conditions where a pure CHA zeolite was formed, while points below the dotted line (referred to as amorphous region) are a combination of CHA and amorphous phase.

(41) TABLE-US-00003 TABLE 3 (Effect of aging time on the crystallization of CHA zeolite using Gel # 1 with a H.sub.2O/SiO.sub.2 ratio of 15) Aging Crystallization # T ( ° C.) time (h) time(h) Phase 11 160 12 72 CHA(Am.) 12 160 12 96 CHA 13 160 12 120 CHA 14 160 24 60 CHA(Am.) 15 160 24 72 CHA 16 160 24 96 CHA 17 160 24 120 CHA 18 160 48 60 CHA 19 160 48 72 CHA 20 160 48 96 CHA

Example 4

Effect of Aging Time On Morphology

(42) Aging time did not only lower the crystallization time but it also influenced the morphology (particles shape and size) of the prepared CHA zeolite. Samples prepared at lower aging time had different particle shape and size. Generally, the particles are small cuboids, which are agglomerated to form a large particle that is similar to a swollen-disk like shape. FIG. 7 shows FE-SEM images of CHA zeolite which was aged for 6, 24 and 48 h at a corresponding minimum crystallization time. For the aging time of 6 h and crystallization time of 108 h, the large particles seem to be interconnected to form a flower-like shape. The size of these large interconnected particles is ranging between 15 to 20 μm, while the small cuboids which are the components of the larger particles had a size of 1.2-2 μm. The increase in aging time affected both the swollen disk-like shape and the small cuboids. The flower-like shape was not anymore interconnected and appeared to be more dispersed with a size ranging between 10 and 18 μm when the aging time was 24 h. Moreover, the size of the small cuboids decreased to 0.8 μm, still at 24 h aging time. A more increase in aging time up to 48 h caused a desertion to the swollen disk-like shape and become more spread and irregular in shape. Additionally, the small cuboids size decreased up to 400 nm.

Example 5

Effect of Varying Al.SUB.2.O—NH.SUB.4.F—K.SUB.2.O/SiO.SUB.2 .Ratios

(43) Table 4 shows different gel compositions (Gel #2, 3 & 4) of the precursor solution. The Si/Al ratio has been varied in in the gel composition in order to have CHA zeolite with different Si/Al ratios and thus different acidity. However, an increase in the Si/Al ratio either by decreasing the source of aluminum or by increasing the source of silica resulted in unwanted phases; either MER as a competitive phase or in amorphous phase as shown in FIG. 8. Similarly, altering concentration of K.sub.2O and NH.sub.4 did not favor the formation of CHA zeolite. The introduction of small concentration of Na.sub.2O beside K.sub.2O (Gel #5, Run #25 & 26, Table 4) for the purpose of varying alkaline metals suppressed the formation of CHA zeolite and favor the growth of MER phase.

(44) TABLE-US-00004 TABLE 4 (Effect of altering fluoride and aluminum content on the formation of CHA zeolite synthesized at a crystallization temperature of 160° C.) T Aging Crystallization # Gel # y z w Si/Al.sup.a (° C.) time (h) time(h) Phase 21 3 — 0.1  — 5 160  6 96 Am. 22 3 — 0.15 — 3.33 160 24 72 MER 23 2 0.4  — — 2.5 160 24 72 Am 24 2 0.25 — — 2.5 160 24 72 CHA(Oth.) 25 4 — — 0.3  2.5 160 24 72 Am.(CHA) 26 5 — — 0.35 2.5 160 24 72 MER(CHA) .sup.agel Si/Al ratio

Example 6

Surface Area and Pore Volume Distribution

(45) Table 5 shows the physical properties of the prepared CHA samples before and after ion-exchange. The as-synthesized material in potassium form (K-CHA) had a very poor surface area, while the ion-exchanged sample in H-form (H-CHA) showed an excellent enhancement in the surface area and pore volume. The parent sample (K-CHA), initially, had a BET surface area of ca. 0.96 m.sup.2/g and total pore volume of 0.0032 cm.sup.3/g. After ion-exchange, the BET surface area and pore volume increased to 485 m.sup.2/g and 0.217 cm.sup.3/g, respectively. The poor adsorption of sample in K-form is due to the large size of the potassium cation (K+), which might block the small pores of the CHA framework. However, the samples in K-form may still have significant surface area for other smaller adsorbates. FIG. 9 shows the N.sub.2 adsorption/desorption isotherm of K-CHA and H-CHA zeolites. The isotherm is classified as Type I isotherm, which is the common isotherm type of CHA zeolite (L. Sommer, D. Mores, S. Svelle, M. Stocker, B. M. Weckhuysen, U. Olsbye, Mesopore formation in zeolite H-SSZ-13 by desilication with NaOH, Microporous and Mesoporous Materials, 132 (2010) 384-394). The pore width of H-CHA zeolite was calculated using the Horvath-Kawazoe model with a main peak at ca. 0.51 nm, as shown in FIG. 10.

(46) TABLE-US-00005 TABLE 5 (Surface Area, Pore Volume and Si/Al Ratio of the CHA Samples) Surface Area (m.sup.2/g) Pore volume (cm.sup.3/g) Sample S.sub.ext S.sub.micR S.sub.BET. S.sub.L V.sub.micro V.sub.meso V.sub.tot Si/Al.sup.a Ref. K-CHA 0.089 0.87 0.96 1.3708 0.0005 0.0027 0.0032 — Current Example H-CHA 25 461 485 584 0.1952 0.0219 0.2172 2.5 Current Example K-CHA — — 17.82 — 0.002 0.050  0.052  2.2 [1] Na-CHA — — 257.26 — 0.10 0.053  0.153  — [2] K-CHA 18 2 — 20 0.0008 — — 2.2 [2] K-CHA — — 7.84 — — — — 2.3 [3] H-CHA — — 396.2 — — — — 2.3 [3] .sup.aproducts Si/Al ratio by XRF; S.sub.L: Langmuir surface area. [1] Ridha, F.N., Y. Yang, and P.A. Webley, Adsorption characteristics of a fully exchanged potassium chabazite zeolite prepared from decomposition of zeolite Y. Microporous and Mesoporous Materials, 2009. 117(1-2): p. 497-507. [2] Shang, J., et al., Potassium Chabazite: A Potential Nanocontainer for Gas Encapsulation. The Journal of Physical Chemistry C, 2010. 114(50): p. 22025-22031. [3] Nedyalkova, R., et al., Interzeolite Conversion of FAU Type Zeolite into CHA and its Application in NH3-SCR. Topics in Catalysis, 2013. 56(9): p. 550-557.

(47) The NH.sub.3-TPD profile of the as synthesized CHA zeolite before and after ion-exchange is depicted in FIG. 11. The sample in K-form had only a single small peak at ca.175° C. attributed to weak acid sites present on the surface of the CHA zeolite. However, after ion-exchange (H-CHA), the TPD profile of ammonia showed two peaks at T=195° C. and 475° C. corresponding to weak and strong acid sites, respectively. The increase in the amount of weak acid sites and the appearance of strong acid sites is more probably assigned to the acid sites in the pores of CHA zeolite. A comparison of the selectivity of the Al-rich CHA catalyst to the commercial ZSM-5 and SSZ-13 at the same reaction conditions is shown in FIG. 14. At TOS of 60 min, SSZ-13 showed the highest selectivity while ZSM-5 and Al-rich CHA almost show the same selectivity. However, at higher TOS (120 and 180 min) the Al-rich CHA of the present invention was the more selective catalyst.

Example 7

Methanol-to-Olefin Reaction

(48) The synthesized and modified CHA samples were evaluated in the MTO reaction using a fixed bed reactor. The reaction was conducted at 350, 400 and 450° C. using 50 mg of the prepared catalyst in pellet form (pellets size between 500 and 800 μm). The feed was 5% methanol and the balance was helium as a carrier gas. The flow rate was sat so that the so called Weight Hourly Space Velocity (WHSV) was 0.95 h.sup.−1. Prior to the reaction analysis, the catalysts were calcined at 500° C. for 1 h under the flow of He. The reaction products were analyzed using an on-line Shimadzu GC-2014 chromatograph equipped with a flame ionization detector and a capillary column HP-PLOT (30 m×0.53 mm, 6 μm film thickness). The conversion of methanol as a function of time on stream (TOS) at the three temperatures is shown in FIG. 12. The conversion was related to the increase in temperature. When the temperature was 350° C., the Al- rich CHA catalyst maintained a 100% methanol conversion for more than 180 min, while when the temperature was increase to 400 and 450° C., the catalyst deactivated after 60 min of the initial of the reaction. The prepared CHA zeolite is rich in alumina (Si/Al=2.5), which give rise to higher amount of acid sites. Thus, the deactivation rate was faster at higher temperatures (400 and 450° C.) and decreased when the temperature was 350° C. The selectivity to olefins as a function of temperatures is shown in FIG. 13. At 350° C., the selectivity to light olefins at TOS of 10 min was ca. 62%, then increased with the increase of TOS before the catalyst deactivated. The increase was up to 93.8% at TOS 180 min. Selectivity to olefins, particularly ethylene, was decreased with the increase of TOS. The increase in the selectivity was explained by the pore blockage which hinder the diffusion of propylene. The pore blockage was more obvious at 450° C., as a result of coke formation. Although, the Al-rich CHA zeolites showed better stability when the reaction temperature was 350° C., the 400 and 450 C.° exhibited better selectivity towards light olefins especially at the beginning of the reaction as presented in Table 6. At TOS of 10 min, the olefins selectivity was ca. 87% and ca. 80% when the reaction temperatures were 400 and 450° C., respectively.

(49) TABLE-US-00006 TABLE 6 (Products Distribution As a Function of Temperatures Over Al-Rich CHA) 350° C. 400° C. 450° C. TOS 10 60 120 180 10 60 120 10 60 120 Conv. (%) 99.9 100.0 99.9 98.7 100.0 98.3 37.4 100.0 96.6 46.0 Propene (%) 15.87 29.3 34.7 28.6 22.2 22.6 0.0 22.53 18.1 0.0 Ethene (%) 44.8 53.1 50.0 60.1 61.2 57.8 0.0 53.4 62.6 0.0 Butenes (%) 1.4 4.2 8.1 5.1 3.2 4 0.0 3.6 3.4 0.0 Total Olefins (%) 62.1 86.6 92.8 93.8 86.6 84.3 0.0 79.5 84.1 0.0 DME (%) 0.00 0.0 0.1 2.7 0.00 1.9 97.3 0.00 2.6 99.0 Paraffins (%) 36.9 12.2 4.3 2.5 12.1 13.2 0.4 19.3 10.0 0.8 C4s (%) 1.42 4.17 8.05 5.2 3.2 4.0 0.00 3.6 3.7 0.00 over C5s (%) 1.01 1.25 2.837 1.1 1.35 0.52 2.291 1.15 3.37 0.257